The Why of Psi

Workshop Presentersfor CertiPHIers Cooperativehellip

o Chris Petit CPHDRegenerative Design LLC

o Rolf Jacobson LEED AP CPHC Research Fellow Center for Sustainable Building Research U of M

The Why of Psi

Copyright copy 2017 Chris Petit and Rolf Jacobson All rights reserved No part of this presentation may be reproduced without their written permission

Outline1) Thermal bridge definition types of TBs and why controlling them is critical for super‐insulated buildings

2) Typical thermal bridge details and design techniques to reduce thermal bridge heat loss

BREAK

3) Knowing which thermal bridges to model and entering them in the PHPP WUFI Passive

4) Overview of PHI protocols and techniques for thermal bridge modeling

BREAK

5) Practice with Flixo 3

The Why of Psi

What is a thermal bridge

4

Section 1 ndash Background + Basics

What is a thermal bridge

Short answerA discontinuity in the thermal envelope

5

Section 1 ndash Background + Basics

What is a thermal bridge

Short answerA discontinuity in the thermal envelope

What types of discontinuities might there be in a thermal envelope

6

Section 1 ndash Background + Basics

What is a thermal bridge

Short answerA discontinuity in the thermal envelope

What types of discontinuities might there be in a thermal envelopebull Repetitive bridges (studs floor joists rafters)bull Material changes (windows insulation)bull Penetrations (pipes fasteners)bull Assembly junctions (roof to wall wall to floor etc)bull Corners

7

Section 1 ndash Background + Basics

Repetitive TBs Penetrations Assembly junctions(point TBs) (linear TBs)

8

Should be accounted for in calculation of assembly U‐values in the PHPP

Usually too minor to be considered for heat loss calculations But some cases could be a durability concern Some cases need calculation (ex ‐commercial facades)

Three types1) Structural (ex ndash rim

joists prefab wall junctions)

2) Geometric (ex ndash wall corners roof ridge)

3) Combination (ex ndashwall to roof wall to slab)

Section 1 ndash Background + Basics

Repetitive TBs ndash entry in PHPP

9

Section 1 ndash Background + Basics

Repetitive TBs ndash entry in WUFI Passive (static side only)

10

Section 1 ndash Background + Basics

Image from David White Right Environments 2010

Circled areas are common linear thermal bridges

bull The wallfoundation intersection is a combination linear TB (structuralgeometric)

bull The roofwall intersection is also a combination (structuralgeometric)

bull The rim joist is purely a structural linear TB

roofwall intersection

rim joist

wallfoundation intersection

11

Section 1 ndash Background + Basics

Thermal bridges ndashdo they matter

bull Thermal bridges make up a small portion of heat loss in a poorly insulated envelope ‐16 in a typical insulated 2x6 wall

bull If same details from a standard stud wall were used to construct an R‐45 wall heat loss through thermal bridges would approach 50

extrapolated from Christian JE and J Kosny 1996

12

Section 1 ndash Background + Basics

How is that possible

1 As insulation levels increase less heat is transmitted but the remaining heat flow through the uninsulated portions of the envelope make up a greater percentage of that remainder

2 Heat begins to move laterally through thermal bridges They can transport more heat than their limited surface area suggests

13

Section 1 ndash Background + Basics

From Pembina Institute Accelerating Market Transformation for High Performance Building Enclosures 2016

14

Section 1 ndash Background + Basics

ldquoThermal bridging is underestimatedhellip Morrison Hershfieldhas calculated that shelf angles parapets window perimeters etc can result in the underestimation of 20 to 70 of the total heat flow through wallsrdquo

Morrison Hershfield Building Envelope Thermal Bridging Guide (2014)

15

graph from Building Science Corp

Section 1 ndash Background + Basics

bull Heat loss through a linear thermal bridge is measured with a Ψvalue

bull A Ψ value is like a U‐value for thermal bridgesU x A x dT = heat loss from a surface of area AΨ x L x dT = heat loss from a linear thermal bridge of length L

bull Ψ values lt= 001 WmK qualify as ldquothermal bridge freerdquo according to Passive House

bull To calculate Ψ values a 2‐D heat flow simulation model (such as THERM or Flixo) is used

16

Section 1 ndash Background + Basics

17

Section 1 ndash Background + Basics

For PHPP the thermal bridge heat loss is conceptually the difference between the ldquotruerdquo heat loss calculated using 2‐dimensional simulation (THERM or Flixo) and the heat loss calculated using the typical UA method (U x A x deltaT = heat loss (or gain))

Image from David White Right Environments 2010

18

Section 1 ndash Background + Basics

ldquo2D heat lossrdquo ndash U1L1 ndash U2L2 = Ψ

Image from David White Right Environments 2010

19

Section 1 ndash Background + Basics

L2d ndash U1L1 ndash U2L2 = Ψ

ldquo2D heat lossrdquo ndash U1L1 ndash U2L2 = Ψ

Image from David White Right Environments 2010

20

Section 1 ndash Background + Basics

L2d ndash U1L1 ndash U2L2 = Ψ

Φ ΔT ndash U1L1 ndash U2L2 = Ψ(heat flux)

Image from David White Right Environments 2010

21

Section 1 ndash Background + Basics

UeqLtotal ndash U1L1 ndash U2L2 = Ψ(equivalent U‐value)

L2d ndash U1L1 ndash U2L2 = Ψ

Φ ΔT ndash U1L1 ndash U2L2 = Ψ(heat flux)

Image from David White Right Environments 2010

22

Section 1 ndash Background + Basics

As used in the PHPP the psi value is always based on a comparison of heat flows ‐ a comparison between the actual heat flow and the estimated heat flow In this sense psi is a correction factor

Image from David White Right Environments 2010

Details coming uphellip1 Wall corners2 Rim joists3 Footings4 Parapets5 Windows

23

Section 1 ndash Background + Basics

When calculating heat loss U x A x dTbull Using exterior dimensions area A = 40 x 10 = 400sfbull Using interior dimensions area A = 36 x 10 = 360sf

Which area A gives the correct heat loss

24

Section 1 ndash Background + Basics

When calculating heat loss U x A x dTbull Using exterior dimensions leads to an overestimatebull Using interior dimensions leads to an underestimate

PH convention is to use exterior dimensions so heat loss is overestimated

25

Section 1 ndash Background + Basics

Section 2 ndash Common Linear Thermal Bridges

2x6 wall no studs Ψ = ‐ 0058 WmK 2x6 wall 2‐stud Ψ = ‐ 0040 WmK

bull By subtraction negative psi values correct for overestimate of heat loss at exterior cornersbull The lower (more negative) the better Higher psi values indicate increasing heat lossbull Positive psi values above 001 WmK indicate net heat transfer (heat gain in summer heat loss in winter)that should be accounted for in PHPP

Step 1 ndash Avoid bridging elements 26

2x6 wall Ψ = ‐ 0040 WmK 2x8 wall Ψ = ‐ 0045 WmK

Is the 2x8 wall corner a ldquobetterrdquo detail

Section 2 ndash Common Linear Thermal Bridges

27

2x6 wall Ψ = ‐ 0040 WmK 2x8 wall Ψ = ‐ 0045 WmK

NoA thicker wall section needs a larger correction factor due to larger overestimate of heat loss

Section 2 ndash Common Linear Thermal Bridges

28

Is the psi value really an indicator of a detailrsquos thermal quality

Section 2 ndash Common Linear Thermal Bridges

29

Is the psi value really an indicator of a detailrsquos thermal qualityYes and no

At geometric bridges it does two things at once ndash it is both a correction factor and an indicator of heat flow ndash but primarily a correction factor

Section 2 ndash Common Linear Thermal Bridges

30

Is the psi value really an indicator of a detailrsquos thermal qualityYes and no

At geometric bridges it does two things at once ndash it is both a correction factor and an indicator of heat flow ndash but primarily a correction factor

Section 2 ndash Common Linear Thermal Bridges

31

Exterior cornerInsulated 2x6 wall w solid post Ψ = ‐ 0004 WmK

rim joist fib batt (R‐11) Ψ = 0089 WmK rim joist rim board (R‐11) Ψ = 0129 WmK

bull Rim joist thermal bridge ‐ challenging to achieve the Ψ = 001 WmK targetbull Maintaining continuity and alignment of insulation layers is a good first step

STEP 2 ndash Align insulation layers

Section 2 ndash Common Linear Thermal Bridges

32

rim joist 2x4 wall w 1rdquo exterior XPS (R‐13) Ψ = 0047 WmK

Section 2 ndash Common Linear Thermal Bridges

33

rim joist fib batt (R‐11) Ψ = 0089 WmK

bull Exterior insulation helps control heat flow through uninsulated studs and plates

STEP 3 ndash Use continuous exterior insulation to isolate bridging elements

rim joist 2x4 wall w 1rdquo exterior XPS (R‐13) Ψ = 0047 WmK

Use enough exterior insulation and the psi value can be driven down below 001 WmK

Section 2 ndash Common Linear Thermal Bridges

34

rim joist 2x4 wall w 4rdquo exterior XPSΨ = 0011 WmK

rim joist 2x4 wall w 4rdquo exterior XPSΨ = 0011 WmK

Question ndash are the psi values for these two details the same or different

Section 2 ndash Common Linear Thermal Bridges

35

rim joist 2x6 wall w 4rdquo exterior XPSΨ =

rim joist 2x4 wall w 4rdquo exterior XPSΨ = 0011 WmK

Is the detail on the left a ldquobetterrdquo detailIs heat flow through the detail on the right really 2x higher than the heat flow on the leftDoes 4rdquo of exterior foam guarantee a good psi value

Section 2 ndash Common Linear Thermal Bridges

36

rim joist 2x6 wall w 4rdquo exterior XPSΨ = 0020 WmK

rim joist 2x4 wall w 4rdquo exterior XPSΨ = 0011 WmK

NoFor the 2x6 wall therersquos now simply a larger difference between the higher R‐value wall assembly and the rim joist R‐value which has remained the same

Section 2 ndash Common Linear Thermal Bridges

37

rim joist 2x6 wall w 4rdquo exterior XPSΨ = 0020 WmK

Is the psi value really an indicator of a detailrsquos thermal quality

Section 2 ndash Common Linear Thermal Bridges

38

Is the psi value really an indicator of a detailrsquos thermal qualityYes and no

At structural thermal bridges a psi value is a comparison between the U‐value of the assembly(ies) and the U‐value of the junction A junction detail that ldquopassesrdquo (001 WmK) for one assembly may not pass with another

Section 2 ndash Common Linear Thermal Bridges

39

Section 2 ndash Common Linear Thermal Bridges

2x6 wall no studs Ψ = ‐ 0058 WmK 2x6 wall 2‐stud Ψ = ‐ 0040 WmK

When is a performance comparison validWhen the two models being compared have the same assemblies and the same geometry ‐the only difference is at the junction Example above

40

stem wall Ψ = ‐0004 WmK FPSF (frost‐protected shallow foundation) Ψ = 0160 WmK

bull Thermal bridge at the foundation is typically the most challenging to addressbull The concrete stem wall and FPSF footing acts as a radiation fin

STEP 4 ndash Avoid accidental ldquoradiation finsrdquo

Section 2 ndash Common Linear Thermal Bridges

41

FPSF (well insulated) Ψ = 0013 WmK

Thick layers of continuous insulation can improve the performance of the detail but even

FPSF Ψ = 0160 WmK

a very well insulated FPSF is still close to the 001 WmK limit

Section 2 ndash Common Linear Thermal Bridges

STEP 4 ‐ Avoid accidental radiation fins ‐ even well‐insulated ones

42

stem wall Ψ = ‐0004 WmK Thermally broken stem wall Ψ = ‐0136 WmK

Section 2 ndash Common Linear Thermal Bridges

43

Thermally broken stem wall provides an insulated break between the stem wall and the floor slab effectively cutting off the ldquoradiation finrdquoAligning exterior insulation layers at junction of stem wall and above grade wall also helpsSTEP 5 ndash An insulated break between the exterior wall and floor slab works best

ICF parapet Ψ = 0200 WmK Foamglas thermal break Ψ = ‐0071 WmK

Another good location to cut off the radiation fin

Section 2 ndash Common Linear Thermal Bridges

44

Window positioned outside of thermal envelope Ψ = 010 WmKEffectively R‐value of window reduced by 20 ‐ 30 depending on window size

Section 2 ndash Common Linear Thermal Bridges

Window positioned on edge of thermal envelope Ψ = 004 WmKR‐value of window reduced by 5 ‐10 depending on window size

45

Window centered in plane of insulation Ψ = 002 to 003 WmKR‐value of window is almost preserved

Section 2 ndash Common Linear Thermal Bridges

46

47

Break

Section 3 ndash Using psi values in PHPP

48

How do I know which thermal bridges need to be modeled and entered in PHPP

Section 3 ndash Using psi values in PHPP

49

How do I know which thermal bridges need to be modeled and entered in PHPP

PHI requires 1 of 2 paths1) Model all thermal bridges enter psi values for both + and ‐2) Model and enter only thermal bridges with psi values over 001 WmK

Path 2 begs the question ndash how do I know which TBs will be over 001 WmK before Irsquove modeled them

Image source httpwwwtheblazecomblog20130124finally‐the‐answer‐sort‐of‐for‐what‐came‐first‐the‐chicken‐or‐the‐egg

Section 3 ndash Using psi values in PHPP

50

EavesMost details will have negative psi value

Rim joistAlmost always positive psi value ‐MODEL

Wall to slabfootingOnly well‐designed details will have negative psi value ‐MODEL

Footing below bearing wall or postOnly well‐designed details will have psi value lt 001 WmK‐MODEL

Roof ridgeMost details will have negative psi value

Section 3 ndash Using psi values in PHPP

51

RakeMost details will have negative psi value

Windowdoor sill on slab MODEL BUThellipCan be entered as a window sill TB + wall‐to‐slab TB (requires two separate psi values)

Window sillAlmost always positive psi value since overinsulationis difficult ndashMODEL

Window headIf overinsulated probably no need to model If not ndashMODEL

Section 3 ndash Using psi values in PHPP

52

Exterior cornerMost details will have negative psi value

Interior cornerAlmost always positive psi value ndashMODEL

Window jambIf overinsulated probably no need to model If not ndashMODEL

Wall junctionIf insulation layers are interrupted ‐MODEL

Section 3 ndash Using psi values in PHPP

53

Other places to keep in mind for possible thermal bridgesbull Plumbing stacksbull Rain pipes (interior)bull ERV vent penetrations (to the exterior)bull Sump pumpsbull Radon remediation pipes (if interior to the building)

Section 3 ndash Using psi values in PHPP

54

Section 3 ndash Using psi values in PHPP

55

Section 3 ndash Using psi values in WUFI Passive

56

Workshop Presentersfor CertiPHIers Cooperativehellip

o Chris Petit CPHDRegenerative Design LLC

o Rolf Jacobson LEED AP CPHC Research Fellow Center for Sustainable Building Research U of M

The Why of Psi

Copyright copy 2017 Chris Petit and Rolf Jacobson All rights reserved No part of this presentation may be reproduced without their written permission

Outline1) Thermal bridge definition types of TBs and why controlling them is critical for super‐insulated buildings

2) Typical thermal bridge details and design techniques to reduce thermal bridge heat loss

BREAK

3) Knowing which thermal bridges to model and entering them in the PHPP WUFI Passive

4) Overview of PHI protocols and techniques for thermal bridge modeling

BREAK

5) Practice with Flixo 3

The Why of Psi

What is a thermal bridge

4

Section 1 ndash Background + Basics

What is a thermal bridge

Short answerA discontinuity in the thermal envelope

5

Section 1 ndash Background + Basics

What is a thermal bridge

Short answerA discontinuity in the thermal envelope

What types of discontinuities might there be in a thermal envelope

6

Section 1 ndash Background + Basics

What is a thermal bridge

Short answerA discontinuity in the thermal envelope

What types of discontinuities might there be in a thermal envelopebull Repetitive bridges (studs floor joists rafters)bull Material changes (windows insulation)bull Penetrations (pipes fasteners)bull Assembly junctions (roof to wall wall to floor etc)bull Corners

7

Section 1 ndash Background + Basics

Repetitive TBs Penetrations Assembly junctions(point TBs) (linear TBs)

8

Should be accounted for in calculation of assembly U‐values in the PHPP

Usually too minor to be considered for heat loss calculations But some cases could be a durability concern Some cases need calculation (ex ‐commercial facades)

Three types1) Structural (ex ndash rim

joists prefab wall junctions)

2) Geometric (ex ndash wall corners roof ridge)

3) Combination (ex ndashwall to roof wall to slab)

Section 1 ndash Background + Basics

Repetitive TBs ndash entry in PHPP

9

Section 1 ndash Background + Basics

Repetitive TBs ndash entry in WUFI Passive (static side only)

10

Section 1 ndash Background + Basics

Image from David White Right Environments 2010

Circled areas are common linear thermal bridges

bull The wallfoundation intersection is a combination linear TB (structuralgeometric)

bull The roofwall intersection is also a combination (structuralgeometric)

bull The rim joist is purely a structural linear TB

roofwall intersection

rim joist

wallfoundation intersection

11

Section 1 ndash Background + Basics

Thermal bridges ndashdo they matter

bull Thermal bridges make up a small portion of heat loss in a poorly insulated envelope ‐16 in a typical insulated 2x6 wall

bull If same details from a standard stud wall were used to construct an R‐45 wall heat loss through thermal bridges would approach 50

extrapolated from Christian JE and J Kosny 1996

12

Section 1 ndash Background + Basics

How is that possible

1 As insulation levels increase less heat is transmitted but the remaining heat flow through the uninsulated portions of the envelope make up a greater percentage of that remainder

2 Heat begins to move laterally through thermal bridges They can transport more heat than their limited surface area suggests

13

Section 1 ndash Background + Basics

From Pembina Institute Accelerating Market Transformation for High Performance Building Enclosures 2016

14

Section 1 ndash Background + Basics

ldquoThermal bridging is underestimatedhellip Morrison Hershfieldhas calculated that shelf angles parapets window perimeters etc can result in the underestimation of 20 to 70 of the total heat flow through wallsrdquo

Morrison Hershfield Building Envelope Thermal Bridging Guide (2014)

15

graph from Building Science Corp

Section 1 ndash Background + Basics

bull Heat loss through a linear thermal bridge is measured with a Ψvalue

bull A Ψ value is like a U‐value for thermal bridgesU x A x dT = heat loss from a surface of area AΨ x L x dT = heat loss from a linear thermal bridge of length L

bull Ψ values lt= 001 WmK qualify as ldquothermal bridge freerdquo according to Passive House

bull To calculate Ψ values a 2‐D heat flow simulation model (such as THERM or Flixo) is used

16

Section 1 ndash Background + Basics

17

Section 1 ndash Background + Basics

For PHPP the thermal bridge heat loss is conceptually the difference between the ldquotruerdquo heat loss calculated using 2‐dimensional simulation (THERM or Flixo) and the heat loss calculated using the typical UA method (U x A x deltaT = heat loss (or gain))

Image from David White Right Environments 2010

18

Section 1 ndash Background + Basics

ldquo2D heat lossrdquo ndash U1L1 ndash U2L2 = Ψ

Image from David White Right Environments 2010

19

Section 1 ndash Background + Basics

L2d ndash U1L1 ndash U2L2 = Ψ

ldquo2D heat lossrdquo ndash U1L1 ndash U2L2 = Ψ

Image from David White Right Environments 2010

20

Section 1 ndash Background + Basics

L2d ndash U1L1 ndash U2L2 = Ψ

Φ ΔT ndash U1L1 ndash U2L2 = Ψ(heat flux)

Image from David White Right Environments 2010

21

Section 1 ndash Background + Basics

UeqLtotal ndash U1L1 ndash U2L2 = Ψ(equivalent U‐value)

L2d ndash U1L1 ndash U2L2 = Ψ

Φ ΔT ndash U1L1 ndash U2L2 = Ψ(heat flux)

Image from David White Right Environments 2010

22

Section 1 ndash Background + Basics

As used in the PHPP the psi value is always based on a comparison of heat flows ‐ a comparison between the actual heat flow and the estimated heat flow In this sense psi is a correction factor

Image from David White Right Environments 2010

Details coming uphellip1 Wall corners2 Rim joists3 Footings4 Parapets5 Windows

23

Section 1 ndash Background + Basics

When calculating heat loss U x A x dTbull Using exterior dimensions area A = 40 x 10 = 400sfbull Using interior dimensions area A = 36 x 10 = 360sf

Which area A gives the correct heat loss

24

Section 1 ndash Background + Basics

When calculating heat loss U x A x dTbull Using exterior dimensions leads to an overestimatebull Using interior dimensions leads to an underestimate

PH convention is to use exterior dimensions so heat loss is overestimated

25

Section 1 ndash Background + Basics

Section 2 ndash Common Linear Thermal Bridges

2x6 wall no studs Ψ = ‐ 0058 WmK 2x6 wall 2‐stud Ψ = ‐ 0040 WmK

bull By subtraction negative psi values correct for overestimate of heat loss at exterior cornersbull The lower (more negative) the better Higher psi values indicate increasing heat lossbull Positive psi values above 001 WmK indicate net heat transfer (heat gain in summer heat loss in winter)that should be accounted for in PHPP

Step 1 ndash Avoid bridging elements 26

2x6 wall Ψ = ‐ 0040 WmK 2x8 wall Ψ = ‐ 0045 WmK

Is the 2x8 wall corner a ldquobetterrdquo detail

Section 2 ndash Common Linear Thermal Bridges

27

2x6 wall Ψ = ‐ 0040 WmK 2x8 wall Ψ = ‐ 0045 WmK

NoA thicker wall section needs a larger correction factor due to larger overestimate of heat loss

Section 2 ndash Common Linear Thermal Bridges

28

Is the psi value really an indicator of a detailrsquos thermal quality

Section 2 ndash Common Linear Thermal Bridges

29

Is the psi value really an indicator of a detailrsquos thermal qualityYes and no

At geometric bridges it does two things at once ndash it is both a correction factor and an indicator of heat flow ndash but primarily a correction factor

Section 2 ndash Common Linear Thermal Bridges

30

Is the psi value really an indicator of a detailrsquos thermal qualityYes and no

At geometric bridges it does two things at once ndash it is both a correction factor and an indicator of heat flow ndash but primarily a correction factor

Section 2 ndash Common Linear Thermal Bridges

31

Exterior cornerInsulated 2x6 wall w solid post Ψ = ‐ 0004 WmK

rim joist fib batt (R‐11) Ψ = 0089 WmK rim joist rim board (R‐11) Ψ = 0129 WmK

bull Rim joist thermal bridge ‐ challenging to achieve the Ψ = 001 WmK targetbull Maintaining continuity and alignment of insulation layers is a good first step

STEP 2 ndash Align insulation layers

Section 2 ndash Common Linear Thermal Bridges

32

rim joist 2x4 wall w 1rdquo exterior XPS (R‐13) Ψ = 0047 WmK

Section 2 ndash Common Linear Thermal Bridges

33

rim joist fib batt (R‐11) Ψ = 0089 WmK

bull Exterior insulation helps control heat flow through uninsulated studs and plates

STEP 3 ndash Use continuous exterior insulation to isolate bridging elements

rim joist 2x4 wall w 1rdquo exterior XPS (R‐13) Ψ = 0047 WmK

Use enough exterior insulation and the psi value can be driven down below 001 WmK

Section 2 ndash Common Linear Thermal Bridges

34

rim joist 2x4 wall w 4rdquo exterior XPSΨ = 0011 WmK

rim joist 2x4 wall w 4rdquo exterior XPSΨ = 0011 WmK

Question ndash are the psi values for these two details the same or different

Section 2 ndash Common Linear Thermal Bridges

35

rim joist 2x6 wall w 4rdquo exterior XPSΨ =

rim joist 2x4 wall w 4rdquo exterior XPSΨ = 0011 WmK

Is the detail on the left a ldquobetterrdquo detailIs heat flow through the detail on the right really 2x higher than the heat flow on the leftDoes 4rdquo of exterior foam guarantee a good psi value

Section 2 ndash Common Linear Thermal Bridges

36

rim joist 2x6 wall w 4rdquo exterior XPSΨ = 0020 WmK

rim joist 2x4 wall w 4rdquo exterior XPSΨ = 0011 WmK

NoFor the 2x6 wall therersquos now simply a larger difference between the higher R‐value wall assembly and the rim joist R‐value which has remained the same

Section 2 ndash Common Linear Thermal Bridges

37

rim joist 2x6 wall w 4rdquo exterior XPSΨ = 0020 WmK

Is the psi value really an indicator of a detailrsquos thermal quality

Section 2 ndash Common Linear Thermal Bridges

38

Is the psi value really an indicator of a detailrsquos thermal qualityYes and no

At structural thermal bridges a psi value is a comparison between the U‐value of the assembly(ies) and the U‐value of the junction A junction detail that ldquopassesrdquo (001 WmK) for one assembly may not pass with another

Section 2 ndash Common Linear Thermal Bridges

39

Section 2 ndash Common Linear Thermal Bridges

2x6 wall no studs Ψ = ‐ 0058 WmK 2x6 wall 2‐stud Ψ = ‐ 0040 WmK

When is a performance comparison validWhen the two models being compared have the same assemblies and the same geometry ‐the only difference is at the junction Example above

40

stem wall Ψ = ‐0004 WmK FPSF (frost‐protected shallow foundation) Ψ = 0160 WmK

bull Thermal bridge at the foundation is typically the most challenging to addressbull The concrete stem wall and FPSF footing acts as a radiation fin

STEP 4 ndash Avoid accidental ldquoradiation finsrdquo

Section 2 ndash Common Linear Thermal Bridges

41

FPSF (well insulated) Ψ = 0013 WmK

Thick layers of continuous insulation can improve the performance of the detail but even

FPSF Ψ = 0160 WmK

a very well insulated FPSF is still close to the 001 WmK limit

Section 2 ndash Common Linear Thermal Bridges

STEP 4 ‐ Avoid accidental radiation fins ‐ even well‐insulated ones

42

stem wall Ψ = ‐0004 WmK Thermally broken stem wall Ψ = ‐0136 WmK

Section 2 ndash Common Linear Thermal Bridges

43

Thermally broken stem wall provides an insulated break between the stem wall and the floor slab effectively cutting off the ldquoradiation finrdquoAligning exterior insulation layers at junction of stem wall and above grade wall also helpsSTEP 5 ndash An insulated break between the exterior wall and floor slab works best

ICF parapet Ψ = 0200 WmK Foamglas thermal break Ψ = ‐0071 WmK

Another good location to cut off the radiation fin

Section 2 ndash Common Linear Thermal Bridges

44

Window positioned outside of thermal envelope Ψ = 010 WmKEffectively R‐value of window reduced by 20 ‐ 30 depending on window size

Section 2 ndash Common Linear Thermal Bridges

Window positioned on edge of thermal envelope Ψ = 004 WmKR‐value of window reduced by 5 ‐10 depending on window size

45

Window centered in plane of insulation Ψ = 002 to 003 WmKR‐value of window is almost preserved

Section 2 ndash Common Linear Thermal Bridges

46

47

Break

Section 3 ndash Using psi values in PHPP

48

How do I know which thermal bridges need to be modeled and entered in PHPP

Section 3 ndash Using psi values in PHPP

49

How do I know which thermal bridges need to be modeled and entered in PHPP

PHI requires 1 of 2 paths1) Model all thermal bridges enter psi values for both + and ‐2) Model and enter only thermal bridges with psi values over 001 WmK

Path 2 begs the question ndash how do I know which TBs will be over 001 WmK before Irsquove modeled them

Image source httpwwwtheblazecomblog20130124finally‐the‐answer‐sort‐of‐for‐what‐came‐first‐the‐chicken‐or‐the‐egg

Section 3 ndash Using psi values in PHPP

50

EavesMost details will have negative psi value

Rim joistAlmost always positive psi value ‐MODEL

Wall to slabfootingOnly well‐designed details will have negative psi value ‐MODEL

Footing below bearing wall or postOnly well‐designed details will have psi value lt 001 WmK‐MODEL

Roof ridgeMost details will have negative psi value

Section 3 ndash Using psi values in PHPP

51

RakeMost details will have negative psi value

Windowdoor sill on slab MODEL BUThellipCan be entered as a window sill TB + wall‐to‐slab TB (requires two separate psi values)

Window sillAlmost always positive psi value since overinsulationis difficult ndashMODEL

Window headIf overinsulated probably no need to model If not ndashMODEL

Section 3 ndash Using psi values in PHPP

52

Exterior cornerMost details will have negative psi value

Interior cornerAlmost always positive psi value ndashMODEL

Window jambIf overinsulated probably no need to model If not ndashMODEL

Wall junctionIf insulation layers are interrupted ‐MODEL

Section 3 ndash Using psi values in PHPP

53

Other places to keep in mind for possible thermal bridgesbull Plumbing stacksbull Rain pipes (interior)bull ERV vent penetrations (to the exterior)bull Sump pumpsbull Radon remediation pipes (if interior to the building)

Section 3 ndash Using psi values in PHPP

54

Section 3 ndash Using psi values in PHPP

55

Section 3 ndash Using psi values in WUFI Passive

56

Outline1) Thermal bridge definition types of TBs and why controlling them is critical for super‐insulated buildings

2) Typical thermal bridge details and design techniques to reduce thermal bridge heat loss

BREAK

3) Knowing which thermal bridges to model and entering them in the PHPP WUFI Passive

4) Overview of PHI protocols and techniques for thermal bridge modeling

BREAK

5) Practice with Flixo 3

The Why of Psi

What is a thermal bridge

4

Section 1 ndash Background + Basics

What is a thermal bridge

Short answerA discontinuity in the thermal envelope

5

Section 1 ndash Background + Basics

What is a thermal bridge

Short answerA discontinuity in the thermal envelope

What types of discontinuities might there be in a thermal envelope

6

Section 1 ndash Background + Basics

What is a thermal bridge

Short answerA discontinuity in the thermal envelope

What types of discontinuities might there be in a thermal envelopebull Repetitive bridges (studs floor joists rafters)bull Material changes (windows insulation)bull Penetrations (pipes fasteners)bull Assembly junctions (roof to wall wall to floor etc)bull Corners

7

Section 1 ndash Background + Basics

Repetitive TBs Penetrations Assembly junctions(point TBs) (linear TBs)

8

Should be accounted for in calculation of assembly U‐values in the PHPP

Usually too minor to be considered for heat loss calculations But some cases could be a durability concern Some cases need calculation (ex ‐commercial facades)

Three types1) Structural (ex ndash rim

joists prefab wall junctions)

2) Geometric (ex ndash wall corners roof ridge)

3) Combination (ex ndashwall to roof wall to slab)

Section 1 ndash Background + Basics

Repetitive TBs ndash entry in PHPP

9

Section 1 ndash Background + Basics

Repetitive TBs ndash entry in WUFI Passive (static side only)

10

Section 1 ndash Background + Basics

Image from David White Right Environments 2010

Circled areas are common linear thermal bridges

bull The wallfoundation intersection is a combination linear TB (structuralgeometric)

bull The roofwall intersection is also a combination (structuralgeometric)

bull The rim joist is purely a structural linear TB

roofwall intersection

rim joist

wallfoundation intersection

11

Section 1 ndash Background + Basics

Thermal bridges ndashdo they matter

bull Thermal bridges make up a small portion of heat loss in a poorly insulated envelope ‐16 in a typical insulated 2x6 wall

bull If same details from a standard stud wall were used to construct an R‐45 wall heat loss through thermal bridges would approach 50

extrapolated from Christian JE and J Kosny 1996

12

Section 1 ndash Background + Basics

How is that possible

1 As insulation levels increase less heat is transmitted but the remaining heat flow through the uninsulated portions of the envelope make up a greater percentage of that remainder

2 Heat begins to move laterally through thermal bridges They can transport more heat than their limited surface area suggests

13

Section 1 ndash Background + Basics

From Pembina Institute Accelerating Market Transformation for High Performance Building Enclosures 2016

14

Section 1 ndash Background + Basics

ldquoThermal bridging is underestimatedhellip Morrison Hershfieldhas calculated that shelf angles parapets window perimeters etc can result in the underestimation of 20 to 70 of the total heat flow through wallsrdquo

Morrison Hershfield Building Envelope Thermal Bridging Guide (2014)

15

graph from Building Science Corp

Section 1 ndash Background + Basics

bull Heat loss through a linear thermal bridge is measured with a Ψvalue

bull A Ψ value is like a U‐value for thermal bridgesU x A x dT = heat loss from a surface of area AΨ x L x dT = heat loss from a linear thermal bridge of length L

bull Ψ values lt= 001 WmK qualify as ldquothermal bridge freerdquo according to Passive House

bull To calculate Ψ values a 2‐D heat flow simulation model (such as THERM or Flixo) is used

16

Section 1 ndash Background + Basics

17

Section 1 ndash Background + Basics

For PHPP the thermal bridge heat loss is conceptually the difference between the ldquotruerdquo heat loss calculated using 2‐dimensional simulation (THERM or Flixo) and the heat loss calculated using the typical UA method (U x A x deltaT = heat loss (or gain))

Image from David White Right Environments 2010

18

Section 1 ndash Background + Basics

ldquo2D heat lossrdquo ndash U1L1 ndash U2L2 = Ψ

Image from David White Right Environments 2010

19

Section 1 ndash Background + Basics

L2d ndash U1L1 ndash U2L2 = Ψ

ldquo2D heat lossrdquo ndash U1L1 ndash U2L2 = Ψ

Image from David White Right Environments 2010

20

Section 1 ndash Background + Basics

L2d ndash U1L1 ndash U2L2 = Ψ

Φ ΔT ndash U1L1 ndash U2L2 = Ψ(heat flux)

Image from David White Right Environments 2010

21

Section 1 ndash Background + Basics

UeqLtotal ndash U1L1 ndash U2L2 = Ψ(equivalent U‐value)

L2d ndash U1L1 ndash U2L2 = Ψ

Φ ΔT ndash U1L1 ndash U2L2 = Ψ(heat flux)

Image from David White Right Environments 2010

22

Section 1 ndash Background + Basics

As used in the PHPP the psi value is always based on a comparison of heat flows ‐ a comparison between the actual heat flow and the estimated heat flow In this sense psi is a correction factor

Image from David White Right Environments 2010

Details coming uphellip1 Wall corners2 Rim joists3 Footings4 Parapets5 Windows

23

Section 1 ndash Background + Basics

When calculating heat loss U x A x dTbull Using exterior dimensions area A = 40 x 10 = 400sfbull Using interior dimensions area A = 36 x 10 = 360sf

Which area A gives the correct heat loss

24

Section 1 ndash Background + Basics

When calculating heat loss U x A x dTbull Using exterior dimensions leads to an overestimatebull Using interior dimensions leads to an underestimate

PH convention is to use exterior dimensions so heat loss is overestimated

25

Section 1 ndash Background + Basics

Section 2 ndash Common Linear Thermal Bridges

2x6 wall no studs Ψ = ‐ 0058 WmK 2x6 wall 2‐stud Ψ = ‐ 0040 WmK

bull By subtraction negative psi values correct for overestimate of heat loss at exterior cornersbull The lower (more negative) the better Higher psi values indicate increasing heat lossbull Positive psi values above 001 WmK indicate net heat transfer (heat gain in summer heat loss in winter)that should be accounted for in PHPP

Step 1 ndash Avoid bridging elements 26

2x6 wall Ψ = ‐ 0040 WmK 2x8 wall Ψ = ‐ 0045 WmK

Is the 2x8 wall corner a ldquobetterrdquo detail

Section 2 ndash Common Linear Thermal Bridges

27

2x6 wall Ψ = ‐ 0040 WmK 2x8 wall Ψ = ‐ 0045 WmK

NoA thicker wall section needs a larger correction factor due to larger overestimate of heat loss

Section 2 ndash Common Linear Thermal Bridges

28

Is the psi value really an indicator of a detailrsquos thermal quality

Section 2 ndash Common Linear Thermal Bridges

29

Is the psi value really an indicator of a detailrsquos thermal qualityYes and no

At geometric bridges it does two things at once ndash it is both a correction factor and an indicator of heat flow ndash but primarily a correction factor

Section 2 ndash Common Linear Thermal Bridges

30

Is the psi value really an indicator of a detailrsquos thermal qualityYes and no

At geometric bridges it does two things at once ndash it is both a correction factor and an indicator of heat flow ndash but primarily a correction factor

Section 2 ndash Common Linear Thermal Bridges

31

Exterior cornerInsulated 2x6 wall w solid post Ψ = ‐ 0004 WmK

rim joist fib batt (R‐11) Ψ = 0089 WmK rim joist rim board (R‐11) Ψ = 0129 WmK

bull Rim joist thermal bridge ‐ challenging to achieve the Ψ = 001 WmK targetbull Maintaining continuity and alignment of insulation layers is a good first step

STEP 2 ndash Align insulation layers

Section 2 ndash Common Linear Thermal Bridges

32

rim joist 2x4 wall w 1rdquo exterior XPS (R‐13) Ψ = 0047 WmK

Section 2 ndash Common Linear Thermal Bridges

33

rim joist fib batt (R‐11) Ψ = 0089 WmK

bull Exterior insulation helps control heat flow through uninsulated studs and plates

STEP 3 ndash Use continuous exterior insulation to isolate bridging elements

rim joist 2x4 wall w 1rdquo exterior XPS (R‐13) Ψ = 0047 WmK

Use enough exterior insulation and the psi value can be driven down below 001 WmK

Section 2 ndash Common Linear Thermal Bridges

34

rim joist 2x4 wall w 4rdquo exterior XPSΨ = 0011 WmK

rim joist 2x4 wall w 4rdquo exterior XPSΨ = 0011 WmK

Question ndash are the psi values for these two details the same or different

Section 2 ndash Common Linear Thermal Bridges

35

rim joist 2x6 wall w 4rdquo exterior XPSΨ =

rim joist 2x4 wall w 4rdquo exterior XPSΨ = 0011 WmK

Is the detail on the left a ldquobetterrdquo detailIs heat flow through the detail on the right really 2x higher than the heat flow on the leftDoes 4rdquo of exterior foam guarantee a good psi value

Section 2 ndash Common Linear Thermal Bridges

36

rim joist 2x6 wall w 4rdquo exterior XPSΨ = 0020 WmK

rim joist 2x4 wall w 4rdquo exterior XPSΨ = 0011 WmK

NoFor the 2x6 wall therersquos now simply a larger difference between the higher R‐value wall assembly and the rim joist R‐value which has remained the same

Section 2 ndash Common Linear Thermal Bridges

37

rim joist 2x6 wall w 4rdquo exterior XPSΨ = 0020 WmK

Is the psi value really an indicator of a detailrsquos thermal quality

Section 2 ndash Common Linear Thermal Bridges

38

Is the psi value really an indicator of a detailrsquos thermal qualityYes and no

At structural thermal bridges a psi value is a comparison between the U‐value of the assembly(ies) and the U‐value of the junction A junction detail that ldquopassesrdquo (001 WmK) for one assembly may not pass with another

Section 2 ndash Common Linear Thermal Bridges

39

Section 2 ndash Common Linear Thermal Bridges

2x6 wall no studs Ψ = ‐ 0058 WmK 2x6 wall 2‐stud Ψ = ‐ 0040 WmK

When is a performance comparison validWhen the two models being compared have the same assemblies and the same geometry ‐the only difference is at the junction Example above

40

stem wall Ψ = ‐0004 WmK FPSF (frost‐protected shallow foundation) Ψ = 0160 WmK

bull Thermal bridge at the foundation is typically the most challenging to addressbull The concrete stem wall and FPSF footing acts as a radiation fin

STEP 4 ndash Avoid accidental ldquoradiation finsrdquo

Section 2 ndash Common Linear Thermal Bridges

41

FPSF (well insulated) Ψ = 0013 WmK

Thick layers of continuous insulation can improve the performance of the detail but even

FPSF Ψ = 0160 WmK

a very well insulated FPSF is still close to the 001 WmK limit

Section 2 ndash Common Linear Thermal Bridges

STEP 4 ‐ Avoid accidental radiation fins ‐ even well‐insulated ones

42

stem wall Ψ = ‐0004 WmK Thermally broken stem wall Ψ = ‐0136 WmK

Section 2 ndash Common Linear Thermal Bridges

43

Thermally broken stem wall provides an insulated break between the stem wall and the floor slab effectively cutting off the ldquoradiation finrdquoAligning exterior insulation layers at junction of stem wall and above grade wall also helpsSTEP 5 ndash An insulated break between the exterior wall and floor slab works best

ICF parapet Ψ = 0200 WmK Foamglas thermal break Ψ = ‐0071 WmK

Another good location to cut off the radiation fin

Section 2 ndash Common Linear Thermal Bridges

44

Window positioned outside of thermal envelope Ψ = 010 WmKEffectively R‐value of window reduced by 20 ‐ 30 depending on window size

Section 2 ndash Common Linear Thermal Bridges

Window positioned on edge of thermal envelope Ψ = 004 WmKR‐value of window reduced by 5 ‐10 depending on window size

45

Window centered in plane of insulation Ψ = 002 to 003 WmKR‐value of window is almost preserved

Section 2 ndash Common Linear Thermal Bridges

46

47

Break

Section 3 ndash Using psi values in PHPP

48

How do I know which thermal bridges need to be modeled and entered in PHPP

Section 3 ndash Using psi values in PHPP

49

How do I know which thermal bridges need to be modeled and entered in PHPP

PHI requires 1 of 2 paths1) Model all thermal bridges enter psi values for both + and ‐2) Model and enter only thermal bridges with psi values over 001 WmK

Path 2 begs the question ndash how do I know which TBs will be over 001 WmK before Irsquove modeled them

Image source httpwwwtheblazecomblog20130124finally‐the‐answer‐sort‐of‐for‐what‐came‐first‐the‐chicken‐or‐the‐egg

Section 3 ndash Using psi values in PHPP

50

EavesMost details will have negative psi value

Rim joistAlmost always positive psi value ‐MODEL

Wall to slabfootingOnly well‐designed details will have negative psi value ‐MODEL

Footing below bearing wall or postOnly well‐designed details will have psi value lt 001 WmK‐MODEL

Roof ridgeMost details will have negative psi value

Section 3 ndash Using psi values in PHPP

51

RakeMost details will have negative psi value

Windowdoor sill on slab MODEL BUThellipCan be entered as a window sill TB + wall‐to‐slab TB (requires two separate psi values)

Window sillAlmost always positive psi value since overinsulationis difficult ndashMODEL

Window headIf overinsulated probably no need to model If not ndashMODEL

Section 3 ndash Using psi values in PHPP

52

Exterior cornerMost details will have negative psi value

Interior cornerAlmost always positive psi value ndashMODEL

Window jambIf overinsulated probably no need to model If not ndashMODEL

Wall junctionIf insulation layers are interrupted ‐MODEL

Section 3 ndash Using psi values in PHPP

53

Other places to keep in mind for possible thermal bridgesbull Plumbing stacksbull Rain pipes (interior)bull ERV vent penetrations (to the exterior)bull Sump pumpsbull Radon remediation pipes (if interior to the building)

Section 3 ndash Using psi values in PHPP

54

Section 3 ndash Using psi values in PHPP

55

Section 3 ndash Using psi values in WUFI Passive

56

What is a thermal bridge

4

Section 1 ndash Background + Basics

What is a thermal bridge

Short answerA discontinuity in the thermal envelope

5

Section 1 ndash Background + Basics

What is a thermal bridge

Short answerA discontinuity in the thermal envelope

What types of discontinuities might there be in a thermal envelope

6

Section 1 ndash Background + Basics

What is a thermal bridge

Short answerA discontinuity in the thermal envelope

What types of discontinuities might there be in a thermal envelopebull Repetitive bridges (studs floor joists rafters)bull Material changes (windows insulation)bull Penetrations (pipes fasteners)bull Assembly junctions (roof to wall wall to floor etc)bull Corners

7

Section 1 ndash Background + Basics

Repetitive TBs Penetrations Assembly junctions(point TBs) (linear TBs)

8

Should be accounted for in calculation of assembly U‐values in the PHPP

Usually too minor to be considered for heat loss calculations But some cases could be a durability concern Some cases need calculation (ex ‐commercial facades)

Three types1) Structural (ex ndash rim

joists prefab wall junctions)

2) Geometric (ex ndash wall corners roof ridge)

3) Combination (ex ndashwall to roof wall to slab)

Section 1 ndash Background + Basics

Repetitive TBs ndash entry in PHPP

9

Section 1 ndash Background + Basics

Repetitive TBs ndash entry in WUFI Passive (static side only)

10

Section 1 ndash Background + Basics

Image from David White Right Environments 2010

Circled areas are common linear thermal bridges

bull The wallfoundation intersection is a combination linear TB (structuralgeometric)

bull The roofwall intersection is also a combination (structuralgeometric)

bull The rim joist is purely a structural linear TB

roofwall intersection

rim joist

wallfoundation intersection

11

Section 1 ndash Background + Basics

Thermal bridges ndashdo they matter

bull Thermal bridges make up a small portion of heat loss in a poorly insulated envelope ‐16 in a typical insulated 2x6 wall

bull If same details from a standard stud wall were used to construct an R‐45 wall heat loss through thermal bridges would approach 50

extrapolated from Christian JE and J Kosny 1996

12

Section 1 ndash Background + Basics

How is that possible

1 As insulation levels increase less heat is transmitted but the remaining heat flow through the uninsulated portions of the envelope make up a greater percentage of that remainder

2 Heat begins to move laterally through thermal bridges They can transport more heat than their limited surface area suggests

13

Section 1 ndash Background + Basics

From Pembina Institute Accelerating Market Transformation for High Performance Building Enclosures 2016

14

Section 1 ndash Background + Basics

ldquoThermal bridging is underestimatedhellip Morrison Hershfieldhas calculated that shelf angles parapets window perimeters etc can result in the underestimation of 20 to 70 of the total heat flow through wallsrdquo

Morrison Hershfield Building Envelope Thermal Bridging Guide (2014)

15

graph from Building Science Corp

Section 1 ndash Background + Basics

bull Heat loss through a linear thermal bridge is measured with a Ψvalue

bull A Ψ value is like a U‐value for thermal bridgesU x A x dT = heat loss from a surface of area AΨ x L x dT = heat loss from a linear thermal bridge of length L

bull Ψ values lt= 001 WmK qualify as ldquothermal bridge freerdquo according to Passive House

bull To calculate Ψ values a 2‐D heat flow simulation model (such as THERM or Flixo) is used

16

Section 1 ndash Background + Basics

17

Section 1 ndash Background + Basics

For PHPP the thermal bridge heat loss is conceptually the difference between the ldquotruerdquo heat loss calculated using 2‐dimensional simulation (THERM or Flixo) and the heat loss calculated using the typical UA method (U x A x deltaT = heat loss (or gain))

Image from David White Right Environments 2010

18

Section 1 ndash Background + Basics

ldquo2D heat lossrdquo ndash U1L1 ndash U2L2 = Ψ

Image from David White Right Environments 2010

19

Section 1 ndash Background + Basics

L2d ndash U1L1 ndash U2L2 = Ψ

ldquo2D heat lossrdquo ndash U1L1 ndash U2L2 = Ψ

Image from David White Right Environments 2010

20

Section 1 ndash Background + Basics

L2d ndash U1L1 ndash U2L2 = Ψ

Φ ΔT ndash U1L1 ndash U2L2 = Ψ(heat flux)

Image from David White Right Environments 2010

21

Section 1 ndash Background + Basics

UeqLtotal ndash U1L1 ndash U2L2 = Ψ(equivalent U‐value)

L2d ndash U1L1 ndash U2L2 = Ψ

Φ ΔT ndash U1L1 ndash U2L2 = Ψ(heat flux)

Image from David White Right Environments 2010

22

Section 1 ndash Background + Basics

As used in the PHPP the psi value is always based on a comparison of heat flows ‐ a comparison between the actual heat flow and the estimated heat flow In this sense psi is a correction factor

Image from David White Right Environments 2010

Details coming uphellip1 Wall corners2 Rim joists3 Footings4 Parapets5 Windows

23

Section 1 ndash Background + Basics

When calculating heat loss U x A x dTbull Using exterior dimensions area A = 40 x 10 = 400sfbull Using interior dimensions area A = 36 x 10 = 360sf

Which area A gives the correct heat loss

24

Section 1 ndash Background + Basics

When calculating heat loss U x A x dTbull Using exterior dimensions leads to an overestimatebull Using interior dimensions leads to an underestimate

PH convention is to use exterior dimensions so heat loss is overestimated

25

Section 1 ndash Background + Basics

Section 2 ndash Common Linear Thermal Bridges

2x6 wall no studs Ψ = ‐ 0058 WmK 2x6 wall 2‐stud Ψ = ‐ 0040 WmK

bull By subtraction negative psi values correct for overestimate of heat loss at exterior cornersbull The lower (more negative) the better Higher psi values indicate increasing heat lossbull Positive psi values above 001 WmK indicate net heat transfer (heat gain in summer heat loss in winter)that should be accounted for in PHPP

Step 1 ndash Avoid bridging elements 26

2x6 wall Ψ = ‐ 0040 WmK 2x8 wall Ψ = ‐ 0045 WmK

Is the 2x8 wall corner a ldquobetterrdquo detail

Section 2 ndash Common Linear Thermal Bridges

27

2x6 wall Ψ = ‐ 0040 WmK 2x8 wall Ψ = ‐ 0045 WmK

NoA thicker wall section needs a larger correction factor due to larger overestimate of heat loss

Section 2 ndash Common Linear Thermal Bridges

28

Is the psi value really an indicator of a detailrsquos thermal quality

Section 2 ndash Common Linear Thermal Bridges

29

Is the psi value really an indicator of a detailrsquos thermal qualityYes and no

At geometric bridges it does two things at once ndash it is both a correction factor and an indicator of heat flow ndash but primarily a correction factor

Section 2 ndash Common Linear Thermal Bridges

30

Is the psi value really an indicator of a detailrsquos thermal qualityYes and no

At geometric bridges it does two things at once ndash it is both a correction factor and an indicator of heat flow ndash but primarily a correction factor

Section 2 ndash Common Linear Thermal Bridges

31

Exterior cornerInsulated 2x6 wall w solid post Ψ = ‐ 0004 WmK

rim joist fib batt (R‐11) Ψ = 0089 WmK rim joist rim board (R‐11) Ψ = 0129 WmK

bull Rim joist thermal bridge ‐ challenging to achieve the Ψ = 001 WmK targetbull Maintaining continuity and alignment of insulation layers is a good first step

STEP 2 ndash Align insulation layers

Section 2 ndash Common Linear Thermal Bridges

32

rim joist 2x4 wall w 1rdquo exterior XPS (R‐13) Ψ = 0047 WmK

Section 2 ndash Common Linear Thermal Bridges

33

rim joist fib batt (R‐11) Ψ = 0089 WmK

bull Exterior insulation helps control heat flow through uninsulated studs and plates

STEP 3 ndash Use continuous exterior insulation to isolate bridging elements

rim joist 2x4 wall w 1rdquo exterior XPS (R‐13) Ψ = 0047 WmK

Use enough exterior insulation and the psi value can be driven down below 001 WmK

Section 2 ndash Common Linear Thermal Bridges

34

rim joist 2x4 wall w 4rdquo exterior XPSΨ = 0011 WmK

rim joist 2x4 wall w 4rdquo exterior XPSΨ = 0011 WmK

Question ndash are the psi values for these two details the same or different

Section 2 ndash Common Linear Thermal Bridges

35

rim joist 2x6 wall w 4rdquo exterior XPSΨ =

rim joist 2x4 wall w 4rdquo exterior XPSΨ = 0011 WmK

Is the detail on the left a ldquobetterrdquo detailIs heat flow through the detail on the right really 2x higher than the heat flow on the leftDoes 4rdquo of exterior foam guarantee a good psi value

Section 2 ndash Common Linear Thermal Bridges

36

rim joist 2x6 wall w 4rdquo exterior XPSΨ = 0020 WmK

rim joist 2x4 wall w 4rdquo exterior XPSΨ = 0011 WmK

NoFor the 2x6 wall therersquos now simply a larger difference between the higher R‐value wall assembly and the rim joist R‐value which has remained the same

Section 2 ndash Common Linear Thermal Bridges

37

rim joist 2x6 wall w 4rdquo exterior XPSΨ = 0020 WmK

Is the psi value really an indicator of a detailrsquos thermal quality

Section 2 ndash Common Linear Thermal Bridges

38

Is the psi value really an indicator of a detailrsquos thermal qualityYes and no

At structural thermal bridges a psi value is a comparison between the U‐value of the assembly(ies) and the U‐value of the junction A junction detail that ldquopassesrdquo (001 WmK) for one assembly may not pass with another

Section 2 ndash Common Linear Thermal Bridges

39

Section 2 ndash Common Linear Thermal Bridges

2x6 wall no studs Ψ = ‐ 0058 WmK 2x6 wall 2‐stud Ψ = ‐ 0040 WmK

When is a performance comparison validWhen the two models being compared have the same assemblies and the same geometry ‐the only difference is at the junction Example above

40

stem wall Ψ = ‐0004 WmK FPSF (frost‐protected shallow foundation) Ψ = 0160 WmK

bull Thermal bridge at the foundation is typically the most challenging to addressbull The concrete stem wall and FPSF footing acts as a radiation fin

STEP 4 ndash Avoid accidental ldquoradiation finsrdquo

Section 2 ndash Common Linear Thermal Bridges

41

FPSF (well insulated) Ψ = 0013 WmK

Thick layers of continuous insulation can improve the performance of the detail but even

FPSF Ψ = 0160 WmK

a very well insulated FPSF is still close to the 001 WmK limit

Section 2 ndash Common Linear Thermal Bridges

STEP 4 ‐ Avoid accidental radiation fins ‐ even well‐insulated ones

42

stem wall Ψ = ‐0004 WmK Thermally broken stem wall Ψ = ‐0136 WmK

Section 2 ndash Common Linear Thermal Bridges

43

Thermally broken stem wall provides an insulated break between the stem wall and the floor slab effectively cutting off the ldquoradiation finrdquoAligning exterior insulation layers at junction of stem wall and above grade wall also helpsSTEP 5 ndash An insulated break between the exterior wall and floor slab works best

ICF parapet Ψ = 0200 WmK Foamglas thermal break Ψ = ‐0071 WmK

Another good location to cut off the radiation fin

Section 2 ndash Common Linear Thermal Bridges

44

Window positioned outside of thermal envelope Ψ = 010 WmKEffectively R‐value of window reduced by 20 ‐ 30 depending on window size

Section 2 ndash Common Linear Thermal Bridges

Window positioned on edge of thermal envelope Ψ = 004 WmKR‐value of window reduced by 5 ‐10 depending on window size

45

Window centered in plane of insulation Ψ = 002 to 003 WmKR‐value of window is almost preserved

Section 2 ndash Common Linear Thermal Bridges

46

47

Break

Section 3 ndash Using psi values in PHPP

48

How do I know which thermal bridges need to be modeled and entered in PHPP

Section 3 ndash Using psi values in PHPP

49

How do I know which thermal bridges need to be modeled and entered in PHPP

PHI requires 1 of 2 paths1) Model all thermal bridges enter psi values for both + and ‐2) Model and enter only thermal bridges with psi values over 001 WmK

Path 2 begs the question ndash how do I know which TBs will be over 001 WmK before Irsquove modeled them

Image source httpwwwtheblazecomblog20130124finally‐the‐answer‐sort‐of‐for‐what‐came‐first‐the‐chicken‐or‐the‐egg

Section 3 ndash Using psi values in PHPP

50

EavesMost details will have negative psi value

Rim joistAlmost always positive psi value ‐MODEL

Wall to slabfootingOnly well‐designed details will have negative psi value ‐MODEL

Footing below bearing wall or postOnly well‐designed details will have psi value lt 001 WmK‐MODEL

Roof ridgeMost details will have negative psi value

Section 3 ndash Using psi values in PHPP

51

RakeMost details will have negative psi value

Windowdoor sill on slab MODEL BUThellipCan be entered as a window sill TB + wall‐to‐slab TB (requires two separate psi values)

Window sillAlmost always positive psi value since overinsulationis difficult ndashMODEL

Window headIf overinsulated probably no need to model If not ndashMODEL

Section 3 ndash Using psi values in PHPP

52

Exterior cornerMost details will have negative psi value

Interior cornerAlmost always positive psi value ndashMODEL

Window jambIf overinsulated probably no need to model If not ndashMODEL

Wall junctionIf insulation layers are interrupted ‐MODEL

Section 3 ndash Using psi values in PHPP

53

Other places to keep in mind for possible thermal bridgesbull Plumbing stacksbull Rain pipes (interior)bull ERV vent penetrations (to the exterior)bull Sump pumpsbull Radon remediation pipes (if interior to the building)

Section 3 ndash Using psi values in PHPP

54

Section 3 ndash Using psi values in PHPP

55

Section 3 ndash Using psi values in WUFI Passive

56

What is a thermal bridge

Short answerA discontinuity in the thermal envelope

5

Section 1 ndash Background + Basics

What is a thermal bridge

Short answerA discontinuity in the thermal envelope

What types of discontinuities might there be in a thermal envelope

6

Section 1 ndash Background + Basics

What is a thermal bridge

Short answerA discontinuity in the thermal envelope

What types of discontinuities might there be in a thermal envelopebull Repetitive bridges (studs floor joists rafters)bull Material changes (windows insulation)bull Penetrations (pipes fasteners)bull Assembly junctions (roof to wall wall to floor etc)bull Corners

7

Section 1 ndash Background + Basics

Repetitive TBs Penetrations Assembly junctions(point TBs) (linear TBs)

8

Should be accounted for in calculation of assembly U‐values in the PHPP

Usually too minor to be considered for heat loss calculations But some cases could be a durability concern Some cases need calculation (ex ‐commercial facades)

Three types1) Structural (ex ndash rim

joists prefab wall junctions)

2) Geometric (ex ndash wall corners roof ridge)

3) Combination (ex ndashwall to roof wall to slab)

Section 1 ndash Background + Basics

Repetitive TBs ndash entry in PHPP

9

Section 1 ndash Background + Basics

Repetitive TBs ndash entry in WUFI Passive (static side only)

10

Section 1 ndash Background + Basics

Image from David White Right Environments 2010

Circled areas are common linear thermal bridges

bull The wallfoundation intersection is a combination linear TB (structuralgeometric)

bull The roofwall intersection is also a combination (structuralgeometric)

bull The rim joist is purely a structural linear TB

roofwall intersection

rim joist

wallfoundation intersection

11

Section 1 ndash Background + Basics

Thermal bridges ndashdo they matter

bull Thermal bridges make up a small portion of heat loss in a poorly insulated envelope ‐16 in a typical insulated 2x6 wall

bull If same details from a standard stud wall were used to construct an R‐45 wall heat loss through thermal bridges would approach 50

extrapolated from Christian JE and J Kosny 1996

12

Section 1 ndash Background + Basics

How is that possible

1 As insulation levels increase less heat is transmitted but the remaining heat flow through the uninsulated portions of the envelope make up a greater percentage of that remainder

2 Heat begins to move laterally through thermal bridges They can transport more heat than their limited surface area suggests

13

Section 1 ndash Background + Basics

From Pembina Institute Accelerating Market Transformation for High Performance Building Enclosures 2016

14

Section 1 ndash Background + Basics

ldquoThermal bridging is underestimatedhellip Morrison Hershfieldhas calculated that shelf angles parapets window perimeters etc can result in the underestimation of 20 to 70 of the total heat flow through wallsrdquo

Morrison Hershfield Building Envelope Thermal Bridging Guide (2014)

15

graph from Building Science Corp

Section 1 ndash Background + Basics

bull Heat loss through a linear thermal bridge is measured with a Ψvalue

bull A Ψ value is like a U‐value for thermal bridgesU x A x dT = heat loss from a surface of area AΨ x L x dT = heat loss from a linear thermal bridge of length L

bull Ψ values lt= 001 WmK qualify as ldquothermal bridge freerdquo according to Passive House

bull To calculate Ψ values a 2‐D heat flow simulation model (such as THERM or Flixo) is used

16

Section 1 ndash Background + Basics

17

Section 1 ndash Background + Basics

For PHPP the thermal bridge heat loss is conceptually the difference between the ldquotruerdquo heat loss calculated using 2‐dimensional simulation (THERM or Flixo) and the heat loss calculated using the typical UA method (U x A x deltaT = heat loss (or gain))

Image from David White Right Environments 2010

18

Section 1 ndash Background + Basics

ldquo2D heat lossrdquo ndash U1L1 ndash U2L2 = Ψ

Image from David White Right Environments 2010

19

Section 1 ndash Background + Basics

L2d ndash U1L1 ndash U2L2 = Ψ

ldquo2D heat lossrdquo ndash U1L1 ndash U2L2 = Ψ

Image from David White Right Environments 2010

20

Section 1 ndash Background + Basics

L2d ndash U1L1 ndash U2L2 = Ψ

Φ ΔT ndash U1L1 ndash U2L2 = Ψ(heat flux)

Image from David White Right Environments 2010

21

Section 1 ndash Background + Basics

UeqLtotal ndash U1L1 ndash U2L2 = Ψ(equivalent U‐value)

L2d ndash U1L1 ndash U2L2 = Ψ

Φ ΔT ndash U1L1 ndash U2L2 = Ψ(heat flux)

Image from David White Right Environments 2010

22

Section 1 ndash Background + Basics

As used in the PHPP the psi value is always based on a comparison of heat flows ‐ a comparison between the actual heat flow and the estimated heat flow In this sense psi is a correction factor

Image from David White Right Environments 2010

Details coming uphellip1 Wall corners2 Rim joists3 Footings4 Parapets5 Windows

23

Section 1 ndash Background + Basics

When calculating heat loss U x A x dTbull Using exterior dimensions area A = 40 x 10 = 400sfbull Using interior dimensions area A = 36 x 10 = 360sf

Which area A gives the correct heat loss

24

Section 1 ndash Background + Basics

When calculating heat loss U x A x dTbull Using exterior dimensions leads to an overestimatebull Using interior dimensions leads to an underestimate

PH convention is to use exterior dimensions so heat loss is overestimated

25

Section 1 ndash Background + Basics

Section 2 ndash Common Linear Thermal Bridges

2x6 wall no studs Ψ = ‐ 0058 WmK 2x6 wall 2‐stud Ψ = ‐ 0040 WmK

bull By subtraction negative psi values correct for overestimate of heat loss at exterior cornersbull The lower (more negative) the better Higher psi values indicate increasing heat lossbull Positive psi values above 001 WmK indicate net heat transfer (heat gain in summer heat loss in winter)that should be accounted for in PHPP

Step 1 ndash Avoid bridging elements 26

2x6 wall Ψ = ‐ 0040 WmK 2x8 wall Ψ = ‐ 0045 WmK

Is the 2x8 wall corner a ldquobetterrdquo detail

Section 2 ndash Common Linear Thermal Bridges

27

2x6 wall Ψ = ‐ 0040 WmK 2x8 wall Ψ = ‐ 0045 WmK

NoA thicker wall section needs a larger correction factor due to larger overestimate of heat loss

Section 2 ndash Common Linear Thermal Bridges

28

Is the psi value really an indicator of a detailrsquos thermal quality

Section 2 ndash Common Linear Thermal Bridges

29

Is the psi value really an indicator of a detailrsquos thermal qualityYes and no

At geometric bridges it does two things at once ndash it is both a correction factor and an indicator of heat flow ndash but primarily a correction factor

Section 2 ndash Common Linear Thermal Bridges

30

Is the psi value really an indicator of a detailrsquos thermal qualityYes and no

At geometric bridges it does two things at once ndash it is both a correction factor and an indicator of heat flow ndash but primarily a correction factor

Section 2 ndash Common Linear Thermal Bridges

31

Exterior cornerInsulated 2x6 wall w solid post Ψ = ‐ 0004 WmK

rim joist fib batt (R‐11) Ψ = 0089 WmK rim joist rim board (R‐11) Ψ = 0129 WmK

bull Rim joist thermal bridge ‐ challenging to achieve the Ψ = 001 WmK targetbull Maintaining continuity and alignment of insulation layers is a good first step

STEP 2 ndash Align insulation layers

Section 2 ndash Common Linear Thermal Bridges

32

rim joist 2x4 wall w 1rdquo exterior XPS (R‐13) Ψ = 0047 WmK

Section 2 ndash Common Linear Thermal Bridges

33

rim joist fib batt (R‐11) Ψ = 0089 WmK

bull Exterior insulation helps control heat flow through uninsulated studs and plates

STEP 3 ndash Use continuous exterior insulation to isolate bridging elements

rim joist 2x4 wall w 1rdquo exterior XPS (R‐13) Ψ = 0047 WmK

Use enough exterior insulation and the psi value can be driven down below 001 WmK

Section 2 ndash Common Linear Thermal Bridges

34

rim joist 2x4 wall w 4rdquo exterior XPSΨ = 0011 WmK

rim joist 2x4 wall w 4rdquo exterior XPSΨ = 0011 WmK

Question ndash are the psi values for these two details the same or different

Section 2 ndash Common Linear Thermal Bridges

35

rim joist 2x6 wall w 4rdquo exterior XPSΨ =

rim joist 2x4 wall w 4rdquo exterior XPSΨ = 0011 WmK

Is the detail on the left a ldquobetterrdquo detailIs heat flow through the detail on the right really 2x higher than the heat flow on the leftDoes 4rdquo of exterior foam guarantee a good psi value

Section 2 ndash Common Linear Thermal Bridges

36

rim joist 2x6 wall w 4rdquo exterior XPSΨ = 0020 WmK

rim joist 2x4 wall w 4rdquo exterior XPSΨ = 0011 WmK

NoFor the 2x6 wall therersquos now simply a larger difference between the higher R‐value wall assembly and the rim joist R‐value which has remained the same

Section 2 ndash Common Linear Thermal Bridges

37

rim joist 2x6 wall w 4rdquo exterior XPSΨ = 0020 WmK

Is the psi value really an indicator of a detailrsquos thermal quality

Section 2 ndash Common Linear Thermal Bridges

38

Is the psi value really an indicator of a detailrsquos thermal qualityYes and no

At structural thermal bridges a psi value is a comparison between the U‐value of the assembly(ies) and the U‐value of the junction A junction detail that ldquopassesrdquo (001 WmK) for one assembly may not pass with another

Section 2 ndash Common Linear Thermal Bridges

39

Section 2 ndash Common Linear Thermal Bridges

2x6 wall no studs Ψ = ‐ 0058 WmK 2x6 wall 2‐stud Ψ = ‐ 0040 WmK

When is a performance comparison validWhen the two models being compared have the same assemblies and the same geometry ‐the only difference is at the junction Example above

40

stem wall Ψ = ‐0004 WmK FPSF (frost‐protected shallow foundation) Ψ = 0160 WmK

bull Thermal bridge at the foundation is typically the most challenging to addressbull The concrete stem wall and FPSF footing acts as a radiation fin

STEP 4 ndash Avoid accidental ldquoradiation finsrdquo

Section 2 ndash Common Linear Thermal Bridges

41

FPSF (well insulated) Ψ = 0013 WmK

Thick layers of continuous insulation can improve the performance of the detail but even

FPSF Ψ = 0160 WmK

a very well insulated FPSF is still close to the 001 WmK limit

Section 2 ndash Common Linear Thermal Bridges

STEP 4 ‐ Avoid accidental radiation fins ‐ even well‐insulated ones

42

stem wall Ψ = ‐0004 WmK Thermally broken stem wall Ψ = ‐0136 WmK

Section 2 ndash Common Linear Thermal Bridges

43

Thermally broken stem wall provides an insulated break between the stem wall and the floor slab effectively cutting off the ldquoradiation finrdquoAligning exterior insulation layers at junction of stem wall and above grade wall also helpsSTEP 5 ndash An insulated break between the exterior wall and floor slab works best

ICF parapet Ψ = 0200 WmK Foamglas thermal break Ψ = ‐0071 WmK

Another good location to cut off the radiation fin

Section 2 ndash Common Linear Thermal Bridges

44

Window positioned outside of thermal envelope Ψ = 010 WmKEffectively R‐value of window reduced by 20 ‐ 30 depending on window size

Section 2 ndash Common Linear Thermal Bridges

Window positioned on edge of thermal envelope Ψ = 004 WmKR‐value of window reduced by 5 ‐10 depending on window size

45

Window centered in plane of insulation Ψ = 002 to 003 WmKR‐value of window is almost preserved

Section 2 ndash Common Linear Thermal Bridges

46

47

Break

Section 3 ndash Using psi values in PHPP

48

How do I know which thermal bridges need to be modeled and entered in PHPP

Section 3 ndash Using psi values in PHPP

49

How do I know which thermal bridges need to be modeled and entered in PHPP

PHI requires 1 of 2 paths1) Model all thermal bridges enter psi values for both + and ‐2) Model and enter only thermal bridges with psi values over 001 WmK

Path 2 begs the question ndash how do I know which TBs will be over 001 WmK before Irsquove modeled them

Image source httpwwwtheblazecomblog20130124finally‐the‐answer‐sort‐of‐for‐what‐came‐first‐the‐chicken‐or‐the‐egg

Section 3 ndash Using psi values in PHPP

50

EavesMost details will have negative psi value

Rim joistAlmost always positive psi value ‐MODEL

Wall to slabfootingOnly well‐designed details will have negative psi value ‐MODEL

Footing below bearing wall or postOnly well‐designed details will have psi value lt 001 WmK‐MODEL

Roof ridgeMost details will have negative psi value

Section 3 ndash Using psi values in PHPP

51

RakeMost details will have negative psi value

Windowdoor sill on slab MODEL BUThellipCan be entered as a window sill TB + wall‐to‐slab TB (requires two separate psi values)

Window sillAlmost always positive psi value since overinsulationis difficult ndashMODEL

Window headIf overinsulated probably no need to model If not ndashMODEL

Section 3 ndash Using psi values in PHPP

52

Exterior cornerMost details will have negative psi value

Interior cornerAlmost always positive psi value ndashMODEL

Window jambIf overinsulated probably no need to model If not ndashMODEL

Wall junctionIf insulation layers are interrupted ‐MODEL

Section 3 ndash Using psi values in PHPP

53

Other places to keep in mind for possible thermal bridgesbull Plumbing stacksbull Rain pipes (interior)bull ERV vent penetrations (to the exterior)bull Sump pumpsbull Radon remediation pipes (if interior to the building)

Section 3 ndash Using psi values in PHPP

54

Section 3 ndash Using psi values in PHPP

55

Section 3 ndash Using psi values in WUFI Passive

56

What is a thermal bridge

Short answerA discontinuity in the thermal envelope

What types of discontinuities might there be in a thermal envelope

6

Section 1 ndash Background + Basics

What is a thermal bridge

Short answerA discontinuity in the thermal envelope

What types of discontinuities might there be in a thermal envelopebull Repetitive bridges (studs floor joists rafters)bull Material changes (windows insulation)bull Penetrations (pipes fasteners)bull Assembly junctions (roof to wall wall to floor etc)bull Corners

7

Section 1 ndash Background + Basics

Repetitive TBs Penetrations Assembly junctions(point TBs) (linear TBs)

8

Should be accounted for in calculation of assembly U‐values in the PHPP

Usually too minor to be considered for heat loss calculations But some cases could be a durability concern Some cases need calculation (ex ‐commercial facades)

Three types1) Structural (ex ndash rim

joists prefab wall junctions)

2) Geometric (ex ndash wall corners roof ridge)

3) Combination (ex ndashwall to roof wall to slab)

Section 1 ndash Background + Basics

Repetitive TBs ndash entry in PHPP

9

Section 1 ndash Background + Basics

Repetitive TBs ndash entry in WUFI Passive (static side only)

10

Section 1 ndash Background + Basics

Image from David White Right Environments 2010

Circled areas are common linear thermal bridges

bull The wallfoundation intersection is a combination linear TB (structuralgeometric)

bull The roofwall intersection is also a combination (structuralgeometric)

bull The rim joist is purely a structural linear TB

roofwall intersection

rim joist

wallfoundation intersection

11

Section 1 ndash Background + Basics

Thermal bridges ndashdo they matter

bull Thermal bridges make up a small portion of heat loss in a poorly insulated envelope ‐16 in a typical insulated 2x6 wall

bull If same details from a standard stud wall were used to construct an R‐45 wall heat loss through thermal bridges would approach 50

extrapolated from Christian JE and J Kosny 1996

12

Section 1 ndash Background + Basics

How is that possible

1 As insulation levels increase less heat is transmitted but the remaining heat flow through the uninsulated portions of the envelope make up a greater percentage of that remainder

2 Heat begins to move laterally through thermal bridges They can transport more heat than their limited surface area suggests

13

Section 1 ndash Background + Basics

From Pembina Institute Accelerating Market Transformation for High Performance Building Enclosures 2016

14

Section 1 ndash Background + Basics

ldquoThermal bridging is underestimatedhellip Morrison Hershfieldhas calculated that shelf angles parapets window perimeters etc can result in the underestimation of 20 to 70 of the total heat flow through wallsrdquo

Morrison Hershfield Building Envelope Thermal Bridging Guide (2014)

15

graph from Building Science Corp

Section 1 ndash Background + Basics

bull Heat loss through a linear thermal bridge is measured with a Ψvalue

bull A Ψ value is like a U‐value for thermal bridgesU x A x dT = heat loss from a surface of area AΨ x L x dT = heat loss from a linear thermal bridge of length L

bull Ψ values lt= 001 WmK qualify as ldquothermal bridge freerdquo according to Passive House

bull To calculate Ψ values a 2‐D heat flow simulation model (such as THERM or Flixo) is used

16

Section 1 ndash Background + Basics

17

Section 1 ndash Background + Basics

For PHPP the thermal bridge heat loss is conceptually the difference between the ldquotruerdquo heat loss calculated using 2‐dimensional simulation (THERM or Flixo) and the heat loss calculated using the typical UA method (U x A x deltaT = heat loss (or gain))

Image from David White Right Environments 2010

18

Section 1 ndash Background + Basics

ldquo2D heat lossrdquo ndash U1L1 ndash U2L2 = Ψ

Image from David White Right Environments 2010

19

Section 1 ndash Background + Basics

L2d ndash U1L1 ndash U2L2 = Ψ

ldquo2D heat lossrdquo ndash U1L1 ndash U2L2 = Ψ

Image from David White Right Environments 2010

20

Section 1 ndash Background + Basics

L2d ndash U1L1 ndash U2L2 = Ψ

Φ ΔT ndash U1L1 ndash U2L2 = Ψ(heat flux)

Image from David White Right Environments 2010

21

Section 1 ndash Background + Basics

UeqLtotal ndash U1L1 ndash U2L2 = Ψ(equivalent U‐value)

L2d ndash U1L1 ndash U2L2 = Ψ

Φ ΔT ndash U1L1 ndash U2L2 = Ψ(heat flux)

Image from David White Right Environments 2010

22

Section 1 ndash Background + Basics

As used in the PHPP the psi value is always based on a comparison of heat flows ‐ a comparison between the actual heat flow and the estimated heat flow In this sense psi is a correction factor

Image from David White Right Environments 2010

Details coming uphellip1 Wall corners2 Rim joists3 Footings4 Parapets5 Windows

23

Section 1 ndash Background + Basics

When calculating heat loss U x A x dTbull Using exterior dimensions area A = 40 x 10 = 400sfbull Using interior dimensions area A = 36 x 10 = 360sf

Which area A gives the correct heat loss

24

Section 1 ndash Background + Basics

When calculating heat loss U x A x dTbull Using exterior dimensions leads to an overestimatebull Using interior dimensions leads to an underestimate

PH convention is to use exterior dimensions so heat loss is overestimated

25

Section 1 ndash Background + Basics

Section 2 ndash Common Linear Thermal Bridges

2x6 wall no studs Ψ = ‐ 0058 WmK 2x6 wall 2‐stud Ψ = ‐ 0040 WmK

bull By subtraction negative psi values correct for overestimate of heat loss at exterior cornersbull The lower (more negative) the better Higher psi values indicate increasing heat lossbull Positive psi values above 001 WmK indicate net heat transfer (heat gain in summer heat loss in winter)that should be accounted for in PHPP

Step 1 ndash Avoid bridging elements 26

2x6 wall Ψ = ‐ 0040 WmK 2x8 wall Ψ = ‐ 0045 WmK

Is the 2x8 wall corner a ldquobetterrdquo detail

Section 2 ndash Common Linear Thermal Bridges

27

2x6 wall Ψ = ‐ 0040 WmK 2x8 wall Ψ = ‐ 0045 WmK

NoA thicker wall section needs a larger correction factor due to larger overestimate of heat loss

Section 2 ndash Common Linear Thermal Bridges

28

Is the psi value really an indicator of a detailrsquos thermal quality

Section 2 ndash Common Linear Thermal Bridges

29

Is the psi value really an indicator of a detailrsquos thermal qualityYes and no

At geometric bridges it does two things at once ndash it is both a correction factor and an indicator of heat flow ndash but primarily a correction factor

Section 2 ndash Common Linear Thermal Bridges

30

Is the psi value really an indicator of a detailrsquos thermal qualityYes and no

At geometric bridges it does two things at once ndash it is both a correction factor and an indicator of heat flow ndash but primarily a correction factor

Section 2 ndash Common Linear Thermal Bridges

31

Exterior cornerInsulated 2x6 wall w solid post Ψ = ‐ 0004 WmK

rim joist fib batt (R‐11) Ψ = 0089 WmK rim joist rim board (R‐11) Ψ = 0129 WmK

bull Rim joist thermal bridge ‐ challenging to achieve the Ψ = 001 WmK targetbull Maintaining continuity and alignment of insulation layers is a good first step

STEP 2 ndash Align insulation layers

Section 2 ndash Common Linear Thermal Bridges

32

rim joist 2x4 wall w 1rdquo exterior XPS (R‐13) Ψ = 0047 WmK

Section 2 ndash Common Linear Thermal Bridges

33

rim joist fib batt (R‐11) Ψ = 0089 WmK

bull Exterior insulation helps control heat flow through uninsulated studs and plates

STEP 3 ndash Use continuous exterior insulation to isolate bridging elements

rim joist 2x4 wall w 1rdquo exterior XPS (R‐13) Ψ = 0047 WmK

Use enough exterior insulation and the psi value can be driven down below 001 WmK

Section 2 ndash Common Linear Thermal Bridges

34

rim joist 2x4 wall w 4rdquo exterior XPSΨ = 0011 WmK

rim joist 2x4 wall w 4rdquo exterior XPSΨ = 0011 WmK

Question ndash are the psi values for these two details the same or different

Section 2 ndash Common Linear Thermal Bridges

35

rim joist 2x6 wall w 4rdquo exterior XPSΨ =

rim joist 2x4 wall w 4rdquo exterior XPSΨ = 0011 WmK

Is the detail on the left a ldquobetterrdquo detailIs heat flow through the detail on the right really 2x higher than the heat flow on the leftDoes 4rdquo of exterior foam guarantee a good psi value

Section 2 ndash Common Linear Thermal Bridges

36

rim joist 2x6 wall w 4rdquo exterior XPSΨ = 0020 WmK

rim joist 2x4 wall w 4rdquo exterior XPSΨ = 0011 WmK

NoFor the 2x6 wall therersquos now simply a larger difference between the higher R‐value wall assembly and the rim joist R‐value which has remained the same

Section 2 ndash Common Linear Thermal Bridges

37

rim joist 2x6 wall w 4rdquo exterior XPSΨ = 0020 WmK

Is the psi value really an indicator of a detailrsquos thermal quality

Section 2 ndash Common Linear Thermal Bridges

38

Is the psi value really an indicator of a detailrsquos thermal qualityYes and no

At structural thermal bridges a psi value is a comparison between the U‐value of the assembly(ies) and the U‐value of the junction A junction detail that ldquopassesrdquo (001 WmK) for one assembly may not pass with another

Section 2 ndash Common Linear Thermal Bridges

39

Section 2 ndash Common Linear Thermal Bridges

2x6 wall no studs Ψ = ‐ 0058 WmK 2x6 wall 2‐stud Ψ = ‐ 0040 WmK

When is a performance comparison validWhen the two models being compared have the same assemblies and the same geometry ‐the only difference is at the junction Example above

40

stem wall Ψ = ‐0004 WmK FPSF (frost‐protected shallow foundation) Ψ = 0160 WmK

bull Thermal bridge at the foundation is typically the most challenging to addressbull The concrete stem wall and FPSF footing acts as a radiation fin

STEP 4 ndash Avoid accidental ldquoradiation finsrdquo

Section 2 ndash Common Linear Thermal Bridges

41

FPSF (well insulated) Ψ = 0013 WmK

Thick layers of continuous insulation can improve the performance of the detail but even

FPSF Ψ = 0160 WmK

a very well insulated FPSF is still close to the 001 WmK limit

Section 2 ndash Common Linear Thermal Bridges

STEP 4 ‐ Avoid accidental radiation fins ‐ even well‐insulated ones

42

stem wall Ψ = ‐0004 WmK Thermally broken stem wall Ψ = ‐0136 WmK

Section 2 ndash Common Linear Thermal Bridges

43

Thermally broken stem wall provides an insulated break between the stem wall and the floor slab effectively cutting off the ldquoradiation finrdquoAligning exterior insulation layers at junction of stem wall and above grade wall also helpsSTEP 5 ndash An insulated break between the exterior wall and floor slab works best

ICF parapet Ψ = 0200 WmK Foamglas thermal break Ψ = ‐0071 WmK

Another good location to cut off the radiation fin

Section 2 ndash Common Linear Thermal Bridges

44

Window positioned outside of thermal envelope Ψ = 010 WmKEffectively R‐value of window reduced by 20 ‐ 30 depending on window size

Section 2 ndash Common Linear Thermal Bridges

Window positioned on edge of thermal envelope Ψ = 004 WmKR‐value of window reduced by 5 ‐10 depending on window size

45

Window centered in plane of insulation Ψ = 002 to 003 WmKR‐value of window is almost preserved

Section 2 ndash Common Linear Thermal Bridges

46

47

Break

Section 3 ndash Using psi values in PHPP

48

How do I know which thermal bridges need to be modeled and entered in PHPP

Section 3 ndash Using psi values in PHPP

49

How do I know which thermal bridges need to be modeled and entered in PHPP

PHI requires 1 of 2 paths1) Model all thermal bridges enter psi values for both + and ‐2) Model and enter only thermal bridges with psi values over 001 WmK

Path 2 begs the question ndash how do I know which TBs will be over 001 WmK before Irsquove modeled them

Image source httpwwwtheblazecomblog20130124finally‐the‐answer‐sort‐of‐for‐what‐came‐first‐the‐chicken‐or‐the‐egg

Section 3 ndash Using psi values in PHPP

50

EavesMost details will have negative psi value

Rim joistAlmost always positive psi value ‐MODEL

Wall to slabfootingOnly well‐designed details will have negative psi value ‐MODEL

Footing below bearing wall or postOnly well‐designed details will have psi value lt 001 WmK‐MODEL

Roof ridgeMost details will have negative psi value

Section 3 ndash Using psi values in PHPP

51

RakeMost details will have negative psi value

Windowdoor sill on slab MODEL BUThellipCan be entered as a window sill TB + wall‐to‐slab TB (requires two separate psi values)

Window sillAlmost always positive psi value since overinsulationis difficult ndashMODEL

Window headIf overinsulated probably no need to model If not ndashMODEL

Section 3 ndash Using psi values in PHPP

52

Exterior cornerMost details will have negative psi value

Interior cornerAlmost always positive psi value ndashMODEL

Window jambIf overinsulated probably no need to model If not ndashMODEL

Wall junctionIf insulation layers are interrupted ‐MODEL

Section 3 ndash Using psi values in PHPP

53

Other places to keep in mind for possible thermal bridgesbull Plumbing stacksbull Rain pipes (interior)bull ERV vent penetrations (to the exterior)bull Sump pumpsbull Radon remediation pipes (if interior to the building)

Section 3 ndash Using psi values in PHPP

54

Section 3 ndash Using psi values in PHPP

55

Section 3 ndash Using psi values in WUFI Passive

56

What is a thermal bridge

Short answerA discontinuity in the thermal envelope

What types of discontinuities might there be in a thermal envelopebull Repetitive bridges (studs floor joists rafters)bull Material changes (windows insulation)bull Penetrations (pipes fasteners)bull Assembly junctions (roof to wall wall to floor etc)bull Corners

7

Section 1 ndash Background + Basics

Repetitive TBs Penetrations Assembly junctions(point TBs) (linear TBs)

8

Should be accounted for in calculation of assembly U‐values in the PHPP

Usually too minor to be considered for heat loss calculations But some cases could be a durability concern Some cases need calculation (ex ‐commercial facades)

Three types1) Structural (ex ndash rim

joists prefab wall junctions)

2) Geometric (ex ndash wall corners roof ridge)

3) Combination (ex ndashwall to roof wall to slab)

Section 1 ndash Background + Basics

Repetitive TBs ndash entry in PHPP

9

Section 1 ndash Background + Basics

Repetitive TBs ndash entry in WUFI Passive (static side only)

10

Section 1 ndash Background + Basics

Image from David White Right Environments 2010

Circled areas are common linear thermal bridges

bull The wallfoundation intersection is a combination linear TB (structuralgeometric)

bull The roofwall intersection is also a combination (structuralgeometric)

bull The rim joist is purely a structural linear TB

roofwall intersection

rim joist

wallfoundation intersection

11

Section 1 ndash Background + Basics

Thermal bridges ndashdo they matter

bull Thermal bridges make up a small portion of heat loss in a poorly insulated envelope ‐16 in a typical insulated 2x6 wall

bull If same details from a standard stud wall were used to construct an R‐45 wall heat loss through thermal bridges would approach 50

extrapolated from Christian JE and J Kosny 1996

12

Section 1 ndash Background + Basics

How is that possible

1 As insulation levels increase less heat is transmitted but the remaining heat flow through the uninsulated portions of the envelope make up a greater percentage of that remainder

2 Heat begins to move laterally through thermal bridges They can transport more heat than their limited surface area suggests

13

Section 1 ndash Background + Basics

From Pembina Institute Accelerating Market Transformation for High Performance Building Enclosures 2016

14

Section 1 ndash Background + Basics

ldquoThermal bridging is underestimatedhellip Morrison Hershfieldhas calculated that shelf angles parapets window perimeters etc can result in the underestimation of 20 to 70 of the total heat flow through wallsrdquo

Morrison Hershfield Building Envelope Thermal Bridging Guide (2014)

15

graph from Building Science Corp

Section 1 ndash Background + Basics

bull Heat loss through a linear thermal bridge is measured with a Ψvalue

bull A Ψ value is like a U‐value for thermal bridgesU x A x dT = heat loss from a surface of area AΨ x L x dT = heat loss from a linear thermal bridge of length L

bull Ψ values lt= 001 WmK qualify as ldquothermal bridge freerdquo according to Passive House

bull To calculate Ψ values a 2‐D heat flow simulation model (such as THERM or Flixo) is used

16

Section 1 ndash Background + Basics

17

Section 1 ndash Background + Basics

For PHPP the thermal bridge heat loss is conceptually the difference between the ldquotruerdquo heat loss calculated using 2‐dimensional simulation (THERM or Flixo) and the heat loss calculated using the typical UA method (U x A x deltaT = heat loss (or gain))

Image from David White Right Environments 2010

18

Section 1 ndash Background + Basics

ldquo2D heat lossrdquo ndash U1L1 ndash U2L2 = Ψ

Image from David White Right Environments 2010

19

Section 1 ndash Background + Basics

L2d ndash U1L1 ndash U2L2 = Ψ

ldquo2D heat lossrdquo ndash U1L1 ndash U2L2 = Ψ

Image from David White Right Environments 2010

20

Section 1 ndash Background + Basics

L2d ndash U1L1 ndash U2L2 = Ψ

Φ ΔT ndash U1L1 ndash U2L2 = Ψ(heat flux)

Image from David White Right Environments 2010

21

Section 1 ndash Background + Basics

UeqLtotal ndash U1L1 ndash U2L2 = Ψ(equivalent U‐value)

L2d ndash U1L1 ndash U2L2 = Ψ

Φ ΔT ndash U1L1 ndash U2L2 = Ψ(heat flux)

Image from David White Right Environments 2010

22

Section 1 ndash Background + Basics

As used in the PHPP the psi value is always based on a comparison of heat flows ‐ a comparison between the actual heat flow and the estimated heat flow In this sense psi is a correction factor

Image from David White Right Environments 2010

Details coming uphellip1 Wall corners2 Rim joists3 Footings4 Parapets5 Windows

23

Section 1 ndash Background + Basics

When calculating heat loss U x A x dTbull Using exterior dimensions area A = 40 x 10 = 400sfbull Using interior dimensions area A = 36 x 10 = 360sf

Which area A gives the correct heat loss

24

Section 1 ndash Background + Basics

When calculating heat loss U x A x dTbull Using exterior dimensions leads to an overestimatebull Using interior dimensions leads to an underestimate

PH convention is to use exterior dimensions so heat loss is overestimated

25

Section 1 ndash Background + Basics

Section 2 ndash Common Linear Thermal Bridges

2x6 wall no studs Ψ = ‐ 0058 WmK 2x6 wall 2‐stud Ψ = ‐ 0040 WmK

bull By subtraction negative psi values correct for overestimate of heat loss at exterior cornersbull The lower (more negative) the better Higher psi values indicate increasing heat lossbull Positive psi values above 001 WmK indicate net heat transfer (heat gain in summer heat loss in winter)that should be accounted for in PHPP

Step 1 ndash Avoid bridging elements 26

2x6 wall Ψ = ‐ 0040 WmK 2x8 wall Ψ = ‐ 0045 WmK

Is the 2x8 wall corner a ldquobetterrdquo detail

Section 2 ndash Common Linear Thermal Bridges

27

2x6 wall Ψ = ‐ 0040 WmK 2x8 wall Ψ = ‐ 0045 WmK

NoA thicker wall section needs a larger correction factor due to larger overestimate of heat loss

Section 2 ndash Common Linear Thermal Bridges

28

Is the psi value really an indicator of a detailrsquos thermal quality

Section 2 ndash Common Linear Thermal Bridges

29

Is the psi value really an indicator of a detailrsquos thermal qualityYes and no

At geometric bridges it does two things at once ndash it is both a correction factor and an indicator of heat flow ndash but primarily a correction factor

Section 2 ndash Common Linear Thermal Bridges

30

Is the psi value really an indicator of a detailrsquos thermal qualityYes and no

At geometric bridges it does two things at once ndash it is both a correction factor and an indicator of heat flow ndash but primarily a correction factor

Section 2 ndash Common Linear Thermal Bridges

31

Exterior cornerInsulated 2x6 wall w solid post Ψ = ‐ 0004 WmK

rim joist fib batt (R‐11) Ψ = 0089 WmK rim joist rim board (R‐11) Ψ = 0129 WmK

bull Rim joist thermal bridge ‐ challenging to achieve the Ψ = 001 WmK targetbull Maintaining continuity and alignment of insulation layers is a good first step

STEP 2 ndash Align insulation layers

Section 2 ndash Common Linear Thermal Bridges

32

rim joist 2x4 wall w 1rdquo exterior XPS (R‐13) Ψ = 0047 WmK

Section 2 ndash Common Linear Thermal Bridges

33

rim joist fib batt (R‐11) Ψ = 0089 WmK

bull Exterior insulation helps control heat flow through uninsulated studs and plates

STEP 3 ndash Use continuous exterior insulation to isolate bridging elements

rim joist 2x4 wall w 1rdquo exterior XPS (R‐13) Ψ = 0047 WmK

Use enough exterior insulation and the psi value can be driven down below 001 WmK

Section 2 ndash Common Linear Thermal Bridges

34

rim joist 2x4 wall w 4rdquo exterior XPSΨ = 0011 WmK

rim joist 2x4 wall w 4rdquo exterior XPSΨ = 0011 WmK

Question ndash are the psi values for these two details the same or different

Section 2 ndash Common Linear Thermal Bridges

35

rim joist 2x6 wall w 4rdquo exterior XPSΨ =

rim joist 2x4 wall w 4rdquo exterior XPSΨ = 0011 WmK

Is the detail on the left a ldquobetterrdquo detailIs heat flow through the detail on the right really 2x higher than the heat flow on the leftDoes 4rdquo of exterior foam guarantee a good psi value

Section 2 ndash Common Linear Thermal Bridges

36

rim joist 2x6 wall w 4rdquo exterior XPSΨ = 0020 WmK

rim joist 2x4 wall w 4rdquo exterior XPSΨ = 0011 WmK

NoFor the 2x6 wall therersquos now simply a larger difference between the higher R‐value wall assembly and the rim joist R‐value which has remained the same

Section 2 ndash Common Linear Thermal Bridges

37

rim joist 2x6 wall w 4rdquo exterior XPSΨ = 0020 WmK

Is the psi value really an indicator of a detailrsquos thermal quality

Section 2 ndash Common Linear Thermal Bridges

38

Is the psi value really an indicator of a detailrsquos thermal qualityYes and no

At structural thermal bridges a psi value is a comparison between the U‐value of the assembly(ies) and the U‐value of the junction A junction detail that ldquopassesrdquo (001 WmK) for one assembly may not pass with another

Section 2 ndash Common Linear Thermal Bridges

39

Section 2 ndash Common Linear Thermal Bridges

2x6 wall no studs Ψ = ‐ 0058 WmK 2x6 wall 2‐stud Ψ = ‐ 0040 WmK

When is a performance comparison validWhen the two models being compared have the same assemblies and the same geometry ‐the only difference is at the junction Example above

40

stem wall Ψ = ‐0004 WmK FPSF (frost‐protected shallow foundation) Ψ = 0160 WmK

bull Thermal bridge at the foundation is typically the most challenging to addressbull The concrete stem wall and FPSF footing acts as a radiation fin

STEP 4 ndash Avoid accidental ldquoradiation finsrdquo

Section 2 ndash Common Linear Thermal Bridges

41

FPSF (well insulated) Ψ = 0013 WmK

Thick layers of continuous insulation can improve the performance of the detail but even

FPSF Ψ = 0160 WmK

a very well insulated FPSF is still close to the 001 WmK limit

Section 2 ndash Common Linear Thermal Bridges

STEP 4 ‐ Avoid accidental radiation fins ‐ even well‐insulated ones

42

stem wall Ψ = ‐0004 WmK Thermally broken stem wall Ψ = ‐0136 WmK

Section 2 ndash Common Linear Thermal Bridges

43

Thermally broken stem wall provides an insulated break between the stem wall and the floor slab effectively cutting off the ldquoradiation finrdquoAligning exterior insulation layers at junction of stem wall and above grade wall also helpsSTEP 5 ndash An insulated break between the exterior wall and floor slab works best

ICF parapet Ψ = 0200 WmK Foamglas thermal break Ψ = ‐0071 WmK

Another good location to cut off the radiation fin

Section 2 ndash Common Linear Thermal Bridges

44

Window positioned outside of thermal envelope Ψ = 010 WmKEffectively R‐value of window reduced by 20 ‐ 30 depending on window size

Section 2 ndash Common Linear Thermal Bridges

Window positioned on edge of thermal envelope Ψ = 004 WmKR‐value of window reduced by 5 ‐10 depending on window size

45

Window centered in plane of insulation Ψ = 002 to 003 WmKR‐value of window is almost preserved

Section 2 ndash Common Linear Thermal Bridges

46

47

Break

Section 3 ndash Using psi values in PHPP

48

How do I know which thermal bridges need to be modeled and entered in PHPP

Section 3 ndash Using psi values in PHPP

49

How do I know which thermal bridges need to be modeled and entered in PHPP

PHI requires 1 of 2 paths1) Model all thermal bridges enter psi values for both + and ‐2) Model and enter only thermal bridges with psi values over 001 WmK

Path 2 begs the question ndash how do I know which TBs will be over 001 WmK before Irsquove modeled them

Image source httpwwwtheblazecomblog20130124finally‐the‐answer‐sort‐of‐for‐what‐came‐first‐the‐chicken‐or‐the‐egg

Section 3 ndash Using psi values in PHPP

50

EavesMost details will have negative psi value

Rim joistAlmost always positive psi value ‐MODEL

Wall to slabfootingOnly well‐designed details will have negative psi value ‐MODEL

Footing below bearing wall or postOnly well‐designed details will have psi value lt 001 WmK‐MODEL

Roof ridgeMost details will have negative psi value

Section 3 ndash Using psi values in PHPP

51

RakeMost details will have negative psi value

Windowdoor sill on slab MODEL BUThellipCan be entered as a window sill TB + wall‐to‐slab TB (requires two separate psi values)

Window sillAlmost always positive psi value since overinsulationis difficult ndashMODEL

Window headIf overinsulated probably no need to model If not ndashMODEL

Section 3 ndash Using psi values in PHPP

52

Exterior cornerMost details will have negative psi value

Interior cornerAlmost always positive psi value ndashMODEL

Window jambIf overinsulated probably no need to model If not ndashMODEL

Wall junctionIf insulation layers are interrupted ‐MODEL

Section 3 ndash Using psi values in PHPP

53

Other places to keep in mind for possible thermal bridgesbull Plumbing stacksbull Rain pipes (interior)bull ERV vent penetrations (to the exterior)bull Sump pumpsbull Radon remediation pipes (if interior to the building)

Section 3 ndash Using psi values in PHPP

54

Section 3 ndash Using psi values in PHPP

55

Section 3 ndash Using psi values in WUFI Passive

56

Repetitive TBs Penetrations Assembly junctions(point TBs) (linear TBs)

8

Should be accounted for in calculation of assembly U‐values in the PHPP

Usually too minor to be considered for heat loss calculations But some cases could be a durability concern Some cases need calculation (ex ‐commercial facades)

Three types1) Structural (ex ndash rim

joists prefab wall junctions)

2) Geometric (ex ndash wall corners roof ridge)

3) Combination (ex ndashwall to roof wall to slab)

Section 1 ndash Background + Basics

Repetitive TBs ndash entry in PHPP

9

Section 1 ndash Background + Basics

Repetitive TBs ndash entry in WUFI Passive (static side only)

10

Section 1 ndash Background + Basics

Image from David White Right Environments 2010

Circled areas are common linear thermal bridges

bull The wallfoundation intersection is a combination linear TB (structuralgeometric)

bull The roofwall intersection is also a combination (structuralgeometric)

bull The rim joist is purely a structural linear TB

roofwall intersection

rim joist

wallfoundation intersection

11

Section 1 ndash Background + Basics

Thermal bridges ndashdo they matter

bull Thermal bridges make up a small portion of heat loss in a poorly insulated envelope ‐16 in a typical insulated 2x6 wall

bull If same details from a standard stud wall were used to construct an R‐45 wall heat loss through thermal bridges would approach 50

extrapolated from Christian JE and J Kosny 1996

12

Section 1 ndash Background + Basics

How is that possible

1 As insulation levels increase less heat is transmitted but the remaining heat flow through the uninsulated portions of the envelope make up a greater percentage of that remainder

2 Heat begins to move laterally through thermal bridges They can transport more heat than their limited surface area suggests

13

Section 1 ndash Background + Basics

From Pembina Institute Accelerating Market Transformation for High Performance Building Enclosures 2016

14

Section 1 ndash Background + Basics

ldquoThermal bridging is underestimatedhellip Morrison Hershfieldhas calculated that shelf angles parapets window perimeters etc can result in the underestimation of 20 to 70 of the total heat flow through wallsrdquo

Morrison Hershfield Building Envelope Thermal Bridging Guide (2014)

15

graph from Building Science Corp

Section 1 ndash Background + Basics

bull Heat loss through a linear thermal bridge is measured with a Ψvalue

bull A Ψ value is like a U‐value for thermal bridgesU x A x dT = heat loss from a surface of area AΨ x L x dT = heat loss from a linear thermal bridge of length L

bull Ψ values lt= 001 WmK qualify as ldquothermal bridge freerdquo according to Passive House

bull To calculate Ψ values a 2‐D heat flow simulation model (such as THERM or Flixo) is used

16

Section 1 ndash Background + Basics

17

Section 1 ndash Background + Basics

For PHPP the thermal bridge heat loss is conceptually the difference between the ldquotruerdquo heat loss calculated using 2‐dimensional simulation (THERM or Flixo) and the heat loss calculated using the typical UA method (U x A x deltaT = heat loss (or gain))

Image from David White Right Environments 2010

18

Section 1 ndash Background + Basics

ldquo2D heat lossrdquo ndash U1L1 ndash U2L2 = Ψ

Image from David White Right Environments 2010

19

Section 1 ndash Background + Basics

L2d ndash U1L1 ndash U2L2 = Ψ

ldquo2D heat lossrdquo ndash U1L1 ndash U2L2 = Ψ

Image from David White Right Environments 2010

20

Section 1 ndash Background + Basics

L2d ndash U1L1 ndash U2L2 = Ψ

Φ ΔT ndash U1L1 ndash U2L2 = Ψ(heat flux)

Image from David White Right Environments 2010

21

Section 1 ndash Background + Basics

UeqLtotal ndash U1L1 ndash U2L2 = Ψ(equivalent U‐value)

L2d ndash U1L1 ndash U2L2 = Ψ

Φ ΔT ndash U1L1 ndash U2L2 = Ψ(heat flux)

Image from David White Right Environments 2010

22

Section 1 ndash Background + Basics

As used in the PHPP the psi value is always based on a comparison of heat flows ‐ a comparison between the actual heat flow and the estimated heat flow In this sense psi is a correction factor

Image from David White Right Environments 2010

Details coming uphellip1 Wall corners2 Rim joists3 Footings4 Parapets5 Windows

23

Section 1 ndash Background + Basics

When calculating heat loss U x A x dTbull Using exterior dimensions area A = 40 x 10 = 400sfbull Using interior dimensions area A = 36 x 10 = 360sf

Which area A gives the correct heat loss

24

Section 1 ndash Background + Basics

When calculating heat loss U x A x dTbull Using exterior dimensions leads to an overestimatebull Using interior dimensions leads to an underestimate

PH convention is to use exterior dimensions so heat loss is overestimated

25

Section 1 ndash Background + Basics

Section 2 ndash Common Linear Thermal Bridges

2x6 wall no studs Ψ = ‐ 0058 WmK 2x6 wall 2‐stud Ψ = ‐ 0040 WmK

bull By subtraction negative psi values correct for overestimate of heat loss at exterior cornersbull The lower (more negative) the better Higher psi values indicate increasing heat lossbull Positive psi values above 001 WmK indicate net heat transfer (heat gain in summer heat loss in winter)that should be accounted for in PHPP

Step 1 ndash Avoid bridging elements 26

2x6 wall Ψ = ‐ 0040 WmK 2x8 wall Ψ = ‐ 0045 WmK

Is the 2x8 wall corner a ldquobetterrdquo detail

Section 2 ndash Common Linear Thermal Bridges

27

2x6 wall Ψ = ‐ 0040 WmK 2x8 wall Ψ = ‐ 0045 WmK

NoA thicker wall section needs a larger correction factor due to larger overestimate of heat loss

Section 2 ndash Common Linear Thermal Bridges

28

Is the psi value really an indicator of a detailrsquos thermal quality

Section 2 ndash Common Linear Thermal Bridges

29

Is the psi value really an indicator of a detailrsquos thermal qualityYes and no

At geometric bridges it does two things at once ndash it is both a correction factor and an indicator of heat flow ndash but primarily a correction factor

Section 2 ndash Common Linear Thermal Bridges

30

Is the psi value really an indicator of a detailrsquos thermal qualityYes and no

At geometric bridges it does two things at once ndash it is both a correction factor and an indicator of heat flow ndash but primarily a correction factor

Section 2 ndash Common Linear Thermal Bridges

31

Exterior cornerInsulated 2x6 wall w solid post Ψ = ‐ 0004 WmK

rim joist fib batt (R‐11) Ψ = 0089 WmK rim joist rim board (R‐11) Ψ = 0129 WmK

bull Rim joist thermal bridge ‐ challenging to achieve the Ψ = 001 WmK targetbull Maintaining continuity and alignment of insulation layers is a good first step

STEP 2 ndash Align insulation layers

Section 2 ndash Common Linear Thermal Bridges

32

rim joist 2x4 wall w 1rdquo exterior XPS (R‐13) Ψ = 0047 WmK

Section 2 ndash Common Linear Thermal Bridges

33

rim joist fib batt (R‐11) Ψ = 0089 WmK

bull Exterior insulation helps control heat flow through uninsulated studs and plates

STEP 3 ndash Use continuous exterior insulation to isolate bridging elements

rim joist 2x4 wall w 1rdquo exterior XPS (R‐13) Ψ = 0047 WmK

Use enough exterior insulation and the psi value can be driven down below 001 WmK

Section 2 ndash Common Linear Thermal Bridges

34

rim joist 2x4 wall w 4rdquo exterior XPSΨ = 0011 WmK

rim joist 2x4 wall w 4rdquo exterior XPSΨ = 0011 WmK

Question ndash are the psi values for these two details the same or different

Section 2 ndash Common Linear Thermal Bridges

35

rim joist 2x6 wall w 4rdquo exterior XPSΨ =

rim joist 2x4 wall w 4rdquo exterior XPSΨ = 0011 WmK

Is the detail on the left a ldquobetterrdquo detailIs heat flow through the detail on the right really 2x higher than the heat flow on the leftDoes 4rdquo of exterior foam guarantee a good psi value

Section 2 ndash Common Linear Thermal Bridges

36

rim joist 2x6 wall w 4rdquo exterior XPSΨ = 0020 WmK

rim joist 2x4 wall w 4rdquo exterior XPSΨ = 0011 WmK

NoFor the 2x6 wall therersquos now simply a larger difference between the higher R‐value wall assembly and the rim joist R‐value which has remained the same

Section 2 ndash Common Linear Thermal Bridges

37

rim joist 2x6 wall w 4rdquo exterior XPSΨ = 0020 WmK

Is the psi value really an indicator of a detailrsquos thermal quality

Section 2 ndash Common Linear Thermal Bridges

38

Is the psi value really an indicator of a detailrsquos thermal qualityYes and no

At structural thermal bridges a psi value is a comparison between the U‐value of the assembly(ies) and the U‐value of the junction A junction detail that ldquopassesrdquo (001 WmK) for one assembly may not pass with another

Section 2 ndash Common Linear Thermal Bridges

39

Section 2 ndash Common Linear Thermal Bridges

2x6 wall no studs Ψ = ‐ 0058 WmK 2x6 wall 2‐stud Ψ = ‐ 0040 WmK

When is a performance comparison validWhen the two models being compared have the same assemblies and the same geometry ‐the only difference is at the junction Example above

40

stem wall Ψ = ‐0004 WmK FPSF (frost‐protected shallow foundation) Ψ = 0160 WmK

bull Thermal bridge at the foundation is typically the most challenging to addressbull The concrete stem wall and FPSF footing acts as a radiation fin

STEP 4 ndash Avoid accidental ldquoradiation finsrdquo

Section 2 ndash Common Linear Thermal Bridges

41

FPSF (well insulated) Ψ = 0013 WmK

Thick layers of continuous insulation can improve the performance of the detail but even

FPSF Ψ = 0160 WmK

a very well insulated FPSF is still close to the 001 WmK limit

Section 2 ndash Common Linear Thermal Bridges

STEP 4 ‐ Avoid accidental radiation fins ‐ even well‐insulated ones

42

stem wall Ψ = ‐0004 WmK Thermally broken stem wall Ψ = ‐0136 WmK

Section 2 ndash Common Linear Thermal Bridges

43

Thermally broken stem wall provides an insulated break between the stem wall and the floor slab effectively cutting off the ldquoradiation finrdquoAligning exterior insulation layers at junction of stem wall and above grade wall also helpsSTEP 5 ndash An insulated break between the exterior wall and floor slab works best

ICF parapet Ψ = 0200 WmK Foamglas thermal break Ψ = ‐0071 WmK

Another good location to cut off the radiation fin

Section 2 ndash Common Linear Thermal Bridges

44

Window positioned outside of thermal envelope Ψ = 010 WmKEffectively R‐value of window reduced by 20 ‐ 30 depending on window size

Section 2 ndash Common Linear Thermal Bridges

Window positioned on edge of thermal envelope Ψ = 004 WmKR‐value of window reduced by 5 ‐10 depending on window size

45

Window centered in plane of insulation Ψ = 002 to 003 WmKR‐value of window is almost preserved

Section 2 ndash Common Linear Thermal Bridges

46

47

Break

Section 3 ndash Using psi values in PHPP

48

How do I know which thermal bridges need to be modeled and entered in PHPP

Section 3 ndash Using psi values in PHPP

49

How do I know which thermal bridges need to be modeled and entered in PHPP

PHI requires 1 of 2 paths1) Model all thermal bridges enter psi values for both + and ‐2) Model and enter only thermal bridges with psi values over 001 WmK

Path 2 begs the question ndash how do I know which TBs will be over 001 WmK before Irsquove modeled them

Image source httpwwwtheblazecomblog20130124finally‐the‐answer‐sort‐of‐for‐what‐came‐first‐the‐chicken‐or‐the‐egg

Section 3 ndash Using psi values in PHPP

50

EavesMost details will have negative psi value

Rim joistAlmost always positive psi value ‐MODEL

Wall to slabfootingOnly well‐designed details will have negative psi value ‐MODEL

Footing below bearing wall or postOnly well‐designed details will have psi value lt 001 WmK‐MODEL

Roof ridgeMost details will have negative psi value

Section 3 ndash Using psi values in PHPP

51

RakeMost details will have negative psi value

Windowdoor sill on slab MODEL BUThellipCan be entered as a window sill TB + wall‐to‐slab TB (requires two separate psi values)

Window sillAlmost always positive psi value since overinsulationis difficult ndashMODEL

Window headIf overinsulated probably no need to model If not ndashMODEL

Section 3 ndash Using psi values in PHPP

52

Exterior cornerMost details will have negative psi value

Interior cornerAlmost always positive psi value ndashMODEL

Window jambIf overinsulated probably no need to model If not ndashMODEL

Wall junctionIf insulation layers are interrupted ‐MODEL

Section 3 ndash Using psi values in PHPP

53

Other places to keep in mind for possible thermal bridgesbull Plumbing stacksbull Rain pipes (interior)bull ERV vent penetrations (to the exterior)bull Sump pumpsbull Radon remediation pipes (if interior to the building)

Section 3 ndash Using psi values in PHPP

54

Section 3 ndash Using psi values in PHPP

55

Section 3 ndash Using psi values in WUFI Passive

56

Repetitive TBs ndash entry in PHPP

9

Section 1 ndash Background + Basics

Repetitive TBs ndash entry in WUFI Passive (static side only)

10

Section 1 ndash Background + Basics

Image from David White Right Environments 2010

Circled areas are common linear thermal bridges

bull The wallfoundation intersection is a combination linear TB (structuralgeometric)

bull The roofwall intersection is also a combination (structuralgeometric)

bull The rim joist is purely a structural linear TB

roofwall intersection

rim joist

wallfoundation intersection

11

Section 1 ndash Background + Basics

Thermal bridges ndashdo they matter

bull Thermal bridges make up a small portion of heat loss in a poorly insulated envelope ‐16 in a typical insulated 2x6 wall

bull If same details from a standard stud wall were used to construct an R‐45 wall heat loss through thermal bridges would approach 50

extrapolated from Christian JE and J Kosny 1996

12

Section 1 ndash Background + Basics

How is that possible

1 As insulation levels increase less heat is transmitted but the remaining heat flow through the uninsulated portions of the envelope make up a greater percentage of that remainder

2 Heat begins to move laterally through thermal bridges They can transport more heat than their limited surface area suggests

13

Section 1 ndash Background + Basics

From Pembina Institute Accelerating Market Transformation for High Performance Building Enclosures 2016

14

Section 1 ndash Background + Basics

ldquoThermal bridging is underestimatedhellip Morrison Hershfieldhas calculated that shelf angles parapets window perimeters etc can result in the underestimation of 20 to 70 of the total heat flow through wallsrdquo

Morrison Hershfield Building Envelope Thermal Bridging Guide (2014)

15

graph from Building Science Corp

Section 1 ndash Background + Basics

bull Heat loss through a linear thermal bridge is measured with a Ψvalue

bull A Ψ value is like a U‐value for thermal bridgesU x A x dT = heat loss from a surface of area AΨ x L x dT = heat loss from a linear thermal bridge of length L

bull Ψ values lt= 001 WmK qualify as ldquothermal bridge freerdquo according to Passive House

bull To calculate Ψ values a 2‐D heat flow simulation model (such as THERM or Flixo) is used

16

Section 1 ndash Background + Basics

17

Section 1 ndash Background + Basics

For PHPP the thermal bridge heat loss is conceptually the difference between the ldquotruerdquo heat loss calculated using 2‐dimensional simulation (THERM or Flixo) and the heat loss calculated using the typical UA method (U x A x deltaT = heat loss (or gain))

Image from David White Right Environments 2010

18

Section 1 ndash Background + Basics

ldquo2D heat lossrdquo ndash U1L1 ndash U2L2 = Ψ

Image from David White Right Environments 2010

19

Section 1 ndash Background + Basics

L2d ndash U1L1 ndash U2L2 = Ψ

ldquo2D heat lossrdquo ndash U1L1 ndash U2L2 = Ψ

Image from David White Right Environments 2010

20

Section 1 ndash Background + Basics

L2d ndash U1L1 ndash U2L2 = Ψ

Φ ΔT ndash U1L1 ndash U2L2 = Ψ(heat flux)

Image from David White Right Environments 2010

21

Section 1 ndash Background + Basics

UeqLtotal ndash U1L1 ndash U2L2 = Ψ(equivalent U‐value)

L2d ndash U1L1 ndash U2L2 = Ψ

Φ ΔT ndash U1L1 ndash U2L2 = Ψ(heat flux)

Image from David White Right Environments 2010

22

Section 1 ndash Background + Basics

As used in the PHPP the psi value is always based on a comparison of heat flows ‐ a comparison between the actual heat flow and the estimated heat flow In this sense psi is a correction factor

Image from David White Right Environments 2010

Details coming uphellip1 Wall corners2 Rim joists3 Footings4 Parapets5 Windows

23

Section 1 ndash Background + Basics

When calculating heat loss U x A x dTbull Using exterior dimensions area A = 40 x 10 = 400sfbull Using interior dimensions area A = 36 x 10 = 360sf

Which area A gives the correct heat loss

24

Section 1 ndash Background + Basics

When calculating heat loss U x A x dTbull Using exterior dimensions leads to an overestimatebull Using interior dimensions leads to an underestimate

PH convention is to use exterior dimensions so heat loss is overestimated

25

Section 1 ndash Background + Basics

Section 2 ndash Common Linear Thermal Bridges

2x6 wall no studs Ψ = ‐ 0058 WmK 2x6 wall 2‐stud Ψ = ‐ 0040 WmK

bull By subtraction negative psi values correct for overestimate of heat loss at exterior cornersbull The lower (more negative) the better Higher psi values indicate increasing heat lossbull Positive psi values above 001 WmK indicate net heat transfer (heat gain in summer heat loss in winter)that should be accounted for in PHPP

Step 1 ndash Avoid bridging elements 26

2x6 wall Ψ = ‐ 0040 WmK 2x8 wall Ψ = ‐ 0045 WmK

Is the 2x8 wall corner a ldquobetterrdquo detail

Section 2 ndash Common Linear Thermal Bridges

27

2x6 wall Ψ = ‐ 0040 WmK 2x8 wall Ψ = ‐ 0045 WmK

NoA thicker wall section needs a larger correction factor due to larger overestimate of heat loss

Section 2 ndash Common Linear Thermal Bridges

28

Is the psi value really an indicator of a detailrsquos thermal quality

Section 2 ndash Common Linear Thermal Bridges

29

Is the psi value really an indicator of a detailrsquos thermal qualityYes and no

At geometric bridges it does two things at once ndash it is both a correction factor and an indicator of heat flow ndash but primarily a correction factor

Section 2 ndash Common Linear Thermal Bridges

30

Is the psi value really an indicator of a detailrsquos thermal qualityYes and no

At geometric bridges it does two things at once ndash it is both a correction factor and an indicator of heat flow ndash but primarily a correction factor

Section 2 ndash Common Linear Thermal Bridges

31

Exterior cornerInsulated 2x6 wall w solid post Ψ = ‐ 0004 WmK

rim joist fib batt (R‐11) Ψ = 0089 WmK rim joist rim board (R‐11) Ψ = 0129 WmK

bull Rim joist thermal bridge ‐ challenging to achieve the Ψ = 001 WmK targetbull Maintaining continuity and alignment of insulation layers is a good first step

STEP 2 ndash Align insulation layers

Section 2 ndash Common Linear Thermal Bridges

32

rim joist 2x4 wall w 1rdquo exterior XPS (R‐13) Ψ = 0047 WmK

Section 2 ndash Common Linear Thermal Bridges

33

rim joist fib batt (R‐11) Ψ = 0089 WmK

bull Exterior insulation helps control heat flow through uninsulated studs and plates

STEP 3 ndash Use continuous exterior insulation to isolate bridging elements

rim joist 2x4 wall w 1rdquo exterior XPS (R‐13) Ψ = 0047 WmK

Use enough exterior insulation and the psi value can be driven down below 001 WmK

Section 2 ndash Common Linear Thermal Bridges

34

rim joist 2x4 wall w 4rdquo exterior XPSΨ = 0011 WmK

rim joist 2x4 wall w 4rdquo exterior XPSΨ = 0011 WmK

Question ndash are the psi values for these two details the same or different

Section 2 ndash Common Linear Thermal Bridges

35

rim joist 2x6 wall w 4rdquo exterior XPSΨ =

rim joist 2x4 wall w 4rdquo exterior XPSΨ = 0011 WmK

Is the detail on the left a ldquobetterrdquo detailIs heat flow through the detail on the right really 2x higher than the heat flow on the leftDoes 4rdquo of exterior foam guarantee a good psi value

Section 2 ndash Common Linear Thermal Bridges

36

rim joist 2x6 wall w 4rdquo exterior XPSΨ = 0020 WmK

rim joist 2x4 wall w 4rdquo exterior XPSΨ = 0011 WmK

NoFor the 2x6 wall therersquos now simply a larger difference between the higher R‐value wall assembly and the rim joist R‐value which has remained the same

Section 2 ndash Common Linear Thermal Bridges

37

rim joist 2x6 wall w 4rdquo exterior XPSΨ = 0020 WmK

Is the psi value really an indicator of a detailrsquos thermal quality

Section 2 ndash Common Linear Thermal Bridges

38

Is the psi value really an indicator of a detailrsquos thermal qualityYes and no

At structural thermal bridges a psi value is a comparison between the U‐value of the assembly(ies) and the U‐value of the junction A junction detail that ldquopassesrdquo (001 WmK) for one assembly may not pass with another

Section 2 ndash Common Linear Thermal Bridges

39

Section 2 ndash Common Linear Thermal Bridges

2x6 wall no studs Ψ = ‐ 0058 WmK 2x6 wall 2‐stud Ψ = ‐ 0040 WmK

When is a performance comparison validWhen the two models being compared have the same assemblies and the same geometry ‐the only difference is at the junction Example above

40

stem wall Ψ = ‐0004 WmK FPSF (frost‐protected shallow foundation) Ψ = 0160 WmK

bull Thermal bridge at the foundation is typically the most challenging to addressbull The concrete stem wall and FPSF footing acts as a radiation fin

STEP 4 ndash Avoid accidental ldquoradiation finsrdquo

Section 2 ndash Common Linear Thermal Bridges

41

FPSF (well insulated) Ψ = 0013 WmK

Thick layers of continuous insulation can improve the performance of the detail but even

FPSF Ψ = 0160 WmK

a very well insulated FPSF is still close to the 001 WmK limit

Section 2 ndash Common Linear Thermal Bridges

STEP 4 ‐ Avoid accidental radiation fins ‐ even well‐insulated ones

42

stem wall Ψ = ‐0004 WmK Thermally broken stem wall Ψ = ‐0136 WmK

Section 2 ndash Common Linear Thermal Bridges

43

Thermally broken stem wall provides an insulated break between the stem wall and the floor slab effectively cutting off the ldquoradiation finrdquoAligning exterior insulation layers at junction of stem wall and above grade wall also helpsSTEP 5 ndash An insulated break between the exterior wall and floor slab works best

ICF parapet Ψ = 0200 WmK Foamglas thermal break Ψ = ‐0071 WmK

Another good location to cut off the radiation fin

Section 2 ndash Common Linear Thermal Bridges

44

Window positioned outside of thermal envelope Ψ = 010 WmKEffectively R‐value of window reduced by 20 ‐ 30 depending on window size

Section 2 ndash Common Linear Thermal Bridges

Window positioned on edge of thermal envelope Ψ = 004 WmKR‐value of window reduced by 5 ‐10 depending on window size

45

Window centered in plane of insulation Ψ = 002 to 003 WmKR‐value of window is almost preserved

Section 2 ndash Common Linear Thermal Bridges

46

47

Break

Section 3 ndash Using psi values in PHPP

48

How do I know which thermal bridges need to be modeled and entered in PHPP

Section 3 ndash Using psi values in PHPP

49

How do I know which thermal bridges need to be modeled and entered in PHPP

PHI requires 1 of 2 paths1) Model all thermal bridges enter psi values for both + and ‐2) Model and enter only thermal bridges with psi values over 001 WmK

Path 2 begs the question ndash how do I know which TBs will be over 001 WmK before Irsquove modeled them

Image source httpwwwtheblazecomblog20130124finally‐the‐answer‐sort‐of‐for‐what‐came‐first‐the‐chicken‐or‐the‐egg

Section 3 ndash Using psi values in PHPP

50

EavesMost details will have negative psi value

Rim joistAlmost always positive psi value ‐MODEL

Wall to slabfootingOnly well‐designed details will have negative psi value ‐MODEL

Footing below bearing wall or postOnly well‐designed details will have psi value lt 001 WmK‐MODEL

Roof ridgeMost details will have negative psi value

Section 3 ndash Using psi values in PHPP

51

RakeMost details will have negative psi value

Windowdoor sill on slab MODEL BUThellipCan be entered as a window sill TB + wall‐to‐slab TB (requires two separate psi values)

Window sillAlmost always positive psi value since overinsulationis difficult ndashMODEL

Window headIf overinsulated probably no need to model If not ndashMODEL

Section 3 ndash Using psi values in PHPP

52

Exterior cornerMost details will have negative psi value

Interior cornerAlmost always positive psi value ndashMODEL

Window jambIf overinsulated probably no need to model If not ndashMODEL

Wall junctionIf insulation layers are interrupted ‐MODEL

Section 3 ndash Using psi values in PHPP

53

Other places to keep in mind for possible thermal bridgesbull Plumbing stacksbull Rain pipes (interior)bull ERV vent penetrations (to the exterior)bull Sump pumpsbull Radon remediation pipes (if interior to the building)

Section 3 ndash Using psi values in PHPP

54

Section 3 ndash Using psi values in PHPP

55

Section 3 ndash Using psi values in WUFI Passive

56

Repetitive TBs ndash entry in WUFI Passive (static side only)

10

Section 1 ndash Background + Basics

Image from David White Right Environments 2010

Circled areas are common linear thermal bridges

bull The wallfoundation intersection is a combination linear TB (structuralgeometric)

bull The roofwall intersection is also a combination (structuralgeometric)

bull The rim joist is purely a structural linear TB

roofwall intersection

rim joist

wallfoundation intersection

11

Section 1 ndash Background + Basics

Thermal bridges ndashdo they matter

bull Thermal bridges make up a small portion of heat loss in a poorly insulated envelope ‐16 in a typical insulated 2x6 wall

bull If same details from a standard stud wall were used to construct an R‐45 wall heat loss through thermal bridges would approach 50

extrapolated from Christian JE and J Kosny 1996

12

Section 1 ndash Background + Basics

How is that possible

1 As insulation levels increase less heat is transmitted but the remaining heat flow through the uninsulated portions of the envelope make up a greater percentage of that remainder

2 Heat begins to move laterally through thermal bridges They can transport more heat than their limited surface area suggests

13

Section 1 ndash Background + Basics

From Pembina Institute Accelerating Market Transformation for High Performance Building Enclosures 2016

14

Section 1 ndash Background + Basics

ldquoThermal bridging is underestimatedhellip Morrison Hershfieldhas calculated that shelf angles parapets window perimeters etc can result in the underestimation of 20 to 70 of the total heat flow through wallsrdquo

Morrison Hershfield Building Envelope Thermal Bridging Guide (2014)

15

graph from Building Science Corp

Section 1 ndash Background + Basics

bull Heat loss through a linear thermal bridge is measured with a Ψvalue

bull A Ψ value is like a U‐value for thermal bridgesU x A x dT = heat loss from a surface of area AΨ x L x dT = heat loss from a linear thermal bridge of length L

bull Ψ values lt= 001 WmK qualify as ldquothermal bridge freerdquo according to Passive House

bull To calculate Ψ values a 2‐D heat flow simulation model (such as THERM or Flixo) is used

16

Section 1 ndash Background + Basics

17

Section 1 ndash Background + Basics

For PHPP the thermal bridge heat loss is conceptually the difference between the ldquotruerdquo heat loss calculated using 2‐dimensional simulation (THERM or Flixo) and the heat loss calculated using the typical UA method (U x A x deltaT = heat loss (or gain))

Image from David White Right Environments 2010

18

Section 1 ndash Background + Basics

ldquo2D heat lossrdquo ndash U1L1 ndash U2L2 = Ψ

Image from David White Right Environments 2010

19

Section 1 ndash Background + Basics

L2d ndash U1L1 ndash U2L2 = Ψ

ldquo2D heat lossrdquo ndash U1L1 ndash U2L2 = Ψ

Image from David White Right Environments 2010

20

Section 1 ndash Background + Basics

L2d ndash U1L1 ndash U2L2 = Ψ

Φ ΔT ndash U1L1 ndash U2L2 = Ψ(heat flux)

Image from David White Right Environments 2010

21

Section 1 ndash Background + Basics

UeqLtotal ndash U1L1 ndash U2L2 = Ψ(equivalent U‐value)

L2d ndash U1L1 ndash U2L2 = Ψ

Φ ΔT ndash U1L1 ndash U2L2 = Ψ(heat flux)

Image from David White Right Environments 2010

22

Section 1 ndash Background + Basics

As used in the PHPP the psi value is always based on a comparison of heat flows ‐ a comparison between the actual heat flow and the estimated heat flow In this sense psi is a correction factor

Image from David White Right Environments 2010

Details coming uphellip1 Wall corners2 Rim joists3 Footings4 Parapets5 Windows

23

Section 1 ndash Background + Basics

When calculating heat loss U x A x dTbull Using exterior dimensions area A = 40 x 10 = 400sfbull Using interior dimensions area A = 36 x 10 = 360sf

Which area A gives the correct heat loss

24

Section 1 ndash Background + Basics

When calculating heat loss U x A x dTbull Using exterior dimensions leads to an overestimatebull Using interior dimensions leads to an underestimate

PH convention is to use exterior dimensions so heat loss is overestimated

25

Section 1 ndash Background + Basics

Section 2 ndash Common Linear Thermal Bridges

2x6 wall no studs Ψ = ‐ 0058 WmK 2x6 wall 2‐stud Ψ = ‐ 0040 WmK

bull By subtraction negative psi values correct for overestimate of heat loss at exterior cornersbull The lower (more negative) the better Higher psi values indicate increasing heat lossbull Positive psi values above 001 WmK indicate net heat transfer (heat gain in summer heat loss in winter)that should be accounted for in PHPP

Step 1 ndash Avoid bridging elements 26

2x6 wall Ψ = ‐ 0040 WmK 2x8 wall Ψ = ‐ 0045 WmK

Is the 2x8 wall corner a ldquobetterrdquo detail

Section 2 ndash Common Linear Thermal Bridges

27

2x6 wall Ψ = ‐ 0040 WmK 2x8 wall Ψ = ‐ 0045 WmK

NoA thicker wall section needs a larger correction factor due to larger overestimate of heat loss

Section 2 ndash Common Linear Thermal Bridges

28

Is the psi value really an indicator of a detailrsquos thermal quality

Section 2 ndash Common Linear Thermal Bridges

29

Is the psi value really an indicator of a detailrsquos thermal qualityYes and no

At geometric bridges it does two things at once ndash it is both a correction factor and an indicator of heat flow ndash but primarily a correction factor

Section 2 ndash Common Linear Thermal Bridges

30

Is the psi value really an indicator of a detailrsquos thermal qualityYes and no

At geometric bridges it does two things at once ndash it is both a correction factor and an indicator of heat flow ndash but primarily a correction factor

Section 2 ndash Common Linear Thermal Bridges

31

Exterior cornerInsulated 2x6 wall w solid post Ψ = ‐ 0004 WmK

rim joist fib batt (R‐11) Ψ = 0089 WmK rim joist rim board (R‐11) Ψ = 0129 WmK

bull Rim joist thermal bridge ‐ challenging to achieve the Ψ = 001 WmK targetbull Maintaining continuity and alignment of insulation layers is a good first step

STEP 2 ndash Align insulation layers

Section 2 ndash Common Linear Thermal Bridges

32

rim joist 2x4 wall w 1rdquo exterior XPS (R‐13) Ψ = 0047 WmK

Section 2 ndash Common Linear Thermal Bridges

33

rim joist fib batt (R‐11) Ψ = 0089 WmK

bull Exterior insulation helps control heat flow through uninsulated studs and plates

STEP 3 ndash Use continuous exterior insulation to isolate bridging elements

rim joist 2x4 wall w 1rdquo exterior XPS (R‐13) Ψ = 0047 WmK

Use enough exterior insulation and the psi value can be driven down below 001 WmK

Section 2 ndash Common Linear Thermal Bridges

34

rim joist 2x4 wall w 4rdquo exterior XPSΨ = 0011 WmK

rim joist 2x4 wall w 4rdquo exterior XPSΨ = 0011 WmK

Question ndash are the psi values for these two details the same or different

Section 2 ndash Common Linear Thermal Bridges

35

rim joist 2x6 wall w 4rdquo exterior XPSΨ =

rim joist 2x4 wall w 4rdquo exterior XPSΨ = 0011 WmK

Is the detail on the left a ldquobetterrdquo detailIs heat flow through the detail on the right really 2x higher than the heat flow on the leftDoes 4rdquo of exterior foam guarantee a good psi value

Section 2 ndash Common Linear Thermal Bridges

36

rim joist 2x6 wall w 4rdquo exterior XPSΨ = 0020 WmK

rim joist 2x4 wall w 4rdquo exterior XPSΨ = 0011 WmK

NoFor the 2x6 wall therersquos now simply a larger difference between the higher R‐value wall assembly and the rim joist R‐value which has remained the same

Section 2 ndash Common Linear Thermal Bridges

37

rim joist 2x6 wall w 4rdquo exterior XPSΨ = 0020 WmK

Is the psi value really an indicator of a detailrsquos thermal quality

Section 2 ndash Common Linear Thermal Bridges

38

Is the psi value really an indicator of a detailrsquos thermal qualityYes and no

At structural thermal bridges a psi value is a comparison between the U‐value of the assembly(ies) and the U‐value of the junction A junction detail that ldquopassesrdquo (001 WmK) for one assembly may not pass with another

Section 2 ndash Common Linear Thermal Bridges

39

Section 2 ndash Common Linear Thermal Bridges

2x6 wall no studs Ψ = ‐ 0058 WmK 2x6 wall 2‐stud Ψ = ‐ 0040 WmK

When is a performance comparison validWhen the two models being compared have the same assemblies and the same geometry ‐the only difference is at the junction Example above

40

stem wall Ψ = ‐0004 WmK FPSF (frost‐protected shallow foundation) Ψ = 0160 WmK

bull Thermal bridge at the foundation is typically the most challenging to addressbull The concrete stem wall and FPSF footing acts as a radiation fin

STEP 4 ndash Avoid accidental ldquoradiation finsrdquo

Section 2 ndash Common Linear Thermal Bridges

41

FPSF (well insulated) Ψ = 0013 WmK

Thick layers of continuous insulation can improve the performance of the detail but even

FPSF Ψ = 0160 WmK

a very well insulated FPSF is still close to the 001 WmK limit

Section 2 ndash Common Linear Thermal Bridges

STEP 4 ‐ Avoid accidental radiation fins ‐ even well‐insulated ones

42

stem wall Ψ = ‐0004 WmK Thermally broken stem wall Ψ = ‐0136 WmK

Section 2 ndash Common Linear Thermal Bridges

43

Thermally broken stem wall provides an insulated break between the stem wall and the floor slab effectively cutting off the ldquoradiation finrdquoAligning exterior insulation layers at junction of stem wall and above grade wall also helpsSTEP 5 ndash An insulated break between the exterior wall and floor slab works best

ICF parapet Ψ = 0200 WmK Foamglas thermal break Ψ = ‐0071 WmK

Another good location to cut off the radiation fin

Section 2 ndash Common Linear Thermal Bridges

44

Window positioned outside of thermal envelope Ψ = 010 WmKEffectively R‐value of window reduced by 20 ‐ 30 depending on window size

Section 2 ndash Common Linear Thermal Bridges

Window positioned on edge of thermal envelope Ψ = 004 WmKR‐value of window reduced by 5 ‐10 depending on window size

45

Window centered in plane of insulation Ψ = 002 to 003 WmKR‐value of window is almost preserved

Section 2 ndash Common Linear Thermal Bridges

46

47

Break

Section 3 ndash Using psi values in PHPP

48

How do I know which thermal bridges need to be modeled and entered in PHPP

Section 3 ndash Using psi values in PHPP

49

How do I know which thermal bridges need to be modeled and entered in PHPP

PHI requires 1 of 2 paths1) Model all thermal bridges enter psi values for both + and ‐2) Model and enter only thermal bridges with psi values over 001 WmK

Path 2 begs the question ndash how do I know which TBs will be over 001 WmK before Irsquove modeled them

Image source httpwwwtheblazecomblog20130124finally‐the‐answer‐sort‐of‐for‐what‐came‐first‐the‐chicken‐or‐the‐egg

Section 3 ndash Using psi values in PHPP

50

EavesMost details will have negative psi value

Rim joistAlmost always positive psi value ‐MODEL

Wall to slabfootingOnly well‐designed details will have negative psi value ‐MODEL

Footing below bearing wall or postOnly well‐designed details will have psi value lt 001 WmK‐MODEL

Roof ridgeMost details will have negative psi value

Section 3 ndash Using psi values in PHPP

51

RakeMost details will have negative psi value

Windowdoor sill on slab MODEL BUThellipCan be entered as a window sill TB + wall‐to‐slab TB (requires two separate psi values)

Window sillAlmost always positive psi value since overinsulationis difficult ndashMODEL

Window headIf overinsulated probably no need to model If not ndashMODEL

Section 3 ndash Using psi values in PHPP

52

Exterior cornerMost details will have negative psi value

Interior cornerAlmost always positive psi value ndashMODEL

Window jambIf overinsulated probably no need to model If not ndashMODEL

Wall junctionIf insulation layers are interrupted ‐MODEL

Section 3 ndash Using psi values in PHPP

53

Other places to keep in mind for possible thermal bridgesbull Plumbing stacksbull Rain pipes (interior)bull ERV vent penetrations (to the exterior)bull Sump pumpsbull Radon remediation pipes (if interior to the building)

Section 3 ndash Using psi values in PHPP

54

Section 3 ndash Using psi values in PHPP

55

Section 3 ndash Using psi values in WUFI Passive

56

Image from David White Right Environments 2010

Circled areas are common linear thermal bridges

bull The wallfoundation intersection is a combination linear TB (structuralgeometric)

bull The roofwall intersection is also a combination (structuralgeometric)

bull The rim joist is purely a structural linear TB

roofwall intersection

rim joist

wallfoundation intersection

11

Section 1 ndash Background + Basics

Thermal bridges ndashdo they matter

bull Thermal bridges make up a small portion of heat loss in a poorly insulated envelope ‐16 in a typical insulated 2x6 wall

bull If same details from a standard stud wall were used to construct an R‐45 wall heat loss through thermal bridges would approach 50

extrapolated from Christian JE and J Kosny 1996

12

Section 1 ndash Background + Basics

How is that possible

1 As insulation levels increase less heat is transmitted but the remaining heat flow through the uninsulated portions of the envelope make up a greater percentage of that remainder

2 Heat begins to move laterally through thermal bridges They can transport more heat than their limited surface area suggests

13

Section 1 ndash Background + Basics

From Pembina Institute Accelerating Market Transformation for High Performance Building Enclosures 2016

14

Section 1 ndash Background + Basics

ldquoThermal bridging is underestimatedhellip Morrison Hershfieldhas calculated that shelf angles parapets window perimeters etc can result in the underestimation of 20 to 70 of the total heat flow through wallsrdquo

Morrison Hershfield Building Envelope Thermal Bridging Guide (2014)

15

graph from Building Science Corp

Section 1 ndash Background + Basics

bull Heat loss through a linear thermal bridge is measured with a Ψvalue

bull A Ψ value is like a U‐value for thermal bridgesU x A x dT = heat loss from a surface of area AΨ x L x dT = heat loss from a linear thermal bridge of length L

bull Ψ values lt= 001 WmK qualify as ldquothermal bridge freerdquo according to Passive House

bull To calculate Ψ values a 2‐D heat flow simulation model (such as THERM or Flixo) is used

16

Section 1 ndash Background + Basics

17

Section 1 ndash Background + Basics

For PHPP the thermal bridge heat loss is conceptually the difference between the ldquotruerdquo heat loss calculated using 2‐dimensional simulation (THERM or Flixo) and the heat loss calculated using the typical UA method (U x A x deltaT = heat loss (or gain))

Image from David White Right Environments 2010

18

Section 1 ndash Background + Basics

ldquo2D heat lossrdquo ndash U1L1 ndash U2L2 = Ψ

Image from David White Right Environments 2010

19

Section 1 ndash Background + Basics

L2d ndash U1L1 ndash U2L2 = Ψ

ldquo2D heat lossrdquo ndash U1L1 ndash U2L2 = Ψ

Image from David White Right Environments 2010

20

Section 1 ndash Background + Basics

L2d ndash U1L1 ndash U2L2 = Ψ

Φ ΔT ndash U1L1 ndash U2L2 = Ψ(heat flux)

Image from David White Right Environments 2010

21

Section 1 ndash Background + Basics

UeqLtotal ndash U1L1 ndash U2L2 = Ψ(equivalent U‐value)

L2d ndash U1L1 ndash U2L2 = Ψ

Φ ΔT ndash U1L1 ndash U2L2 = Ψ(heat flux)

Image from David White Right Environments 2010

22

Section 1 ndash Background + Basics

As used in the PHPP the psi value is always based on a comparison of heat flows ‐ a comparison between the actual heat flow and the estimated heat flow In this sense psi is a correction factor

Image from David White Right Environments 2010

Details coming uphellip1 Wall corners2 Rim joists3 Footings4 Parapets5 Windows

23

Section 1 ndash Background + Basics

When calculating heat loss U x A x dTbull Using exterior dimensions area A = 40 x 10 = 400sfbull Using interior dimensions area A = 36 x 10 = 360sf

Which area A gives the correct heat loss

24

Section 1 ndash Background + Basics

When calculating heat loss U x A x dTbull Using exterior dimensions leads to an overestimatebull Using interior dimensions leads to an underestimate

PH convention is to use exterior dimensions so heat loss is overestimated

25

Section 1 ndash Background + Basics

Section 2 ndash Common Linear Thermal Bridges

2x6 wall no studs Ψ = ‐ 0058 WmK 2x6 wall 2‐stud Ψ = ‐ 0040 WmK

bull By subtraction negative psi values correct for overestimate of heat loss at exterior cornersbull The lower (more negative) the better Higher psi values indicate increasing heat lossbull Positive psi values above 001 WmK indicate net heat transfer (heat gain in summer heat loss in winter)that should be accounted for in PHPP

Step 1 ndash Avoid bridging elements 26

2x6 wall Ψ = ‐ 0040 WmK 2x8 wall Ψ = ‐ 0045 WmK

Is the 2x8 wall corner a ldquobetterrdquo detail

Section 2 ndash Common Linear Thermal Bridges

27

2x6 wall Ψ = ‐ 0040 WmK 2x8 wall Ψ = ‐ 0045 WmK

NoA thicker wall section needs a larger correction factor due to larger overestimate of heat loss

Section 2 ndash Common Linear Thermal Bridges

28

Is the psi value really an indicator of a detailrsquos thermal quality

Section 2 ndash Common Linear Thermal Bridges

29

Is the psi value really an indicator of a detailrsquos thermal qualityYes and no

At geometric bridges it does two things at once ndash it is both a correction factor and an indicator of heat flow ndash but primarily a correction factor

Section 2 ndash Common Linear Thermal Bridges

30

Is the psi value really an indicator of a detailrsquos thermal qualityYes and no

At geometric bridges it does two things at once ndash it is both a correction factor and an indicator of heat flow ndash but primarily a correction factor

Section 2 ndash Common Linear Thermal Bridges

31

Exterior cornerInsulated 2x6 wall w solid post Ψ = ‐ 0004 WmK

rim joist fib batt (R‐11) Ψ = 0089 WmK rim joist rim board (R‐11) Ψ = 0129 WmK

bull Rim joist thermal bridge ‐ challenging to achieve the Ψ = 001 WmK targetbull Maintaining continuity and alignment of insulation layers is a good first step

STEP 2 ndash Align insulation layers

Section 2 ndash Common Linear Thermal Bridges

32

rim joist 2x4 wall w 1rdquo exterior XPS (R‐13) Ψ = 0047 WmK

Section 2 ndash Common Linear Thermal Bridges

33

rim joist fib batt (R‐11) Ψ = 0089 WmK

bull Exterior insulation helps control heat flow through uninsulated studs and plates

STEP 3 ndash Use continuous exterior insulation to isolate bridging elements

rim joist 2x4 wall w 1rdquo exterior XPS (R‐13) Ψ = 0047 WmK

Use enough exterior insulation and the psi value can be driven down below 001 WmK

Section 2 ndash Common Linear Thermal Bridges

34

rim joist 2x4 wall w 4rdquo exterior XPSΨ = 0011 WmK

rim joist 2x4 wall w 4rdquo exterior XPSΨ = 0011 WmK

Question ndash are the psi values for these two details the same or different

Section 2 ndash Common Linear Thermal Bridges

35

rim joist 2x6 wall w 4rdquo exterior XPSΨ =

rim joist 2x4 wall w 4rdquo exterior XPSΨ = 0011 WmK

Is the detail on the left a ldquobetterrdquo detailIs heat flow through the detail on the right really 2x higher than the heat flow on the leftDoes 4rdquo of exterior foam guarantee a good psi value

Section 2 ndash Common Linear Thermal Bridges

36

rim joist 2x6 wall w 4rdquo exterior XPSΨ = 0020 WmK

rim joist 2x4 wall w 4rdquo exterior XPSΨ = 0011 WmK

NoFor the 2x6 wall therersquos now simply a larger difference between the higher R‐value wall assembly and the rim joist R‐value which has remained the same

Section 2 ndash Common Linear Thermal Bridges

37

rim joist 2x6 wall w 4rdquo exterior XPSΨ = 0020 WmK

Is the psi value really an indicator of a detailrsquos thermal quality

Section 2 ndash Common Linear Thermal Bridges

38

Is the psi value really an indicator of a detailrsquos thermal qualityYes and no

At structural thermal bridges a psi value is a comparison between the U‐value of the assembly(ies) and the U‐value of the junction A junction detail that ldquopassesrdquo (001 WmK) for one assembly may not pass with another

Section 2 ndash Common Linear Thermal Bridges

39

Section 2 ndash Common Linear Thermal Bridges

2x6 wall no studs Ψ = ‐ 0058 WmK 2x6 wall 2‐stud Ψ = ‐ 0040 WmK

When is a performance comparison validWhen the two models being compared have the same assemblies and the same geometry ‐the only difference is at the junction Example above

40

stem wall Ψ = ‐0004 WmK FPSF (frost‐protected shallow foundation) Ψ = 0160 WmK

bull Thermal bridge at the foundation is typically the most challenging to addressbull The concrete stem wall and FPSF footing acts as a radiation fin

STEP 4 ndash Avoid accidental ldquoradiation finsrdquo

Section 2 ndash Common Linear Thermal Bridges

41

FPSF (well insulated) Ψ = 0013 WmK

Thick layers of continuous insulation can improve the performance of the detail but even

FPSF Ψ = 0160 WmK

a very well insulated FPSF is still close to the 001 WmK limit

Section 2 ndash Common Linear Thermal Bridges

STEP 4 ‐ Avoid accidental radiation fins ‐ even well‐insulated ones

42

stem wall Ψ = ‐0004 WmK Thermally broken stem wall Ψ = ‐0136 WmK

Section 2 ndash Common Linear Thermal Bridges

43

Thermally broken stem wall provides an insulated break between the stem wall and the floor slab effectively cutting off the ldquoradiation finrdquoAligning exterior insulation layers at junction of stem wall and above grade wall also helpsSTEP 5 ndash An insulated break between the exterior wall and floor slab works best

ICF parapet Ψ = 0200 WmK Foamglas thermal break Ψ = ‐0071 WmK

Another good location to cut off the radiation fin

Section 2 ndash Common Linear Thermal Bridges

44

Window positioned outside of thermal envelope Ψ = 010 WmKEffectively R‐value of window reduced by 20 ‐ 30 depending on window size

Section 2 ndash Common Linear Thermal Bridges

Window positioned on edge of thermal envelope Ψ = 004 WmKR‐value of window reduced by 5 ‐10 depending on window size

45

Window centered in plane of insulation Ψ = 002 to 003 WmKR‐value of window is almost preserved

Section 2 ndash Common Linear Thermal Bridges

46

47

Break

Section 3 ndash Using psi values in PHPP

48

How do I know which thermal bridges need to be modeled and entered in PHPP

Section 3 ndash Using psi values in PHPP

49

How do I know which thermal bridges need to be modeled and entered in PHPP

PHI requires 1 of 2 paths1) Model all thermal bridges enter psi values for both + and ‐2) Model and enter only thermal bridges with psi values over 001 WmK

Path 2 begs the question ndash how do I know which TBs will be over 001 WmK before Irsquove modeled them

Image source httpwwwtheblazecomblog20130124finally‐the‐answer‐sort‐of‐for‐what‐came‐first‐the‐chicken‐or‐the‐egg

Section 3 ndash Using psi values in PHPP

50

EavesMost details will have negative psi value

Rim joistAlmost always positive psi value ‐MODEL

Wall to slabfootingOnly well‐designed details will have negative psi value ‐MODEL

Footing below bearing wall or postOnly well‐designed details will have psi value lt 001 WmK‐MODEL

Roof ridgeMost details will have negative psi value

Section 3 ndash Using psi values in PHPP

51

RakeMost details will have negative psi value

Windowdoor sill on slab MODEL BUThellipCan be entered as a window sill TB + wall‐to‐slab TB (requires two separate psi values)

Window sillAlmost always positive psi value since overinsulationis difficult ndashMODEL

Window headIf overinsulated probably no need to model If not ndashMODEL

Section 3 ndash Using psi values in PHPP

52

Exterior cornerMost details will have negative psi value

Interior cornerAlmost always positive psi value ndashMODEL

Window jambIf overinsulated probably no need to model If not ndashMODEL

Wall junctionIf insulation layers are interrupted ‐MODEL

Section 3 ndash Using psi values in PHPP

53

Other places to keep in mind for possible thermal bridgesbull Plumbing stacksbull Rain pipes (interior)bull ERV vent penetrations (to the exterior)bull Sump pumpsbull Radon remediation pipes (if interior to the building)

Section 3 ndash Using psi values in PHPP

54

Section 3 ndash Using psi values in PHPP

55

Section 3 ndash Using psi values in WUFI Passive

56

Thermal bridges ndashdo they matter

bull Thermal bridges make up a small portion of heat loss in a poorly insulated envelope ‐16 in a typical insulated 2x6 wall

bull If same details from a standard stud wall were used to construct an R‐45 wall heat loss through thermal bridges would approach 50

extrapolated from Christian JE and J Kosny 1996

12

Section 1 ndash Background + Basics

How is that possible

1 As insulation levels increase less heat is transmitted but the remaining heat flow through the uninsulated portions of the envelope make up a greater percentage of that remainder

2 Heat begins to move laterally through thermal bridges They can transport more heat than their limited surface area suggests

13

Section 1 ndash Background + Basics

From Pembina Institute Accelerating Market Transformation for High Performance Building Enclosures 2016

14

Section 1 ndash Background + Basics

ldquoThermal bridging is underestimatedhellip Morrison Hershfieldhas calculated that shelf angles parapets window perimeters etc can result in the underestimation of 20 to 70 of the total heat flow through wallsrdquo

Morrison Hershfield Building Envelope Thermal Bridging Guide (2014)

15

graph from Building Science Corp

Section 1 ndash Background + Basics

bull Heat loss through a linear thermal bridge is measured with a Ψvalue

bull A Ψ value is like a U‐value for thermal bridgesU x A x dT = heat loss from a surface of area AΨ x L x dT = heat loss from a linear thermal bridge of length L

bull Ψ values lt= 001 WmK qualify as ldquothermal bridge freerdquo according to Passive House

bull To calculate Ψ values a 2‐D heat flow simulation model (such as THERM or Flixo) is used

16

Section 1 ndash Background + Basics

17

Section 1 ndash Background + Basics

For PHPP the thermal bridge heat loss is conceptually the difference between the ldquotruerdquo heat loss calculated using 2‐dimensional simulation (THERM or Flixo) and the heat loss calculated using the typical UA method (U x A x deltaT = heat loss (or gain))

Image from David White Right Environments 2010

18

Section 1 ndash Background + Basics

ldquo2D heat lossrdquo ndash U1L1 ndash U2L2 = Ψ

Image from David White Right Environments 2010

19

Section 1 ndash Background + Basics

L2d ndash U1L1 ndash U2L2 = Ψ

ldquo2D heat lossrdquo ndash U1L1 ndash U2L2 = Ψ

Image from David White Right Environments 2010

20

Section 1 ndash Background + Basics

L2d ndash U1L1 ndash U2L2 = Ψ

Φ ΔT ndash U1L1 ndash U2L2 = Ψ(heat flux)

Image from David White Right Environments 2010

21

Section 1 ndash Background + Basics

UeqLtotal ndash U1L1 ndash U2L2 = Ψ(equivalent U‐value)

L2d ndash U1L1 ndash U2L2 = Ψ

Φ ΔT ndash U1L1 ndash U2L2 = Ψ(heat flux)

Image from David White Right Environments 2010

22

Section 1 ndash Background + Basics

As used in the PHPP the psi value is always based on a comparison of heat flows ‐ a comparison between the actual heat flow and the estimated heat flow In this sense psi is a correction factor

Image from David White Right Environments 2010

Details coming uphellip1 Wall corners2 Rim joists3 Footings4 Parapets5 Windows

23

Section 1 ndash Background + Basics

When calculating heat loss U x A x dTbull Using exterior dimensions area A = 40 x 10 = 400sfbull Using interior dimensions area A = 36 x 10 = 360sf

Which area A gives the correct heat loss

24

Section 1 ndash Background + Basics

When calculating heat loss U x A x dTbull Using exterior dimensions leads to an overestimatebull Using interior dimensions leads to an underestimate

PH convention is to use exterior dimensions so heat loss is overestimated

25

Section 1 ndash Background + Basics

Section 2 ndash Common Linear Thermal Bridges

2x6 wall no studs Ψ = ‐ 0058 WmK 2x6 wall 2‐stud Ψ = ‐ 0040 WmK

bull By subtraction negative psi values correct for overestimate of heat loss at exterior cornersbull The lower (more negative) the better Higher psi values indicate increasing heat lossbull Positive psi values above 001 WmK indicate net heat transfer (heat gain in summer heat loss in winter)that should be accounted for in PHPP

Step 1 ndash Avoid bridging elements 26

2x6 wall Ψ = ‐ 0040 WmK 2x8 wall Ψ = ‐ 0045 WmK

Is the 2x8 wall corner a ldquobetterrdquo detail

Section 2 ndash Common Linear Thermal Bridges

27

2x6 wall Ψ = ‐ 0040 WmK 2x8 wall Ψ = ‐ 0045 WmK

NoA thicker wall section needs a larger correction factor due to larger overestimate of heat loss

Section 2 ndash Common Linear Thermal Bridges

28

Is the psi value really an indicator of a detailrsquos thermal quality

Section 2 ndash Common Linear Thermal Bridges

29

Is the psi value really an indicator of a detailrsquos thermal qualityYes and no

At geometric bridges it does two things at once ndash it is both a correction factor and an indicator of heat flow ndash but primarily a correction factor

Section 2 ndash Common Linear Thermal Bridges

30

Is the psi value really an indicator of a detailrsquos thermal qualityYes and no

At geometric bridges it does two things at once ndash it is both a correction factor and an indicator of heat flow ndash but primarily a correction factor

Section 2 ndash Common Linear Thermal Bridges

31

Exterior cornerInsulated 2x6 wall w solid post Ψ = ‐ 0004 WmK

rim joist fib batt (R‐11) Ψ = 0089 WmK rim joist rim board (R‐11) Ψ = 0129 WmK

bull Rim joist thermal bridge ‐ challenging to achieve the Ψ = 001 WmK targetbull Maintaining continuity and alignment of insulation layers is a good first step

STEP 2 ndash Align insulation layers

Section 2 ndash Common Linear Thermal Bridges

32

rim joist 2x4 wall w 1rdquo exterior XPS (R‐13) Ψ = 0047 WmK

Section 2 ndash Common Linear Thermal Bridges

33

rim joist fib batt (R‐11) Ψ = 0089 WmK

bull Exterior insulation helps control heat flow through uninsulated studs and plates

STEP 3 ndash Use continuous exterior insulation to isolate bridging elements

rim joist 2x4 wall w 1rdquo exterior XPS (R‐13) Ψ = 0047 WmK

Use enough exterior insulation and the psi value can be driven down below 001 WmK

Section 2 ndash Common Linear Thermal Bridges

34

rim joist 2x4 wall w 4rdquo exterior XPSΨ = 0011 WmK

rim joist 2x4 wall w 4rdquo exterior XPSΨ = 0011 WmK

Question ndash are the psi values for these two details the same or different

Section 2 ndash Common Linear Thermal Bridges

35

rim joist 2x6 wall w 4rdquo exterior XPSΨ =

rim joist 2x4 wall w 4rdquo exterior XPSΨ = 0011 WmK

Is the detail on the left a ldquobetterrdquo detailIs heat flow through the detail on the right really 2x higher than the heat flow on the leftDoes 4rdquo of exterior foam guarantee a good psi value

Section 2 ndash Common Linear Thermal Bridges

36

rim joist 2x6 wall w 4rdquo exterior XPSΨ = 0020 WmK

rim joist 2x4 wall w 4rdquo exterior XPSΨ = 0011 WmK

NoFor the 2x6 wall therersquos now simply a larger difference between the higher R‐value wall assembly and the rim joist R‐value which has remained the same

Section 2 ndash Common Linear Thermal Bridges

37

rim joist 2x6 wall w 4rdquo exterior XPSΨ = 0020 WmK

Is the psi value really an indicator of a detailrsquos thermal quality

Section 2 ndash Common Linear Thermal Bridges

38

Is the psi value really an indicator of a detailrsquos thermal qualityYes and no

At structural thermal bridges a psi value is a comparison between the U‐value of the assembly(ies) and the U‐value of the junction A junction detail that ldquopassesrdquo (001 WmK) for one assembly may not pass with another

Section 2 ndash Common Linear Thermal Bridges

39

Section 2 ndash Common Linear Thermal Bridges

2x6 wall no studs Ψ = ‐ 0058 WmK 2x6 wall 2‐stud Ψ = ‐ 0040 WmK

When is a performance comparison validWhen the two models being compared have the same assemblies and the same geometry ‐the only difference is at the junction Example above

40

stem wall Ψ = ‐0004 WmK FPSF (frost‐protected shallow foundation) Ψ = 0160 WmK

bull Thermal bridge at the foundation is typically the most challenging to addressbull The concrete stem wall and FPSF footing acts as a radiation fin

STEP 4 ndash Avoid accidental ldquoradiation finsrdquo

Section 2 ndash Common Linear Thermal Bridges

41

FPSF (well insulated) Ψ = 0013 WmK

Thick layers of continuous insulation can improve the performance of the detail but even

FPSF Ψ = 0160 WmK

a very well insulated FPSF is still close to the 001 WmK limit

Section 2 ndash Common Linear Thermal Bridges

STEP 4 ‐ Avoid accidental radiation fins ‐ even well‐insulated ones

42

stem wall Ψ = ‐0004 WmK Thermally broken stem wall Ψ = ‐0136 WmK

Section 2 ndash Common Linear Thermal Bridges

43

Thermally broken stem wall provides an insulated break between the stem wall and the floor slab effectively cutting off the ldquoradiation finrdquoAligning exterior insulation layers at junction of stem wall and above grade wall also helpsSTEP 5 ndash An insulated break between the exterior wall and floor slab works best

ICF parapet Ψ = 0200 WmK Foamglas thermal break Ψ = ‐0071 WmK

Another good location to cut off the radiation fin

Section 2 ndash Common Linear Thermal Bridges

44

Window positioned outside of thermal envelope Ψ = 010 WmKEffectively R‐value of window reduced by 20 ‐ 30 depending on window size

Section 2 ndash Common Linear Thermal Bridges

Window positioned on edge of thermal envelope Ψ = 004 WmKR‐value of window reduced by 5 ‐10 depending on window size

45

Window centered in plane of insulation Ψ = 002 to 003 WmKR‐value of window is almost preserved

Section 2 ndash Common Linear Thermal Bridges

46

47

Break

Section 3 ndash Using psi values in PHPP

48

How do I know which thermal bridges need to be modeled and entered in PHPP

Section 3 ndash Using psi values in PHPP

49

How do I know which thermal bridges need to be modeled and entered in PHPP

PHI requires 1 of 2 paths1) Model all thermal bridges enter psi values for both + and ‐2) Model and enter only thermal bridges with psi values over 001 WmK

Path 2 begs the question ndash how do I know which TBs will be over 001 WmK before Irsquove modeled them

Image source httpwwwtheblazecomblog20130124finally‐the‐answer‐sort‐of‐for‐what‐came‐first‐the‐chicken‐or‐the‐egg

Section 3 ndash Using psi values in PHPP

50

EavesMost details will have negative psi value

Rim joistAlmost always positive psi value ‐MODEL

Wall to slabfootingOnly well‐designed details will have negative psi value ‐MODEL

Footing below bearing wall or postOnly well‐designed details will have psi value lt 001 WmK‐MODEL

Roof ridgeMost details will have negative psi value

Section 3 ndash Using psi values in PHPP

51

RakeMost details will have negative psi value

Windowdoor sill on slab MODEL BUThellipCan be entered as a window sill TB + wall‐to‐slab TB (requires two separate psi values)

Window sillAlmost always positive psi value since overinsulationis difficult ndashMODEL

Window headIf overinsulated probably no need to model If not ndashMODEL

Section 3 ndash Using psi values in PHPP

52

Exterior cornerMost details will have negative psi value

Interior cornerAlmost always positive psi value ndashMODEL

Window jambIf overinsulated probably no need to model If not ndashMODEL

Wall junctionIf insulation layers are interrupted ‐MODEL

Section 3 ndash Using psi values in PHPP

53

Other places to keep in mind for possible thermal bridgesbull Plumbing stacksbull Rain pipes (interior)bull ERV vent penetrations (to the exterior)bull Sump pumpsbull Radon remediation pipes (if interior to the building)

Section 3 ndash Using psi values in PHPP

54

Section 3 ndash Using psi values in PHPP

55

Section 3 ndash Using psi values in WUFI Passive

56

How is that possible

1 As insulation levels increase less heat is transmitted but the remaining heat flow through the uninsulated portions of the envelope make up a greater percentage of that remainder

2 Heat begins to move laterally through thermal bridges They can transport more heat than their limited surface area suggests

13

Section 1 ndash Background + Basics

From Pembina Institute Accelerating Market Transformation for High Performance Building Enclosures 2016

14

Section 1 ndash Background + Basics

ldquoThermal bridging is underestimatedhellip Morrison Hershfieldhas calculated that shelf angles parapets window perimeters etc can result in the underestimation of 20 to 70 of the total heat flow through wallsrdquo

Morrison Hershfield Building Envelope Thermal Bridging Guide (2014)

15

graph from Building Science Corp

Section 1 ndash Background + Basics

bull Heat loss through a linear thermal bridge is measured with a Ψvalue

bull A Ψ value is like a U‐value for thermal bridgesU x A x dT = heat loss from a surface of area AΨ x L x dT = heat loss from a linear thermal bridge of length L

bull Ψ values lt= 001 WmK qualify as ldquothermal bridge freerdquo according to Passive House

bull To calculate Ψ values a 2‐D heat flow simulation model (such as THERM or Flixo) is used

16

Section 1 ndash Background + Basics

17

Section 1 ndash Background + Basics

For PHPP the thermal bridge heat loss is conceptually the difference between the ldquotruerdquo heat loss calculated using 2‐dimensional simulation (THERM or Flixo) and the heat loss calculated using the typical UA method (U x A x deltaT = heat loss (or gain))

Image from David White Right Environments 2010

18

Section 1 ndash Background + Basics

ldquo2D heat lossrdquo ndash U1L1 ndash U2L2 = Ψ

Image from David White Right Environments 2010

19

Section 1 ndash Background + Basics

L2d ndash U1L1 ndash U2L2 = Ψ

ldquo2D heat lossrdquo ndash U1L1 ndash U2L2 = Ψ

Image from David White Right Environments 2010

20

Section 1 ndash Background + Basics

L2d ndash U1L1 ndash U2L2 = Ψ

Φ ΔT ndash U1L1 ndash U2L2 = Ψ(heat flux)

Image from David White Right Environments 2010

21

Section 1 ndash Background + Basics

UeqLtotal ndash U1L1 ndash U2L2 = Ψ(equivalent U‐value)

L2d ndash U1L1 ndash U2L2 = Ψ

Φ ΔT ndash U1L1 ndash U2L2 = Ψ(heat flux)

Image from David White Right Environments 2010

22

Section 1 ndash Background + Basics

As used in the PHPP the psi value is always based on a comparison of heat flows ‐ a comparison between the actual heat flow and the estimated heat flow In this sense psi is a correction factor

Image from David White Right Environments 2010

Details coming uphellip1 Wall corners2 Rim joists3 Footings4 Parapets5 Windows

23

Section 1 ndash Background + Basics

When calculating heat loss U x A x dTbull Using exterior dimensions area A = 40 x 10 = 400sfbull Using interior dimensions area A = 36 x 10 = 360sf

Which area A gives the correct heat loss

24

Section 1 ndash Background + Basics

When calculating heat loss U x A x dTbull Using exterior dimensions leads to an overestimatebull Using interior dimensions leads to an underestimate

PH convention is to use exterior dimensions so heat loss is overestimated

25

Section 1 ndash Background + Basics

Section 2 ndash Common Linear Thermal Bridges

2x6 wall no studs Ψ = ‐ 0058 WmK 2x6 wall 2‐stud Ψ = ‐ 0040 WmK

bull By subtraction negative psi values correct for overestimate of heat loss at exterior cornersbull The lower (more negative) the better Higher psi values indicate increasing heat lossbull Positive psi values above 001 WmK indicate net heat transfer (heat gain in summer heat loss in winter)that should be accounted for in PHPP

Step 1 ndash Avoid bridging elements 26

2x6 wall Ψ = ‐ 0040 WmK 2x8 wall Ψ = ‐ 0045 WmK

Is the 2x8 wall corner a ldquobetterrdquo detail

Section 2 ndash Common Linear Thermal Bridges

27

2x6 wall Ψ = ‐ 0040 WmK 2x8 wall Ψ = ‐ 0045 WmK

NoA thicker wall section needs a larger correction factor due to larger overestimate of heat loss

Section 2 ndash Common Linear Thermal Bridges

28

Is the psi value really an indicator of a detailrsquos thermal quality

Section 2 ndash Common Linear Thermal Bridges

29

Is the psi value really an indicator of a detailrsquos thermal qualityYes and no

At geometric bridges it does two things at once ndash it is both a correction factor and an indicator of heat flow ndash but primarily a correction factor

Section 2 ndash Common Linear Thermal Bridges

30

Is the psi value really an indicator of a detailrsquos thermal qualityYes and no

At geometric bridges it does two things at once ndash it is both a correction factor and an indicator of heat flow ndash but primarily a correction factor

Section 2 ndash Common Linear Thermal Bridges

31

Exterior cornerInsulated 2x6 wall w solid post Ψ = ‐ 0004 WmK

rim joist fib batt (R‐11) Ψ = 0089 WmK rim joist rim board (R‐11) Ψ = 0129 WmK

bull Rim joist thermal bridge ‐ challenging to achieve the Ψ = 001 WmK targetbull Maintaining continuity and alignment of insulation layers is a good first step

STEP 2 ndash Align insulation layers

Section 2 ndash Common Linear Thermal Bridges

32

rim joist 2x4 wall w 1rdquo exterior XPS (R‐13) Ψ = 0047 WmK

Section 2 ndash Common Linear Thermal Bridges

33

rim joist fib batt (R‐11) Ψ = 0089 WmK

bull Exterior insulation helps control heat flow through uninsulated studs and plates

STEP 3 ndash Use continuous exterior insulation to isolate bridging elements

rim joist 2x4 wall w 1rdquo exterior XPS (R‐13) Ψ = 0047 WmK

Use enough exterior insulation and the psi value can be driven down below 001 WmK

Section 2 ndash Common Linear Thermal Bridges

34

rim joist 2x4 wall w 4rdquo exterior XPSΨ = 0011 WmK

rim joist 2x4 wall w 4rdquo exterior XPSΨ = 0011 WmK

Question ndash are the psi values for these two details the same or different

Section 2 ndash Common Linear Thermal Bridges

35

rim joist 2x6 wall w 4rdquo exterior XPSΨ =

rim joist 2x4 wall w 4rdquo exterior XPSΨ = 0011 WmK

Is the detail on the left a ldquobetterrdquo detailIs heat flow through the detail on the right really 2x higher than the heat flow on the leftDoes 4rdquo of exterior foam guarantee a good psi value

Section 2 ndash Common Linear Thermal Bridges

36

rim joist 2x6 wall w 4rdquo exterior XPSΨ = 0020 WmK

rim joist 2x4 wall w 4rdquo exterior XPSΨ = 0011 WmK

NoFor the 2x6 wall therersquos now simply a larger difference between the higher R‐value wall assembly and the rim joist R‐value which has remained the same

Section 2 ndash Common Linear Thermal Bridges

37

rim joist 2x6 wall w 4rdquo exterior XPSΨ = 0020 WmK

Is the psi value really an indicator of a detailrsquos thermal quality

Section 2 ndash Common Linear Thermal Bridges

38

Is the psi value really an indicator of a detailrsquos thermal qualityYes and no

At structural thermal bridges a psi value is a comparison between the U‐value of the assembly(ies) and the U‐value of the junction A junction detail that ldquopassesrdquo (001 WmK) for one assembly may not pass with another

Section 2 ndash Common Linear Thermal Bridges

39

Section 2 ndash Common Linear Thermal Bridges

2x6 wall no studs Ψ = ‐ 0058 WmK 2x6 wall 2‐stud Ψ = ‐ 0040 WmK

When is a performance comparison validWhen the two models being compared have the same assemblies and the same geometry ‐the only difference is at the junction Example above

40

stem wall Ψ = ‐0004 WmK FPSF (frost‐protected shallow foundation) Ψ = 0160 WmK

bull Thermal bridge at the foundation is typically the most challenging to addressbull The concrete stem wall and FPSF footing acts as a radiation fin

STEP 4 ndash Avoid accidental ldquoradiation finsrdquo

Section 2 ndash Common Linear Thermal Bridges

41

FPSF (well insulated) Ψ = 0013 WmK

Thick layers of continuous insulation can improve the performance of the detail but even

FPSF Ψ = 0160 WmK

a very well insulated FPSF is still close to the 001 WmK limit

Section 2 ndash Common Linear Thermal Bridges

STEP 4 ‐ Avoid accidental radiation fins ‐ even well‐insulated ones

42

stem wall Ψ = ‐0004 WmK Thermally broken stem wall Ψ = ‐0136 WmK

Section 2 ndash Common Linear Thermal Bridges

43

Thermally broken stem wall provides an insulated break between the stem wall and the floor slab effectively cutting off the ldquoradiation finrdquoAligning exterior insulation layers at junction of stem wall and above grade wall also helpsSTEP 5 ndash An insulated break between the exterior wall and floor slab works best

ICF parapet Ψ = 0200 WmK Foamglas thermal break Ψ = ‐0071 WmK

Another good location to cut off the radiation fin

Section 2 ndash Common Linear Thermal Bridges

44

Window positioned outside of thermal envelope Ψ = 010 WmKEffectively R‐value of window reduced by 20 ‐ 30 depending on window size

Section 2 ndash Common Linear Thermal Bridges

Window positioned on edge of thermal envelope Ψ = 004 WmKR‐value of window reduced by 5 ‐10 depending on window size

45

Window centered in plane of insulation Ψ = 002 to 003 WmKR‐value of window is almost preserved

Section 2 ndash Common Linear Thermal Bridges

46

47

Break

Section 3 ndash Using psi values in PHPP

48

How do I know which thermal bridges need to be modeled and entered in PHPP

Section 3 ndash Using psi values in PHPP

49

How do I know which thermal bridges need to be modeled and entered in PHPP

PHI requires 1 of 2 paths1) Model all thermal bridges enter psi values for both + and ‐2) Model and enter only thermal bridges with psi values over 001 WmK

Path 2 begs the question ndash how do I know which TBs will be over 001 WmK before Irsquove modeled them

Image source httpwwwtheblazecomblog20130124finally‐the‐answer‐sort‐of‐for‐what‐came‐first‐the‐chicken‐or‐the‐egg

Section 3 ndash Using psi values in PHPP

50

EavesMost details will have negative psi value

Rim joistAlmost always positive psi value ‐MODEL

Wall to slabfootingOnly well‐designed details will have negative psi value ‐MODEL

Footing below bearing wall or postOnly well‐designed details will have psi value lt 001 WmK‐MODEL

Roof ridgeMost details will have negative psi value

Section 3 ndash Using psi values in PHPP

51

RakeMost details will have negative psi value

Windowdoor sill on slab MODEL BUThellipCan be entered as a window sill TB + wall‐to‐slab TB (requires two separate psi values)

Window sillAlmost always positive psi value since overinsulationis difficult ndashMODEL

Window headIf overinsulated probably no need to model If not ndashMODEL

Section 3 ndash Using psi values in PHPP

52

Exterior cornerMost details will have negative psi value

Interior cornerAlmost always positive psi value ndashMODEL

Window jambIf overinsulated probably no need to model If not ndashMODEL

Wall junctionIf insulation layers are interrupted ‐MODEL

Section 3 ndash Using psi values in PHPP

53

Other places to keep in mind for possible thermal bridgesbull Plumbing stacksbull Rain pipes (interior)bull ERV vent penetrations (to the exterior)bull Sump pumpsbull Radon remediation pipes (if interior to the building)

Section 3 ndash Using psi values in PHPP

54

Section 3 ndash Using psi values in PHPP

55

Section 3 ndash Using psi values in WUFI Passive

56

From Pembina Institute Accelerating Market Transformation for High Performance Building Enclosures 2016

14

Section 1 ndash Background + Basics

ldquoThermal bridging is underestimatedhellip Morrison Hershfieldhas calculated that shelf angles parapets window perimeters etc can result in the underestimation of 20 to 70 of the total heat flow through wallsrdquo

Morrison Hershfield Building Envelope Thermal Bridging Guide (2014)

15

graph from Building Science Corp

Section 1 ndash Background + Basics

bull Heat loss through a linear thermal bridge is measured with a Ψvalue

bull A Ψ value is like a U‐value for thermal bridgesU x A x dT = heat loss from a surface of area AΨ x L x dT = heat loss from a linear thermal bridge of length L

bull Ψ values lt= 001 WmK qualify as ldquothermal bridge freerdquo according to Passive House

bull To calculate Ψ values a 2‐D heat flow simulation model (such as THERM or Flixo) is used

16

Section 1 ndash Background + Basics

17

Section 1 ndash Background + Basics

For PHPP the thermal bridge heat loss is conceptually the difference between the ldquotruerdquo heat loss calculated using 2‐dimensional simulation (THERM or Flixo) and the heat loss calculated using the typical UA method (U x A x deltaT = heat loss (or gain))

Image from David White Right Environments 2010

18

Section 1 ndash Background + Basics

ldquo2D heat lossrdquo ndash U1L1 ndash U2L2 = Ψ

Image from David White Right Environments 2010

19

Section 1 ndash Background + Basics

L2d ndash U1L1 ndash U2L2 = Ψ

ldquo2D heat lossrdquo ndash U1L1 ndash U2L2 = Ψ

Image from David White Right Environments 2010

20

Section 1 ndash Background + Basics

L2d ndash U1L1 ndash U2L2 = Ψ

Φ ΔT ndash U1L1 ndash U2L2 = Ψ(heat flux)

Image from David White Right Environments 2010

21

Section 1 ndash Background + Basics

UeqLtotal ndash U1L1 ndash U2L2 = Ψ(equivalent U‐value)

L2d ndash U1L1 ndash U2L2 = Ψ

Φ ΔT ndash U1L1 ndash U2L2 = Ψ(heat flux)

Image from David White Right Environments 2010

22

Section 1 ndash Background + Basics

As used in the PHPP the psi value is always based on a comparison of heat flows ‐ a comparison between the actual heat flow and the estimated heat flow In this sense psi is a correction factor

Image from David White Right Environments 2010

Details coming uphellip1 Wall corners2 Rim joists3 Footings4 Parapets5 Windows

23

Section 1 ndash Background + Basics

When calculating heat loss U x A x dTbull Using exterior dimensions area A = 40 x 10 = 400sfbull Using interior dimensions area A = 36 x 10 = 360sf

Which area A gives the correct heat loss

24

Section 1 ndash Background + Basics

When calculating heat loss U x A x dTbull Using exterior dimensions leads to an overestimatebull Using interior dimensions leads to an underestimate

PH convention is to use exterior dimensions so heat loss is overestimated

25

Section 1 ndash Background + Basics

Section 2 ndash Common Linear Thermal Bridges

2x6 wall no studs Ψ = ‐ 0058 WmK 2x6 wall 2‐stud Ψ = ‐ 0040 WmK

bull By subtraction negative psi values correct for overestimate of heat loss at exterior cornersbull The lower (more negative) the better Higher psi values indicate increasing heat lossbull Positive psi values above 001 WmK indicate net heat transfer (heat gain in summer heat loss in winter)that should be accounted for in PHPP

Step 1 ndash Avoid bridging elements 26

2x6 wall Ψ = ‐ 0040 WmK 2x8 wall Ψ = ‐ 0045 WmK

Is the 2x8 wall corner a ldquobetterrdquo detail

Section 2 ndash Common Linear Thermal Bridges

27

2x6 wall Ψ = ‐ 0040 WmK 2x8 wall Ψ = ‐ 0045 WmK

NoA thicker wall section needs a larger correction factor due to larger overestimate of heat loss

Section 2 ndash Common Linear Thermal Bridges

28

Is the psi value really an indicator of a detailrsquos thermal quality

Section 2 ndash Common Linear Thermal Bridges

29

Is the psi value really an indicator of a detailrsquos thermal qualityYes and no

At geometric bridges it does two things at once ndash it is both a correction factor and an indicator of heat flow ndash but primarily a correction factor

Section 2 ndash Common Linear Thermal Bridges

30

Is the psi value really an indicator of a detailrsquos thermal qualityYes and no

At geometric bridges it does two things at once ndash it is both a correction factor and an indicator of heat flow ndash but primarily a correction factor

Section 2 ndash Common Linear Thermal Bridges

31

Exterior cornerInsulated 2x6 wall w solid post Ψ = ‐ 0004 WmK

rim joist fib batt (R‐11) Ψ = 0089 WmK rim joist rim board (R‐11) Ψ = 0129 WmK

bull Rim joist thermal bridge ‐ challenging to achieve the Ψ = 001 WmK targetbull Maintaining continuity and alignment of insulation layers is a good first step

STEP 2 ndash Align insulation layers

Section 2 ndash Common Linear Thermal Bridges

32

rim joist 2x4 wall w 1rdquo exterior XPS (R‐13) Ψ = 0047 WmK

Section 2 ndash Common Linear Thermal Bridges

33

rim joist fib batt (R‐11) Ψ = 0089 WmK

bull Exterior insulation helps control heat flow through uninsulated studs and plates

STEP 3 ndash Use continuous exterior insulation to isolate bridging elements

rim joist 2x4 wall w 1rdquo exterior XPS (R‐13) Ψ = 0047 WmK

Use enough exterior insulation and the psi value can be driven down below 001 WmK

Section 2 ndash Common Linear Thermal Bridges

34

rim joist 2x4 wall w 4rdquo exterior XPSΨ = 0011 WmK

rim joist 2x4 wall w 4rdquo exterior XPSΨ = 0011 WmK

Question ndash are the psi values for these two details the same or different

Section 2 ndash Common Linear Thermal Bridges

35

rim joist 2x6 wall w 4rdquo exterior XPSΨ =

rim joist 2x4 wall w 4rdquo exterior XPSΨ = 0011 WmK

Is the detail on the left a ldquobetterrdquo detailIs heat flow through the detail on the right really 2x higher than the heat flow on the leftDoes 4rdquo of exterior foam guarantee a good psi value

Section 2 ndash Common Linear Thermal Bridges

36

rim joist 2x6 wall w 4rdquo exterior XPSΨ = 0020 WmK

rim joist 2x4 wall w 4rdquo exterior XPSΨ = 0011 WmK

NoFor the 2x6 wall therersquos now simply a larger difference between the higher R‐value wall assembly and the rim joist R‐value which has remained the same

Section 2 ndash Common Linear Thermal Bridges

37

rim joist 2x6 wall w 4rdquo exterior XPSΨ = 0020 WmK

Is the psi value really an indicator of a detailrsquos thermal quality

Section 2 ndash Common Linear Thermal Bridges

38

Is the psi value really an indicator of a detailrsquos thermal qualityYes and no

At structural thermal bridges a psi value is a comparison between the U‐value of the assembly(ies) and the U‐value of the junction A junction detail that ldquopassesrdquo (001 WmK) for one assembly may not pass with another

Section 2 ndash Common Linear Thermal Bridges

39

Section 2 ndash Common Linear Thermal Bridges

2x6 wall no studs Ψ = ‐ 0058 WmK 2x6 wall 2‐stud Ψ = ‐ 0040 WmK

When is a performance comparison validWhen the two models being compared have the same assemblies and the same geometry ‐the only difference is at the junction Example above

40

stem wall Ψ = ‐0004 WmK FPSF (frost‐protected shallow foundation) Ψ = 0160 WmK

bull Thermal bridge at the foundation is typically the most challenging to addressbull The concrete stem wall and FPSF footing acts as a radiation fin

STEP 4 ndash Avoid accidental ldquoradiation finsrdquo

Section 2 ndash Common Linear Thermal Bridges

41

FPSF (well insulated) Ψ = 0013 WmK

Thick layers of continuous insulation can improve the performance of the detail but even

FPSF Ψ = 0160 WmK

a very well insulated FPSF is still close to the 001 WmK limit

Section 2 ndash Common Linear Thermal Bridges

STEP 4 ‐ Avoid accidental radiation fins ‐ even well‐insulated ones

42

stem wall Ψ = ‐0004 WmK Thermally broken stem wall Ψ = ‐0136 WmK

Section 2 ndash Common Linear Thermal Bridges

43

Thermally broken stem wall provides an insulated break between the stem wall and the floor slab effectively cutting off the ldquoradiation finrdquoAligning exterior insulation layers at junction of stem wall and above grade wall also helpsSTEP 5 ndash An insulated break between the exterior wall and floor slab works best

ICF parapet Ψ = 0200 WmK Foamglas thermal break Ψ = ‐0071 WmK

Another good location to cut off the radiation fin

Section 2 ndash Common Linear Thermal Bridges

44

Window positioned outside of thermal envelope Ψ = 010 WmKEffectively R‐value of window reduced by 20 ‐ 30 depending on window size

Section 2 ndash Common Linear Thermal Bridges

Window positioned on edge of thermal envelope Ψ = 004 WmKR‐value of window reduced by 5 ‐10 depending on window size

45

Window centered in plane of insulation Ψ = 002 to 003 WmKR‐value of window is almost preserved

Section 2 ndash Common Linear Thermal Bridges

46

47

Break

Section 3 ndash Using psi values in PHPP

48

How do I know which thermal bridges need to be modeled and entered in PHPP

Section 3 ndash Using psi values in PHPP

49

How do I know which thermal bridges need to be modeled and entered in PHPP

PHI requires 1 of 2 paths1) Model all thermal bridges enter psi values for both + and ‐2) Model and enter only thermal bridges with psi values over 001 WmK

Path 2 begs the question ndash how do I know which TBs will be over 001 WmK before Irsquove modeled them

Image source httpwwwtheblazecomblog20130124finally‐the‐answer‐sort‐of‐for‐what‐came‐first‐the‐chicken‐or‐the‐egg

Section 3 ndash Using psi values in PHPP

50

EavesMost details will have negative psi value

Rim joistAlmost always positive psi value ‐MODEL

Wall to slabfootingOnly well‐designed details will have negative psi value ‐MODEL

Footing below bearing wall or postOnly well‐designed details will have psi value lt 001 WmK‐MODEL

Roof ridgeMost details will have negative psi value

Section 3 ndash Using psi values in PHPP

51

RakeMost details will have negative psi value

Windowdoor sill on slab MODEL BUThellipCan be entered as a window sill TB + wall‐to‐slab TB (requires two separate psi values)

Window sillAlmost always positive psi value since overinsulationis difficult ndashMODEL

Window headIf overinsulated probably no need to model If not ndashMODEL

Section 3 ndash Using psi values in PHPP

52

Exterior cornerMost details will have negative psi value

Interior cornerAlmost always positive psi value ndashMODEL

Window jambIf overinsulated probably no need to model If not ndashMODEL

Wall junctionIf insulation layers are interrupted ‐MODEL

Section 3 ndash Using psi values in PHPP

53

Other places to keep in mind for possible thermal bridgesbull Plumbing stacksbull Rain pipes (interior)bull ERV vent penetrations (to the exterior)bull Sump pumpsbull Radon remediation pipes (if interior to the building)

Section 3 ndash Using psi values in PHPP

54

Section 3 ndash Using psi values in PHPP

55

Section 3 ndash Using psi values in WUFI Passive

56

15

graph from Building Science Corp

Section 1 ndash Background + Basics

bull Heat loss through a linear thermal bridge is measured with a Ψvalue

bull A Ψ value is like a U‐value for thermal bridgesU x A x dT = heat loss from a surface of area AΨ x L x dT = heat loss from a linear thermal bridge of length L

bull Ψ values lt= 001 WmK qualify as ldquothermal bridge freerdquo according to Passive House

bull To calculate Ψ values a 2‐D heat flow simulation model (such as THERM or Flixo) is used

16

Section 1 ndash Background + Basics

17

Section 1 ndash Background + Basics

For PHPP the thermal bridge heat loss is conceptually the difference between the ldquotruerdquo heat loss calculated using 2‐dimensional simulation (THERM or Flixo) and the heat loss calculated using the typical UA method (U x A x deltaT = heat loss (or gain))

Image from David White Right Environments 2010

18

Section 1 ndash Background + Basics

ldquo2D heat lossrdquo ndash U1L1 ndash U2L2 = Ψ

Image from David White Right Environments 2010

19

Section 1 ndash Background + Basics

L2d ndash U1L1 ndash U2L2 = Ψ

ldquo2D heat lossrdquo ndash U1L1 ndash U2L2 = Ψ

Image from David White Right Environments 2010

20

Section 1 ndash Background + Basics

L2d ndash U1L1 ndash U2L2 = Ψ

Φ ΔT ndash U1L1 ndash U2L2 = Ψ(heat flux)

Image from David White Right Environments 2010

21

Section 1 ndash Background + Basics

UeqLtotal ndash U1L1 ndash U2L2 = Ψ(equivalent U‐value)

L2d ndash U1L1 ndash U2L2 = Ψ

Φ ΔT ndash U1L1 ndash U2L2 = Ψ(heat flux)

Image from David White Right Environments 2010

22

Section 1 ndash Background + Basics

As used in the PHPP the psi value is always based on a comparison of heat flows ‐ a comparison between the actual heat flow and the estimated heat flow In this sense psi is a correction factor

Image from David White Right Environments 2010

Details coming uphellip1 Wall corners2 Rim joists3 Footings4 Parapets5 Windows

23

Section 1 ndash Background + Basics

When calculating heat loss U x A x dTbull Using exterior dimensions area A = 40 x 10 = 400sfbull Using interior dimensions area A = 36 x 10 = 360sf

Which area A gives the correct heat loss

24

Section 1 ndash Background + Basics

When calculating heat loss U x A x dTbull Using exterior dimensions leads to an overestimatebull Using interior dimensions leads to an underestimate

PH convention is to use exterior dimensions so heat loss is overestimated

25

Section 1 ndash Background + Basics

Section 2 ndash Common Linear Thermal Bridges

2x6 wall no studs Ψ = ‐ 0058 WmK 2x6 wall 2‐stud Ψ = ‐ 0040 WmK

bull By subtraction negative psi values correct for overestimate of heat loss at exterior cornersbull The lower (more negative) the better Higher psi values indicate increasing heat lossbull Positive psi values above 001 WmK indicate net heat transfer (heat gain in summer heat loss in winter)that should be accounted for in PHPP

Step 1 ndash Avoid bridging elements 26

2x6 wall Ψ = ‐ 0040 WmK 2x8 wall Ψ = ‐ 0045 WmK

Is the 2x8 wall corner a ldquobetterrdquo detail

Section 2 ndash Common Linear Thermal Bridges

27

2x6 wall Ψ = ‐ 0040 WmK 2x8 wall Ψ = ‐ 0045 WmK

NoA thicker wall section needs a larger correction factor due to larger overestimate of heat loss

Section 2 ndash Common Linear Thermal Bridges

28

Is the psi value really an indicator of a detailrsquos thermal quality

Section 2 ndash Common Linear Thermal Bridges

29

Is the psi value really an indicator of a detailrsquos thermal qualityYes and no

At geometric bridges it does two things at once ndash it is both a correction factor and an indicator of heat flow ndash but primarily a correction factor

Section 2 ndash Common Linear Thermal Bridges

30

Is the psi value really an indicator of a detailrsquos thermal qualityYes and no

At geometric bridges it does two things at once ndash it is both a correction factor and an indicator of heat flow ndash but primarily a correction factor

Section 2 ndash Common Linear Thermal Bridges

31

Exterior cornerInsulated 2x6 wall w solid post Ψ = ‐ 0004 WmK

rim joist fib batt (R‐11) Ψ = 0089 WmK rim joist rim board (R‐11) Ψ = 0129 WmK

bull Rim joist thermal bridge ‐ challenging to achieve the Ψ = 001 WmK targetbull Maintaining continuity and alignment of insulation layers is a good first step

STEP 2 ndash Align insulation layers

Section 2 ndash Common Linear Thermal Bridges

32

rim joist 2x4 wall w 1rdquo exterior XPS (R‐13) Ψ = 0047 WmK

Section 2 ndash Common Linear Thermal Bridges

33

rim joist fib batt (R‐11) Ψ = 0089 WmK

bull Exterior insulation helps control heat flow through uninsulated studs and plates

STEP 3 ndash Use continuous exterior insulation to isolate bridging elements

rim joist 2x4 wall w 1rdquo exterior XPS (R‐13) Ψ = 0047 WmK

Use enough exterior insulation and the psi value can be driven down below 001 WmK

Section 2 ndash Common Linear Thermal Bridges

34

rim joist 2x4 wall w 4rdquo exterior XPSΨ = 0011 WmK

rim joist 2x4 wall w 4rdquo exterior XPSΨ = 0011 WmK

Question ndash are the psi values for these two details the same or different

Section 2 ndash Common Linear Thermal Bridges

35

rim joist 2x6 wall w 4rdquo exterior XPSΨ =

rim joist 2x4 wall w 4rdquo exterior XPSΨ = 0011 WmK

Is the detail on the left a ldquobetterrdquo detailIs heat flow through the detail on the right really 2x higher than the heat flow on the leftDoes 4rdquo of exterior foam guarantee a good psi value

Section 2 ndash Common Linear Thermal Bridges

36

rim joist 2x6 wall w 4rdquo exterior XPSΨ = 0020 WmK

rim joist 2x4 wall w 4rdquo exterior XPSΨ = 0011 WmK

NoFor the 2x6 wall therersquos now simply a larger difference between the higher R‐value wall assembly and the rim joist R‐value which has remained the same

Section 2 ndash Common Linear Thermal Bridges

37

rim joist 2x6 wall w 4rdquo exterior XPSΨ = 0020 WmK

Is the psi value really an indicator of a detailrsquos thermal quality

Section 2 ndash Common Linear Thermal Bridges

38

Is the psi value really an indicator of a detailrsquos thermal qualityYes and no

At structural thermal bridges a psi value is a comparison between the U‐value of the assembly(ies) and the U‐value of the junction A junction detail that ldquopassesrdquo (001 WmK) for one assembly may not pass with another

Section 2 ndash Common Linear Thermal Bridges

39

Section 2 ndash Common Linear Thermal Bridges

2x6 wall no studs Ψ = ‐ 0058 WmK 2x6 wall 2‐stud Ψ = ‐ 0040 WmK

When is a performance comparison validWhen the two models being compared have the same assemblies and the same geometry ‐the only difference is at the junction Example above

40

stem wall Ψ = ‐0004 WmK FPSF (frost‐protected shallow foundation) Ψ = 0160 WmK

bull Thermal bridge at the foundation is typically the most challenging to addressbull The concrete stem wall and FPSF footing acts as a radiation fin

STEP 4 ndash Avoid accidental ldquoradiation finsrdquo

Section 2 ndash Common Linear Thermal Bridges

41

FPSF (well insulated) Ψ = 0013 WmK

Thick layers of continuous insulation can improve the performance of the detail but even

FPSF Ψ = 0160 WmK

a very well insulated FPSF is still close to the 001 WmK limit

Section 2 ndash Common Linear Thermal Bridges

STEP 4 ‐ Avoid accidental radiation fins ‐ even well‐insulated ones

42

stem wall Ψ = ‐0004 WmK Thermally broken stem wall Ψ = ‐0136 WmK

Section 2 ndash Common Linear Thermal Bridges

43

Thermally broken stem wall provides an insulated break between the stem wall and the floor slab effectively cutting off the ldquoradiation finrdquoAligning exterior insulation layers at junction of stem wall and above grade wall also helpsSTEP 5 ndash An insulated break between the exterior wall and floor slab works best

ICF parapet Ψ = 0200 WmK Foamglas thermal break Ψ = ‐0071 WmK

Another good location to cut off the radiation fin

Section 2 ndash Common Linear Thermal Bridges

44

Window positioned outside of thermal envelope Ψ = 010 WmKEffectively R‐value of window reduced by 20 ‐ 30 depending on window size

Section 2 ndash Common Linear Thermal Bridges

Window positioned on edge of thermal envelope Ψ = 004 WmKR‐value of window reduced by 5 ‐10 depending on window size

45

Window centered in plane of insulation Ψ = 002 to 003 WmKR‐value of window is almost preserved

Section 2 ndash Common Linear Thermal Bridges

46

47

Break

Section 3 ndash Using psi values in PHPP

48

How do I know which thermal bridges need to be modeled and entered in PHPP

Section 3 ndash Using psi values in PHPP

49

How do I know which thermal bridges need to be modeled and entered in PHPP

PHI requires 1 of 2 paths1) Model all thermal bridges enter psi values for both + and ‐2) Model and enter only thermal bridges with psi values over 001 WmK

Path 2 begs the question ndash how do I know which TBs will be over 001 WmK before Irsquove modeled them

Image source httpwwwtheblazecomblog20130124finally‐the‐answer‐sort‐of‐for‐what‐came‐first‐the‐chicken‐or‐the‐egg

Section 3 ndash Using psi values in PHPP

50

EavesMost details will have negative psi value

Rim joistAlmost always positive psi value ‐MODEL

Wall to slabfootingOnly well‐designed details will have negative psi value ‐MODEL

Footing below bearing wall or postOnly well‐designed details will have psi value lt 001 WmK‐MODEL

Roof ridgeMost details will have negative psi value

Section 3 ndash Using psi values in PHPP

51

RakeMost details will have negative psi value

Windowdoor sill on slab MODEL BUThellipCan be entered as a window sill TB + wall‐to‐slab TB (requires two separate psi values)

Window sillAlmost always positive psi value since overinsulationis difficult ndashMODEL

Window headIf overinsulated probably no need to model If not ndashMODEL

Section 3 ndash Using psi values in PHPP

52

Exterior cornerMost details will have negative psi value

Interior cornerAlmost always positive psi value ndashMODEL

Window jambIf overinsulated probably no need to model If not ndashMODEL

Wall junctionIf insulation layers are interrupted ‐MODEL

Section 3 ndash Using psi values in PHPP

53

Other places to keep in mind for possible thermal bridgesbull Plumbing stacksbull Rain pipes (interior)bull ERV vent penetrations (to the exterior)bull Sump pumpsbull Radon remediation pipes (if interior to the building)

Section 3 ndash Using psi values in PHPP

54

Section 3 ndash Using psi values in PHPP

55

Section 3 ndash Using psi values in WUFI Passive

56

bull Heat loss through a linear thermal bridge is measured with a Ψvalue

bull A Ψ value is like a U‐value for thermal bridgesU x A x dT = heat loss from a surface of area AΨ x L x dT = heat loss from a linear thermal bridge of length L

bull Ψ values lt= 001 WmK qualify as ldquothermal bridge freerdquo according to Passive House

bull To calculate Ψ values a 2‐D heat flow simulation model (such as THERM or Flixo) is used

16

Section 1 ndash Background + Basics

17

Section 1 ndash Background + Basics

For PHPP the thermal bridge heat loss is conceptually the difference between the ldquotruerdquo heat loss calculated using 2‐dimensional simulation (THERM or Flixo) and the heat loss calculated using the typical UA method (U x A x deltaT = heat loss (or gain))

Image from David White Right Environments 2010

18

Section 1 ndash Background + Basics

ldquo2D heat lossrdquo ndash U1L1 ndash U2L2 = Ψ

Image from David White Right Environments 2010

19

Section 1 ndash Background + Basics

L2d ndash U1L1 ndash U2L2 = Ψ

ldquo2D heat lossrdquo ndash U1L1 ndash U2L2 = Ψ

Image from David White Right Environments 2010

20

Section 1 ndash Background + Basics

L2d ndash U1L1 ndash U2L2 = Ψ

Φ ΔT ndash U1L1 ndash U2L2 = Ψ(heat flux)

Image from David White Right Environments 2010

21

Section 1 ndash Background + Basics

UeqLtotal ndash U1L1 ndash U2L2 = Ψ(equivalent U‐value)

L2d ndash U1L1 ndash U2L2 = Ψ

Φ ΔT ndash U1L1 ndash U2L2 = Ψ(heat flux)

Image from David White Right Environments 2010

22

Section 1 ndash Background + Basics

As used in the PHPP the psi value is always based on a comparison of heat flows ‐ a comparison between the actual heat flow and the estimated heat flow In this sense psi is a correction factor

Image from David White Right Environments 2010

Details coming uphellip1 Wall corners2 Rim joists3 Footings4 Parapets5 Windows

23

Section 1 ndash Background + Basics

When calculating heat loss U x A x dTbull Using exterior dimensions area A = 40 x 10 = 400sfbull Using interior dimensions area A = 36 x 10 = 360sf

Which area A gives the correct heat loss

24

Section 1 ndash Background + Basics

When calculating heat loss U x A x dTbull Using exterior dimensions leads to an overestimatebull Using interior dimensions leads to an underestimate

PH convention is to use exterior dimensions so heat loss is overestimated

25

Section 1 ndash Background + Basics

Section 2 ndash Common Linear Thermal Bridges

2x6 wall no studs Ψ = ‐ 0058 WmK 2x6 wall 2‐stud Ψ = ‐ 0040 WmK

bull By subtraction negative psi values correct for overestimate of heat loss at exterior cornersbull The lower (more negative) the better Higher psi values indicate increasing heat lossbull Positive psi values above 001 WmK indicate net heat transfer (heat gain in summer heat loss in winter)that should be accounted for in PHPP

Step 1 ndash Avoid bridging elements 26

2x6 wall Ψ = ‐ 0040 WmK 2x8 wall Ψ = ‐ 0045 WmK

Is the 2x8 wall corner a ldquobetterrdquo detail

Section 2 ndash Common Linear Thermal Bridges

27

2x6 wall Ψ = ‐ 0040 WmK 2x8 wall Ψ = ‐ 0045 WmK

NoA thicker wall section needs a larger correction factor due to larger overestimate of heat loss

Section 2 ndash Common Linear Thermal Bridges

28

Is the psi value really an indicator of a detailrsquos thermal quality

Section 2 ndash Common Linear Thermal Bridges

29

Is the psi value really an indicator of a detailrsquos thermal qualityYes and no

At geometric bridges it does two things at once ndash it is both a correction factor and an indicator of heat flow ndash but primarily a correction factor

Section 2 ndash Common Linear Thermal Bridges

30

Is the psi value really an indicator of a detailrsquos thermal qualityYes and no

At geometric bridges it does two things at once ndash it is both a correction factor and an indicator of heat flow ndash but primarily a correction factor

Section 2 ndash Common Linear Thermal Bridges

31

Exterior cornerInsulated 2x6 wall w solid post Ψ = ‐ 0004 WmK

rim joist fib batt (R‐11) Ψ = 0089 WmK rim joist rim board (R‐11) Ψ = 0129 WmK

bull Rim joist thermal bridge ‐ challenging to achieve the Ψ = 001 WmK targetbull Maintaining continuity and alignment of insulation layers is a good first step

STEP 2 ndash Align insulation layers

Section 2 ndash Common Linear Thermal Bridges

32

rim joist 2x4 wall w 1rdquo exterior XPS (R‐13) Ψ = 0047 WmK

Section 2 ndash Common Linear Thermal Bridges

33

rim joist fib batt (R‐11) Ψ = 0089 WmK

bull Exterior insulation helps control heat flow through uninsulated studs and plates

STEP 3 ndash Use continuous exterior insulation to isolate bridging elements

rim joist 2x4 wall w 1rdquo exterior XPS (R‐13) Ψ = 0047 WmK

Use enough exterior insulation and the psi value can be driven down below 001 WmK

Section 2 ndash Common Linear Thermal Bridges

34

rim joist 2x4 wall w 4rdquo exterior XPSΨ = 0011 WmK

rim joist 2x4 wall w 4rdquo exterior XPSΨ = 0011 WmK

Question ndash are the psi values for these two details the same or different

Section 2 ndash Common Linear Thermal Bridges

35

rim joist 2x6 wall w 4rdquo exterior XPSΨ =

rim joist 2x4 wall w 4rdquo exterior XPSΨ = 0011 WmK

Is the detail on the left a ldquobetterrdquo detailIs heat flow through the detail on the right really 2x higher than the heat flow on the leftDoes 4rdquo of exterior foam guarantee a good psi value

Section 2 ndash Common Linear Thermal Bridges

36

rim joist 2x6 wall w 4rdquo exterior XPSΨ = 0020 WmK

rim joist 2x4 wall w 4rdquo exterior XPSΨ = 0011 WmK

NoFor the 2x6 wall therersquos now simply a larger difference between the higher R‐value wall assembly and the rim joist R‐value which has remained the same

Section 2 ndash Common Linear Thermal Bridges

37

rim joist 2x6 wall w 4rdquo exterior XPSΨ = 0020 WmK

Is the psi value really an indicator of a detailrsquos thermal quality

Section 2 ndash Common Linear Thermal Bridges

38

Is the psi value really an indicator of a detailrsquos thermal qualityYes and no

At structural thermal bridges a psi value is a comparison between the U‐value of the assembly(ies) and the U‐value of the junction A junction detail that ldquopassesrdquo (001 WmK) for one assembly may not pass with another

Section 2 ndash Common Linear Thermal Bridges

39

Section 2 ndash Common Linear Thermal Bridges

2x6 wall no studs Ψ = ‐ 0058 WmK 2x6 wall 2‐stud Ψ = ‐ 0040 WmK

When is a performance comparison validWhen the two models being compared have the same assemblies and the same geometry ‐the only difference is at the junction Example above

40

stem wall Ψ = ‐0004 WmK FPSF (frost‐protected shallow foundation) Ψ = 0160 WmK

bull Thermal bridge at the foundation is typically the most challenging to addressbull The concrete stem wall and FPSF footing acts as a radiation fin

STEP 4 ndash Avoid accidental ldquoradiation finsrdquo

Section 2 ndash Common Linear Thermal Bridges

41

FPSF (well insulated) Ψ = 0013 WmK

Thick layers of continuous insulation can improve the performance of the detail but even

FPSF Ψ = 0160 WmK

a very well insulated FPSF is still close to the 001 WmK limit

Section 2 ndash Common Linear Thermal Bridges

STEP 4 ‐ Avoid accidental radiation fins ‐ even well‐insulated ones

42

stem wall Ψ = ‐0004 WmK Thermally broken stem wall Ψ = ‐0136 WmK

Section 2 ndash Common Linear Thermal Bridges

43

Thermally broken stem wall provides an insulated break between the stem wall and the floor slab effectively cutting off the ldquoradiation finrdquoAligning exterior insulation layers at junction of stem wall and above grade wall also helpsSTEP 5 ndash An insulated break between the exterior wall and floor slab works best

ICF parapet Ψ = 0200 WmK Foamglas thermal break Ψ = ‐0071 WmK

Another good location to cut off the radiation fin

Section 2 ndash Common Linear Thermal Bridges

44

Window positioned outside of thermal envelope Ψ = 010 WmKEffectively R‐value of window reduced by 20 ‐ 30 depending on window size

Section 2 ndash Common Linear Thermal Bridges

Window positioned on edge of thermal envelope Ψ = 004 WmKR‐value of window reduced by 5 ‐10 depending on window size

45

Window centered in plane of insulation Ψ = 002 to 003 WmKR‐value of window is almost preserved

Section 2 ndash Common Linear Thermal Bridges

46

47

Break

Section 3 ndash Using psi values in PHPP

48

How do I know which thermal bridges need to be modeled and entered in PHPP

Section 3 ndash Using psi values in PHPP

49

How do I know which thermal bridges need to be modeled and entered in PHPP

PHI requires 1 of 2 paths1) Model all thermal bridges enter psi values for both + and ‐2) Model and enter only thermal bridges with psi values over 001 WmK

Path 2 begs the question ndash how do I know which TBs will be over 001 WmK before Irsquove modeled them

Image source httpwwwtheblazecomblog20130124finally‐the‐answer‐sort‐of‐for‐what‐came‐first‐the‐chicken‐or‐the‐egg

Section 3 ndash Using psi values in PHPP

50

EavesMost details will have negative psi value

Rim joistAlmost always positive psi value ‐MODEL

Wall to slabfootingOnly well‐designed details will have negative psi value ‐MODEL

Footing below bearing wall or postOnly well‐designed details will have psi value lt 001 WmK‐MODEL

Roof ridgeMost details will have negative psi value

Section 3 ndash Using psi values in PHPP

51

RakeMost details will have negative psi value

Windowdoor sill on slab MODEL BUThellipCan be entered as a window sill TB + wall‐to‐slab TB (requires two separate psi values)

Window sillAlmost always positive psi value since overinsulationis difficult ndashMODEL

Window headIf overinsulated probably no need to model If not ndashMODEL

Section 3 ndash Using psi values in PHPP

52

Exterior cornerMost details will have negative psi value

Interior cornerAlmost always positive psi value ndashMODEL

Window jambIf overinsulated probably no need to model If not ndashMODEL

Wall junctionIf insulation layers are interrupted ‐MODEL

Section 3 ndash Using psi values in PHPP

53

Other places to keep in mind for possible thermal bridgesbull Plumbing stacksbull Rain pipes (interior)bull ERV vent penetrations (to the exterior)bull Sump pumpsbull Radon remediation pipes (if interior to the building)

Section 3 ndash Using psi values in PHPP

54

Section 3 ndash Using psi values in PHPP

55

Section 3 ndash Using psi values in WUFI Passive

56

17

Section 1 ndash Background + Basics

For PHPP the thermal bridge heat loss is conceptually the difference between the ldquotruerdquo heat loss calculated using 2‐dimensional simulation (THERM or Flixo) and the heat loss calculated using the typical UA method (U x A x deltaT = heat loss (or gain))

Image from David White Right Environments 2010

18

Section 1 ndash Background + Basics

ldquo2D heat lossrdquo ndash U1L1 ndash U2L2 = Ψ

Image from David White Right Environments 2010

19

Section 1 ndash Background + Basics

L2d ndash U1L1 ndash U2L2 = Ψ

ldquo2D heat lossrdquo ndash U1L1 ndash U2L2 = Ψ

Image from David White Right Environments 2010

20

Section 1 ndash Background + Basics

L2d ndash U1L1 ndash U2L2 = Ψ

Φ ΔT ndash U1L1 ndash U2L2 = Ψ(heat flux)

Image from David White Right Environments 2010

21

Section 1 ndash Background + Basics

UeqLtotal ndash U1L1 ndash U2L2 = Ψ(equivalent U‐value)

L2d ndash U1L1 ndash U2L2 = Ψ

Φ ΔT ndash U1L1 ndash U2L2 = Ψ(heat flux)

Image from David White Right Environments 2010

22

Section 1 ndash Background + Basics

As used in the PHPP the psi value is always based on a comparison of heat flows ‐ a comparison between the actual heat flow and the estimated heat flow In this sense psi is a correction factor

Image from David White Right Environments 2010

Details coming uphellip1 Wall corners2 Rim joists3 Footings4 Parapets5 Windows

23

Section 1 ndash Background + Basics

When calculating heat loss U x A x dTbull Using exterior dimensions area A = 40 x 10 = 400sfbull Using interior dimensions area A = 36 x 10 = 360sf

Which area A gives the correct heat loss

24

Section 1 ndash Background + Basics

When calculating heat loss U x A x dTbull Using exterior dimensions leads to an overestimatebull Using interior dimensions leads to an underestimate

PH convention is to use exterior dimensions so heat loss is overestimated

25

Section 1 ndash Background + Basics

Section 2 ndash Common Linear Thermal Bridges

2x6 wall no studs Ψ = ‐ 0058 WmK 2x6 wall 2‐stud Ψ = ‐ 0040 WmK

bull By subtraction negative psi values correct for overestimate of heat loss at exterior cornersbull The lower (more negative) the better Higher psi values indicate increasing heat lossbull Positive psi values above 001 WmK indicate net heat transfer (heat gain in summer heat loss in winter)that should be accounted for in PHPP

Step 1 ndash Avoid bridging elements 26

2x6 wall Ψ = ‐ 0040 WmK 2x8 wall Ψ = ‐ 0045 WmK

Is the 2x8 wall corner a ldquobetterrdquo detail

Section 2 ndash Common Linear Thermal Bridges

27

2x6 wall Ψ = ‐ 0040 WmK 2x8 wall Ψ = ‐ 0045 WmK

NoA thicker wall section needs a larger correction factor due to larger overestimate of heat loss

Section 2 ndash Common Linear Thermal Bridges

28

Is the psi value really an indicator of a detailrsquos thermal quality

Section 2 ndash Common Linear Thermal Bridges

29

Is the psi value really an indicator of a detailrsquos thermal qualityYes and no

At geometric bridges it does two things at once ndash it is both a correction factor and an indicator of heat flow ndash but primarily a correction factor

Section 2 ndash Common Linear Thermal Bridges

30

Is the psi value really an indicator of a detailrsquos thermal qualityYes and no

At geometric bridges it does two things at once ndash it is both a correction factor and an indicator of heat flow ndash but primarily a correction factor

Section 2 ndash Common Linear Thermal Bridges

31

Exterior cornerInsulated 2x6 wall w solid post Ψ = ‐ 0004 WmK

rim joist fib batt (R‐11) Ψ = 0089 WmK rim joist rim board (R‐11) Ψ = 0129 WmK

bull Rim joist thermal bridge ‐ challenging to achieve the Ψ = 001 WmK targetbull Maintaining continuity and alignment of insulation layers is a good first step

STEP 2 ndash Align insulation layers

Section 2 ndash Common Linear Thermal Bridges

32

rim joist 2x4 wall w 1rdquo exterior XPS (R‐13) Ψ = 0047 WmK

Section 2 ndash Common Linear Thermal Bridges

33

rim joist fib batt (R‐11) Ψ = 0089 WmK

bull Exterior insulation helps control heat flow through uninsulated studs and plates

STEP 3 ndash Use continuous exterior insulation to isolate bridging elements

rim joist 2x4 wall w 1rdquo exterior XPS (R‐13) Ψ = 0047 WmK

Use enough exterior insulation and the psi value can be driven down below 001 WmK

Section 2 ndash Common Linear Thermal Bridges

34

rim joist 2x4 wall w 4rdquo exterior XPSΨ = 0011 WmK

rim joist 2x4 wall w 4rdquo exterior XPSΨ = 0011 WmK

Question ndash are the psi values for these two details the same or different

Section 2 ndash Common Linear Thermal Bridges

35

rim joist 2x6 wall w 4rdquo exterior XPSΨ =

rim joist 2x4 wall w 4rdquo exterior XPSΨ = 0011 WmK

Is the detail on the left a ldquobetterrdquo detailIs heat flow through the detail on the right really 2x higher than the heat flow on the leftDoes 4rdquo of exterior foam guarantee a good psi value

Section 2 ndash Common Linear Thermal Bridges

36

rim joist 2x6 wall w 4rdquo exterior XPSΨ = 0020 WmK

rim joist 2x4 wall w 4rdquo exterior XPSΨ = 0011 WmK

NoFor the 2x6 wall therersquos now simply a larger difference between the higher R‐value wall assembly and the rim joist R‐value which has remained the same

Section 2 ndash Common Linear Thermal Bridges

37

rim joist 2x6 wall w 4rdquo exterior XPSΨ = 0020 WmK

Is the psi value really an indicator of a detailrsquos thermal quality

Section 2 ndash Common Linear Thermal Bridges

38

Is the psi value really an indicator of a detailrsquos thermal qualityYes and no

At structural thermal bridges a psi value is a comparison between the U‐value of the assembly(ies) and the U‐value of the junction A junction detail that ldquopassesrdquo (001 WmK) for one assembly may not pass with another

Section 2 ndash Common Linear Thermal Bridges

39

Section 2 ndash Common Linear Thermal Bridges

2x6 wall no studs Ψ = ‐ 0058 WmK 2x6 wall 2‐stud Ψ = ‐ 0040 WmK

When is a performance comparison validWhen the two models being compared have the same assemblies and the same geometry ‐the only difference is at the junction Example above

40

stem wall Ψ = ‐0004 WmK FPSF (frost‐protected shallow foundation) Ψ = 0160 WmK

bull Thermal bridge at the foundation is typically the most challenging to addressbull The concrete stem wall and FPSF footing acts as a radiation fin

STEP 4 ndash Avoid accidental ldquoradiation finsrdquo

Section 2 ndash Common Linear Thermal Bridges

41

FPSF (well insulated) Ψ = 0013 WmK

Thick layers of continuous insulation can improve the performance of the detail but even

FPSF Ψ = 0160 WmK

a very well insulated FPSF is still close to the 001 WmK limit

Section 2 ndash Common Linear Thermal Bridges

STEP 4 ‐ Avoid accidental radiation fins ‐ even well‐insulated ones

42

stem wall Ψ = ‐0004 WmK Thermally broken stem wall Ψ = ‐0136 WmK

Section 2 ndash Common Linear Thermal Bridges

43

Thermally broken stem wall provides an insulated break between the stem wall and the floor slab effectively cutting off the ldquoradiation finrdquoAligning exterior insulation layers at junction of stem wall and above grade wall also helpsSTEP 5 ndash An insulated break between the exterior wall and floor slab works best

ICF parapet Ψ = 0200 WmK Foamglas thermal break Ψ = ‐0071 WmK

Another good location to cut off the radiation fin

Section 2 ndash Common Linear Thermal Bridges

44

Window positioned outside of thermal envelope Ψ = 010 WmKEffectively R‐value of window reduced by 20 ‐ 30 depending on window size

Section 2 ndash Common Linear Thermal Bridges

Window positioned on edge of thermal envelope Ψ = 004 WmKR‐value of window reduced by 5 ‐10 depending on window size

45

Window centered in plane of insulation Ψ = 002 to 003 WmKR‐value of window is almost preserved

Section 2 ndash Common Linear Thermal Bridges

46

47

Break

Section 3 ndash Using psi values in PHPP

48

How do I know which thermal bridges need to be modeled and entered in PHPP

Section 3 ndash Using psi values in PHPP

49

How do I know which thermal bridges need to be modeled and entered in PHPP

PHI requires 1 of 2 paths1) Model all thermal bridges enter psi values for both + and ‐2) Model and enter only thermal bridges with psi values over 001 WmK

Path 2 begs the question ndash how do I know which TBs will be over 001 WmK before Irsquove modeled them

Image source httpwwwtheblazecomblog20130124finally‐the‐answer‐sort‐of‐for‐what‐came‐first‐the‐chicken‐or‐the‐egg

Section 3 ndash Using psi values in PHPP

50

EavesMost details will have negative psi value

Rim joistAlmost always positive psi value ‐MODEL

Wall to slabfootingOnly well‐designed details will have negative psi value ‐MODEL

Footing below bearing wall or postOnly well‐designed details will have psi value lt 001 WmK‐MODEL

Roof ridgeMost details will have negative psi value

Section 3 ndash Using psi values in PHPP

51

RakeMost details will have negative psi value

Windowdoor sill on slab MODEL BUThellipCan be entered as a window sill TB + wall‐to‐slab TB (requires two separate psi values)

Window sillAlmost always positive psi value since overinsulationis difficult ndashMODEL

Window headIf overinsulated probably no need to model If not ndashMODEL

Section 3 ndash Using psi values in PHPP

52

Exterior cornerMost details will have negative psi value

Interior cornerAlmost always positive psi value ndashMODEL

Window jambIf overinsulated probably no need to model If not ndashMODEL

Wall junctionIf insulation layers are interrupted ‐MODEL

Section 3 ndash Using psi values in PHPP

53

Other places to keep in mind for possible thermal bridgesbull Plumbing stacksbull Rain pipes (interior)bull ERV vent penetrations (to the exterior)bull Sump pumpsbull Radon remediation pipes (if interior to the building)

Section 3 ndash Using psi values in PHPP

54

Section 3 ndash Using psi values in PHPP

55

Section 3 ndash Using psi values in WUFI Passive

56

18

Section 1 ndash Background + Basics

ldquo2D heat lossrdquo ndash U1L1 ndash U2L2 = Ψ

Image from David White Right Environments 2010

19

Section 1 ndash Background + Basics

L2d ndash U1L1 ndash U2L2 = Ψ

ldquo2D heat lossrdquo ndash U1L1 ndash U2L2 = Ψ

Image from David White Right Environments 2010

20

Section 1 ndash Background + Basics

L2d ndash U1L1 ndash U2L2 = Ψ

Φ ΔT ndash U1L1 ndash U2L2 = Ψ(heat flux)

Image from David White Right Environments 2010

21

Section 1 ndash Background + Basics

UeqLtotal ndash U1L1 ndash U2L2 = Ψ(equivalent U‐value)

L2d ndash U1L1 ndash U2L2 = Ψ

Φ ΔT ndash U1L1 ndash U2L2 = Ψ(heat flux)

Image from David White Right Environments 2010

22

Section 1 ndash Background + Basics

As used in the PHPP the psi value is always based on a comparison of heat flows ‐ a comparison between the actual heat flow and the estimated heat flow In this sense psi is a correction factor

Image from David White Right Environments 2010

Details coming uphellip1 Wall corners2 Rim joists3 Footings4 Parapets5 Windows

23

Section 1 ndash Background + Basics

When calculating heat loss U x A x dTbull Using exterior dimensions area A = 40 x 10 = 400sfbull Using interior dimensions area A = 36 x 10 = 360sf

Which area A gives the correct heat loss

24

Section 1 ndash Background + Basics

When calculating heat loss U x A x dTbull Using exterior dimensions leads to an overestimatebull Using interior dimensions leads to an underestimate

PH convention is to use exterior dimensions so heat loss is overestimated

25

Section 1 ndash Background + Basics

Section 2 ndash Common Linear Thermal Bridges

2x6 wall no studs Ψ = ‐ 0058 WmK 2x6 wall 2‐stud Ψ = ‐ 0040 WmK

bull By subtraction negative psi values correct for overestimate of heat loss at exterior cornersbull The lower (more negative) the better Higher psi values indicate increasing heat lossbull Positive psi values above 001 WmK indicate net heat transfer (heat gain in summer heat loss in winter)that should be accounted for in PHPP

Step 1 ndash Avoid bridging elements 26

2x6 wall Ψ = ‐ 0040 WmK 2x8 wall Ψ = ‐ 0045 WmK

Is the 2x8 wall corner a ldquobetterrdquo detail

Section 2 ndash Common Linear Thermal Bridges

27

2x6 wall Ψ = ‐ 0040 WmK 2x8 wall Ψ = ‐ 0045 WmK

NoA thicker wall section needs a larger correction factor due to larger overestimate of heat loss

Section 2 ndash Common Linear Thermal Bridges

28

Is the psi value really an indicator of a detailrsquos thermal quality

Section 2 ndash Common Linear Thermal Bridges

29

Is the psi value really an indicator of a detailrsquos thermal qualityYes and no

At geometric bridges it does two things at once ndash it is both a correction factor and an indicator of heat flow ndash but primarily a correction factor

Section 2 ndash Common Linear Thermal Bridges

30

Is the psi value really an indicator of a detailrsquos thermal qualityYes and no

At geometric bridges it does two things at once ndash it is both a correction factor and an indicator of heat flow ndash but primarily a correction factor

Section 2 ndash Common Linear Thermal Bridges

31

Exterior cornerInsulated 2x6 wall w solid post Ψ = ‐ 0004 WmK

rim joist fib batt (R‐11) Ψ = 0089 WmK rim joist rim board (R‐11) Ψ = 0129 WmK

bull Rim joist thermal bridge ‐ challenging to achieve the Ψ = 001 WmK targetbull Maintaining continuity and alignment of insulation layers is a good first step

STEP 2 ndash Align insulation layers

Section 2 ndash Common Linear Thermal Bridges

32

rim joist 2x4 wall w 1rdquo exterior XPS (R‐13) Ψ = 0047 WmK

Section 2 ndash Common Linear Thermal Bridges

33

rim joist fib batt (R‐11) Ψ = 0089 WmK

bull Exterior insulation helps control heat flow through uninsulated studs and plates

STEP 3 ndash Use continuous exterior insulation to isolate bridging elements

rim joist 2x4 wall w 1rdquo exterior XPS (R‐13) Ψ = 0047 WmK

Use enough exterior insulation and the psi value can be driven down below 001 WmK

Section 2 ndash Common Linear Thermal Bridges

34

rim joist 2x4 wall w 4rdquo exterior XPSΨ = 0011 WmK

rim joist 2x4 wall w 4rdquo exterior XPSΨ = 0011 WmK

Question ndash are the psi values for these two details the same or different

Section 2 ndash Common Linear Thermal Bridges

35

rim joist 2x6 wall w 4rdquo exterior XPSΨ =

rim joist 2x4 wall w 4rdquo exterior XPSΨ = 0011 WmK

Is the detail on the left a ldquobetterrdquo detailIs heat flow through the detail on the right really 2x higher than the heat flow on the leftDoes 4rdquo of exterior foam guarantee a good psi value

Section 2 ndash Common Linear Thermal Bridges

36

rim joist 2x6 wall w 4rdquo exterior XPSΨ = 0020 WmK

rim joist 2x4 wall w 4rdquo exterior XPSΨ = 0011 WmK

NoFor the 2x6 wall therersquos now simply a larger difference between the higher R‐value wall assembly and the rim joist R‐value which has remained the same

Section 2 ndash Common Linear Thermal Bridges

37

rim joist 2x6 wall w 4rdquo exterior XPSΨ = 0020 WmK

Is the psi value really an indicator of a detailrsquos thermal quality

Section 2 ndash Common Linear Thermal Bridges

38

Is the psi value really an indicator of a detailrsquos thermal qualityYes and no

At structural thermal bridges a psi value is a comparison between the U‐value of the assembly(ies) and the U‐value of the junction A junction detail that ldquopassesrdquo (001 WmK) for one assembly may not pass with another

Section 2 ndash Common Linear Thermal Bridges

39

Section 2 ndash Common Linear Thermal Bridges

2x6 wall no studs Ψ = ‐ 0058 WmK 2x6 wall 2‐stud Ψ = ‐ 0040 WmK

When is a performance comparison validWhen the two models being compared have the same assemblies and the same geometry ‐the only difference is at the junction Example above

40

stem wall Ψ = ‐0004 WmK FPSF (frost‐protected shallow foundation) Ψ = 0160 WmK

bull Thermal bridge at the foundation is typically the most challenging to addressbull The concrete stem wall and FPSF footing acts as a radiation fin

STEP 4 ndash Avoid accidental ldquoradiation finsrdquo

Section 2 ndash Common Linear Thermal Bridges

41

FPSF (well insulated) Ψ = 0013 WmK

Thick layers of continuous insulation can improve the performance of the detail but even

FPSF Ψ = 0160 WmK

a very well insulated FPSF is still close to the 001 WmK limit

Section 2 ndash Common Linear Thermal Bridges

STEP 4 ‐ Avoid accidental radiation fins ‐ even well‐insulated ones

42

stem wall Ψ = ‐0004 WmK Thermally broken stem wall Ψ = ‐0136 WmK

Section 2 ndash Common Linear Thermal Bridges

43

Thermally broken stem wall provides an insulated break between the stem wall and the floor slab effectively cutting off the ldquoradiation finrdquoAligning exterior insulation layers at junction of stem wall and above grade wall also helpsSTEP 5 ndash An insulated break between the exterior wall and floor slab works best

ICF parapet Ψ = 0200 WmK Foamglas thermal break Ψ = ‐0071 WmK

Another good location to cut off the radiation fin

Section 2 ndash Common Linear Thermal Bridges

44

Window positioned outside of thermal envelope Ψ = 010 WmKEffectively R‐value of window reduced by 20 ‐ 30 depending on window size

Section 2 ndash Common Linear Thermal Bridges

Window positioned on edge of thermal envelope Ψ = 004 WmKR‐value of window reduced by 5 ‐10 depending on window size

45

Window centered in plane of insulation Ψ = 002 to 003 WmKR‐value of window is almost preserved

Section 2 ndash Common Linear Thermal Bridges

46

47

Break

Section 3 ndash Using psi values in PHPP

48

How do I know which thermal bridges need to be modeled and entered in PHPP

Section 3 ndash Using psi values in PHPP

49

How do I know which thermal bridges need to be modeled and entered in PHPP

PHI requires 1 of 2 paths1) Model all thermal bridges enter psi values for both + and ‐2) Model and enter only thermal bridges with psi values over 001 WmK

Path 2 begs the question ndash how do I know which TBs will be over 001 WmK before Irsquove modeled them

Image source httpwwwtheblazecomblog20130124finally‐the‐answer‐sort‐of‐for‐what‐came‐first‐the‐chicken‐or‐the‐egg

Section 3 ndash Using psi values in PHPP

50

EavesMost details will have negative psi value

Rim joistAlmost always positive psi value ‐MODEL

Wall to slabfootingOnly well‐designed details will have negative psi value ‐MODEL

Footing below bearing wall or postOnly well‐designed details will have psi value lt 001 WmK‐MODEL

Roof ridgeMost details will have negative psi value

Section 3 ndash Using psi values in PHPP

51

RakeMost details will have negative psi value

Windowdoor sill on slab MODEL BUThellipCan be entered as a window sill TB + wall‐to‐slab TB (requires two separate psi values)

Window sillAlmost always positive psi value since overinsulationis difficult ndashMODEL

Window headIf overinsulated probably no need to model If not ndashMODEL

Section 3 ndash Using psi values in PHPP

52

Exterior cornerMost details will have negative psi value

Interior cornerAlmost always positive psi value ndashMODEL

Window jambIf overinsulated probably no need to model If not ndashMODEL

Wall junctionIf insulation layers are interrupted ‐MODEL

Section 3 ndash Using psi values in PHPP

53

Other places to keep in mind for possible thermal bridgesbull Plumbing stacksbull Rain pipes (interior)bull ERV vent penetrations (to the exterior)bull Sump pumpsbull Radon remediation pipes (if interior to the building)

Section 3 ndash Using psi values in PHPP

54

Section 3 ndash Using psi values in PHPP

55

Section 3 ndash Using psi values in WUFI Passive

56

19

Section 1 ndash Background + Basics

L2d ndash U1L1 ndash U2L2 = Ψ

ldquo2D heat lossrdquo ndash U1L1 ndash U2L2 = Ψ

Image from David White Right Environments 2010

20

Section 1 ndash Background + Basics

L2d ndash U1L1 ndash U2L2 = Ψ

Φ ΔT ndash U1L1 ndash U2L2 = Ψ(heat flux)

Image from David White Right Environments 2010

21

Section 1 ndash Background + Basics

UeqLtotal ndash U1L1 ndash U2L2 = Ψ(equivalent U‐value)

L2d ndash U1L1 ndash U2L2 = Ψ

Φ ΔT ndash U1L1 ndash U2L2 = Ψ(heat flux)

Image from David White Right Environments 2010

22

Section 1 ndash Background + Basics

As used in the PHPP the psi value is always based on a comparison of heat flows ‐ a comparison between the actual heat flow and the estimated heat flow In this sense psi is a correction factor

Image from David White Right Environments 2010

Details coming uphellip1 Wall corners2 Rim joists3 Footings4 Parapets5 Windows

23

Section 1 ndash Background + Basics

When calculating heat loss U x A x dTbull Using exterior dimensions area A = 40 x 10 = 400sfbull Using interior dimensions area A = 36 x 10 = 360sf

Which area A gives the correct heat loss

24

Section 1 ndash Background + Basics

When calculating heat loss U x A x dTbull Using exterior dimensions leads to an overestimatebull Using interior dimensions leads to an underestimate

PH convention is to use exterior dimensions so heat loss is overestimated

25

Section 1 ndash Background + Basics

Section 2 ndash Common Linear Thermal Bridges

2x6 wall no studs Ψ = ‐ 0058 WmK 2x6 wall 2‐stud Ψ = ‐ 0040 WmK

bull By subtraction negative psi values correct for overestimate of heat loss at exterior cornersbull The lower (more negative) the better Higher psi values indicate increasing heat lossbull Positive psi values above 001 WmK indicate net heat transfer (heat gain in summer heat loss in winter)that should be accounted for in PHPP

Step 1 ndash Avoid bridging elements 26

2x6 wall Ψ = ‐ 0040 WmK 2x8 wall Ψ = ‐ 0045 WmK

Is the 2x8 wall corner a ldquobetterrdquo detail

Section 2 ndash Common Linear Thermal Bridges

27

2x6 wall Ψ = ‐ 0040 WmK 2x8 wall Ψ = ‐ 0045 WmK

NoA thicker wall section needs a larger correction factor due to larger overestimate of heat loss

Section 2 ndash Common Linear Thermal Bridges

28

Is the psi value really an indicator of a detailrsquos thermal quality

Section 2 ndash Common Linear Thermal Bridges

29

Is the psi value really an indicator of a detailrsquos thermal qualityYes and no

At geometric bridges it does two things at once ndash it is both a correction factor and an indicator of heat flow ndash but primarily a correction factor

Section 2 ndash Common Linear Thermal Bridges

30

Is the psi value really an indicator of a detailrsquos thermal qualityYes and no

At geometric bridges it does two things at once ndash it is both a correction factor and an indicator of heat flow ndash but primarily a correction factor

Section 2 ndash Common Linear Thermal Bridges

31

Exterior cornerInsulated 2x6 wall w solid post Ψ = ‐ 0004 WmK

rim joist fib batt (R‐11) Ψ = 0089 WmK rim joist rim board (R‐11) Ψ = 0129 WmK

bull Rim joist thermal bridge ‐ challenging to achieve the Ψ = 001 WmK targetbull Maintaining continuity and alignment of insulation layers is a good first step

STEP 2 ndash Align insulation layers

Section 2 ndash Common Linear Thermal Bridges

32

rim joist 2x4 wall w 1rdquo exterior XPS (R‐13) Ψ = 0047 WmK

Section 2 ndash Common Linear Thermal Bridges

33

rim joist fib batt (R‐11) Ψ = 0089 WmK

bull Exterior insulation helps control heat flow through uninsulated studs and plates

STEP 3 ndash Use continuous exterior insulation to isolate bridging elements

rim joist 2x4 wall w 1rdquo exterior XPS (R‐13) Ψ = 0047 WmK

Use enough exterior insulation and the psi value can be driven down below 001 WmK

Section 2 ndash Common Linear Thermal Bridges

34

rim joist 2x4 wall w 4rdquo exterior XPSΨ = 0011 WmK

rim joist 2x4 wall w 4rdquo exterior XPSΨ = 0011 WmK

Question ndash are the psi values for these two details the same or different

Section 2 ndash Common Linear Thermal Bridges

35

rim joist 2x6 wall w 4rdquo exterior XPSΨ =

rim joist 2x4 wall w 4rdquo exterior XPSΨ = 0011 WmK

Is the detail on the left a ldquobetterrdquo detailIs heat flow through the detail on the right really 2x higher than the heat flow on the leftDoes 4rdquo of exterior foam guarantee a good psi value

Section 2 ndash Common Linear Thermal Bridges

36

rim joist 2x6 wall w 4rdquo exterior XPSΨ = 0020 WmK

rim joist 2x4 wall w 4rdquo exterior XPSΨ = 0011 WmK

NoFor the 2x6 wall therersquos now simply a larger difference between the higher R‐value wall assembly and the rim joist R‐value which has remained the same

Section 2 ndash Common Linear Thermal Bridges

37

rim joist 2x6 wall w 4rdquo exterior XPSΨ = 0020 WmK

Is the psi value really an indicator of a detailrsquos thermal quality

Section 2 ndash Common Linear Thermal Bridges

38

Is the psi value really an indicator of a detailrsquos thermal qualityYes and no

At structural thermal bridges a psi value is a comparison between the U‐value of the assembly(ies) and the U‐value of the junction A junction detail that ldquopassesrdquo (001 WmK) for one assembly may not pass with another

Section 2 ndash Common Linear Thermal Bridges

39

Section 2 ndash Common Linear Thermal Bridges

2x6 wall no studs Ψ = ‐ 0058 WmK 2x6 wall 2‐stud Ψ = ‐ 0040 WmK

When is a performance comparison validWhen the two models being compared have the same assemblies and the same geometry ‐the only difference is at the junction Example above

40

stem wall Ψ = ‐0004 WmK FPSF (frost‐protected shallow foundation) Ψ = 0160 WmK

bull Thermal bridge at the foundation is typically the most challenging to addressbull The concrete stem wall and FPSF footing acts as a radiation fin

STEP 4 ndash Avoid accidental ldquoradiation finsrdquo

Section 2 ndash Common Linear Thermal Bridges

41

FPSF (well insulated) Ψ = 0013 WmK

Thick layers of continuous insulation can improve the performance of the detail but even

FPSF Ψ = 0160 WmK

a very well insulated FPSF is still close to the 001 WmK limit

Section 2 ndash Common Linear Thermal Bridges

STEP 4 ‐ Avoid accidental radiation fins ‐ even well‐insulated ones

42

stem wall Ψ = ‐0004 WmK Thermally broken stem wall Ψ = ‐0136 WmK

Section 2 ndash Common Linear Thermal Bridges

43

Thermally broken stem wall provides an insulated break between the stem wall and the floor slab effectively cutting off the ldquoradiation finrdquoAligning exterior insulation layers at junction of stem wall and above grade wall also helpsSTEP 5 ndash An insulated break between the exterior wall and floor slab works best

ICF parapet Ψ = 0200 WmK Foamglas thermal break Ψ = ‐0071 WmK

Another good location to cut off the radiation fin

Section 2 ndash Common Linear Thermal Bridges

44

Window positioned outside of thermal envelope Ψ = 010 WmKEffectively R‐value of window reduced by 20 ‐ 30 depending on window size

Section 2 ndash Common Linear Thermal Bridges

Window positioned on edge of thermal envelope Ψ = 004 WmKR‐value of window reduced by 5 ‐10 depending on window size

45

Window centered in plane of insulation Ψ = 002 to 003 WmKR‐value of window is almost preserved

Section 2 ndash Common Linear Thermal Bridges

46

47

Break

Section 3 ndash Using psi values in PHPP

48

How do I know which thermal bridges need to be modeled and entered in PHPP

Section 3 ndash Using psi values in PHPP

49

How do I know which thermal bridges need to be modeled and entered in PHPP

PHI requires 1 of 2 paths1) Model all thermal bridges enter psi values for both + and ‐2) Model and enter only thermal bridges with psi values over 001 WmK

Path 2 begs the question ndash how do I know which TBs will be over 001 WmK before Irsquove modeled them

Image source httpwwwtheblazecomblog20130124finally‐the‐answer‐sort‐of‐for‐what‐came‐first‐the‐chicken‐or‐the‐egg

Section 3 ndash Using psi values in PHPP

50

EavesMost details will have negative psi value

Rim joistAlmost always positive psi value ‐MODEL

Wall to slabfootingOnly well‐designed details will have negative psi value ‐MODEL

Footing below bearing wall or postOnly well‐designed details will have psi value lt 001 WmK‐MODEL

Roof ridgeMost details will have negative psi value

Section 3 ndash Using psi values in PHPP

51

RakeMost details will have negative psi value

Windowdoor sill on slab MODEL BUThellipCan be entered as a window sill TB + wall‐to‐slab TB (requires two separate psi values)

Window sillAlmost always positive psi value since overinsulationis difficult ndashMODEL

Window headIf overinsulated probably no need to model If not ndashMODEL

Section 3 ndash Using psi values in PHPP

52

Exterior cornerMost details will have negative psi value

Interior cornerAlmost always positive psi value ndashMODEL

Window jambIf overinsulated probably no need to model If not ndashMODEL

Wall junctionIf insulation layers are interrupted ‐MODEL

Section 3 ndash Using psi values in PHPP

53

Other places to keep in mind for possible thermal bridgesbull Plumbing stacksbull Rain pipes (interior)bull ERV vent penetrations (to the exterior)bull Sump pumpsbull Radon remediation pipes (if interior to the building)

Section 3 ndash Using psi values in PHPP

54

Section 3 ndash Using psi values in PHPP

55

Section 3 ndash Using psi values in WUFI Passive

56

20

Section 1 ndash Background + Basics

L2d ndash U1L1 ndash U2L2 = Ψ

Φ ΔT ndash U1L1 ndash U2L2 = Ψ(heat flux)

Image from David White Right Environments 2010

21

Section 1 ndash Background + Basics

UeqLtotal ndash U1L1 ndash U2L2 = Ψ(equivalent U‐value)

L2d ndash U1L1 ndash U2L2 = Ψ

Φ ΔT ndash U1L1 ndash U2L2 = Ψ(heat flux)

Image from David White Right Environments 2010

22

Section 1 ndash Background + Basics

As used in the PHPP the psi value is always based on a comparison of heat flows ‐ a comparison between the actual heat flow and the estimated heat flow In this sense psi is a correction factor

Image from David White Right Environments 2010

Details coming uphellip1 Wall corners2 Rim joists3 Footings4 Parapets5 Windows

23

Section 1 ndash Background + Basics

When calculating heat loss U x A x dTbull Using exterior dimensions area A = 40 x 10 = 400sfbull Using interior dimensions area A = 36 x 10 = 360sf

Which area A gives the correct heat loss

24

Section 1 ndash Background + Basics

When calculating heat loss U x A x dTbull Using exterior dimensions leads to an overestimatebull Using interior dimensions leads to an underestimate

PH convention is to use exterior dimensions so heat loss is overestimated

25

Section 1 ndash Background + Basics

Section 2 ndash Common Linear Thermal Bridges

2x6 wall no studs Ψ = ‐ 0058 WmK 2x6 wall 2‐stud Ψ = ‐ 0040 WmK

bull By subtraction negative psi values correct for overestimate of heat loss at exterior cornersbull The lower (more negative) the better Higher psi values indicate increasing heat lossbull Positive psi values above 001 WmK indicate net heat transfer (heat gain in summer heat loss in winter)that should be accounted for in PHPP

Step 1 ndash Avoid bridging elements 26

2x6 wall Ψ = ‐ 0040 WmK 2x8 wall Ψ = ‐ 0045 WmK

Is the 2x8 wall corner a ldquobetterrdquo detail

Section 2 ndash Common Linear Thermal Bridges

27

2x6 wall Ψ = ‐ 0040 WmK 2x8 wall Ψ = ‐ 0045 WmK

NoA thicker wall section needs a larger correction factor due to larger overestimate of heat loss

Section 2 ndash Common Linear Thermal Bridges

28

Is the psi value really an indicator of a detailrsquos thermal quality

Section 2 ndash Common Linear Thermal Bridges

29

Is the psi value really an indicator of a detailrsquos thermal qualityYes and no

At geometric bridges it does two things at once ndash it is both a correction factor and an indicator of heat flow ndash but primarily a correction factor

Section 2 ndash Common Linear Thermal Bridges

30

Is the psi value really an indicator of a detailrsquos thermal qualityYes and no

At geometric bridges it does two things at once ndash it is both a correction factor and an indicator of heat flow ndash but primarily a correction factor

Section 2 ndash Common Linear Thermal Bridges

31

Exterior cornerInsulated 2x6 wall w solid post Ψ = ‐ 0004 WmK

rim joist fib batt (R‐11) Ψ = 0089 WmK rim joist rim board (R‐11) Ψ = 0129 WmK

bull Rim joist thermal bridge ‐ challenging to achieve the Ψ = 001 WmK targetbull Maintaining continuity and alignment of insulation layers is a good first step

STEP 2 ndash Align insulation layers

Section 2 ndash Common Linear Thermal Bridges

32

rim joist 2x4 wall w 1rdquo exterior XPS (R‐13) Ψ = 0047 WmK

Section 2 ndash Common Linear Thermal Bridges

33

rim joist fib batt (R‐11) Ψ = 0089 WmK

bull Exterior insulation helps control heat flow through uninsulated studs and plates

STEP 3 ndash Use continuous exterior insulation to isolate bridging elements

rim joist 2x4 wall w 1rdquo exterior XPS (R‐13) Ψ = 0047 WmK

Use enough exterior insulation and the psi value can be driven down below 001 WmK

Section 2 ndash Common Linear Thermal Bridges

34

rim joist 2x4 wall w 4rdquo exterior XPSΨ = 0011 WmK

rim joist 2x4 wall w 4rdquo exterior XPSΨ = 0011 WmK

Question ndash are the psi values for these two details the same or different

Section 2 ndash Common Linear Thermal Bridges

35

rim joist 2x6 wall w 4rdquo exterior XPSΨ =

rim joist 2x4 wall w 4rdquo exterior XPSΨ = 0011 WmK

Is the detail on the left a ldquobetterrdquo detailIs heat flow through the detail on the right really 2x higher than the heat flow on the leftDoes 4rdquo of exterior foam guarantee a good psi value

Section 2 ndash Common Linear Thermal Bridges

36

rim joist 2x6 wall w 4rdquo exterior XPSΨ = 0020 WmK

rim joist 2x4 wall w 4rdquo exterior XPSΨ = 0011 WmK

NoFor the 2x6 wall therersquos now simply a larger difference between the higher R‐value wall assembly and the rim joist R‐value which has remained the same

Section 2 ndash Common Linear Thermal Bridges

37

rim joist 2x6 wall w 4rdquo exterior XPSΨ = 0020 WmK

Is the psi value really an indicator of a detailrsquos thermal quality

Section 2 ndash Common Linear Thermal Bridges

38

Is the psi value really an indicator of a detailrsquos thermal qualityYes and no

At structural thermal bridges a psi value is a comparison between the U‐value of the assembly(ies) and the U‐value of the junction A junction detail that ldquopassesrdquo (001 WmK) for one assembly may not pass with another

Section 2 ndash Common Linear Thermal Bridges

39

Section 2 ndash Common Linear Thermal Bridges

2x6 wall no studs Ψ = ‐ 0058 WmK 2x6 wall 2‐stud Ψ = ‐ 0040 WmK

When is a performance comparison validWhen the two models being compared have the same assemblies and the same geometry ‐the only difference is at the junction Example above

40

stem wall Ψ = ‐0004 WmK FPSF (frost‐protected shallow foundation) Ψ = 0160 WmK

bull Thermal bridge at the foundation is typically the most challenging to addressbull The concrete stem wall and FPSF footing acts as a radiation fin

STEP 4 ndash Avoid accidental ldquoradiation finsrdquo

Section 2 ndash Common Linear Thermal Bridges

41

FPSF (well insulated) Ψ = 0013 WmK

Thick layers of continuous insulation can improve the performance of the detail but even

FPSF Ψ = 0160 WmK

a very well insulated FPSF is still close to the 001 WmK limit

Section 2 ndash Common Linear Thermal Bridges

STEP 4 ‐ Avoid accidental radiation fins ‐ even well‐insulated ones

42

stem wall Ψ = ‐0004 WmK Thermally broken stem wall Ψ = ‐0136 WmK

Section 2 ndash Common Linear Thermal Bridges

43

Thermally broken stem wall provides an insulated break between the stem wall and the floor slab effectively cutting off the ldquoradiation finrdquoAligning exterior insulation layers at junction of stem wall and above grade wall also helpsSTEP 5 ndash An insulated break between the exterior wall and floor slab works best

ICF parapet Ψ = 0200 WmK Foamglas thermal break Ψ = ‐0071 WmK

Another good location to cut off the radiation fin

Section 2 ndash Common Linear Thermal Bridges

44

Window positioned outside of thermal envelope Ψ = 010 WmKEffectively R‐value of window reduced by 20 ‐ 30 depending on window size

Section 2 ndash Common Linear Thermal Bridges

Window positioned on edge of thermal envelope Ψ = 004 WmKR‐value of window reduced by 5 ‐10 depending on window size

45

Window centered in plane of insulation Ψ = 002 to 003 WmKR‐value of window is almost preserved

Section 2 ndash Common Linear Thermal Bridges

46

47

Break

Section 3 ndash Using psi values in PHPP

48

How do I know which thermal bridges need to be modeled and entered in PHPP

Section 3 ndash Using psi values in PHPP

49

How do I know which thermal bridges need to be modeled and entered in PHPP

PHI requires 1 of 2 paths1) Model all thermal bridges enter psi values for both + and ‐2) Model and enter only thermal bridges with psi values over 001 WmK

Path 2 begs the question ndash how do I know which TBs will be over 001 WmK before Irsquove modeled them

Image source httpwwwtheblazecomblog20130124finally‐the‐answer‐sort‐of‐for‐what‐came‐first‐the‐chicken‐or‐the‐egg

Section 3 ndash Using psi values in PHPP

50

EavesMost details will have negative psi value

Rim joistAlmost always positive psi value ‐MODEL

Wall to slabfootingOnly well‐designed details will have negative psi value ‐MODEL

Footing below bearing wall or postOnly well‐designed details will have psi value lt 001 WmK‐MODEL

Roof ridgeMost details will have negative psi value

Section 3 ndash Using psi values in PHPP

51

RakeMost details will have negative psi value

Windowdoor sill on slab MODEL BUThellipCan be entered as a window sill TB + wall‐to‐slab TB (requires two separate psi values)

Window sillAlmost always positive psi value since overinsulationis difficult ndashMODEL

Window headIf overinsulated probably no need to model If not ndashMODEL

Section 3 ndash Using psi values in PHPP

52

Exterior cornerMost details will have negative psi value

Interior cornerAlmost always positive psi value ndashMODEL

Window jambIf overinsulated probably no need to model If not ndashMODEL

Wall junctionIf insulation layers are interrupted ‐MODEL

Section 3 ndash Using psi values in PHPP

53

Other places to keep in mind for possible thermal bridgesbull Plumbing stacksbull Rain pipes (interior)bull ERV vent penetrations (to the exterior)bull Sump pumpsbull Radon remediation pipes (if interior to the building)

Section 3 ndash Using psi values in PHPP

54

Section 3 ndash Using psi values in PHPP

55

Section 3 ndash Using psi values in WUFI Passive

56

21

Section 1 ndash Background + Basics

UeqLtotal ndash U1L1 ndash U2L2 = Ψ(equivalent U‐value)

L2d ndash U1L1 ndash U2L2 = Ψ

Φ ΔT ndash U1L1 ndash U2L2 = Ψ(heat flux)

Image from David White Right Environments 2010

22

Section 1 ndash Background + Basics

As used in the PHPP the psi value is always based on a comparison of heat flows ‐ a comparison between the actual heat flow and the estimated heat flow In this sense psi is a correction factor

Image from David White Right Environments 2010

Details coming uphellip1 Wall corners2 Rim joists3 Footings4 Parapets5 Windows

23

Section 1 ndash Background + Basics

When calculating heat loss U x A x dTbull Using exterior dimensions area A = 40 x 10 = 400sfbull Using interior dimensions area A = 36 x 10 = 360sf

Which area A gives the correct heat loss

24

Section 1 ndash Background + Basics

When calculating heat loss U x A x dTbull Using exterior dimensions leads to an overestimatebull Using interior dimensions leads to an underestimate

PH convention is to use exterior dimensions so heat loss is overestimated

25

Section 1 ndash Background + Basics

Section 2 ndash Common Linear Thermal Bridges

2x6 wall no studs Ψ = ‐ 0058 WmK 2x6 wall 2‐stud Ψ = ‐ 0040 WmK

bull By subtraction negative psi values correct for overestimate of heat loss at exterior cornersbull The lower (more negative) the better Higher psi values indicate increasing heat lossbull Positive psi values above 001 WmK indicate net heat transfer (heat gain in summer heat loss in winter)that should be accounted for in PHPP

Step 1 ndash Avoid bridging elements 26

2x6 wall Ψ = ‐ 0040 WmK 2x8 wall Ψ = ‐ 0045 WmK

Is the 2x8 wall corner a ldquobetterrdquo detail

Section 2 ndash Common Linear Thermal Bridges

27

2x6 wall Ψ = ‐ 0040 WmK 2x8 wall Ψ = ‐ 0045 WmK

NoA thicker wall section needs a larger correction factor due to larger overestimate of heat loss

Section 2 ndash Common Linear Thermal Bridges

28

Is the psi value really an indicator of a detailrsquos thermal quality

Section 2 ndash Common Linear Thermal Bridges

29

Is the psi value really an indicator of a detailrsquos thermal qualityYes and no

At geometric bridges it does two things at once ndash it is both a correction factor and an indicator of heat flow ndash but primarily a correction factor

Section 2 ndash Common Linear Thermal Bridges

30

Is the psi value really an indicator of a detailrsquos thermal qualityYes and no

At geometric bridges it does two things at once ndash it is both a correction factor and an indicator of heat flow ndash but primarily a correction factor

Section 2 ndash Common Linear Thermal Bridges

31

Exterior cornerInsulated 2x6 wall w solid post Ψ = ‐ 0004 WmK

rim joist fib batt (R‐11) Ψ = 0089 WmK rim joist rim board (R‐11) Ψ = 0129 WmK

bull Rim joist thermal bridge ‐ challenging to achieve the Ψ = 001 WmK targetbull Maintaining continuity and alignment of insulation layers is a good first step

STEP 2 ndash Align insulation layers

Section 2 ndash Common Linear Thermal Bridges

32

rim joist 2x4 wall w 1rdquo exterior XPS (R‐13) Ψ = 0047 WmK

Section 2 ndash Common Linear Thermal Bridges

33

rim joist fib batt (R‐11) Ψ = 0089 WmK

bull Exterior insulation helps control heat flow through uninsulated studs and plates

STEP 3 ndash Use continuous exterior insulation to isolate bridging elements

rim joist 2x4 wall w 1rdquo exterior XPS (R‐13) Ψ = 0047 WmK

Use enough exterior insulation and the psi value can be driven down below 001 WmK

Section 2 ndash Common Linear Thermal Bridges

34

rim joist 2x4 wall w 4rdquo exterior XPSΨ = 0011 WmK

rim joist 2x4 wall w 4rdquo exterior XPSΨ = 0011 WmK

Question ndash are the psi values for these two details the same or different

Section 2 ndash Common Linear Thermal Bridges

35

rim joist 2x6 wall w 4rdquo exterior XPSΨ =

rim joist 2x4 wall w 4rdquo exterior XPSΨ = 0011 WmK

Is the detail on the left a ldquobetterrdquo detailIs heat flow through the detail on the right really 2x higher than the heat flow on the leftDoes 4rdquo of exterior foam guarantee a good psi value

Section 2 ndash Common Linear Thermal Bridges

36

rim joist 2x6 wall w 4rdquo exterior XPSΨ = 0020 WmK

rim joist 2x4 wall w 4rdquo exterior XPSΨ = 0011 WmK

NoFor the 2x6 wall therersquos now simply a larger difference between the higher R‐value wall assembly and the rim joist R‐value which has remained the same

Section 2 ndash Common Linear Thermal Bridges

37

rim joist 2x6 wall w 4rdquo exterior XPSΨ = 0020 WmK

Is the psi value really an indicator of a detailrsquos thermal quality

Section 2 ndash Common Linear Thermal Bridges

38

Is the psi value really an indicator of a detailrsquos thermal qualityYes and no

At structural thermal bridges a psi value is a comparison between the U‐value of the assembly(ies) and the U‐value of the junction A junction detail that ldquopassesrdquo (001 WmK) for one assembly may not pass with another

Section 2 ndash Common Linear Thermal Bridges

39

Section 2 ndash Common Linear Thermal Bridges

2x6 wall no studs Ψ = ‐ 0058 WmK 2x6 wall 2‐stud Ψ = ‐ 0040 WmK

When is a performance comparison validWhen the two models being compared have the same assemblies and the same geometry ‐the only difference is at the junction Example above

40

stem wall Ψ = ‐0004 WmK FPSF (frost‐protected shallow foundation) Ψ = 0160 WmK

bull Thermal bridge at the foundation is typically the most challenging to addressbull The concrete stem wall and FPSF footing acts as a radiation fin

STEP 4 ndash Avoid accidental ldquoradiation finsrdquo

Section 2 ndash Common Linear Thermal Bridges

41

FPSF (well insulated) Ψ = 0013 WmK

Thick layers of continuous insulation can improve the performance of the detail but even

FPSF Ψ = 0160 WmK

a very well insulated FPSF is still close to the 001 WmK limit

Section 2 ndash Common Linear Thermal Bridges

STEP 4 ‐ Avoid accidental radiation fins ‐ even well‐insulated ones

42

stem wall Ψ = ‐0004 WmK Thermally broken stem wall Ψ = ‐0136 WmK

Section 2 ndash Common Linear Thermal Bridges

43

Thermally broken stem wall provides an insulated break between the stem wall and the floor slab effectively cutting off the ldquoradiation finrdquoAligning exterior insulation layers at junction of stem wall and above grade wall also helpsSTEP 5 ndash An insulated break between the exterior wall and floor slab works best

ICF parapet Ψ = 0200 WmK Foamglas thermal break Ψ = ‐0071 WmK

Another good location to cut off the radiation fin

Section 2 ndash Common Linear Thermal Bridges

44

Window positioned outside of thermal envelope Ψ = 010 WmKEffectively R‐value of window reduced by 20 ‐ 30 depending on window size

Section 2 ndash Common Linear Thermal Bridges

Window positioned on edge of thermal envelope Ψ = 004 WmKR‐value of window reduced by 5 ‐10 depending on window size

45

Window centered in plane of insulation Ψ = 002 to 003 WmKR‐value of window is almost preserved

Section 2 ndash Common Linear Thermal Bridges

46

47

Break

Section 3 ndash Using psi values in PHPP

48

How do I know which thermal bridges need to be modeled and entered in PHPP

Section 3 ndash Using psi values in PHPP

49

How do I know which thermal bridges need to be modeled and entered in PHPP

PHI requires 1 of 2 paths1) Model all thermal bridges enter psi values for both + and ‐2) Model and enter only thermal bridges with psi values over 001 WmK

Path 2 begs the question ndash how do I know which TBs will be over 001 WmK before Irsquove modeled them

Image source httpwwwtheblazecomblog20130124finally‐the‐answer‐sort‐of‐for‐what‐came‐first‐the‐chicken‐or‐the‐egg

Section 3 ndash Using psi values in PHPP

50

EavesMost details will have negative psi value

Rim joistAlmost always positive psi value ‐MODEL

Wall to slabfootingOnly well‐designed details will have negative psi value ‐MODEL

Footing below bearing wall or postOnly well‐designed details will have psi value lt 001 WmK‐MODEL

Roof ridgeMost details will have negative psi value

Section 3 ndash Using psi values in PHPP

51

RakeMost details will have negative psi value

Windowdoor sill on slab MODEL BUThellipCan be entered as a window sill TB + wall‐to‐slab TB (requires two separate psi values)

Window sillAlmost always positive psi value since overinsulationis difficult ndashMODEL

Window headIf overinsulated probably no need to model If not ndashMODEL

Section 3 ndash Using psi values in PHPP

52

Exterior cornerMost details will have negative psi value

Interior cornerAlmost always positive psi value ndashMODEL

Window jambIf overinsulated probably no need to model If not ndashMODEL

Wall junctionIf insulation layers are interrupted ‐MODEL

Section 3 ndash Using psi values in PHPP

53

Other places to keep in mind for possible thermal bridgesbull Plumbing stacksbull Rain pipes (interior)bull ERV vent penetrations (to the exterior)bull Sump pumpsbull Radon remediation pipes (if interior to the building)

Section 3 ndash Using psi values in PHPP

54

Section 3 ndash Using psi values in PHPP

55

Section 3 ndash Using psi values in WUFI Passive

56

22

Section 1 ndash Background + Basics

As used in the PHPP the psi value is always based on a comparison of heat flows ‐ a comparison between the actual heat flow and the estimated heat flow In this sense psi is a correction factor

Image from David White Right Environments 2010

Details coming uphellip1 Wall corners2 Rim joists3 Footings4 Parapets5 Windows

23

Section 1 ndash Background + Basics

When calculating heat loss U x A x dTbull Using exterior dimensions area A = 40 x 10 = 400sfbull Using interior dimensions area A = 36 x 10 = 360sf

Which area A gives the correct heat loss

24

Section 1 ndash Background + Basics

When calculating heat loss U x A x dTbull Using exterior dimensions leads to an overestimatebull Using interior dimensions leads to an underestimate

PH convention is to use exterior dimensions so heat loss is overestimated

25

Section 1 ndash Background + Basics

Section 2 ndash Common Linear Thermal Bridges

2x6 wall no studs Ψ = ‐ 0058 WmK 2x6 wall 2‐stud Ψ = ‐ 0040 WmK

bull By subtraction negative psi values correct for overestimate of heat loss at exterior cornersbull The lower (more negative) the better Higher psi values indicate increasing heat lossbull Positive psi values above 001 WmK indicate net heat transfer (heat gain in summer heat loss in winter)that should be accounted for in PHPP

Step 1 ndash Avoid bridging elements 26

2x6 wall Ψ = ‐ 0040 WmK 2x8 wall Ψ = ‐ 0045 WmK

Is the 2x8 wall corner a ldquobetterrdquo detail

Section 2 ndash Common Linear Thermal Bridges

27

2x6 wall Ψ = ‐ 0040 WmK 2x8 wall Ψ = ‐ 0045 WmK

NoA thicker wall section needs a larger correction factor due to larger overestimate of heat loss

Section 2 ndash Common Linear Thermal Bridges

28

Is the psi value really an indicator of a detailrsquos thermal quality

Section 2 ndash Common Linear Thermal Bridges

29

Is the psi value really an indicator of a detailrsquos thermal qualityYes and no

At geometric bridges it does two things at once ndash it is both a correction factor and an indicator of heat flow ndash but primarily a correction factor

Section 2 ndash Common Linear Thermal Bridges

30

Is the psi value really an indicator of a detailrsquos thermal qualityYes and no

At geometric bridges it does two things at once ndash it is both a correction factor and an indicator of heat flow ndash but primarily a correction factor

Section 2 ndash Common Linear Thermal Bridges

31

Exterior cornerInsulated 2x6 wall w solid post Ψ = ‐ 0004 WmK

rim joist fib batt (R‐11) Ψ = 0089 WmK rim joist rim board (R‐11) Ψ = 0129 WmK

bull Rim joist thermal bridge ‐ challenging to achieve the Ψ = 001 WmK targetbull Maintaining continuity and alignment of insulation layers is a good first step

STEP 2 ndash Align insulation layers

Section 2 ndash Common Linear Thermal Bridges

32

rim joist 2x4 wall w 1rdquo exterior XPS (R‐13) Ψ = 0047 WmK

Section 2 ndash Common Linear Thermal Bridges

33

rim joist fib batt (R‐11) Ψ = 0089 WmK

bull Exterior insulation helps control heat flow through uninsulated studs and plates

STEP 3 ndash Use continuous exterior insulation to isolate bridging elements

rim joist 2x4 wall w 1rdquo exterior XPS (R‐13) Ψ = 0047 WmK

Use enough exterior insulation and the psi value can be driven down below 001 WmK

Section 2 ndash Common Linear Thermal Bridges

34

rim joist 2x4 wall w 4rdquo exterior XPSΨ = 0011 WmK

rim joist 2x4 wall w 4rdquo exterior XPSΨ = 0011 WmK

Question ndash are the psi values for these two details the same or different

Section 2 ndash Common Linear Thermal Bridges

35

rim joist 2x6 wall w 4rdquo exterior XPSΨ =

rim joist 2x4 wall w 4rdquo exterior XPSΨ = 0011 WmK

Is the detail on the left a ldquobetterrdquo detailIs heat flow through the detail on the right really 2x higher than the heat flow on the leftDoes 4rdquo of exterior foam guarantee a good psi value

Section 2 ndash Common Linear Thermal Bridges

36

rim joist 2x6 wall w 4rdquo exterior XPSΨ = 0020 WmK

rim joist 2x4 wall w 4rdquo exterior XPSΨ = 0011 WmK

NoFor the 2x6 wall therersquos now simply a larger difference between the higher R‐value wall assembly and the rim joist R‐value which has remained the same

Section 2 ndash Common Linear Thermal Bridges

37

rim joist 2x6 wall w 4rdquo exterior XPSΨ = 0020 WmK

Is the psi value really an indicator of a detailrsquos thermal quality

Section 2 ndash Common Linear Thermal Bridges

38

Is the psi value really an indicator of a detailrsquos thermal qualityYes and no

At structural thermal bridges a psi value is a comparison between the U‐value of the assembly(ies) and the U‐value of the junction A junction detail that ldquopassesrdquo (001 WmK) for one assembly may not pass with another

Section 2 ndash Common Linear Thermal Bridges

39

Section 2 ndash Common Linear Thermal Bridges

2x6 wall no studs Ψ = ‐ 0058 WmK 2x6 wall 2‐stud Ψ = ‐ 0040 WmK

When is a performance comparison validWhen the two models being compared have the same assemblies and the same geometry ‐the only difference is at the junction Example above

40

stem wall Ψ = ‐0004 WmK FPSF (frost‐protected shallow foundation) Ψ = 0160 WmK

bull Thermal bridge at the foundation is typically the most challenging to addressbull The concrete stem wall and FPSF footing acts as a radiation fin

STEP 4 ndash Avoid accidental ldquoradiation finsrdquo

Section 2 ndash Common Linear Thermal Bridges

41

FPSF (well insulated) Ψ = 0013 WmK

Thick layers of continuous insulation can improve the performance of the detail but even

FPSF Ψ = 0160 WmK

a very well insulated FPSF is still close to the 001 WmK limit

Section 2 ndash Common Linear Thermal Bridges

STEP 4 ‐ Avoid accidental radiation fins ‐ even well‐insulated ones

42

stem wall Ψ = ‐0004 WmK Thermally broken stem wall Ψ = ‐0136 WmK

Section 2 ndash Common Linear Thermal Bridges

43

Thermally broken stem wall provides an insulated break between the stem wall and the floor slab effectively cutting off the ldquoradiation finrdquoAligning exterior insulation layers at junction of stem wall and above grade wall also helpsSTEP 5 ndash An insulated break between the exterior wall and floor slab works best

ICF parapet Ψ = 0200 WmK Foamglas thermal break Ψ = ‐0071 WmK

Another good location to cut off the radiation fin

Section 2 ndash Common Linear Thermal Bridges

44

Window positioned outside of thermal envelope Ψ = 010 WmKEffectively R‐value of window reduced by 20 ‐ 30 depending on window size

Section 2 ndash Common Linear Thermal Bridges

Window positioned on edge of thermal envelope Ψ = 004 WmKR‐value of window reduced by 5 ‐10 depending on window size

45

Window centered in plane of insulation Ψ = 002 to 003 WmKR‐value of window is almost preserved

Section 2 ndash Common Linear Thermal Bridges

46

47

Break

Section 3 ndash Using psi values in PHPP

48

How do I know which thermal bridges need to be modeled and entered in PHPP

Section 3 ndash Using psi values in PHPP

49

How do I know which thermal bridges need to be modeled and entered in PHPP

PHI requires 1 of 2 paths1) Model all thermal bridges enter psi values for both + and ‐2) Model and enter only thermal bridges with psi values over 001 WmK

Path 2 begs the question ndash how do I know which TBs will be over 001 WmK before Irsquove modeled them

Image source httpwwwtheblazecomblog20130124finally‐the‐answer‐sort‐of‐for‐what‐came‐first‐the‐chicken‐or‐the‐egg

Section 3 ndash Using psi values in PHPP

50

EavesMost details will have negative psi value

Rim joistAlmost always positive psi value ‐MODEL

Wall to slabfootingOnly well‐designed details will have negative psi value ‐MODEL

Footing below bearing wall or postOnly well‐designed details will have psi value lt 001 WmK‐MODEL

Roof ridgeMost details will have negative psi value

Section 3 ndash Using psi values in PHPP

51

RakeMost details will have negative psi value

Windowdoor sill on slab MODEL BUThellipCan be entered as a window sill TB + wall‐to‐slab TB (requires two separate psi values)

Window sillAlmost always positive psi value since overinsulationis difficult ndashMODEL

Window headIf overinsulated probably no need to model If not ndashMODEL

Section 3 ndash Using psi values in PHPP

52

Exterior cornerMost details will have negative psi value

Interior cornerAlmost always positive psi value ndashMODEL

Window jambIf overinsulated probably no need to model If not ndashMODEL

Wall junctionIf insulation layers are interrupted ‐MODEL

Section 3 ndash Using psi values in PHPP

53

Other places to keep in mind for possible thermal bridgesbull Plumbing stacksbull Rain pipes (interior)bull ERV vent penetrations (to the exterior)bull Sump pumpsbull Radon remediation pipes (if interior to the building)

Section 3 ndash Using psi values in PHPP

54

Section 3 ndash Using psi values in PHPP

55

Section 3 ndash Using psi values in WUFI Passive

56

Details coming uphellip1 Wall corners2 Rim joists3 Footings4 Parapets5 Windows

23

Section 1 ndash Background + Basics

When calculating heat loss U x A x dTbull Using exterior dimensions area A = 40 x 10 = 400sfbull Using interior dimensions area A = 36 x 10 = 360sf

Which area A gives the correct heat loss

24

Section 1 ndash Background + Basics

When calculating heat loss U x A x dTbull Using exterior dimensions leads to an overestimatebull Using interior dimensions leads to an underestimate

PH convention is to use exterior dimensions so heat loss is overestimated

25

Section 1 ndash Background + Basics

Section 2 ndash Common Linear Thermal Bridges

2x6 wall no studs Ψ = ‐ 0058 WmK 2x6 wall 2‐stud Ψ = ‐ 0040 WmK

bull By subtraction negative psi values correct for overestimate of heat loss at exterior cornersbull The lower (more negative) the better Higher psi values indicate increasing heat lossbull Positive psi values above 001 WmK indicate net heat transfer (heat gain in summer heat loss in winter)that should be accounted for in PHPP

Step 1 ndash Avoid bridging elements 26

2x6 wall Ψ = ‐ 0040 WmK 2x8 wall Ψ = ‐ 0045 WmK

Is the 2x8 wall corner a ldquobetterrdquo detail

Section 2 ndash Common Linear Thermal Bridges

27

2x6 wall Ψ = ‐ 0040 WmK 2x8 wall Ψ = ‐ 0045 WmK

NoA thicker wall section needs a larger correction factor due to larger overestimate of heat loss

Section 2 ndash Common Linear Thermal Bridges

28

Is the psi value really an indicator of a detailrsquos thermal quality

Section 2 ndash Common Linear Thermal Bridges

29

Is the psi value really an indicator of a detailrsquos thermal qualityYes and no

At geometric bridges it does two things at once ndash it is both a correction factor and an indicator of heat flow ndash but primarily a correction factor

Section 2 ndash Common Linear Thermal Bridges

30

Is the psi value really an indicator of a detailrsquos thermal qualityYes and no

At geometric bridges it does two things at once ndash it is both a correction factor and an indicator of heat flow ndash but primarily a correction factor

Section 2 ndash Common Linear Thermal Bridges

31

Exterior cornerInsulated 2x6 wall w solid post Ψ = ‐ 0004 WmK

rim joist fib batt (R‐11) Ψ = 0089 WmK rim joist rim board (R‐11) Ψ = 0129 WmK

bull Rim joist thermal bridge ‐ challenging to achieve the Ψ = 001 WmK targetbull Maintaining continuity and alignment of insulation layers is a good first step

STEP 2 ndash Align insulation layers

Section 2 ndash Common Linear Thermal Bridges

32

rim joist 2x4 wall w 1rdquo exterior XPS (R‐13) Ψ = 0047 WmK

Section 2 ndash Common Linear Thermal Bridges

33

rim joist fib batt (R‐11) Ψ = 0089 WmK

bull Exterior insulation helps control heat flow through uninsulated studs and plates

STEP 3 ndash Use continuous exterior insulation to isolate bridging elements

rim joist 2x4 wall w 1rdquo exterior XPS (R‐13) Ψ = 0047 WmK

Use enough exterior insulation and the psi value can be driven down below 001 WmK

Section 2 ndash Common Linear Thermal Bridges

34

rim joist 2x4 wall w 4rdquo exterior XPSΨ = 0011 WmK

rim joist 2x4 wall w 4rdquo exterior XPSΨ = 0011 WmK

Question ndash are the psi values for these two details the same or different

Section 2 ndash Common Linear Thermal Bridges

35

rim joist 2x6 wall w 4rdquo exterior XPSΨ =

rim joist 2x4 wall w 4rdquo exterior XPSΨ = 0011 WmK

Is the detail on the left a ldquobetterrdquo detailIs heat flow through the detail on the right really 2x higher than the heat flow on the leftDoes 4rdquo of exterior foam guarantee a good psi value

Section 2 ndash Common Linear Thermal Bridges

36

rim joist 2x6 wall w 4rdquo exterior XPSΨ = 0020 WmK

rim joist 2x4 wall w 4rdquo exterior XPSΨ = 0011 WmK

NoFor the 2x6 wall therersquos now simply a larger difference between the higher R‐value wall assembly and the rim joist R‐value which has remained the same

Section 2 ndash Common Linear Thermal Bridges

37

rim joist 2x6 wall w 4rdquo exterior XPSΨ = 0020 WmK

Is the psi value really an indicator of a detailrsquos thermal quality

Section 2 ndash Common Linear Thermal Bridges

38

Is the psi value really an indicator of a detailrsquos thermal qualityYes and no

At structural thermal bridges a psi value is a comparison between the U‐value of the assembly(ies) and the U‐value of the junction A junction detail that ldquopassesrdquo (001 WmK) for one assembly may not pass with another

Section 2 ndash Common Linear Thermal Bridges

39

Section 2 ndash Common Linear Thermal Bridges

2x6 wall no studs Ψ = ‐ 0058 WmK 2x6 wall 2‐stud Ψ = ‐ 0040 WmK

When is a performance comparison validWhen the two models being compared have the same assemblies and the same geometry ‐the only difference is at the junction Example above

40

stem wall Ψ = ‐0004 WmK FPSF (frost‐protected shallow foundation) Ψ = 0160 WmK

bull Thermal bridge at the foundation is typically the most challenging to addressbull The concrete stem wall and FPSF footing acts as a radiation fin

STEP 4 ndash Avoid accidental ldquoradiation finsrdquo

Section 2 ndash Common Linear Thermal Bridges

41

FPSF (well insulated) Ψ = 0013 WmK

Thick layers of continuous insulation can improve the performance of the detail but even

FPSF Ψ = 0160 WmK

a very well insulated FPSF is still close to the 001 WmK limit

Section 2 ndash Common Linear Thermal Bridges

STEP 4 ‐ Avoid accidental radiation fins ‐ even well‐insulated ones

42

stem wall Ψ = ‐0004 WmK Thermally broken stem wall Ψ = ‐0136 WmK

Section 2 ndash Common Linear Thermal Bridges

43

Thermally broken stem wall provides an insulated break between the stem wall and the floor slab effectively cutting off the ldquoradiation finrdquoAligning exterior insulation layers at junction of stem wall and above grade wall also helpsSTEP 5 ndash An insulated break between the exterior wall and floor slab works best

ICF parapet Ψ = 0200 WmK Foamglas thermal break Ψ = ‐0071 WmK

Another good location to cut off the radiation fin

Section 2 ndash Common Linear Thermal Bridges

44

Window positioned outside of thermal envelope Ψ = 010 WmKEffectively R‐value of window reduced by 20 ‐ 30 depending on window size

Section 2 ndash Common Linear Thermal Bridges

Window positioned on edge of thermal envelope Ψ = 004 WmKR‐value of window reduced by 5 ‐10 depending on window size

45

Window centered in plane of insulation Ψ = 002 to 003 WmKR‐value of window is almost preserved

Section 2 ndash Common Linear Thermal Bridges

46

47

Break

Section 3 ndash Using psi values in PHPP

48

How do I know which thermal bridges need to be modeled and entered in PHPP

Section 3 ndash Using psi values in PHPP

49

How do I know which thermal bridges need to be modeled and entered in PHPP

PHI requires 1 of 2 paths1) Model all thermal bridges enter psi values for both + and ‐2) Model and enter only thermal bridges with psi values over 001 WmK

Path 2 begs the question ndash how do I know which TBs will be over 001 WmK before Irsquove modeled them

Image source httpwwwtheblazecomblog20130124finally‐the‐answer‐sort‐of‐for‐what‐came‐first‐the‐chicken‐or‐the‐egg

Section 3 ndash Using psi values in PHPP

50

EavesMost details will have negative psi value

Rim joistAlmost always positive psi value ‐MODEL

Wall to slabfootingOnly well‐designed details will have negative psi value ‐MODEL

Footing below bearing wall or postOnly well‐designed details will have psi value lt 001 WmK‐MODEL

Roof ridgeMost details will have negative psi value

Section 3 ndash Using psi values in PHPP

51

RakeMost details will have negative psi value

Windowdoor sill on slab MODEL BUThellipCan be entered as a window sill TB + wall‐to‐slab TB (requires two separate psi values)

Window sillAlmost always positive psi value since overinsulationis difficult ndashMODEL

Window headIf overinsulated probably no need to model If not ndashMODEL

Section 3 ndash Using psi values in PHPP

52

Exterior cornerMost details will have negative psi value

Interior cornerAlmost always positive psi value ndashMODEL

Window jambIf overinsulated probably no need to model If not ndashMODEL

Wall junctionIf insulation layers are interrupted ‐MODEL

Section 3 ndash Using psi values in PHPP

53

Other places to keep in mind for possible thermal bridgesbull Plumbing stacksbull Rain pipes (interior)bull ERV vent penetrations (to the exterior)bull Sump pumpsbull Radon remediation pipes (if interior to the building)

Section 3 ndash Using psi values in PHPP

54

Section 3 ndash Using psi values in PHPP

55

Section 3 ndash Using psi values in WUFI Passive

56

When calculating heat loss U x A x dTbull Using exterior dimensions area A = 40 x 10 = 400sfbull Using interior dimensions area A = 36 x 10 = 360sf

Which area A gives the correct heat loss

24

Section 1 ndash Background + Basics

When calculating heat loss U x A x dTbull Using exterior dimensions leads to an overestimatebull Using interior dimensions leads to an underestimate

PH convention is to use exterior dimensions so heat loss is overestimated

25

Section 1 ndash Background + Basics

Section 2 ndash Common Linear Thermal Bridges

2x6 wall no studs Ψ = ‐ 0058 WmK 2x6 wall 2‐stud Ψ = ‐ 0040 WmK

bull By subtraction negative psi values correct for overestimate of heat loss at exterior cornersbull The lower (more negative) the better Higher psi values indicate increasing heat lossbull Positive psi values above 001 WmK indicate net heat transfer (heat gain in summer heat loss in winter)that should be accounted for in PHPP

Step 1 ndash Avoid bridging elements 26

2x6 wall Ψ = ‐ 0040 WmK 2x8 wall Ψ = ‐ 0045 WmK

Is the 2x8 wall corner a ldquobetterrdquo detail

Section 2 ndash Common Linear Thermal Bridges

27

2x6 wall Ψ = ‐ 0040 WmK 2x8 wall Ψ = ‐ 0045 WmK

NoA thicker wall section needs a larger correction factor due to larger overestimate of heat loss

Section 2 ndash Common Linear Thermal Bridges

28

Is the psi value really an indicator of a detailrsquos thermal quality

Section 2 ndash Common Linear Thermal Bridges

29

Is the psi value really an indicator of a detailrsquos thermal qualityYes and no

At geometric bridges it does two things at once ndash it is both a correction factor and an indicator of heat flow ndash but primarily a correction factor

Section 2 ndash Common Linear Thermal Bridges

30

Is the psi value really an indicator of a detailrsquos thermal qualityYes and no

At geometric bridges it does two things at once ndash it is both a correction factor and an indicator of heat flow ndash but primarily a correction factor

Section 2 ndash Common Linear Thermal Bridges

31

Exterior cornerInsulated 2x6 wall w solid post Ψ = ‐ 0004 WmK

rim joist fib batt (R‐11) Ψ = 0089 WmK rim joist rim board (R‐11) Ψ = 0129 WmK

bull Rim joist thermal bridge ‐ challenging to achieve the Ψ = 001 WmK targetbull Maintaining continuity and alignment of insulation layers is a good first step

STEP 2 ndash Align insulation layers

Section 2 ndash Common Linear Thermal Bridges

32

rim joist 2x4 wall w 1rdquo exterior XPS (R‐13) Ψ = 0047 WmK

Section 2 ndash Common Linear Thermal Bridges

33

rim joist fib batt (R‐11) Ψ = 0089 WmK

bull Exterior insulation helps control heat flow through uninsulated studs and plates

STEP 3 ndash Use continuous exterior insulation to isolate bridging elements

rim joist 2x4 wall w 1rdquo exterior XPS (R‐13) Ψ = 0047 WmK

Use enough exterior insulation and the psi value can be driven down below 001 WmK

Section 2 ndash Common Linear Thermal Bridges

34

rim joist 2x4 wall w 4rdquo exterior XPSΨ = 0011 WmK

rim joist 2x4 wall w 4rdquo exterior XPSΨ = 0011 WmK

Question ndash are the psi values for these two details the same or different

Section 2 ndash Common Linear Thermal Bridges

35

rim joist 2x6 wall w 4rdquo exterior XPSΨ =

rim joist 2x4 wall w 4rdquo exterior XPSΨ = 0011 WmK

Is the detail on the left a ldquobetterrdquo detailIs heat flow through the detail on the right really 2x higher than the heat flow on the leftDoes 4rdquo of exterior foam guarantee a good psi value

Section 2 ndash Common Linear Thermal Bridges

36

rim joist 2x6 wall w 4rdquo exterior XPSΨ = 0020 WmK

rim joist 2x4 wall w 4rdquo exterior XPSΨ = 0011 WmK

NoFor the 2x6 wall therersquos now simply a larger difference between the higher R‐value wall assembly and the rim joist R‐value which has remained the same

Section 2 ndash Common Linear Thermal Bridges

37

rim joist 2x6 wall w 4rdquo exterior XPSΨ = 0020 WmK

Is the psi value really an indicator of a detailrsquos thermal quality

Section 2 ndash Common Linear Thermal Bridges

38

Is the psi value really an indicator of a detailrsquos thermal qualityYes and no

At structural thermal bridges a psi value is a comparison between the U‐value of the assembly(ies) and the U‐value of the junction A junction detail that ldquopassesrdquo (001 WmK) for one assembly may not pass with another

Section 2 ndash Common Linear Thermal Bridges

39

Section 2 ndash Common Linear Thermal Bridges

2x6 wall no studs Ψ = ‐ 0058 WmK 2x6 wall 2‐stud Ψ = ‐ 0040 WmK

When is a performance comparison validWhen the two models being compared have the same assemblies and the same geometry ‐the only difference is at the junction Example above

40

stem wall Ψ = ‐0004 WmK FPSF (frost‐protected shallow foundation) Ψ = 0160 WmK

bull Thermal bridge at the foundation is typically the most challenging to addressbull The concrete stem wall and FPSF footing acts as a radiation fin

STEP 4 ndash Avoid accidental ldquoradiation finsrdquo

Section 2 ndash Common Linear Thermal Bridges

41

FPSF (well insulated) Ψ = 0013 WmK

Thick layers of continuous insulation can improve the performance of the detail but even

FPSF Ψ = 0160 WmK

a very well insulated FPSF is still close to the 001 WmK limit

Section 2 ndash Common Linear Thermal Bridges

STEP 4 ‐ Avoid accidental radiation fins ‐ even well‐insulated ones

42

stem wall Ψ = ‐0004 WmK Thermally broken stem wall Ψ = ‐0136 WmK

Section 2 ndash Common Linear Thermal Bridges

43

Thermally broken stem wall provides an insulated break between the stem wall and the floor slab effectively cutting off the ldquoradiation finrdquoAligning exterior insulation layers at junction of stem wall and above grade wall also helpsSTEP 5 ndash An insulated break between the exterior wall and floor slab works best

ICF parapet Ψ = 0200 WmK Foamglas thermal break Ψ = ‐0071 WmK

Another good location to cut off the radiation fin

Section 2 ndash Common Linear Thermal Bridges

44

Window positioned outside of thermal envelope Ψ = 010 WmKEffectively R‐value of window reduced by 20 ‐ 30 depending on window size

Section 2 ndash Common Linear Thermal Bridges

Window positioned on edge of thermal envelope Ψ = 004 WmKR‐value of window reduced by 5 ‐10 depending on window size

45

Window centered in plane of insulation Ψ = 002 to 003 WmKR‐value of window is almost preserved

Section 2 ndash Common Linear Thermal Bridges

46

47

Break

Section 3 ndash Using psi values in PHPP

48

How do I know which thermal bridges need to be modeled and entered in PHPP

Section 3 ndash Using psi values in PHPP

49

How do I know which thermal bridges need to be modeled and entered in PHPP

PHI requires 1 of 2 paths1) Model all thermal bridges enter psi values for both + and ‐2) Model and enter only thermal bridges with psi values over 001 WmK

Path 2 begs the question ndash how do I know which TBs will be over 001 WmK before Irsquove modeled them

Image source httpwwwtheblazecomblog20130124finally‐the‐answer‐sort‐of‐for‐what‐came‐first‐the‐chicken‐or‐the‐egg

Section 3 ndash Using psi values in PHPP

50

EavesMost details will have negative psi value

Rim joistAlmost always positive psi value ‐MODEL

Wall to slabfootingOnly well‐designed details will have negative psi value ‐MODEL

Footing below bearing wall or postOnly well‐designed details will have psi value lt 001 WmK‐MODEL

Roof ridgeMost details will have negative psi value

Section 3 ndash Using psi values in PHPP

51

RakeMost details will have negative psi value

Windowdoor sill on slab MODEL BUThellipCan be entered as a window sill TB + wall‐to‐slab TB (requires two separate psi values)

Window sillAlmost always positive psi value since overinsulationis difficult ndashMODEL

Window headIf overinsulated probably no need to model If not ndashMODEL

Section 3 ndash Using psi values in PHPP

52

Exterior cornerMost details will have negative psi value

Interior cornerAlmost always positive psi value ndashMODEL

Window jambIf overinsulated probably no need to model If not ndashMODEL

Wall junctionIf insulation layers are interrupted ‐MODEL

Section 3 ndash Using psi values in PHPP

53

Other places to keep in mind for possible thermal bridgesbull Plumbing stacksbull Rain pipes (interior)bull ERV vent penetrations (to the exterior)bull Sump pumpsbull Radon remediation pipes (if interior to the building)

Section 3 ndash Using psi values in PHPP

54

Section 3 ndash Using psi values in PHPP

55

Section 3 ndash Using psi values in WUFI Passive

56

When calculating heat loss U x A x dTbull Using exterior dimensions leads to an overestimatebull Using interior dimensions leads to an underestimate

PH convention is to use exterior dimensions so heat loss is overestimated

25

Section 1 ndash Background + Basics

Section 2 ndash Common Linear Thermal Bridges

2x6 wall no studs Ψ = ‐ 0058 WmK 2x6 wall 2‐stud Ψ = ‐ 0040 WmK

bull By subtraction negative psi values correct for overestimate of heat loss at exterior cornersbull The lower (more negative) the better Higher psi values indicate increasing heat lossbull Positive psi values above 001 WmK indicate net heat transfer (heat gain in summer heat loss in winter)that should be accounted for in PHPP

Step 1 ndash Avoid bridging elements 26

2x6 wall Ψ = ‐ 0040 WmK 2x8 wall Ψ = ‐ 0045 WmK

Is the 2x8 wall corner a ldquobetterrdquo detail

Section 2 ndash Common Linear Thermal Bridges

27

2x6 wall Ψ = ‐ 0040 WmK 2x8 wall Ψ = ‐ 0045 WmK

NoA thicker wall section needs a larger correction factor due to larger overestimate of heat loss

Section 2 ndash Common Linear Thermal Bridges

28

Is the psi value really an indicator of a detailrsquos thermal quality

Section 2 ndash Common Linear Thermal Bridges

29

Is the psi value really an indicator of a detailrsquos thermal qualityYes and no

At geometric bridges it does two things at once ndash it is both a correction factor and an indicator of heat flow ndash but primarily a correction factor

Section 2 ndash Common Linear Thermal Bridges

30

Is the psi value really an indicator of a detailrsquos thermal qualityYes and no

At geometric bridges it does two things at once ndash it is both a correction factor and an indicator of heat flow ndash but primarily a correction factor

Section 2 ndash Common Linear Thermal Bridges

31

Exterior cornerInsulated 2x6 wall w solid post Ψ = ‐ 0004 WmK

rim joist fib batt (R‐11) Ψ = 0089 WmK rim joist rim board (R‐11) Ψ = 0129 WmK

bull Rim joist thermal bridge ‐ challenging to achieve the Ψ = 001 WmK targetbull Maintaining continuity and alignment of insulation layers is a good first step

STEP 2 ndash Align insulation layers

Section 2 ndash Common Linear Thermal Bridges

32

rim joist 2x4 wall w 1rdquo exterior XPS (R‐13) Ψ = 0047 WmK

Section 2 ndash Common Linear Thermal Bridges

33

rim joist fib batt (R‐11) Ψ = 0089 WmK

bull Exterior insulation helps control heat flow through uninsulated studs and plates

STEP 3 ndash Use continuous exterior insulation to isolate bridging elements

rim joist 2x4 wall w 1rdquo exterior XPS (R‐13) Ψ = 0047 WmK

Use enough exterior insulation and the psi value can be driven down below 001 WmK

Section 2 ndash Common Linear Thermal Bridges

34

rim joist 2x4 wall w 4rdquo exterior XPSΨ = 0011 WmK

rim joist 2x4 wall w 4rdquo exterior XPSΨ = 0011 WmK

Question ndash are the psi values for these two details the same or different

Section 2 ndash Common Linear Thermal Bridges

35

rim joist 2x6 wall w 4rdquo exterior XPSΨ =

rim joist 2x4 wall w 4rdquo exterior XPSΨ = 0011 WmK

Is the detail on the left a ldquobetterrdquo detailIs heat flow through the detail on the right really 2x higher than the heat flow on the leftDoes 4rdquo of exterior foam guarantee a good psi value

Section 2 ndash Common Linear Thermal Bridges

36

rim joist 2x6 wall w 4rdquo exterior XPSΨ = 0020 WmK

rim joist 2x4 wall w 4rdquo exterior XPSΨ = 0011 WmK

NoFor the 2x6 wall therersquos now simply a larger difference between the higher R‐value wall assembly and the rim joist R‐value which has remained the same

Section 2 ndash Common Linear Thermal Bridges

37

rim joist 2x6 wall w 4rdquo exterior XPSΨ = 0020 WmK

Is the psi value really an indicator of a detailrsquos thermal quality

Section 2 ndash Common Linear Thermal Bridges

38

Is the psi value really an indicator of a detailrsquos thermal qualityYes and no

At structural thermal bridges a psi value is a comparison between the U‐value of the assembly(ies) and the U‐value of the junction A junction detail that ldquopassesrdquo (001 WmK) for one assembly may not pass with another

Section 2 ndash Common Linear Thermal Bridges

39

Section 2 ndash Common Linear Thermal Bridges

2x6 wall no studs Ψ = ‐ 0058 WmK 2x6 wall 2‐stud Ψ = ‐ 0040 WmK

When is a performance comparison validWhen the two models being compared have the same assemblies and the same geometry ‐the only difference is at the junction Example above

40

stem wall Ψ = ‐0004 WmK FPSF (frost‐protected shallow foundation) Ψ = 0160 WmK

bull Thermal bridge at the foundation is typically the most challenging to addressbull The concrete stem wall and FPSF footing acts as a radiation fin

STEP 4 ndash Avoid accidental ldquoradiation finsrdquo

Section 2 ndash Common Linear Thermal Bridges

41

FPSF (well insulated) Ψ = 0013 WmK

Thick layers of continuous insulation can improve the performance of the detail but even

FPSF Ψ = 0160 WmK

a very well insulated FPSF is still close to the 001 WmK limit

Section 2 ndash Common Linear Thermal Bridges

STEP 4 ‐ Avoid accidental radiation fins ‐ even well‐insulated ones

42

stem wall Ψ = ‐0004 WmK Thermally broken stem wall Ψ = ‐0136 WmK

Section 2 ndash Common Linear Thermal Bridges

43

Thermally broken stem wall provides an insulated break between the stem wall and the floor slab effectively cutting off the ldquoradiation finrdquoAligning exterior insulation layers at junction of stem wall and above grade wall also helpsSTEP 5 ndash An insulated break between the exterior wall and floor slab works best

ICF parapet Ψ = 0200 WmK Foamglas thermal break Ψ = ‐0071 WmK

Another good location to cut off the radiation fin

Section 2 ndash Common Linear Thermal Bridges

44

Window positioned outside of thermal envelope Ψ = 010 WmKEffectively R‐value of window reduced by 20 ‐ 30 depending on window size

Section 2 ndash Common Linear Thermal Bridges

Window positioned on edge of thermal envelope Ψ = 004 WmKR‐value of window reduced by 5 ‐10 depending on window size

45

Window centered in plane of insulation Ψ = 002 to 003 WmKR‐value of window is almost preserved

Section 2 ndash Common Linear Thermal Bridges

46

47

Break

Section 3 ndash Using psi values in PHPP

48

How do I know which thermal bridges need to be modeled and entered in PHPP

Section 3 ndash Using psi values in PHPP

49

How do I know which thermal bridges need to be modeled and entered in PHPP

PHI requires 1 of 2 paths1) Model all thermal bridges enter psi values for both + and ‐2) Model and enter only thermal bridges with psi values over 001 WmK

Path 2 begs the question ndash how do I know which TBs will be over 001 WmK before Irsquove modeled them

Image source httpwwwtheblazecomblog20130124finally‐the‐answer‐sort‐of‐for‐what‐came‐first‐the‐chicken‐or‐the‐egg

Section 3 ndash Using psi values in PHPP

50

EavesMost details will have negative psi value

Rim joistAlmost always positive psi value ‐MODEL

Wall to slabfootingOnly well‐designed details will have negative psi value ‐MODEL

Footing below bearing wall or postOnly well‐designed details will have psi value lt 001 WmK‐MODEL

Roof ridgeMost details will have negative psi value

Section 3 ndash Using psi values in PHPP

51

RakeMost details will have negative psi value

Windowdoor sill on slab MODEL BUThellipCan be entered as a window sill TB + wall‐to‐slab TB (requires two separate psi values)

Window sillAlmost always positive psi value since overinsulationis difficult ndashMODEL

Window headIf overinsulated probably no need to model If not ndashMODEL

Section 3 ndash Using psi values in PHPP

52

Exterior cornerMost details will have negative psi value

Interior cornerAlmost always positive psi value ndashMODEL

Window jambIf overinsulated probably no need to model If not ndashMODEL

Wall junctionIf insulation layers are interrupted ‐MODEL

Section 3 ndash Using psi values in PHPP

53

Other places to keep in mind for possible thermal bridgesbull Plumbing stacksbull Rain pipes (interior)bull ERV vent penetrations (to the exterior)bull Sump pumpsbull Radon remediation pipes (if interior to the building)

Section 3 ndash Using psi values in PHPP

54

Section 3 ndash Using psi values in PHPP

55

Section 3 ndash Using psi values in WUFI Passive

56

Section 2 ndash Common Linear Thermal Bridges

2x6 wall no studs Ψ = ‐ 0058 WmK 2x6 wall 2‐stud Ψ = ‐ 0040 WmK

bull By subtraction negative psi values correct for overestimate of heat loss at exterior cornersbull The lower (more negative) the better Higher psi values indicate increasing heat lossbull Positive psi values above 001 WmK indicate net heat transfer (heat gain in summer heat loss in winter)that should be accounted for in PHPP

Step 1 ndash Avoid bridging elements 26

2x6 wall Ψ = ‐ 0040 WmK 2x8 wall Ψ = ‐ 0045 WmK

Is the 2x8 wall corner a ldquobetterrdquo detail

Section 2 ndash Common Linear Thermal Bridges

27

2x6 wall Ψ = ‐ 0040 WmK 2x8 wall Ψ = ‐ 0045 WmK

NoA thicker wall section needs a larger correction factor due to larger overestimate of heat loss

Section 2 ndash Common Linear Thermal Bridges

28

Is the psi value really an indicator of a detailrsquos thermal quality

Section 2 ndash Common Linear Thermal Bridges

29

Is the psi value really an indicator of a detailrsquos thermal qualityYes and no

At geometric bridges it does two things at once ndash it is both a correction factor and an indicator of heat flow ndash but primarily a correction factor

Section 2 ndash Common Linear Thermal Bridges

30

Is the psi value really an indicator of a detailrsquos thermal qualityYes and no

At geometric bridges it does two things at once ndash it is both a correction factor and an indicator of heat flow ndash but primarily a correction factor

Section 2 ndash Common Linear Thermal Bridges

31

Exterior cornerInsulated 2x6 wall w solid post Ψ = ‐ 0004 WmK

rim joist fib batt (R‐11) Ψ = 0089 WmK rim joist rim board (R‐11) Ψ = 0129 WmK

bull Rim joist thermal bridge ‐ challenging to achieve the Ψ = 001 WmK targetbull Maintaining continuity and alignment of insulation layers is a good first step

STEP 2 ndash Align insulation layers

Section 2 ndash Common Linear Thermal Bridges

32

rim joist 2x4 wall w 1rdquo exterior XPS (R‐13) Ψ = 0047 WmK

Section 2 ndash Common Linear Thermal Bridges

33

rim joist fib batt (R‐11) Ψ = 0089 WmK

bull Exterior insulation helps control heat flow through uninsulated studs and plates

STEP 3 ndash Use continuous exterior insulation to isolate bridging elements

rim joist 2x4 wall w 1rdquo exterior XPS (R‐13) Ψ = 0047 WmK

Use enough exterior insulation and the psi value can be driven down below 001 WmK

Section 2 ndash Common Linear Thermal Bridges

34

rim joist 2x4 wall w 4rdquo exterior XPSΨ = 0011 WmK

rim joist 2x4 wall w 4rdquo exterior XPSΨ = 0011 WmK

Question ndash are the psi values for these two details the same or different

Section 2 ndash Common Linear Thermal Bridges

35

rim joist 2x6 wall w 4rdquo exterior XPSΨ =

rim joist 2x4 wall w 4rdquo exterior XPSΨ = 0011 WmK

Is the detail on the left a ldquobetterrdquo detailIs heat flow through the detail on the right really 2x higher than the heat flow on the leftDoes 4rdquo of exterior foam guarantee a good psi value

Section 2 ndash Common Linear Thermal Bridges

36

rim joist 2x6 wall w 4rdquo exterior XPSΨ = 0020 WmK

rim joist 2x4 wall w 4rdquo exterior XPSΨ = 0011 WmK

NoFor the 2x6 wall therersquos now simply a larger difference between the higher R‐value wall assembly and the rim joist R‐value which has remained the same

Section 2 ndash Common Linear Thermal Bridges

37

rim joist 2x6 wall w 4rdquo exterior XPSΨ = 0020 WmK

Is the psi value really an indicator of a detailrsquos thermal quality

Section 2 ndash Common Linear Thermal Bridges

38

Is the psi value really an indicator of a detailrsquos thermal qualityYes and no

At structural thermal bridges a psi value is a comparison between the U‐value of the assembly(ies) and the U‐value of the junction A junction detail that ldquopassesrdquo (001 WmK) for one assembly may not pass with another

Section 2 ndash Common Linear Thermal Bridges

39

Section 2 ndash Common Linear Thermal Bridges

2x6 wall no studs Ψ = ‐ 0058 WmK 2x6 wall 2‐stud Ψ = ‐ 0040 WmK

When is a performance comparison validWhen the two models being compared have the same assemblies and the same geometry ‐the only difference is at the junction Example above

40

stem wall Ψ = ‐0004 WmK FPSF (frost‐protected shallow foundation) Ψ = 0160 WmK

bull Thermal bridge at the foundation is typically the most challenging to addressbull The concrete stem wall and FPSF footing acts as a radiation fin

STEP 4 ndash Avoid accidental ldquoradiation finsrdquo

Section 2 ndash Common Linear Thermal Bridges

41

FPSF (well insulated) Ψ = 0013 WmK

Thick layers of continuous insulation can improve the performance of the detail but even

FPSF Ψ = 0160 WmK

a very well insulated FPSF is still close to the 001 WmK limit

Section 2 ndash Common Linear Thermal Bridges

STEP 4 ‐ Avoid accidental radiation fins ‐ even well‐insulated ones

42

stem wall Ψ = ‐0004 WmK Thermally broken stem wall Ψ = ‐0136 WmK

Section 2 ndash Common Linear Thermal Bridges

43

Thermally broken stem wall provides an insulated break between the stem wall and the floor slab effectively cutting off the ldquoradiation finrdquoAligning exterior insulation layers at junction of stem wall and above grade wall also helpsSTEP 5 ndash An insulated break between the exterior wall and floor slab works best

ICF parapet Ψ = 0200 WmK Foamglas thermal break Ψ = ‐0071 WmK

Another good location to cut off the radiation fin

Section 2 ndash Common Linear Thermal Bridges

44

Window positioned outside of thermal envelope Ψ = 010 WmKEffectively R‐value of window reduced by 20 ‐ 30 depending on window size

Section 2 ndash Common Linear Thermal Bridges

Window positioned on edge of thermal envelope Ψ = 004 WmKR‐value of window reduced by 5 ‐10 depending on window size

45

Window centered in plane of insulation Ψ = 002 to 003 WmKR‐value of window is almost preserved

Section 2 ndash Common Linear Thermal Bridges

46

47

Break

Section 3 ndash Using psi values in PHPP

48

How do I know which thermal bridges need to be modeled and entered in PHPP

Section 3 ndash Using psi values in PHPP

49

How do I know which thermal bridges need to be modeled and entered in PHPP

PHI requires 1 of 2 paths1) Model all thermal bridges enter psi values for both + and ‐2) Model and enter only thermal bridges with psi values over 001 WmK

Path 2 begs the question ndash how do I know which TBs will be over 001 WmK before Irsquove modeled them

Image source httpwwwtheblazecomblog20130124finally‐the‐answer‐sort‐of‐for‐what‐came‐first‐the‐chicken‐or‐the‐egg

Section 3 ndash Using psi values in PHPP

50

EavesMost details will have negative psi value

Rim joistAlmost always positive psi value ‐MODEL

Wall to slabfootingOnly well‐designed details will have negative psi value ‐MODEL

Footing below bearing wall or postOnly well‐designed details will have psi value lt 001 WmK‐MODEL

Roof ridgeMost details will have negative psi value

Section 3 ndash Using psi values in PHPP

51

RakeMost details will have negative psi value

Windowdoor sill on slab MODEL BUThellipCan be entered as a window sill TB + wall‐to‐slab TB (requires two separate psi values)

Window sillAlmost always positive psi value since overinsulationis difficult ndashMODEL

Window headIf overinsulated probably no need to model If not ndashMODEL

Section 3 ndash Using psi values in PHPP

52

Exterior cornerMost details will have negative psi value

Interior cornerAlmost always positive psi value ndashMODEL

Window jambIf overinsulated probably no need to model If not ndashMODEL

Wall junctionIf insulation layers are interrupted ‐MODEL

Section 3 ndash Using psi values in PHPP

53

Other places to keep in mind for possible thermal bridgesbull Plumbing stacksbull Rain pipes (interior)bull ERV vent penetrations (to the exterior)bull Sump pumpsbull Radon remediation pipes (if interior to the building)

Section 3 ndash Using psi values in PHPP

54

Section 3 ndash Using psi values in PHPP

55

Section 3 ndash Using psi values in WUFI Passive

56

2x6 wall Ψ = ‐ 0040 WmK 2x8 wall Ψ = ‐ 0045 WmK

Is the 2x8 wall corner a ldquobetterrdquo detail

Section 2 ndash Common Linear Thermal Bridges

27

2x6 wall Ψ = ‐ 0040 WmK 2x8 wall Ψ = ‐ 0045 WmK

NoA thicker wall section needs a larger correction factor due to larger overestimate of heat loss

Section 2 ndash Common Linear Thermal Bridges

28

Is the psi value really an indicator of a detailrsquos thermal quality

Section 2 ndash Common Linear Thermal Bridges

29

Is the psi value really an indicator of a detailrsquos thermal qualityYes and no

At geometric bridges it does two things at once ndash it is both a correction factor and an indicator of heat flow ndash but primarily a correction factor

Section 2 ndash Common Linear Thermal Bridges

30

Is the psi value really an indicator of a detailrsquos thermal qualityYes and no

At geometric bridges it does two things at once ndash it is both a correction factor and an indicator of heat flow ndash but primarily a correction factor

Section 2 ndash Common Linear Thermal Bridges

31

Exterior cornerInsulated 2x6 wall w solid post Ψ = ‐ 0004 WmK

rim joist fib batt (R‐11) Ψ = 0089 WmK rim joist rim board (R‐11) Ψ = 0129 WmK

bull Rim joist thermal bridge ‐ challenging to achieve the Ψ = 001 WmK targetbull Maintaining continuity and alignment of insulation layers is a good first step

STEP 2 ndash Align insulation layers

Section 2 ndash Common Linear Thermal Bridges

32

rim joist 2x4 wall w 1rdquo exterior XPS (R‐13) Ψ = 0047 WmK

Section 2 ndash Common Linear Thermal Bridges

33

rim joist fib batt (R‐11) Ψ = 0089 WmK

bull Exterior insulation helps control heat flow through uninsulated studs and plates

STEP 3 ndash Use continuous exterior insulation to isolate bridging elements

rim joist 2x4 wall w 1rdquo exterior XPS (R‐13) Ψ = 0047 WmK

Use enough exterior insulation and the psi value can be driven down below 001 WmK

Section 2 ndash Common Linear Thermal Bridges

34

rim joist 2x4 wall w 4rdquo exterior XPSΨ = 0011 WmK

rim joist 2x4 wall w 4rdquo exterior XPSΨ = 0011 WmK

Question ndash are the psi values for these two details the same or different

Section 2 ndash Common Linear Thermal Bridges

35

rim joist 2x6 wall w 4rdquo exterior XPSΨ =

rim joist 2x4 wall w 4rdquo exterior XPSΨ = 0011 WmK

Is the detail on the left a ldquobetterrdquo detailIs heat flow through the detail on the right really 2x higher than the heat flow on the leftDoes 4rdquo of exterior foam guarantee a good psi value

Section 2 ndash Common Linear Thermal Bridges

36

rim joist 2x6 wall w 4rdquo exterior XPSΨ = 0020 WmK

rim joist 2x4 wall w 4rdquo exterior XPSΨ = 0011 WmK

NoFor the 2x6 wall therersquos now simply a larger difference between the higher R‐value wall assembly and the rim joist R‐value which has remained the same

Section 2 ndash Common Linear Thermal Bridges

37

rim joist 2x6 wall w 4rdquo exterior XPSΨ = 0020 WmK

Is the psi value really an indicator of a detailrsquos thermal quality

Section 2 ndash Common Linear Thermal Bridges

38

Is the psi value really an indicator of a detailrsquos thermal qualityYes and no

At structural thermal bridges a psi value is a comparison between the U‐value of the assembly(ies) and the U‐value of the junction A junction detail that ldquopassesrdquo (001 WmK) for one assembly may not pass with another

Section 2 ndash Common Linear Thermal Bridges

39

Section 2 ndash Common Linear Thermal Bridges

2x6 wall no studs Ψ = ‐ 0058 WmK 2x6 wall 2‐stud Ψ = ‐ 0040 WmK

When is a performance comparison validWhen the two models being compared have the same assemblies and the same geometry ‐the only difference is at the junction Example above

40

stem wall Ψ = ‐0004 WmK FPSF (frost‐protected shallow foundation) Ψ = 0160 WmK

bull Thermal bridge at the foundation is typically the most challenging to addressbull The concrete stem wall and FPSF footing acts as a radiation fin

STEP 4 ndash Avoid accidental ldquoradiation finsrdquo

Section 2 ndash Common Linear Thermal Bridges

41

FPSF (well insulated) Ψ = 0013 WmK

Thick layers of continuous insulation can improve the performance of the detail but even

FPSF Ψ = 0160 WmK

a very well insulated FPSF is still close to the 001 WmK limit

Section 2 ndash Common Linear Thermal Bridges

STEP 4 ‐ Avoid accidental radiation fins ‐ even well‐insulated ones

42

stem wall Ψ = ‐0004 WmK Thermally broken stem wall Ψ = ‐0136 WmK

Section 2 ndash Common Linear Thermal Bridges

43

Thermally broken stem wall provides an insulated break between the stem wall and the floor slab effectively cutting off the ldquoradiation finrdquoAligning exterior insulation layers at junction of stem wall and above grade wall also helpsSTEP 5 ndash An insulated break between the exterior wall and floor slab works best

ICF parapet Ψ = 0200 WmK Foamglas thermal break Ψ = ‐0071 WmK

Another good location to cut off the radiation fin

Section 2 ndash Common Linear Thermal Bridges

44

Window positioned outside of thermal envelope Ψ = 010 WmKEffectively R‐value of window reduced by 20 ‐ 30 depending on window size

Section 2 ndash Common Linear Thermal Bridges

Window positioned on edge of thermal envelope Ψ = 004 WmKR‐value of window reduced by 5 ‐10 depending on window size

45

Window centered in plane of insulation Ψ = 002 to 003 WmKR‐value of window is almost preserved

Section 2 ndash Common Linear Thermal Bridges

46

47

Break

Section 3 ndash Using psi values in PHPP

48

How do I know which thermal bridges need to be modeled and entered in PHPP

Section 3 ndash Using psi values in PHPP

49

How do I know which thermal bridges need to be modeled and entered in PHPP

PHI requires 1 of 2 paths1) Model all thermal bridges enter psi values for both + and ‐2) Model and enter only thermal bridges with psi values over 001 WmK

Path 2 begs the question ndash how do I know which TBs will be over 001 WmK before Irsquove modeled them

Image source httpwwwtheblazecomblog20130124finally‐the‐answer‐sort‐of‐for‐what‐came‐first‐the‐chicken‐or‐the‐egg

Section 3 ndash Using psi values in PHPP

50

EavesMost details will have negative psi value

Rim joistAlmost always positive psi value ‐MODEL

Wall to slabfootingOnly well‐designed details will have negative psi value ‐MODEL

Footing below bearing wall or postOnly well‐designed details will have psi value lt 001 WmK‐MODEL

Roof ridgeMost details will have negative psi value

Section 3 ndash Using psi values in PHPP

51

RakeMost details will have negative psi value

Windowdoor sill on slab MODEL BUThellipCan be entered as a window sill TB + wall‐to‐slab TB (requires two separate psi values)

Window sillAlmost always positive psi value since overinsulationis difficult ndashMODEL

Window headIf overinsulated probably no need to model If not ndashMODEL

Section 3 ndash Using psi values in PHPP

52

Exterior cornerMost details will have negative psi value

Interior cornerAlmost always positive psi value ndashMODEL

Window jambIf overinsulated probably no need to model If not ndashMODEL

Wall junctionIf insulation layers are interrupted ‐MODEL

Section 3 ndash Using psi values in PHPP

53

Other places to keep in mind for possible thermal bridgesbull Plumbing stacksbull Rain pipes (interior)bull ERV vent penetrations (to the exterior)bull Sump pumpsbull Radon remediation pipes (if interior to the building)

Section 3 ndash Using psi values in PHPP

54

Section 3 ndash Using psi values in PHPP

55

Section 3 ndash Using psi values in WUFI Passive

56

2x6 wall Ψ = ‐ 0040 WmK 2x8 wall Ψ = ‐ 0045 WmK

NoA thicker wall section needs a larger correction factor due to larger overestimate of heat loss

Section 2 ndash Common Linear Thermal Bridges

28

Is the psi value really an indicator of a detailrsquos thermal quality

Section 2 ndash Common Linear Thermal Bridges

29

Is the psi value really an indicator of a detailrsquos thermal qualityYes and no

At geometric bridges it does two things at once ndash it is both a correction factor and an indicator of heat flow ndash but primarily a correction factor

Section 2 ndash Common Linear Thermal Bridges

30

Is the psi value really an indicator of a detailrsquos thermal qualityYes and no

At geometric bridges it does two things at once ndash it is both a correction factor and an indicator of heat flow ndash but primarily a correction factor

Section 2 ndash Common Linear Thermal Bridges

31

Exterior cornerInsulated 2x6 wall w solid post Ψ = ‐ 0004 WmK

rim joist fib batt (R‐11) Ψ = 0089 WmK rim joist rim board (R‐11) Ψ = 0129 WmK

bull Rim joist thermal bridge ‐ challenging to achieve the Ψ = 001 WmK targetbull Maintaining continuity and alignment of insulation layers is a good first step

STEP 2 ndash Align insulation layers

Section 2 ndash Common Linear Thermal Bridges

32

rim joist 2x4 wall w 1rdquo exterior XPS (R‐13) Ψ = 0047 WmK

Section 2 ndash Common Linear Thermal Bridges

33

rim joist fib batt (R‐11) Ψ = 0089 WmK

bull Exterior insulation helps control heat flow through uninsulated studs and plates

STEP 3 ndash Use continuous exterior insulation to isolate bridging elements

rim joist 2x4 wall w 1rdquo exterior XPS (R‐13) Ψ = 0047 WmK

Use enough exterior insulation and the psi value can be driven down below 001 WmK

Section 2 ndash Common Linear Thermal Bridges

34

rim joist 2x4 wall w 4rdquo exterior XPSΨ = 0011 WmK

rim joist 2x4 wall w 4rdquo exterior XPSΨ = 0011 WmK

Question ndash are the psi values for these two details the same or different

Section 2 ndash Common Linear Thermal Bridges

35

rim joist 2x6 wall w 4rdquo exterior XPSΨ =

rim joist 2x4 wall w 4rdquo exterior XPSΨ = 0011 WmK

Is the detail on the left a ldquobetterrdquo detailIs heat flow through the detail on the right really 2x higher than the heat flow on the leftDoes 4rdquo of exterior foam guarantee a good psi value

Section 2 ndash Common Linear Thermal Bridges

36

rim joist 2x6 wall w 4rdquo exterior XPSΨ = 0020 WmK

rim joist 2x4 wall w 4rdquo exterior XPSΨ = 0011 WmK

NoFor the 2x6 wall therersquos now simply a larger difference between the higher R‐value wall assembly and the rim joist R‐value which has remained the same

Section 2 ndash Common Linear Thermal Bridges

37

rim joist 2x6 wall w 4rdquo exterior XPSΨ = 0020 WmK

Is the psi value really an indicator of a detailrsquos thermal quality

Section 2 ndash Common Linear Thermal Bridges

38

Is the psi value really an indicator of a detailrsquos thermal qualityYes and no

At structural thermal bridges a psi value is a comparison between the U‐value of the assembly(ies) and the U‐value of the junction A junction detail that ldquopassesrdquo (001 WmK) for one assembly may not pass with another

Section 2 ndash Common Linear Thermal Bridges

39

Section 2 ndash Common Linear Thermal Bridges

2x6 wall no studs Ψ = ‐ 0058 WmK 2x6 wall 2‐stud Ψ = ‐ 0040 WmK

When is a performance comparison validWhen the two models being compared have the same assemblies and the same geometry ‐the only difference is at the junction Example above

40

stem wall Ψ = ‐0004 WmK FPSF (frost‐protected shallow foundation) Ψ = 0160 WmK

bull Thermal bridge at the foundation is typically the most challenging to addressbull The concrete stem wall and FPSF footing acts as a radiation fin

STEP 4 ndash Avoid accidental ldquoradiation finsrdquo

Section 2 ndash Common Linear Thermal Bridges

41

FPSF (well insulated) Ψ = 0013 WmK

Thick layers of continuous insulation can improve the performance of the detail but even

FPSF Ψ = 0160 WmK

a very well insulated FPSF is still close to the 001 WmK limit

Section 2 ndash Common Linear Thermal Bridges

STEP 4 ‐ Avoid accidental radiation fins ‐ even well‐insulated ones

42

stem wall Ψ = ‐0004 WmK Thermally broken stem wall Ψ = ‐0136 WmK

Section 2 ndash Common Linear Thermal Bridges

43

Thermally broken stem wall provides an insulated break between the stem wall and the floor slab effectively cutting off the ldquoradiation finrdquoAligning exterior insulation layers at junction of stem wall and above grade wall also helpsSTEP 5 ndash An insulated break between the exterior wall and floor slab works best

ICF parapet Ψ = 0200 WmK Foamglas thermal break Ψ = ‐0071 WmK

Another good location to cut off the radiation fin

Section 2 ndash Common Linear Thermal Bridges

44

Window positioned outside of thermal envelope Ψ = 010 WmKEffectively R‐value of window reduced by 20 ‐ 30 depending on window size

Section 2 ndash Common Linear Thermal Bridges

Window positioned on edge of thermal envelope Ψ = 004 WmKR‐value of window reduced by 5 ‐10 depending on window size

45

Window centered in plane of insulation Ψ = 002 to 003 WmKR‐value of window is almost preserved

Section 2 ndash Common Linear Thermal Bridges

46

47

Break

Section 3 ndash Using psi values in PHPP

48

How do I know which thermal bridges need to be modeled and entered in PHPP

Section 3 ndash Using psi values in PHPP

49

How do I know which thermal bridges need to be modeled and entered in PHPP

PHI requires 1 of 2 paths1) Model all thermal bridges enter psi values for both + and ‐2) Model and enter only thermal bridges with psi values over 001 WmK

Path 2 begs the question ndash how do I know which TBs will be over 001 WmK before Irsquove modeled them

Image source httpwwwtheblazecomblog20130124finally‐the‐answer‐sort‐of‐for‐what‐came‐first‐the‐chicken‐or‐the‐egg

Section 3 ndash Using psi values in PHPP

50

EavesMost details will have negative psi value

Rim joistAlmost always positive psi value ‐MODEL

Wall to slabfootingOnly well‐designed details will have negative psi value ‐MODEL

Footing below bearing wall or postOnly well‐designed details will have psi value lt 001 WmK‐MODEL

Roof ridgeMost details will have negative psi value

Section 3 ndash Using psi values in PHPP

51

RakeMost details will have negative psi value

Windowdoor sill on slab MODEL BUThellipCan be entered as a window sill TB + wall‐to‐slab TB (requires two separate psi values)

Window sillAlmost always positive psi value since overinsulationis difficult ndashMODEL

Window headIf overinsulated probably no need to model If not ndashMODEL

Section 3 ndash Using psi values in PHPP

52

Exterior cornerMost details will have negative psi value

Interior cornerAlmost always positive psi value ndashMODEL

Window jambIf overinsulated probably no need to model If not ndashMODEL

Wall junctionIf insulation layers are interrupted ‐MODEL

Section 3 ndash Using psi values in PHPP

53

Other places to keep in mind for possible thermal bridgesbull Plumbing stacksbull Rain pipes (interior)bull ERV vent penetrations (to the exterior)bull Sump pumpsbull Radon remediation pipes (if interior to the building)

Section 3 ndash Using psi values in PHPP

54

Section 3 ndash Using psi values in PHPP

55

Section 3 ndash Using psi values in WUFI Passive

56

Is the psi value really an indicator of a detailrsquos thermal quality

Section 2 ndash Common Linear Thermal Bridges

29

Is the psi value really an indicator of a detailrsquos thermal qualityYes and no

At geometric bridges it does two things at once ndash it is both a correction factor and an indicator of heat flow ndash but primarily a correction factor

Section 2 ndash Common Linear Thermal Bridges

30

Is the psi value really an indicator of a detailrsquos thermal qualityYes and no

At geometric bridges it does two things at once ndash it is both a correction factor and an indicator of heat flow ndash but primarily a correction factor

Section 2 ndash Common Linear Thermal Bridges

31

Exterior cornerInsulated 2x6 wall w solid post Ψ = ‐ 0004 WmK

rim joist fib batt (R‐11) Ψ = 0089 WmK rim joist rim board (R‐11) Ψ = 0129 WmK

bull Rim joist thermal bridge ‐ challenging to achieve the Ψ = 001 WmK targetbull Maintaining continuity and alignment of insulation layers is a good first step

STEP 2 ndash Align insulation layers

Section 2 ndash Common Linear Thermal Bridges

32

rim joist 2x4 wall w 1rdquo exterior XPS (R‐13) Ψ = 0047 WmK

Section 2 ndash Common Linear Thermal Bridges

33

rim joist fib batt (R‐11) Ψ = 0089 WmK

bull Exterior insulation helps control heat flow through uninsulated studs and plates

STEP 3 ndash Use continuous exterior insulation to isolate bridging elements

rim joist 2x4 wall w 1rdquo exterior XPS (R‐13) Ψ = 0047 WmK

Use enough exterior insulation and the psi value can be driven down below 001 WmK

Section 2 ndash Common Linear Thermal Bridges

34

rim joist 2x4 wall w 4rdquo exterior XPSΨ = 0011 WmK

rim joist 2x4 wall w 4rdquo exterior XPSΨ = 0011 WmK

Question ndash are the psi values for these two details the same or different

Section 2 ndash Common Linear Thermal Bridges

35

rim joist 2x6 wall w 4rdquo exterior XPSΨ =

rim joist 2x4 wall w 4rdquo exterior XPSΨ = 0011 WmK

Is the detail on the left a ldquobetterrdquo detailIs heat flow through the detail on the right really 2x higher than the heat flow on the leftDoes 4rdquo of exterior foam guarantee a good psi value

Section 2 ndash Common Linear Thermal Bridges

36

rim joist 2x6 wall w 4rdquo exterior XPSΨ = 0020 WmK

rim joist 2x4 wall w 4rdquo exterior XPSΨ = 0011 WmK

NoFor the 2x6 wall therersquos now simply a larger difference between the higher R‐value wall assembly and the rim joist R‐value which has remained the same

Section 2 ndash Common Linear Thermal Bridges

37

rim joist 2x6 wall w 4rdquo exterior XPSΨ = 0020 WmK

Is the psi value really an indicator of a detailrsquos thermal quality

Section 2 ndash Common Linear Thermal Bridges

38

Is the psi value really an indicator of a detailrsquos thermal qualityYes and no

At structural thermal bridges a psi value is a comparison between the U‐value of the assembly(ies) and the U‐value of the junction A junction detail that ldquopassesrdquo (001 WmK) for one assembly may not pass with another

Section 2 ndash Common Linear Thermal Bridges

39

Section 2 ndash Common Linear Thermal Bridges

2x6 wall no studs Ψ = ‐ 0058 WmK 2x6 wall 2‐stud Ψ = ‐ 0040 WmK

When is a performance comparison validWhen the two models being compared have the same assemblies and the same geometry ‐the only difference is at the junction Example above

40

stem wall Ψ = ‐0004 WmK FPSF (frost‐protected shallow foundation) Ψ = 0160 WmK

bull Thermal bridge at the foundation is typically the most challenging to addressbull The concrete stem wall and FPSF footing acts as a radiation fin

STEP 4 ndash Avoid accidental ldquoradiation finsrdquo

Section 2 ndash Common Linear Thermal Bridges

41

FPSF (well insulated) Ψ = 0013 WmK

Thick layers of continuous insulation can improve the performance of the detail but even

FPSF Ψ = 0160 WmK

a very well insulated FPSF is still close to the 001 WmK limit

Section 2 ndash Common Linear Thermal Bridges

STEP 4 ‐ Avoid accidental radiation fins ‐ even well‐insulated ones

42

stem wall Ψ = ‐0004 WmK Thermally broken stem wall Ψ = ‐0136 WmK

Section 2 ndash Common Linear Thermal Bridges

43

Thermally broken stem wall provides an insulated break between the stem wall and the floor slab effectively cutting off the ldquoradiation finrdquoAligning exterior insulation layers at junction of stem wall and above grade wall also helpsSTEP 5 ndash An insulated break between the exterior wall and floor slab works best

ICF parapet Ψ = 0200 WmK Foamglas thermal break Ψ = ‐0071 WmK

Another good location to cut off the radiation fin

Section 2 ndash Common Linear Thermal Bridges

44

Window positioned outside of thermal envelope Ψ = 010 WmKEffectively R‐value of window reduced by 20 ‐ 30 depending on window size

Section 2 ndash Common Linear Thermal Bridges

Window positioned on edge of thermal envelope Ψ = 004 WmKR‐value of window reduced by 5 ‐10 depending on window size

45

Window centered in plane of insulation Ψ = 002 to 003 WmKR‐value of window is almost preserved

Section 2 ndash Common Linear Thermal Bridges

46

47

Break

Section 3 ndash Using psi values in PHPP

48

How do I know which thermal bridges need to be modeled and entered in PHPP

Section 3 ndash Using psi values in PHPP

49

How do I know which thermal bridges need to be modeled and entered in PHPP

PHI requires 1 of 2 paths1) Model all thermal bridges enter psi values for both + and ‐2) Model and enter only thermal bridges with psi values over 001 WmK

Path 2 begs the question ndash how do I know which TBs will be over 001 WmK before Irsquove modeled them

Image source httpwwwtheblazecomblog20130124finally‐the‐answer‐sort‐of‐for‐what‐came‐first‐the‐chicken‐or‐the‐egg

Section 3 ndash Using psi values in PHPP

50

EavesMost details will have negative psi value

Rim joistAlmost always positive psi value ‐MODEL

Wall to slabfootingOnly well‐designed details will have negative psi value ‐MODEL

Footing below bearing wall or postOnly well‐designed details will have psi value lt 001 WmK‐MODEL

Roof ridgeMost details will have negative psi value

Section 3 ndash Using psi values in PHPP

51

RakeMost details will have negative psi value

Windowdoor sill on slab MODEL BUThellipCan be entered as a window sill TB + wall‐to‐slab TB (requires two separate psi values)

Window sillAlmost always positive psi value since overinsulationis difficult ndashMODEL

Window headIf overinsulated probably no need to model If not ndashMODEL

Section 3 ndash Using psi values in PHPP

52

Exterior cornerMost details will have negative psi value

Interior cornerAlmost always positive psi value ndashMODEL

Window jambIf overinsulated probably no need to model If not ndashMODEL

Wall junctionIf insulation layers are interrupted ‐MODEL

Section 3 ndash Using psi values in PHPP

53

Other places to keep in mind for possible thermal bridgesbull Plumbing stacksbull Rain pipes (interior)bull ERV vent penetrations (to the exterior)bull Sump pumpsbull Radon remediation pipes (if interior to the building)

Section 3 ndash Using psi values in PHPP

54

Section 3 ndash Using psi values in PHPP

55

Section 3 ndash Using psi values in WUFI Passive

56

Is the psi value really an indicator of a detailrsquos thermal qualityYes and no

At geometric bridges it does two things at once ndash it is both a correction factor and an indicator of heat flow ndash but primarily a correction factor

Section 2 ndash Common Linear Thermal Bridges

30

Is the psi value really an indicator of a detailrsquos thermal qualityYes and no

At geometric bridges it does two things at once ndash it is both a correction factor and an indicator of heat flow ndash but primarily a correction factor

Section 2 ndash Common Linear Thermal Bridges

31

Exterior cornerInsulated 2x6 wall w solid post Ψ = ‐ 0004 WmK

rim joist fib batt (R‐11) Ψ = 0089 WmK rim joist rim board (R‐11) Ψ = 0129 WmK

bull Rim joist thermal bridge ‐ challenging to achieve the Ψ = 001 WmK targetbull Maintaining continuity and alignment of insulation layers is a good first step

STEP 2 ndash Align insulation layers

Section 2 ndash Common Linear Thermal Bridges

32

rim joist 2x4 wall w 1rdquo exterior XPS (R‐13) Ψ = 0047 WmK

Section 2 ndash Common Linear Thermal Bridges

33

rim joist fib batt (R‐11) Ψ = 0089 WmK

bull Exterior insulation helps control heat flow through uninsulated studs and plates

STEP 3 ndash Use continuous exterior insulation to isolate bridging elements

rim joist 2x4 wall w 1rdquo exterior XPS (R‐13) Ψ = 0047 WmK

Use enough exterior insulation and the psi value can be driven down below 001 WmK

Section 2 ndash Common Linear Thermal Bridges

34

rim joist 2x4 wall w 4rdquo exterior XPSΨ = 0011 WmK

rim joist 2x4 wall w 4rdquo exterior XPSΨ = 0011 WmK

Question ndash are the psi values for these two details the same or different

Section 2 ndash Common Linear Thermal Bridges

35

rim joist 2x6 wall w 4rdquo exterior XPSΨ =

rim joist 2x4 wall w 4rdquo exterior XPSΨ = 0011 WmK

Is the detail on the left a ldquobetterrdquo detailIs heat flow through the detail on the right really 2x higher than the heat flow on the leftDoes 4rdquo of exterior foam guarantee a good psi value

Section 2 ndash Common Linear Thermal Bridges

36

rim joist 2x6 wall w 4rdquo exterior XPSΨ = 0020 WmK

rim joist 2x4 wall w 4rdquo exterior XPSΨ = 0011 WmK

NoFor the 2x6 wall therersquos now simply a larger difference between the higher R‐value wall assembly and the rim joist R‐value which has remained the same

Section 2 ndash Common Linear Thermal Bridges

37

rim joist 2x6 wall w 4rdquo exterior XPSΨ = 0020 WmK

Is the psi value really an indicator of a detailrsquos thermal quality

Section 2 ndash Common Linear Thermal Bridges

38

Is the psi value really an indicator of a detailrsquos thermal qualityYes and no

At structural thermal bridges a psi value is a comparison between the U‐value of the assembly(ies) and the U‐value of the junction A junction detail that ldquopassesrdquo (001 WmK) for one assembly may not pass with another

Section 2 ndash Common Linear Thermal Bridges

39

Section 2 ndash Common Linear Thermal Bridges

2x6 wall no studs Ψ = ‐ 0058 WmK 2x6 wall 2‐stud Ψ = ‐ 0040 WmK

When is a performance comparison validWhen the two models being compared have the same assemblies and the same geometry ‐the only difference is at the junction Example above

40

stem wall Ψ = ‐0004 WmK FPSF (frost‐protected shallow foundation) Ψ = 0160 WmK

bull Thermal bridge at the foundation is typically the most challenging to addressbull The concrete stem wall and FPSF footing acts as a radiation fin

STEP 4 ndash Avoid accidental ldquoradiation finsrdquo

Section 2 ndash Common Linear Thermal Bridges

41

FPSF (well insulated) Ψ = 0013 WmK

Thick layers of continuous insulation can improve the performance of the detail but even

FPSF Ψ = 0160 WmK

a very well insulated FPSF is still close to the 001 WmK limit

Section 2 ndash Common Linear Thermal Bridges

STEP 4 ‐ Avoid accidental radiation fins ‐ even well‐insulated ones

42

stem wall Ψ = ‐0004 WmK Thermally broken stem wall Ψ = ‐0136 WmK

Section 2 ndash Common Linear Thermal Bridges

43

Thermally broken stem wall provides an insulated break between the stem wall and the floor slab effectively cutting off the ldquoradiation finrdquoAligning exterior insulation layers at junction of stem wall and above grade wall also helpsSTEP 5 ndash An insulated break between the exterior wall and floor slab works best

ICF parapet Ψ = 0200 WmK Foamglas thermal break Ψ = ‐0071 WmK

Another good location to cut off the radiation fin

Section 2 ndash Common Linear Thermal Bridges

44

Window positioned outside of thermal envelope Ψ = 010 WmKEffectively R‐value of window reduced by 20 ‐ 30 depending on window size

Section 2 ndash Common Linear Thermal Bridges

Window positioned on edge of thermal envelope Ψ = 004 WmKR‐value of window reduced by 5 ‐10 depending on window size

45

Window centered in plane of insulation Ψ = 002 to 003 WmKR‐value of window is almost preserved

Section 2 ndash Common Linear Thermal Bridges

46

47

Break

Section 3 ndash Using psi values in PHPP

48

How do I know which thermal bridges need to be modeled and entered in PHPP

Section 3 ndash Using psi values in PHPP

49

How do I know which thermal bridges need to be modeled and entered in PHPP

PHI requires 1 of 2 paths1) Model all thermal bridges enter psi values for both + and ‐2) Model and enter only thermal bridges with psi values over 001 WmK

Path 2 begs the question ndash how do I know which TBs will be over 001 WmK before Irsquove modeled them

Image source httpwwwtheblazecomblog20130124finally‐the‐answer‐sort‐of‐for‐what‐came‐first‐the‐chicken‐or‐the‐egg

Section 3 ndash Using psi values in PHPP

50

EavesMost details will have negative psi value

Rim joistAlmost always positive psi value ‐MODEL

Wall to slabfootingOnly well‐designed details will have negative psi value ‐MODEL

Footing below bearing wall or postOnly well‐designed details will have psi value lt 001 WmK‐MODEL

Roof ridgeMost details will have negative psi value

Section 3 ndash Using psi values in PHPP

51

RakeMost details will have negative psi value

Windowdoor sill on slab MODEL BUThellipCan be entered as a window sill TB + wall‐to‐slab TB (requires two separate psi values)

Window sillAlmost always positive psi value since overinsulationis difficult ndashMODEL

Window headIf overinsulated probably no need to model If not ndashMODEL

Section 3 ndash Using psi values in PHPP

52

Exterior cornerMost details will have negative psi value

Interior cornerAlmost always positive psi value ndashMODEL

Window jambIf overinsulated probably no need to model If not ndashMODEL

Wall junctionIf insulation layers are interrupted ‐MODEL

Section 3 ndash Using psi values in PHPP

53

Other places to keep in mind for possible thermal bridgesbull Plumbing stacksbull Rain pipes (interior)bull ERV vent penetrations (to the exterior)bull Sump pumpsbull Radon remediation pipes (if interior to the building)

Section 3 ndash Using psi values in PHPP

54

Section 3 ndash Using psi values in PHPP

55

Section 3 ndash Using psi values in WUFI Passive

56

Is the psi value really an indicator of a detailrsquos thermal qualityYes and no

At geometric bridges it does two things at once ndash it is both a correction factor and an indicator of heat flow ndash but primarily a correction factor

Section 2 ndash Common Linear Thermal Bridges

31

Exterior cornerInsulated 2x6 wall w solid post Ψ = ‐ 0004 WmK

rim joist fib batt (R‐11) Ψ = 0089 WmK rim joist rim board (R‐11) Ψ = 0129 WmK

bull Rim joist thermal bridge ‐ challenging to achieve the Ψ = 001 WmK targetbull Maintaining continuity and alignment of insulation layers is a good first step

STEP 2 ndash Align insulation layers

Section 2 ndash Common Linear Thermal Bridges

32

rim joist 2x4 wall w 1rdquo exterior XPS (R‐13) Ψ = 0047 WmK

Section 2 ndash Common Linear Thermal Bridges

33

rim joist fib batt (R‐11) Ψ = 0089 WmK

bull Exterior insulation helps control heat flow through uninsulated studs and plates

STEP 3 ndash Use continuous exterior insulation to isolate bridging elements

rim joist 2x4 wall w 1rdquo exterior XPS (R‐13) Ψ = 0047 WmK

Use enough exterior insulation and the psi value can be driven down below 001 WmK

Section 2 ndash Common Linear Thermal Bridges

34

rim joist 2x4 wall w 4rdquo exterior XPSΨ = 0011 WmK

rim joist 2x4 wall w 4rdquo exterior XPSΨ = 0011 WmK

Question ndash are the psi values for these two details the same or different

Section 2 ndash Common Linear Thermal Bridges

35

rim joist 2x6 wall w 4rdquo exterior XPSΨ =

rim joist 2x4 wall w 4rdquo exterior XPSΨ = 0011 WmK

Is the detail on the left a ldquobetterrdquo detailIs heat flow through the detail on the right really 2x higher than the heat flow on the leftDoes 4rdquo of exterior foam guarantee a good psi value

Section 2 ndash Common Linear Thermal Bridges

36

rim joist 2x6 wall w 4rdquo exterior XPSΨ = 0020 WmK

rim joist 2x4 wall w 4rdquo exterior XPSΨ = 0011 WmK

NoFor the 2x6 wall therersquos now simply a larger difference between the higher R‐value wall assembly and the rim joist R‐value which has remained the same

Section 2 ndash Common Linear Thermal Bridges

37

rim joist 2x6 wall w 4rdquo exterior XPSΨ = 0020 WmK

Is the psi value really an indicator of a detailrsquos thermal quality

Section 2 ndash Common Linear Thermal Bridges

38

Is the psi value really an indicator of a detailrsquos thermal qualityYes and no

At structural thermal bridges a psi value is a comparison between the U‐value of the assembly(ies) and the U‐value of the junction A junction detail that ldquopassesrdquo (001 WmK) for one assembly may not pass with another

Section 2 ndash Common Linear Thermal Bridges

39

Section 2 ndash Common Linear Thermal Bridges

2x6 wall no studs Ψ = ‐ 0058 WmK 2x6 wall 2‐stud Ψ = ‐ 0040 WmK

When is a performance comparison validWhen the two models being compared have the same assemblies and the same geometry ‐the only difference is at the junction Example above

40

stem wall Ψ = ‐0004 WmK FPSF (frost‐protected shallow foundation) Ψ = 0160 WmK

bull Thermal bridge at the foundation is typically the most challenging to addressbull The concrete stem wall and FPSF footing acts as a radiation fin

STEP 4 ndash Avoid accidental ldquoradiation finsrdquo

Section 2 ndash Common Linear Thermal Bridges

41

FPSF (well insulated) Ψ = 0013 WmK

Thick layers of continuous insulation can improve the performance of the detail but even

FPSF Ψ = 0160 WmK

a very well insulated FPSF is still close to the 001 WmK limit

Section 2 ndash Common Linear Thermal Bridges

STEP 4 ‐ Avoid accidental radiation fins ‐ even well‐insulated ones

42

stem wall Ψ = ‐0004 WmK Thermally broken stem wall Ψ = ‐0136 WmK

Section 2 ndash Common Linear Thermal Bridges

43

Thermally broken stem wall provides an insulated break between the stem wall and the floor slab effectively cutting off the ldquoradiation finrdquoAligning exterior insulation layers at junction of stem wall and above grade wall also helpsSTEP 5 ndash An insulated break between the exterior wall and floor slab works best

ICF parapet Ψ = 0200 WmK Foamglas thermal break Ψ = ‐0071 WmK

Another good location to cut off the radiation fin

Section 2 ndash Common Linear Thermal Bridges

44

Window positioned outside of thermal envelope Ψ = 010 WmKEffectively R‐value of window reduced by 20 ‐ 30 depending on window size

Section 2 ndash Common Linear Thermal Bridges

Window positioned on edge of thermal envelope Ψ = 004 WmKR‐value of window reduced by 5 ‐10 depending on window size

45

Window centered in plane of insulation Ψ = 002 to 003 WmKR‐value of window is almost preserved

Section 2 ndash Common Linear Thermal Bridges

46

47

Break

Section 3 ndash Using psi values in PHPP

48

How do I know which thermal bridges need to be modeled and entered in PHPP

Section 3 ndash Using psi values in PHPP

49

How do I know which thermal bridges need to be modeled and entered in PHPP

PHI requires 1 of 2 paths1) Model all thermal bridges enter psi values for both + and ‐2) Model and enter only thermal bridges with psi values over 001 WmK

Path 2 begs the question ndash how do I know which TBs will be over 001 WmK before Irsquove modeled them

Image source httpwwwtheblazecomblog20130124finally‐the‐answer‐sort‐of‐for‐what‐came‐first‐the‐chicken‐or‐the‐egg

Section 3 ndash Using psi values in PHPP

50

EavesMost details will have negative psi value

Rim joistAlmost always positive psi value ‐MODEL

Wall to slabfootingOnly well‐designed details will have negative psi value ‐MODEL

Footing below bearing wall or postOnly well‐designed details will have psi value lt 001 WmK‐MODEL

Roof ridgeMost details will have negative psi value

Section 3 ndash Using psi values in PHPP

51

RakeMost details will have negative psi value

Windowdoor sill on slab MODEL BUThellipCan be entered as a window sill TB + wall‐to‐slab TB (requires two separate psi values)

Window sillAlmost always positive psi value since overinsulationis difficult ndashMODEL

Window headIf overinsulated probably no need to model If not ndashMODEL

Section 3 ndash Using psi values in PHPP

52

Exterior cornerMost details will have negative psi value

Interior cornerAlmost always positive psi value ndashMODEL

Window jambIf overinsulated probably no need to model If not ndashMODEL

Wall junctionIf insulation layers are interrupted ‐MODEL

Section 3 ndash Using psi values in PHPP

53

Other places to keep in mind for possible thermal bridgesbull Plumbing stacksbull Rain pipes (interior)bull ERV vent penetrations (to the exterior)bull Sump pumpsbull Radon remediation pipes (if interior to the building)

Section 3 ndash Using psi values in PHPP

54

Section 3 ndash Using psi values in PHPP

55

Section 3 ndash Using psi values in WUFI Passive

56

rim joist fib batt (R‐11) Ψ = 0089 WmK rim joist rim board (R‐11) Ψ = 0129 WmK

bull Rim joist thermal bridge ‐ challenging to achieve the Ψ = 001 WmK targetbull Maintaining continuity and alignment of insulation layers is a good first step

STEP 2 ndash Align insulation layers

Section 2 ndash Common Linear Thermal Bridges

32

rim joist 2x4 wall w 1rdquo exterior XPS (R‐13) Ψ = 0047 WmK

Section 2 ndash Common Linear Thermal Bridges

33

rim joist fib batt (R‐11) Ψ = 0089 WmK

bull Exterior insulation helps control heat flow through uninsulated studs and plates

STEP 3 ndash Use continuous exterior insulation to isolate bridging elements

rim joist 2x4 wall w 1rdquo exterior XPS (R‐13) Ψ = 0047 WmK

Use enough exterior insulation and the psi value can be driven down below 001 WmK

Section 2 ndash Common Linear Thermal Bridges

34

rim joist 2x4 wall w 4rdquo exterior XPSΨ = 0011 WmK

rim joist 2x4 wall w 4rdquo exterior XPSΨ = 0011 WmK

Question ndash are the psi values for these two details the same or different

Section 2 ndash Common Linear Thermal Bridges

35

rim joist 2x6 wall w 4rdquo exterior XPSΨ =

rim joist 2x4 wall w 4rdquo exterior XPSΨ = 0011 WmK

Is the detail on the left a ldquobetterrdquo detailIs heat flow through the detail on the right really 2x higher than the heat flow on the leftDoes 4rdquo of exterior foam guarantee a good psi value

Section 2 ndash Common Linear Thermal Bridges

36

rim joist 2x6 wall w 4rdquo exterior XPSΨ = 0020 WmK

rim joist 2x4 wall w 4rdquo exterior XPSΨ = 0011 WmK

NoFor the 2x6 wall therersquos now simply a larger difference between the higher R‐value wall assembly and the rim joist R‐value which has remained the same

Section 2 ndash Common Linear Thermal Bridges

37

rim joist 2x6 wall w 4rdquo exterior XPSΨ = 0020 WmK

Is the psi value really an indicator of a detailrsquos thermal quality

Section 2 ndash Common Linear Thermal Bridges

38

Is the psi value really an indicator of a detailrsquos thermal qualityYes and no

At structural thermal bridges a psi value is a comparison between the U‐value of the assembly(ies) and the U‐value of the junction A junction detail that ldquopassesrdquo (001 WmK) for one assembly may not pass with another

Section 2 ndash Common Linear Thermal Bridges

39

Section 2 ndash Common Linear Thermal Bridges

2x6 wall no studs Ψ = ‐ 0058 WmK 2x6 wall 2‐stud Ψ = ‐ 0040 WmK

When is a performance comparison validWhen the two models being compared have the same assemblies and the same geometry ‐the only difference is at the junction Example above

40

stem wall Ψ = ‐0004 WmK FPSF (frost‐protected shallow foundation) Ψ = 0160 WmK

bull Thermal bridge at the foundation is typically the most challenging to addressbull The concrete stem wall and FPSF footing acts as a radiation fin

STEP 4 ndash Avoid accidental ldquoradiation finsrdquo

Section 2 ndash Common Linear Thermal Bridges

41

FPSF (well insulated) Ψ = 0013 WmK

Thick layers of continuous insulation can improve the performance of the detail but even

FPSF Ψ = 0160 WmK

a very well insulated FPSF is still close to the 001 WmK limit

Section 2 ndash Common Linear Thermal Bridges

STEP 4 ‐ Avoid accidental radiation fins ‐ even well‐insulated ones

42

stem wall Ψ = ‐0004 WmK Thermally broken stem wall Ψ = ‐0136 WmK

Section 2 ndash Common Linear Thermal Bridges

43

Thermally broken stem wall provides an insulated break between the stem wall and the floor slab effectively cutting off the ldquoradiation finrdquoAligning exterior insulation layers at junction of stem wall and above grade wall also helpsSTEP 5 ndash An insulated break between the exterior wall and floor slab works best

ICF parapet Ψ = 0200 WmK Foamglas thermal break Ψ = ‐0071 WmK

Another good location to cut off the radiation fin

Section 2 ndash Common Linear Thermal Bridges

44

Window positioned outside of thermal envelope Ψ = 010 WmKEffectively R‐value of window reduced by 20 ‐ 30 depending on window size

Section 2 ndash Common Linear Thermal Bridges

Window positioned on edge of thermal envelope Ψ = 004 WmKR‐value of window reduced by 5 ‐10 depending on window size

45

Window centered in plane of insulation Ψ = 002 to 003 WmKR‐value of window is almost preserved

Section 2 ndash Common Linear Thermal Bridges

46

47

Break

Section 3 ndash Using psi values in PHPP

48

How do I know which thermal bridges need to be modeled and entered in PHPP

Section 3 ndash Using psi values in PHPP

49

How do I know which thermal bridges need to be modeled and entered in PHPP

PHI requires 1 of 2 paths1) Model all thermal bridges enter psi values for both + and ‐2) Model and enter only thermal bridges with psi values over 001 WmK

Path 2 begs the question ndash how do I know which TBs will be over 001 WmK before Irsquove modeled them

Image source httpwwwtheblazecomblog20130124finally‐the‐answer‐sort‐of‐for‐what‐came‐first‐the‐chicken‐or‐the‐egg

Section 3 ndash Using psi values in PHPP

50

EavesMost details will have negative psi value

Rim joistAlmost always positive psi value ‐MODEL

Wall to slabfootingOnly well‐designed details will have negative psi value ‐MODEL

Footing below bearing wall or postOnly well‐designed details will have psi value lt 001 WmK‐MODEL

Roof ridgeMost details will have negative psi value

Section 3 ndash Using psi values in PHPP

51

RakeMost details will have negative psi value

Windowdoor sill on slab MODEL BUThellipCan be entered as a window sill TB + wall‐to‐slab TB (requires two separate psi values)

Window sillAlmost always positive psi value since overinsulationis difficult ndashMODEL

Window headIf overinsulated probably no need to model If not ndashMODEL

Section 3 ndash Using psi values in PHPP

52

Exterior cornerMost details will have negative psi value

Interior cornerAlmost always positive psi value ndashMODEL

Window jambIf overinsulated probably no need to model If not ndashMODEL

Wall junctionIf insulation layers are interrupted ‐MODEL

Section 3 ndash Using psi values in PHPP

53

Other places to keep in mind for possible thermal bridgesbull Plumbing stacksbull Rain pipes (interior)bull ERV vent penetrations (to the exterior)bull Sump pumpsbull Radon remediation pipes (if interior to the building)

Section 3 ndash Using psi values in PHPP

54

Section 3 ndash Using psi values in PHPP

55

Section 3 ndash Using psi values in WUFI Passive

56

rim joist 2x4 wall w 1rdquo exterior XPS (R‐13) Ψ = 0047 WmK

Section 2 ndash Common Linear Thermal Bridges

33

rim joist fib batt (R‐11) Ψ = 0089 WmK

bull Exterior insulation helps control heat flow through uninsulated studs and plates

STEP 3 ndash Use continuous exterior insulation to isolate bridging elements

rim joist 2x4 wall w 1rdquo exterior XPS (R‐13) Ψ = 0047 WmK

Use enough exterior insulation and the psi value can be driven down below 001 WmK

Section 2 ndash Common Linear Thermal Bridges

34

rim joist 2x4 wall w 4rdquo exterior XPSΨ = 0011 WmK

rim joist 2x4 wall w 4rdquo exterior XPSΨ = 0011 WmK

Question ndash are the psi values for these two details the same or different

Section 2 ndash Common Linear Thermal Bridges

35

rim joist 2x6 wall w 4rdquo exterior XPSΨ =

rim joist 2x4 wall w 4rdquo exterior XPSΨ = 0011 WmK

Is the detail on the left a ldquobetterrdquo detailIs heat flow through the detail on the right really 2x higher than the heat flow on the leftDoes 4rdquo of exterior foam guarantee a good psi value

Section 2 ndash Common Linear Thermal Bridges

36

rim joist 2x6 wall w 4rdquo exterior XPSΨ = 0020 WmK

rim joist 2x4 wall w 4rdquo exterior XPSΨ = 0011 WmK

NoFor the 2x6 wall therersquos now simply a larger difference between the higher R‐value wall assembly and the rim joist R‐value which has remained the same

Section 2 ndash Common Linear Thermal Bridges

37

rim joist 2x6 wall w 4rdquo exterior XPSΨ = 0020 WmK

Is the psi value really an indicator of a detailrsquos thermal quality

Section 2 ndash Common Linear Thermal Bridges

38

Is the psi value really an indicator of a detailrsquos thermal qualityYes and no

At structural thermal bridges a psi value is a comparison between the U‐value of the assembly(ies) and the U‐value of the junction A junction detail that ldquopassesrdquo (001 WmK) for one assembly may not pass with another

Section 2 ndash Common Linear Thermal Bridges

39

Section 2 ndash Common Linear Thermal Bridges

2x6 wall no studs Ψ = ‐ 0058 WmK 2x6 wall 2‐stud Ψ = ‐ 0040 WmK

When is a performance comparison validWhen the two models being compared have the same assemblies and the same geometry ‐the only difference is at the junction Example above

40

stem wall Ψ = ‐0004 WmK FPSF (frost‐protected shallow foundation) Ψ = 0160 WmK

bull Thermal bridge at the foundation is typically the most challenging to addressbull The concrete stem wall and FPSF footing acts as a radiation fin

STEP 4 ndash Avoid accidental ldquoradiation finsrdquo

Section 2 ndash Common Linear Thermal Bridges

41

FPSF (well insulated) Ψ = 0013 WmK

Thick layers of continuous insulation can improve the performance of the detail but even

FPSF Ψ = 0160 WmK

a very well insulated FPSF is still close to the 001 WmK limit

Section 2 ndash Common Linear Thermal Bridges

STEP 4 ‐ Avoid accidental radiation fins ‐ even well‐insulated ones

42

stem wall Ψ = ‐0004 WmK Thermally broken stem wall Ψ = ‐0136 WmK

Section 2 ndash Common Linear Thermal Bridges

43

Thermally broken stem wall provides an insulated break between the stem wall and the floor slab effectively cutting off the ldquoradiation finrdquoAligning exterior insulation layers at junction of stem wall and above grade wall also helpsSTEP 5 ndash An insulated break between the exterior wall and floor slab works best

ICF parapet Ψ = 0200 WmK Foamglas thermal break Ψ = ‐0071 WmK

Another good location to cut off the radiation fin

Section 2 ndash Common Linear Thermal Bridges

44

Window positioned outside of thermal envelope Ψ = 010 WmKEffectively R‐value of window reduced by 20 ‐ 30 depending on window size

Section 2 ndash Common Linear Thermal Bridges

Window positioned on edge of thermal envelope Ψ = 004 WmKR‐value of window reduced by 5 ‐10 depending on window size

45

Window centered in plane of insulation Ψ = 002 to 003 WmKR‐value of window is almost preserved

Section 2 ndash Common Linear Thermal Bridges

46

47

Break

Section 3 ndash Using psi values in PHPP

48

How do I know which thermal bridges need to be modeled and entered in PHPP

Section 3 ndash Using psi values in PHPP

49

How do I know which thermal bridges need to be modeled and entered in PHPP

PHI requires 1 of 2 paths1) Model all thermal bridges enter psi values for both + and ‐2) Model and enter only thermal bridges with psi values over 001 WmK

Path 2 begs the question ndash how do I know which TBs will be over 001 WmK before Irsquove modeled them

Image source httpwwwtheblazecomblog20130124finally‐the‐answer‐sort‐of‐for‐what‐came‐first‐the‐chicken‐or‐the‐egg

Section 3 ndash Using psi values in PHPP

50

EavesMost details will have negative psi value

Rim joistAlmost always positive psi value ‐MODEL

Wall to slabfootingOnly well‐designed details will have negative psi value ‐MODEL

Footing below bearing wall or postOnly well‐designed details will have psi value lt 001 WmK‐MODEL

Roof ridgeMost details will have negative psi value

Section 3 ndash Using psi values in PHPP

51

RakeMost details will have negative psi value

Windowdoor sill on slab MODEL BUThellipCan be entered as a window sill TB + wall‐to‐slab TB (requires two separate psi values)

Window sillAlmost always positive psi value since overinsulationis difficult ndashMODEL

Window headIf overinsulated probably no need to model If not ndashMODEL

Section 3 ndash Using psi values in PHPP

52

Exterior cornerMost details will have negative psi value

Interior cornerAlmost always positive psi value ndashMODEL

Window jambIf overinsulated probably no need to model If not ndashMODEL

Wall junctionIf insulation layers are interrupted ‐MODEL

Section 3 ndash Using psi values in PHPP

53

Other places to keep in mind for possible thermal bridgesbull Plumbing stacksbull Rain pipes (interior)bull ERV vent penetrations (to the exterior)bull Sump pumpsbull Radon remediation pipes (if interior to the building)

Section 3 ndash Using psi values in PHPP

54

Section 3 ndash Using psi values in PHPP

55

Section 3 ndash Using psi values in WUFI Passive

56

rim joist 2x4 wall w 1rdquo exterior XPS (R‐13) Ψ = 0047 WmK

Use enough exterior insulation and the psi value can be driven down below 001 WmK

Section 2 ndash Common Linear Thermal Bridges

34

rim joist 2x4 wall w 4rdquo exterior XPSΨ = 0011 WmK

rim joist 2x4 wall w 4rdquo exterior XPSΨ = 0011 WmK

Question ndash are the psi values for these two details the same or different

Section 2 ndash Common Linear Thermal Bridges

35

rim joist 2x6 wall w 4rdquo exterior XPSΨ =

rim joist 2x4 wall w 4rdquo exterior XPSΨ = 0011 WmK

Is the detail on the left a ldquobetterrdquo detailIs heat flow through the detail on the right really 2x higher than the heat flow on the leftDoes 4rdquo of exterior foam guarantee a good psi value

Section 2 ndash Common Linear Thermal Bridges

36

rim joist 2x6 wall w 4rdquo exterior XPSΨ = 0020 WmK

rim joist 2x4 wall w 4rdquo exterior XPSΨ = 0011 WmK

NoFor the 2x6 wall therersquos now simply a larger difference between the higher R‐value wall assembly and the rim joist R‐value which has remained the same

Section 2 ndash Common Linear Thermal Bridges

37

rim joist 2x6 wall w 4rdquo exterior XPSΨ = 0020 WmK

Is the psi value really an indicator of a detailrsquos thermal quality

Section 2 ndash Common Linear Thermal Bridges

38

Is the psi value really an indicator of a detailrsquos thermal qualityYes and no

At structural thermal bridges a psi value is a comparison between the U‐value of the assembly(ies) and the U‐value of the junction A junction detail that ldquopassesrdquo (001 WmK) for one assembly may not pass with another

Section 2 ndash Common Linear Thermal Bridges

39

Section 2 ndash Common Linear Thermal Bridges

2x6 wall no studs Ψ = ‐ 0058 WmK 2x6 wall 2‐stud Ψ = ‐ 0040 WmK

When is a performance comparison validWhen the two models being compared have the same assemblies and the same geometry ‐the only difference is at the junction Example above

40

stem wall Ψ = ‐0004 WmK FPSF (frost‐protected shallow foundation) Ψ = 0160 WmK

bull Thermal bridge at the foundation is typically the most challenging to addressbull The concrete stem wall and FPSF footing acts as a radiation fin

STEP 4 ndash Avoid accidental ldquoradiation finsrdquo

Section 2 ndash Common Linear Thermal Bridges

41

FPSF (well insulated) Ψ = 0013 WmK

Thick layers of continuous insulation can improve the performance of the detail but even

FPSF Ψ = 0160 WmK

a very well insulated FPSF is still close to the 001 WmK limit

Section 2 ndash Common Linear Thermal Bridges

STEP 4 ‐ Avoid accidental radiation fins ‐ even well‐insulated ones

42

stem wall Ψ = ‐0004 WmK Thermally broken stem wall Ψ = ‐0136 WmK

Section 2 ndash Common Linear Thermal Bridges

43

Thermally broken stem wall provides an insulated break between the stem wall and the floor slab effectively cutting off the ldquoradiation finrdquoAligning exterior insulation layers at junction of stem wall and above grade wall also helpsSTEP 5 ndash An insulated break between the exterior wall and floor slab works best

ICF parapet Ψ = 0200 WmK Foamglas thermal break Ψ = ‐0071 WmK

Another good location to cut off the radiation fin

Section 2 ndash Common Linear Thermal Bridges

44

Window positioned outside of thermal envelope Ψ = 010 WmKEffectively R‐value of window reduced by 20 ‐ 30 depending on window size

Section 2 ndash Common Linear Thermal Bridges

Window positioned on edge of thermal envelope Ψ = 004 WmKR‐value of window reduced by 5 ‐10 depending on window size

45

Window centered in plane of insulation Ψ = 002 to 003 WmKR‐value of window is almost preserved

Section 2 ndash Common Linear Thermal Bridges

46

47

Break

Section 3 ndash Using psi values in PHPP

48

How do I know which thermal bridges need to be modeled and entered in PHPP

Section 3 ndash Using psi values in PHPP

49

How do I know which thermal bridges need to be modeled and entered in PHPP

PHI requires 1 of 2 paths1) Model all thermal bridges enter psi values for both + and ‐2) Model and enter only thermal bridges with psi values over 001 WmK

Path 2 begs the question ndash how do I know which TBs will be over 001 WmK before Irsquove modeled them

Image source httpwwwtheblazecomblog20130124finally‐the‐answer‐sort‐of‐for‐what‐came‐first‐the‐chicken‐or‐the‐egg

Section 3 ndash Using psi values in PHPP

50

EavesMost details will have negative psi value

Rim joistAlmost always positive psi value ‐MODEL

Wall to slabfootingOnly well‐designed details will have negative psi value ‐MODEL

Footing below bearing wall or postOnly well‐designed details will have psi value lt 001 WmK‐MODEL

Roof ridgeMost details will have negative psi value

Section 3 ndash Using psi values in PHPP

51

RakeMost details will have negative psi value

Windowdoor sill on slab MODEL BUThellipCan be entered as a window sill TB + wall‐to‐slab TB (requires two separate psi values)

Window sillAlmost always positive psi value since overinsulationis difficult ndashMODEL

Window headIf overinsulated probably no need to model If not ndashMODEL

Section 3 ndash Using psi values in PHPP

52

Exterior cornerMost details will have negative psi value

Interior cornerAlmost always positive psi value ndashMODEL

Window jambIf overinsulated probably no need to model If not ndashMODEL

Wall junctionIf insulation layers are interrupted ‐MODEL

Section 3 ndash Using psi values in PHPP

53

Other places to keep in mind for possible thermal bridgesbull Plumbing stacksbull Rain pipes (interior)bull ERV vent penetrations (to the exterior)bull Sump pumpsbull Radon remediation pipes (if interior to the building)

Section 3 ndash Using psi values in PHPP

54

Section 3 ndash Using psi values in PHPP

55

Section 3 ndash Using psi values in WUFI Passive

56

rim joist 2x4 wall w 4rdquo exterior XPSΨ = 0011 WmK

Question ndash are the psi values for these two details the same or different

Section 2 ndash Common Linear Thermal Bridges

35

rim joist 2x6 wall w 4rdquo exterior XPSΨ =

rim joist 2x4 wall w 4rdquo exterior XPSΨ = 0011 WmK

Is the detail on the left a ldquobetterrdquo detailIs heat flow through the detail on the right really 2x higher than the heat flow on the leftDoes 4rdquo of exterior foam guarantee a good psi value

Section 2 ndash Common Linear Thermal Bridges

36

rim joist 2x6 wall w 4rdquo exterior XPSΨ = 0020 WmK

rim joist 2x4 wall w 4rdquo exterior XPSΨ = 0011 WmK

NoFor the 2x6 wall therersquos now simply a larger difference between the higher R‐value wall assembly and the rim joist R‐value which has remained the same

Section 2 ndash Common Linear Thermal Bridges

37

rim joist 2x6 wall w 4rdquo exterior XPSΨ = 0020 WmK

Is the psi value really an indicator of a detailrsquos thermal quality

Section 2 ndash Common Linear Thermal Bridges

38

Is the psi value really an indicator of a detailrsquos thermal qualityYes and no

At structural thermal bridges a psi value is a comparison between the U‐value of the assembly(ies) and the U‐value of the junction A junction detail that ldquopassesrdquo (001 WmK) for one assembly may not pass with another

Section 2 ndash Common Linear Thermal Bridges

39

Section 2 ndash Common Linear Thermal Bridges

2x6 wall no studs Ψ = ‐ 0058 WmK 2x6 wall 2‐stud Ψ = ‐ 0040 WmK

When is a performance comparison validWhen the two models being compared have the same assemblies and the same geometry ‐the only difference is at the junction Example above

40

stem wall Ψ = ‐0004 WmK FPSF (frost‐protected shallow foundation) Ψ = 0160 WmK

bull Thermal bridge at the foundation is typically the most challenging to addressbull The concrete stem wall and FPSF footing acts as a radiation fin

STEP 4 ndash Avoid accidental ldquoradiation finsrdquo

Section 2 ndash Common Linear Thermal Bridges

41

FPSF (well insulated) Ψ = 0013 WmK

Thick layers of continuous insulation can improve the performance of the detail but even

FPSF Ψ = 0160 WmK

a very well insulated FPSF is still close to the 001 WmK limit

Section 2 ndash Common Linear Thermal Bridges

STEP 4 ‐ Avoid accidental radiation fins ‐ even well‐insulated ones

42

stem wall Ψ = ‐0004 WmK Thermally broken stem wall Ψ = ‐0136 WmK

Section 2 ndash Common Linear Thermal Bridges

43

Thermally broken stem wall provides an insulated break between the stem wall and the floor slab effectively cutting off the ldquoradiation finrdquoAligning exterior insulation layers at junction of stem wall and above grade wall also helpsSTEP 5 ndash An insulated break between the exterior wall and floor slab works best

ICF parapet Ψ = 0200 WmK Foamglas thermal break Ψ = ‐0071 WmK

Another good location to cut off the radiation fin

Section 2 ndash Common Linear Thermal Bridges

44

Window positioned outside of thermal envelope Ψ = 010 WmKEffectively R‐value of window reduced by 20 ‐ 30 depending on window size

Section 2 ndash Common Linear Thermal Bridges

Window positioned on edge of thermal envelope Ψ = 004 WmKR‐value of window reduced by 5 ‐10 depending on window size

45

Window centered in plane of insulation Ψ = 002 to 003 WmKR‐value of window is almost preserved

Section 2 ndash Common Linear Thermal Bridges

46

47

Break

Section 3 ndash Using psi values in PHPP

48

How do I know which thermal bridges need to be modeled and entered in PHPP

Section 3 ndash Using psi values in PHPP

49

How do I know which thermal bridges need to be modeled and entered in PHPP

PHI requires 1 of 2 paths1) Model all thermal bridges enter psi values for both + and ‐2) Model and enter only thermal bridges with psi values over 001 WmK

Path 2 begs the question ndash how do I know which TBs will be over 001 WmK before Irsquove modeled them

Image source httpwwwtheblazecomblog20130124finally‐the‐answer‐sort‐of‐for‐what‐came‐first‐the‐chicken‐or‐the‐egg

Section 3 ndash Using psi values in PHPP

50

EavesMost details will have negative psi value

Rim joistAlmost always positive psi value ‐MODEL

Wall to slabfootingOnly well‐designed details will have negative psi value ‐MODEL

Footing below bearing wall or postOnly well‐designed details will have psi value lt 001 WmK‐MODEL

Roof ridgeMost details will have negative psi value

Section 3 ndash Using psi values in PHPP

51

RakeMost details will have negative psi value

Windowdoor sill on slab MODEL BUThellipCan be entered as a window sill TB + wall‐to‐slab TB (requires two separate psi values)

Window sillAlmost always positive psi value since overinsulationis difficult ndashMODEL

Window headIf overinsulated probably no need to model If not ndashMODEL

Section 3 ndash Using psi values in PHPP

52

Exterior cornerMost details will have negative psi value

Interior cornerAlmost always positive psi value ndashMODEL

Window jambIf overinsulated probably no need to model If not ndashMODEL

Wall junctionIf insulation layers are interrupted ‐MODEL

Section 3 ndash Using psi values in PHPP

53

Other places to keep in mind for possible thermal bridgesbull Plumbing stacksbull Rain pipes (interior)bull ERV vent penetrations (to the exterior)bull Sump pumpsbull Radon remediation pipes (if interior to the building)

Section 3 ndash Using psi values in PHPP

54

Section 3 ndash Using psi values in PHPP

55

Section 3 ndash Using psi values in WUFI Passive

56

rim joist 2x4 wall w 4rdquo exterior XPSΨ = 0011 WmK

Is the detail on the left a ldquobetterrdquo detailIs heat flow through the detail on the right really 2x higher than the heat flow on the leftDoes 4rdquo of exterior foam guarantee a good psi value

Section 2 ndash Common Linear Thermal Bridges

36

rim joist 2x6 wall w 4rdquo exterior XPSΨ = 0020 WmK

rim joist 2x4 wall w 4rdquo exterior XPSΨ = 0011 WmK

NoFor the 2x6 wall therersquos now simply a larger difference between the higher R‐value wall assembly and the rim joist R‐value which has remained the same

Section 2 ndash Common Linear Thermal Bridges

37

rim joist 2x6 wall w 4rdquo exterior XPSΨ = 0020 WmK

Is the psi value really an indicator of a detailrsquos thermal quality

Section 2 ndash Common Linear Thermal Bridges

38

Is the psi value really an indicator of a detailrsquos thermal qualityYes and no

At structural thermal bridges a psi value is a comparison between the U‐value of the assembly(ies) and the U‐value of the junction A junction detail that ldquopassesrdquo (001 WmK) for one assembly may not pass with another

Section 2 ndash Common Linear Thermal Bridges

39

Section 2 ndash Common Linear Thermal Bridges

2x6 wall no studs Ψ = ‐ 0058 WmK 2x6 wall 2‐stud Ψ = ‐ 0040 WmK

When is a performance comparison validWhen the two models being compared have the same assemblies and the same geometry ‐the only difference is at the junction Example above

40

stem wall Ψ = ‐0004 WmK FPSF (frost‐protected shallow foundation) Ψ = 0160 WmK

bull Thermal bridge at the foundation is typically the most challenging to addressbull The concrete stem wall and FPSF footing acts as a radiation fin

STEP 4 ndash Avoid accidental ldquoradiation finsrdquo

Section 2 ndash Common Linear Thermal Bridges

41

FPSF (well insulated) Ψ = 0013 WmK

Thick layers of continuous insulation can improve the performance of the detail but even

FPSF Ψ = 0160 WmK

a very well insulated FPSF is still close to the 001 WmK limit

Section 2 ndash Common Linear Thermal Bridges

STEP 4 ‐ Avoid accidental radiation fins ‐ even well‐insulated ones

42

stem wall Ψ = ‐0004 WmK Thermally broken stem wall Ψ = ‐0136 WmK

Section 2 ndash Common Linear Thermal Bridges

43

Thermally broken stem wall provides an insulated break between the stem wall and the floor slab effectively cutting off the ldquoradiation finrdquoAligning exterior insulation layers at junction of stem wall and above grade wall also helpsSTEP 5 ndash An insulated break between the exterior wall and floor slab works best

ICF parapet Ψ = 0200 WmK Foamglas thermal break Ψ = ‐0071 WmK

Another good location to cut off the radiation fin

Section 2 ndash Common Linear Thermal Bridges

44

Window positioned outside of thermal envelope Ψ = 010 WmKEffectively R‐value of window reduced by 20 ‐ 30 depending on window size

Section 2 ndash Common Linear Thermal Bridges

Window positioned on edge of thermal envelope Ψ = 004 WmKR‐value of window reduced by 5 ‐10 depending on window size

45

Window centered in plane of insulation Ψ = 002 to 003 WmKR‐value of window is almost preserved

Section 2 ndash Common Linear Thermal Bridges

46

47

Break

Section 3 ndash Using psi values in PHPP

48

How do I know which thermal bridges need to be modeled and entered in PHPP

Section 3 ndash Using psi values in PHPP

49

How do I know which thermal bridges need to be modeled and entered in PHPP

PHI requires 1 of 2 paths1) Model all thermal bridges enter psi values for both + and ‐2) Model and enter only thermal bridges with psi values over 001 WmK

Path 2 begs the question ndash how do I know which TBs will be over 001 WmK before Irsquove modeled them

Image source httpwwwtheblazecomblog20130124finally‐the‐answer‐sort‐of‐for‐what‐came‐first‐the‐chicken‐or‐the‐egg

Section 3 ndash Using psi values in PHPP

50

EavesMost details will have negative psi value

Rim joistAlmost always positive psi value ‐MODEL

Wall to slabfootingOnly well‐designed details will have negative psi value ‐MODEL

Footing below bearing wall or postOnly well‐designed details will have psi value lt 001 WmK‐MODEL

Roof ridgeMost details will have negative psi value

Section 3 ndash Using psi values in PHPP

51

RakeMost details will have negative psi value

Windowdoor sill on slab MODEL BUThellipCan be entered as a window sill TB + wall‐to‐slab TB (requires two separate psi values)

Window sillAlmost always positive psi value since overinsulationis difficult ndashMODEL

Window headIf overinsulated probably no need to model If not ndashMODEL

Section 3 ndash Using psi values in PHPP

52

Exterior cornerMost details will have negative psi value

Interior cornerAlmost always positive psi value ndashMODEL

Window jambIf overinsulated probably no need to model If not ndashMODEL

Wall junctionIf insulation layers are interrupted ‐MODEL

Section 3 ndash Using psi values in PHPP

53

Other places to keep in mind for possible thermal bridgesbull Plumbing stacksbull Rain pipes (interior)bull ERV vent penetrations (to the exterior)bull Sump pumpsbull Radon remediation pipes (if interior to the building)

Section 3 ndash Using psi values in PHPP

54

Section 3 ndash Using psi values in PHPP

55

Section 3 ndash Using psi values in WUFI Passive

56

rim joist 2x4 wall w 4rdquo exterior XPSΨ = 0011 WmK

NoFor the 2x6 wall therersquos now simply a larger difference between the higher R‐value wall assembly and the rim joist R‐value which has remained the same

Section 2 ndash Common Linear Thermal Bridges

37

rim joist 2x6 wall w 4rdquo exterior XPSΨ = 0020 WmK

Is the psi value really an indicator of a detailrsquos thermal quality

Section 2 ndash Common Linear Thermal Bridges

38

Is the psi value really an indicator of a detailrsquos thermal qualityYes and no

At structural thermal bridges a psi value is a comparison between the U‐value of the assembly(ies) and the U‐value of the junction A junction detail that ldquopassesrdquo (001 WmK) for one assembly may not pass with another

Section 2 ndash Common Linear Thermal Bridges

39

Section 2 ndash Common Linear Thermal Bridges

2x6 wall no studs Ψ = ‐ 0058 WmK 2x6 wall 2‐stud Ψ = ‐ 0040 WmK

When is a performance comparison validWhen the two models being compared have the same assemblies and the same geometry ‐the only difference is at the junction Example above

40

stem wall Ψ = ‐0004 WmK FPSF (frost‐protected shallow foundation) Ψ = 0160 WmK

bull Thermal bridge at the foundation is typically the most challenging to addressbull The concrete stem wall and FPSF footing acts as a radiation fin

STEP 4 ndash Avoid accidental ldquoradiation finsrdquo

Section 2 ndash Common Linear Thermal Bridges

41

FPSF (well insulated) Ψ = 0013 WmK

Thick layers of continuous insulation can improve the performance of the detail but even

FPSF Ψ = 0160 WmK

a very well insulated FPSF is still close to the 001 WmK limit

Section 2 ndash Common Linear Thermal Bridges

STEP 4 ‐ Avoid accidental radiation fins ‐ even well‐insulated ones

42

stem wall Ψ = ‐0004 WmK Thermally broken stem wall Ψ = ‐0136 WmK

Section 2 ndash Common Linear Thermal Bridges

43

Thermally broken stem wall provides an insulated break between the stem wall and the floor slab effectively cutting off the ldquoradiation finrdquoAligning exterior insulation layers at junction of stem wall and above grade wall also helpsSTEP 5 ndash An insulated break between the exterior wall and floor slab works best

ICF parapet Ψ = 0200 WmK Foamglas thermal break Ψ = ‐0071 WmK

Another good location to cut off the radiation fin

Section 2 ndash Common Linear Thermal Bridges

44

Window positioned outside of thermal envelope Ψ = 010 WmKEffectively R‐value of window reduced by 20 ‐ 30 depending on window size

Section 2 ndash Common Linear Thermal Bridges

Window positioned on edge of thermal envelope Ψ = 004 WmKR‐value of window reduced by 5 ‐10 depending on window size

45

Window centered in plane of insulation Ψ = 002 to 003 WmKR‐value of window is almost preserved

Section 2 ndash Common Linear Thermal Bridges

46

47

Break

Section 3 ndash Using psi values in PHPP

48

How do I know which thermal bridges need to be modeled and entered in PHPP

Section 3 ndash Using psi values in PHPP

49

How do I know which thermal bridges need to be modeled and entered in PHPP

PHI requires 1 of 2 paths1) Model all thermal bridges enter psi values for both + and ‐2) Model and enter only thermal bridges with psi values over 001 WmK

Path 2 begs the question ndash how do I know which TBs will be over 001 WmK before Irsquove modeled them

Image source httpwwwtheblazecomblog20130124finally‐the‐answer‐sort‐of‐for‐what‐came‐first‐the‐chicken‐or‐the‐egg

Section 3 ndash Using psi values in PHPP

50

EavesMost details will have negative psi value

Rim joistAlmost always positive psi value ‐MODEL

Wall to slabfootingOnly well‐designed details will have negative psi value ‐MODEL

Footing below bearing wall or postOnly well‐designed details will have psi value lt 001 WmK‐MODEL

Roof ridgeMost details will have negative psi value

Section 3 ndash Using psi values in PHPP

51

RakeMost details will have negative psi value

Windowdoor sill on slab MODEL BUThellipCan be entered as a window sill TB + wall‐to‐slab TB (requires two separate psi values)

Window sillAlmost always positive psi value since overinsulationis difficult ndashMODEL

Window headIf overinsulated probably no need to model If not ndashMODEL

Section 3 ndash Using psi values in PHPP

52

Exterior cornerMost details will have negative psi value

Interior cornerAlmost always positive psi value ndashMODEL

Window jambIf overinsulated probably no need to model If not ndashMODEL

Wall junctionIf insulation layers are interrupted ‐MODEL

Section 3 ndash Using psi values in PHPP

53

Other places to keep in mind for possible thermal bridgesbull Plumbing stacksbull Rain pipes (interior)bull ERV vent penetrations (to the exterior)bull Sump pumpsbull Radon remediation pipes (if interior to the building)

Section 3 ndash Using psi values in PHPP

54

Section 3 ndash Using psi values in PHPP

55

Section 3 ndash Using psi values in WUFI Passive

56

Is the psi value really an indicator of a detailrsquos thermal quality

Section 2 ndash Common Linear Thermal Bridges

38

Is the psi value really an indicator of a detailrsquos thermal qualityYes and no

At structural thermal bridges a psi value is a comparison between the U‐value of the assembly(ies) and the U‐value of the junction A junction detail that ldquopassesrdquo (001 WmK) for one assembly may not pass with another

Section 2 ndash Common Linear Thermal Bridges

39

Section 2 ndash Common Linear Thermal Bridges

2x6 wall no studs Ψ = ‐ 0058 WmK 2x6 wall 2‐stud Ψ = ‐ 0040 WmK

When is a performance comparison validWhen the two models being compared have the same assemblies and the same geometry ‐the only difference is at the junction Example above

40

stem wall Ψ = ‐0004 WmK FPSF (frost‐protected shallow foundation) Ψ = 0160 WmK

bull Thermal bridge at the foundation is typically the most challenging to addressbull The concrete stem wall and FPSF footing acts as a radiation fin

STEP 4 ndash Avoid accidental ldquoradiation finsrdquo

Section 2 ndash Common Linear Thermal Bridges

41

FPSF (well insulated) Ψ = 0013 WmK

Thick layers of continuous insulation can improve the performance of the detail but even

FPSF Ψ = 0160 WmK

a very well insulated FPSF is still close to the 001 WmK limit

Section 2 ndash Common Linear Thermal Bridges

STEP 4 ‐ Avoid accidental radiation fins ‐ even well‐insulated ones

42

stem wall Ψ = ‐0004 WmK Thermally broken stem wall Ψ = ‐0136 WmK

Section 2 ndash Common Linear Thermal Bridges

43

Thermally broken stem wall provides an insulated break between the stem wall and the floor slab effectively cutting off the ldquoradiation finrdquoAligning exterior insulation layers at junction of stem wall and above grade wall also helpsSTEP 5 ndash An insulated break between the exterior wall and floor slab works best

ICF parapet Ψ = 0200 WmK Foamglas thermal break Ψ = ‐0071 WmK

Another good location to cut off the radiation fin

Section 2 ndash Common Linear Thermal Bridges

44

Window positioned outside of thermal envelope Ψ = 010 WmKEffectively R‐value of window reduced by 20 ‐ 30 depending on window size

Section 2 ndash Common Linear Thermal Bridges

Window positioned on edge of thermal envelope Ψ = 004 WmKR‐value of window reduced by 5 ‐10 depending on window size

45

Window centered in plane of insulation Ψ = 002 to 003 WmKR‐value of window is almost preserved

Section 2 ndash Common Linear Thermal Bridges

46

47

Break

Section 3 ndash Using psi values in PHPP

48

How do I know which thermal bridges need to be modeled and entered in PHPP

Section 3 ndash Using psi values in PHPP

49

How do I know which thermal bridges need to be modeled and entered in PHPP

PHI requires 1 of 2 paths1) Model all thermal bridges enter psi values for both + and ‐2) Model and enter only thermal bridges with psi values over 001 WmK

Path 2 begs the question ndash how do I know which TBs will be over 001 WmK before Irsquove modeled them

Image source httpwwwtheblazecomblog20130124finally‐the‐answer‐sort‐of‐for‐what‐came‐first‐the‐chicken‐or‐the‐egg

Section 3 ndash Using psi values in PHPP

50

EavesMost details will have negative psi value

Rim joistAlmost always positive psi value ‐MODEL

Wall to slabfootingOnly well‐designed details will have negative psi value ‐MODEL

Footing below bearing wall or postOnly well‐designed details will have psi value lt 001 WmK‐MODEL

Roof ridgeMost details will have negative psi value

Section 3 ndash Using psi values in PHPP

51

RakeMost details will have negative psi value

Windowdoor sill on slab MODEL BUThellipCan be entered as a window sill TB + wall‐to‐slab TB (requires two separate psi values)

Window sillAlmost always positive psi value since overinsulationis difficult ndashMODEL

Window headIf overinsulated probably no need to model If not ndashMODEL

Section 3 ndash Using psi values in PHPP

52

Exterior cornerMost details will have negative psi value

Interior cornerAlmost always positive psi value ndashMODEL

Window jambIf overinsulated probably no need to model If not ndashMODEL

Wall junctionIf insulation layers are interrupted ‐MODEL

Section 3 ndash Using psi values in PHPP

53

Other places to keep in mind for possible thermal bridgesbull Plumbing stacksbull Rain pipes (interior)bull ERV vent penetrations (to the exterior)bull Sump pumpsbull Radon remediation pipes (if interior to the building)

Section 3 ndash Using psi values in PHPP

54

Section 3 ndash Using psi values in PHPP

55

Section 3 ndash Using psi values in WUFI Passive

56

Is the psi value really an indicator of a detailrsquos thermal qualityYes and no

At structural thermal bridges a psi value is a comparison between the U‐value of the assembly(ies) and the U‐value of the junction A junction detail that ldquopassesrdquo (001 WmK) for one assembly may not pass with another

Section 2 ndash Common Linear Thermal Bridges

39

Section 2 ndash Common Linear Thermal Bridges

2x6 wall no studs Ψ = ‐ 0058 WmK 2x6 wall 2‐stud Ψ = ‐ 0040 WmK

When is a performance comparison validWhen the two models being compared have the same assemblies and the same geometry ‐the only difference is at the junction Example above

40

stem wall Ψ = ‐0004 WmK FPSF (frost‐protected shallow foundation) Ψ = 0160 WmK

bull Thermal bridge at the foundation is typically the most challenging to addressbull The concrete stem wall and FPSF footing acts as a radiation fin

STEP 4 ndash Avoid accidental ldquoradiation finsrdquo

Section 2 ndash Common Linear Thermal Bridges

41

FPSF (well insulated) Ψ = 0013 WmK

Thick layers of continuous insulation can improve the performance of the detail but even

FPSF Ψ = 0160 WmK

a very well insulated FPSF is still close to the 001 WmK limit

Section 2 ndash Common Linear Thermal Bridges

STEP 4 ‐ Avoid accidental radiation fins ‐ even well‐insulated ones

42

stem wall Ψ = ‐0004 WmK Thermally broken stem wall Ψ = ‐0136 WmK

Section 2 ndash Common Linear Thermal Bridges

43

Thermally broken stem wall provides an insulated break between the stem wall and the floor slab effectively cutting off the ldquoradiation finrdquoAligning exterior insulation layers at junction of stem wall and above grade wall also helpsSTEP 5 ndash An insulated break between the exterior wall and floor slab works best

ICF parapet Ψ = 0200 WmK Foamglas thermal break Ψ = ‐0071 WmK

Another good location to cut off the radiation fin

Section 2 ndash Common Linear Thermal Bridges

44

Window positioned outside of thermal envelope Ψ = 010 WmKEffectively R‐value of window reduced by 20 ‐ 30 depending on window size

Section 2 ndash Common Linear Thermal Bridges

Window positioned on edge of thermal envelope Ψ = 004 WmKR‐value of window reduced by 5 ‐10 depending on window size

45

Window centered in plane of insulation Ψ = 002 to 003 WmKR‐value of window is almost preserved

Section 2 ndash Common Linear Thermal Bridges

46

47

Break

Section 3 ndash Using psi values in PHPP

48

How do I know which thermal bridges need to be modeled and entered in PHPP

Section 3 ndash Using psi values in PHPP

49

How do I know which thermal bridges need to be modeled and entered in PHPP

PHI requires 1 of 2 paths1) Model all thermal bridges enter psi values for both + and ‐2) Model and enter only thermal bridges with psi values over 001 WmK

Path 2 begs the question ndash how do I know which TBs will be over 001 WmK before Irsquove modeled them

Image source httpwwwtheblazecomblog20130124finally‐the‐answer‐sort‐of‐for‐what‐came‐first‐the‐chicken‐or‐the‐egg

Section 3 ndash Using psi values in PHPP

50

EavesMost details will have negative psi value

Rim joistAlmost always positive psi value ‐MODEL

Wall to slabfootingOnly well‐designed details will have negative psi value ‐MODEL

Footing below bearing wall or postOnly well‐designed details will have psi value lt 001 WmK‐MODEL

Roof ridgeMost details will have negative psi value

Section 3 ndash Using psi values in PHPP

51

RakeMost details will have negative psi value

Windowdoor sill on slab MODEL BUThellipCan be entered as a window sill TB + wall‐to‐slab TB (requires two separate psi values)

Window sillAlmost always positive psi value since overinsulationis difficult ndashMODEL

Window headIf overinsulated probably no need to model If not ndashMODEL

Section 3 ndash Using psi values in PHPP

52

Exterior cornerMost details will have negative psi value

Interior cornerAlmost always positive psi value ndashMODEL

Window jambIf overinsulated probably no need to model If not ndashMODEL

Wall junctionIf insulation layers are interrupted ‐MODEL

Section 3 ndash Using psi values in PHPP

53

Other places to keep in mind for possible thermal bridgesbull Plumbing stacksbull Rain pipes (interior)bull ERV vent penetrations (to the exterior)bull Sump pumpsbull Radon remediation pipes (if interior to the building)

Section 3 ndash Using psi values in PHPP

54

Section 3 ndash Using psi values in PHPP

55

Section 3 ndash Using psi values in WUFI Passive

56

Section 2 ndash Common Linear Thermal Bridges

2x6 wall no studs Ψ = ‐ 0058 WmK 2x6 wall 2‐stud Ψ = ‐ 0040 WmK

When is a performance comparison validWhen the two models being compared have the same assemblies and the same geometry ‐the only difference is at the junction Example above

40

stem wall Ψ = ‐0004 WmK FPSF (frost‐protected shallow foundation) Ψ = 0160 WmK

bull Thermal bridge at the foundation is typically the most challenging to addressbull The concrete stem wall and FPSF footing acts as a radiation fin

STEP 4 ndash Avoid accidental ldquoradiation finsrdquo

Section 2 ndash Common Linear Thermal Bridges

41

FPSF (well insulated) Ψ = 0013 WmK

Thick layers of continuous insulation can improve the performance of the detail but even

FPSF Ψ = 0160 WmK

a very well insulated FPSF is still close to the 001 WmK limit

Section 2 ndash Common Linear Thermal Bridges

STEP 4 ‐ Avoid accidental radiation fins ‐ even well‐insulated ones

42

stem wall Ψ = ‐0004 WmK Thermally broken stem wall Ψ = ‐0136 WmK

Section 2 ndash Common Linear Thermal Bridges

43

Thermally broken stem wall provides an insulated break between the stem wall and the floor slab effectively cutting off the ldquoradiation finrdquoAligning exterior insulation layers at junction of stem wall and above grade wall also helpsSTEP 5 ndash An insulated break between the exterior wall and floor slab works best

ICF parapet Ψ = 0200 WmK Foamglas thermal break Ψ = ‐0071 WmK

Another good location to cut off the radiation fin

Section 2 ndash Common Linear Thermal Bridges

44

Window positioned outside of thermal envelope Ψ = 010 WmKEffectively R‐value of window reduced by 20 ‐ 30 depending on window size

Section 2 ndash Common Linear Thermal Bridges

Window positioned on edge of thermal envelope Ψ = 004 WmKR‐value of window reduced by 5 ‐10 depending on window size

45

Window centered in plane of insulation Ψ = 002 to 003 WmKR‐value of window is almost preserved

Section 2 ndash Common Linear Thermal Bridges

46

47

Break

Section 3 ndash Using psi values in PHPP

48

How do I know which thermal bridges need to be modeled and entered in PHPP

Section 3 ndash Using psi values in PHPP

49

How do I know which thermal bridges need to be modeled and entered in PHPP

PHI requires 1 of 2 paths1) Model all thermal bridges enter psi values for both + and ‐2) Model and enter only thermal bridges with psi values over 001 WmK

Path 2 begs the question ndash how do I know which TBs will be over 001 WmK before Irsquove modeled them

Image source httpwwwtheblazecomblog20130124finally‐the‐answer‐sort‐of‐for‐what‐came‐first‐the‐chicken‐or‐the‐egg

Section 3 ndash Using psi values in PHPP

50

EavesMost details will have negative psi value

Rim joistAlmost always positive psi value ‐MODEL

Wall to slabfootingOnly well‐designed details will have negative psi value ‐MODEL

Footing below bearing wall or postOnly well‐designed details will have psi value lt 001 WmK‐MODEL

Roof ridgeMost details will have negative psi value

Section 3 ndash Using psi values in PHPP

51

RakeMost details will have negative psi value

Windowdoor sill on slab MODEL BUThellipCan be entered as a window sill TB + wall‐to‐slab TB (requires two separate psi values)

Window sillAlmost always positive psi value since overinsulationis difficult ndashMODEL

Window headIf overinsulated probably no need to model If not ndashMODEL

Section 3 ndash Using psi values in PHPP

52

Exterior cornerMost details will have negative psi value

Interior cornerAlmost always positive psi value ndashMODEL

Window jambIf overinsulated probably no need to model If not ndashMODEL

Wall junctionIf insulation layers are interrupted ‐MODEL

Section 3 ndash Using psi values in PHPP

53

Other places to keep in mind for possible thermal bridgesbull Plumbing stacksbull Rain pipes (interior)bull ERV vent penetrations (to the exterior)bull Sump pumpsbull Radon remediation pipes (if interior to the building)

Section 3 ndash Using psi values in PHPP

54

Section 3 ndash Using psi values in PHPP

55

Section 3 ndash Using psi values in WUFI Passive

56

stem wall Ψ = ‐0004 WmK FPSF (frost‐protected shallow foundation) Ψ = 0160 WmK

bull Thermal bridge at the foundation is typically the most challenging to addressbull The concrete stem wall and FPSF footing acts as a radiation fin

STEP 4 ndash Avoid accidental ldquoradiation finsrdquo

Section 2 ndash Common Linear Thermal Bridges

41

FPSF (well insulated) Ψ = 0013 WmK

Thick layers of continuous insulation can improve the performance of the detail but even

FPSF Ψ = 0160 WmK

a very well insulated FPSF is still close to the 001 WmK limit

Section 2 ndash Common Linear Thermal Bridges

STEP 4 ‐ Avoid accidental radiation fins ‐ even well‐insulated ones

42

stem wall Ψ = ‐0004 WmK Thermally broken stem wall Ψ = ‐0136 WmK

Section 2 ndash Common Linear Thermal Bridges

43

Thermally broken stem wall provides an insulated break between the stem wall and the floor slab effectively cutting off the ldquoradiation finrdquoAligning exterior insulation layers at junction of stem wall and above grade wall also helpsSTEP 5 ndash An insulated break between the exterior wall and floor slab works best

ICF parapet Ψ = 0200 WmK Foamglas thermal break Ψ = ‐0071 WmK

Another good location to cut off the radiation fin

Section 2 ndash Common Linear Thermal Bridges

44

Window positioned outside of thermal envelope Ψ = 010 WmKEffectively R‐value of window reduced by 20 ‐ 30 depending on window size

Section 2 ndash Common Linear Thermal Bridges

Window positioned on edge of thermal envelope Ψ = 004 WmKR‐value of window reduced by 5 ‐10 depending on window size

45

Window centered in plane of insulation Ψ = 002 to 003 WmKR‐value of window is almost preserved

Section 2 ndash Common Linear Thermal Bridges

46

47

Break

Section 3 ndash Using psi values in PHPP

48

How do I know which thermal bridges need to be modeled and entered in PHPP

Section 3 ndash Using psi values in PHPP

49

How do I know which thermal bridges need to be modeled and entered in PHPP

PHI requires 1 of 2 paths1) Model all thermal bridges enter psi values for both + and ‐2) Model and enter only thermal bridges with psi values over 001 WmK

Path 2 begs the question ndash how do I know which TBs will be over 001 WmK before Irsquove modeled them

Image source httpwwwtheblazecomblog20130124finally‐the‐answer‐sort‐of‐for‐what‐came‐first‐the‐chicken‐or‐the‐egg

Section 3 ndash Using psi values in PHPP

50

EavesMost details will have negative psi value

Rim joistAlmost always positive psi value ‐MODEL

Wall to slabfootingOnly well‐designed details will have negative psi value ‐MODEL

Footing below bearing wall or postOnly well‐designed details will have psi value lt 001 WmK‐MODEL

Roof ridgeMost details will have negative psi value

Section 3 ndash Using psi values in PHPP

51

RakeMost details will have negative psi value

Windowdoor sill on slab MODEL BUThellipCan be entered as a window sill TB + wall‐to‐slab TB (requires two separate psi values)

Window sillAlmost always positive psi value since overinsulationis difficult ndashMODEL

Window headIf overinsulated probably no need to model If not ndashMODEL

Section 3 ndash Using psi values in PHPP

52

Exterior cornerMost details will have negative psi value

Interior cornerAlmost always positive psi value ndashMODEL

Window jambIf overinsulated probably no need to model If not ndashMODEL

Wall junctionIf insulation layers are interrupted ‐MODEL

Section 3 ndash Using psi values in PHPP

53

Other places to keep in mind for possible thermal bridgesbull Plumbing stacksbull Rain pipes (interior)bull ERV vent penetrations (to the exterior)bull Sump pumpsbull Radon remediation pipes (if interior to the building)

Section 3 ndash Using psi values in PHPP

54

Section 3 ndash Using psi values in PHPP

55

Section 3 ndash Using psi values in WUFI Passive

56

FPSF (well insulated) Ψ = 0013 WmK

Thick layers of continuous insulation can improve the performance of the detail but even

FPSF Ψ = 0160 WmK

a very well insulated FPSF is still close to the 001 WmK limit

Section 2 ndash Common Linear Thermal Bridges

STEP 4 ‐ Avoid accidental radiation fins ‐ even well‐insulated ones

42

stem wall Ψ = ‐0004 WmK Thermally broken stem wall Ψ = ‐0136 WmK

Section 2 ndash Common Linear Thermal Bridges

43

Thermally broken stem wall provides an insulated break between the stem wall and the floor slab effectively cutting off the ldquoradiation finrdquoAligning exterior insulation layers at junction of stem wall and above grade wall also helpsSTEP 5 ndash An insulated break between the exterior wall and floor slab works best

ICF parapet Ψ = 0200 WmK Foamglas thermal break Ψ = ‐0071 WmK

Another good location to cut off the radiation fin

Section 2 ndash Common Linear Thermal Bridges

44

Window positioned outside of thermal envelope Ψ = 010 WmKEffectively R‐value of window reduced by 20 ‐ 30 depending on window size

Section 2 ndash Common Linear Thermal Bridges

Window positioned on edge of thermal envelope Ψ = 004 WmKR‐value of window reduced by 5 ‐10 depending on window size

45

Window centered in plane of insulation Ψ = 002 to 003 WmKR‐value of window is almost preserved

Section 2 ndash Common Linear Thermal Bridges

46

47

Break

Section 3 ndash Using psi values in PHPP

48

How do I know which thermal bridges need to be modeled and entered in PHPP

Section 3 ndash Using psi values in PHPP

49

How do I know which thermal bridges need to be modeled and entered in PHPP

PHI requires 1 of 2 paths1) Model all thermal bridges enter psi values for both + and ‐2) Model and enter only thermal bridges with psi values over 001 WmK

Path 2 begs the question ndash how do I know which TBs will be over 001 WmK before Irsquove modeled them

Image source httpwwwtheblazecomblog20130124finally‐the‐answer‐sort‐of‐for‐what‐came‐first‐the‐chicken‐or‐the‐egg

Section 3 ndash Using psi values in PHPP

50

EavesMost details will have negative psi value

Rim joistAlmost always positive psi value ‐MODEL

Wall to slabfootingOnly well‐designed details will have negative psi value ‐MODEL

Footing below bearing wall or postOnly well‐designed details will have psi value lt 001 WmK‐MODEL

Roof ridgeMost details will have negative psi value

Section 3 ndash Using psi values in PHPP

51

RakeMost details will have negative psi value

Windowdoor sill on slab MODEL BUThellipCan be entered as a window sill TB + wall‐to‐slab TB (requires two separate psi values)

Window sillAlmost always positive psi value since overinsulationis difficult ndashMODEL

Window headIf overinsulated probably no need to model If not ndashMODEL

Section 3 ndash Using psi values in PHPP

52

Exterior cornerMost details will have negative psi value

Interior cornerAlmost always positive psi value ndashMODEL

Window jambIf overinsulated probably no need to model If not ndashMODEL

Wall junctionIf insulation layers are interrupted ‐MODEL

Section 3 ndash Using psi values in PHPP

53

Other places to keep in mind for possible thermal bridgesbull Plumbing stacksbull Rain pipes (interior)bull ERV vent penetrations (to the exterior)bull Sump pumpsbull Radon remediation pipes (if interior to the building)

Section 3 ndash Using psi values in PHPP

54

Section 3 ndash Using psi values in PHPP

55

Section 3 ndash Using psi values in WUFI Passive

56

stem wall Ψ = ‐0004 WmK Thermally broken stem wall Ψ = ‐0136 WmK

Section 2 ndash Common Linear Thermal Bridges

43

Thermally broken stem wall provides an insulated break between the stem wall and the floor slab effectively cutting off the ldquoradiation finrdquoAligning exterior insulation layers at junction of stem wall and above grade wall also helpsSTEP 5 ndash An insulated break between the exterior wall and floor slab works best

ICF parapet Ψ = 0200 WmK Foamglas thermal break Ψ = ‐0071 WmK

Another good location to cut off the radiation fin

Section 2 ndash Common Linear Thermal Bridges

44

Window positioned outside of thermal envelope Ψ = 010 WmKEffectively R‐value of window reduced by 20 ‐ 30 depending on window size

Section 2 ndash Common Linear Thermal Bridges

Window positioned on edge of thermal envelope Ψ = 004 WmKR‐value of window reduced by 5 ‐10 depending on window size

45

Window centered in plane of insulation Ψ = 002 to 003 WmKR‐value of window is almost preserved

Section 2 ndash Common Linear Thermal Bridges

46

47

Break

Section 3 ndash Using psi values in PHPP

48

How do I know which thermal bridges need to be modeled and entered in PHPP

Section 3 ndash Using psi values in PHPP

49

How do I know which thermal bridges need to be modeled and entered in PHPP

PHI requires 1 of 2 paths1) Model all thermal bridges enter psi values for both + and ‐2) Model and enter only thermal bridges with psi values over 001 WmK

Path 2 begs the question ndash how do I know which TBs will be over 001 WmK before Irsquove modeled them

Image source httpwwwtheblazecomblog20130124finally‐the‐answer‐sort‐of‐for‐what‐came‐first‐the‐chicken‐or‐the‐egg

Section 3 ndash Using psi values in PHPP

50

EavesMost details will have negative psi value

Rim joistAlmost always positive psi value ‐MODEL

Wall to slabfootingOnly well‐designed details will have negative psi value ‐MODEL

Footing below bearing wall or postOnly well‐designed details will have psi value lt 001 WmK‐MODEL

Roof ridgeMost details will have negative psi value

Section 3 ndash Using psi values in PHPP

51

RakeMost details will have negative psi value

Windowdoor sill on slab MODEL BUThellipCan be entered as a window sill TB + wall‐to‐slab TB (requires two separate psi values)

Window sillAlmost always positive psi value since overinsulationis difficult ndashMODEL

Window headIf overinsulated probably no need to model If not ndashMODEL

Section 3 ndash Using psi values in PHPP

52

Exterior cornerMost details will have negative psi value

Interior cornerAlmost always positive psi value ndashMODEL

Window jambIf overinsulated probably no need to model If not ndashMODEL

Wall junctionIf insulation layers are interrupted ‐MODEL

Section 3 ndash Using psi values in PHPP

53

Other places to keep in mind for possible thermal bridgesbull Plumbing stacksbull Rain pipes (interior)bull ERV vent penetrations (to the exterior)bull Sump pumpsbull Radon remediation pipes (if interior to the building)

Section 3 ndash Using psi values in PHPP

54

Section 3 ndash Using psi values in PHPP

55

Section 3 ndash Using psi values in WUFI Passive

56

ICF parapet Ψ = 0200 WmK Foamglas thermal break Ψ = ‐0071 WmK

Another good location to cut off the radiation fin

Section 2 ndash Common Linear Thermal Bridges

44

Window positioned outside of thermal envelope Ψ = 010 WmKEffectively R‐value of window reduced by 20 ‐ 30 depending on window size

Section 2 ndash Common Linear Thermal Bridges

Window positioned on edge of thermal envelope Ψ = 004 WmKR‐value of window reduced by 5 ‐10 depending on window size

45

Window centered in plane of insulation Ψ = 002 to 003 WmKR‐value of window is almost preserved

Section 2 ndash Common Linear Thermal Bridges

46

47

Break

Section 3 ndash Using psi values in PHPP

48

How do I know which thermal bridges need to be modeled and entered in PHPP

Section 3 ndash Using psi values in PHPP

49

How do I know which thermal bridges need to be modeled and entered in PHPP

PHI requires 1 of 2 paths1) Model all thermal bridges enter psi values for both + and ‐2) Model and enter only thermal bridges with psi values over 001 WmK

Path 2 begs the question ndash how do I know which TBs will be over 001 WmK before Irsquove modeled them

Image source httpwwwtheblazecomblog20130124finally‐the‐answer‐sort‐of‐for‐what‐came‐first‐the‐chicken‐or‐the‐egg

Section 3 ndash Using psi values in PHPP

50

EavesMost details will have negative psi value

Rim joistAlmost always positive psi value ‐MODEL

Wall to slabfootingOnly well‐designed details will have negative psi value ‐MODEL

Footing below bearing wall or postOnly well‐designed details will have psi value lt 001 WmK‐MODEL

Roof ridgeMost details will have negative psi value

Section 3 ndash Using psi values in PHPP

51

RakeMost details will have negative psi value

Windowdoor sill on slab MODEL BUThellipCan be entered as a window sill TB + wall‐to‐slab TB (requires two separate psi values)

Window sillAlmost always positive psi value since overinsulationis difficult ndashMODEL

Window headIf overinsulated probably no need to model If not ndashMODEL

Section 3 ndash Using psi values in PHPP

52

Exterior cornerMost details will have negative psi value

Interior cornerAlmost always positive psi value ndashMODEL

Window jambIf overinsulated probably no need to model If not ndashMODEL

Wall junctionIf insulation layers are interrupted ‐MODEL

Section 3 ndash Using psi values in PHPP

53

Other places to keep in mind for possible thermal bridgesbull Plumbing stacksbull Rain pipes (interior)bull ERV vent penetrations (to the exterior)bull Sump pumpsbull Radon remediation pipes (if interior to the building)

Section 3 ndash Using psi values in PHPP

54

Section 3 ndash Using psi values in PHPP

55

Section 3 ndash Using psi values in WUFI Passive

56

Window positioned outside of thermal envelope Ψ = 010 WmKEffectively R‐value of window reduced by 20 ‐ 30 depending on window size

Section 2 ndash Common Linear Thermal Bridges

Window positioned on edge of thermal envelope Ψ = 004 WmKR‐value of window reduced by 5 ‐10 depending on window size

45

Window centered in plane of insulation Ψ = 002 to 003 WmKR‐value of window is almost preserved

Section 2 ndash Common Linear Thermal Bridges

46

47

Break

Section 3 ndash Using psi values in PHPP

48

How do I know which thermal bridges need to be modeled and entered in PHPP

Section 3 ndash Using psi values in PHPP

49

How do I know which thermal bridges need to be modeled and entered in PHPP

PHI requires 1 of 2 paths1) Model all thermal bridges enter psi values for both + and ‐2) Model and enter only thermal bridges with psi values over 001 WmK

Path 2 begs the question ndash how do I know which TBs will be over 001 WmK before Irsquove modeled them

Image source httpwwwtheblazecomblog20130124finally‐the‐answer‐sort‐of‐for‐what‐came‐first‐the‐chicken‐or‐the‐egg

Section 3 ndash Using psi values in PHPP

50

EavesMost details will have negative psi value

Rim joistAlmost always positive psi value ‐MODEL

Wall to slabfootingOnly well‐designed details will have negative psi value ‐MODEL

Footing below bearing wall or postOnly well‐designed details will have psi value lt 001 WmK‐MODEL

Roof ridgeMost details will have negative psi value

Section 3 ndash Using psi values in PHPP

51

RakeMost details will have negative psi value

Windowdoor sill on slab MODEL BUThellipCan be entered as a window sill TB + wall‐to‐slab TB (requires two separate psi values)

Window sillAlmost always positive psi value since overinsulationis difficult ndashMODEL

Window headIf overinsulated probably no need to model If not ndashMODEL

Section 3 ndash Using psi values in PHPP

52

Exterior cornerMost details will have negative psi value

Interior cornerAlmost always positive psi value ndashMODEL

Window jambIf overinsulated probably no need to model If not ndashMODEL

Wall junctionIf insulation layers are interrupted ‐MODEL

Section 3 ndash Using psi values in PHPP

53

Other places to keep in mind for possible thermal bridgesbull Plumbing stacksbull Rain pipes (interior)bull ERV vent penetrations (to the exterior)bull Sump pumpsbull Radon remediation pipes (if interior to the building)

Section 3 ndash Using psi values in PHPP

54

Section 3 ndash Using psi values in PHPP

55

Section 3 ndash Using psi values in WUFI Passive

56

Window centered in plane of insulation Ψ = 002 to 003 WmKR‐value of window is almost preserved

Section 2 ndash Common Linear Thermal Bridges

46

47

Break

Section 3 ndash Using psi values in PHPP

48

How do I know which thermal bridges need to be modeled and entered in PHPP

Section 3 ndash Using psi values in PHPP

49

How do I know which thermal bridges need to be modeled and entered in PHPP

PHI requires 1 of 2 paths1) Model all thermal bridges enter psi values for both + and ‐2) Model and enter only thermal bridges with psi values over 001 WmK

Path 2 begs the question ndash how do I know which TBs will be over 001 WmK before Irsquove modeled them

Image source httpwwwtheblazecomblog20130124finally‐the‐answer‐sort‐of‐for‐what‐came‐first‐the‐chicken‐or‐the‐egg

Section 3 ndash Using psi values in PHPP

50

EavesMost details will have negative psi value

Rim joistAlmost always positive psi value ‐MODEL

Wall to slabfootingOnly well‐designed details will have negative psi value ‐MODEL

Footing below bearing wall or postOnly well‐designed details will have psi value lt 001 WmK‐MODEL

Roof ridgeMost details will have negative psi value

Section 3 ndash Using psi values in PHPP

51

RakeMost details will have negative psi value

Windowdoor sill on slab MODEL BUThellipCan be entered as a window sill TB + wall‐to‐slab TB (requires two separate psi values)

Window sillAlmost always positive psi value since overinsulationis difficult ndashMODEL

Window headIf overinsulated probably no need to model If not ndashMODEL

Section 3 ndash Using psi values in PHPP

52

Exterior cornerMost details will have negative psi value

Interior cornerAlmost always positive psi value ndashMODEL

Window jambIf overinsulated probably no need to model If not ndashMODEL

Wall junctionIf insulation layers are interrupted ‐MODEL

Section 3 ndash Using psi values in PHPP

53

Other places to keep in mind for possible thermal bridgesbull Plumbing stacksbull Rain pipes (interior)bull ERV vent penetrations (to the exterior)bull Sump pumpsbull Radon remediation pipes (if interior to the building)

Section 3 ndash Using psi values in PHPP

54

Section 3 ndash Using psi values in PHPP

55

Section 3 ndash Using psi values in WUFI Passive

56

47

Break

Section 3 ndash Using psi values in PHPP

48

How do I know which thermal bridges need to be modeled and entered in PHPP

Section 3 ndash Using psi values in PHPP

49

How do I know which thermal bridges need to be modeled and entered in PHPP

PHI requires 1 of 2 paths1) Model all thermal bridges enter psi values for both + and ‐2) Model and enter only thermal bridges with psi values over 001 WmK

Path 2 begs the question ndash how do I know which TBs will be over 001 WmK before Irsquove modeled them

Image source httpwwwtheblazecomblog20130124finally‐the‐answer‐sort‐of‐for‐what‐came‐first‐the‐chicken‐or‐the‐egg

Section 3 ndash Using psi values in PHPP

50

EavesMost details will have negative psi value

Rim joistAlmost always positive psi value ‐MODEL

Wall to slabfootingOnly well‐designed details will have negative psi value ‐MODEL

Footing below bearing wall or postOnly well‐designed details will have psi value lt 001 WmK‐MODEL

Roof ridgeMost details will have negative psi value

Section 3 ndash Using psi values in PHPP

51

RakeMost details will have negative psi value

Windowdoor sill on slab MODEL BUThellipCan be entered as a window sill TB + wall‐to‐slab TB (requires two separate psi values)

Window sillAlmost always positive psi value since overinsulationis difficult ndashMODEL

Window headIf overinsulated probably no need to model If not ndashMODEL

Section 3 ndash Using psi values in PHPP

52

Exterior cornerMost details will have negative psi value

Interior cornerAlmost always positive psi value ndashMODEL

Window jambIf overinsulated probably no need to model If not ndashMODEL

Wall junctionIf insulation layers are interrupted ‐MODEL

Section 3 ndash Using psi values in PHPP

53

Other places to keep in mind for possible thermal bridgesbull Plumbing stacksbull Rain pipes (interior)bull ERV vent penetrations (to the exterior)bull Sump pumpsbull Radon remediation pipes (if interior to the building)

Section 3 ndash Using psi values in PHPP

54

Section 3 ndash Using psi values in PHPP

55

Section 3 ndash Using psi values in WUFI Passive

56

Section 3 ndash Using psi values in PHPP

48

How do I know which thermal bridges need to be modeled and entered in PHPP

Section 3 ndash Using psi values in PHPP

49

How do I know which thermal bridges need to be modeled and entered in PHPP

PHI requires 1 of 2 paths1) Model all thermal bridges enter psi values for both + and ‐2) Model and enter only thermal bridges with psi values over 001 WmK

Path 2 begs the question ndash how do I know which TBs will be over 001 WmK before Irsquove modeled them

Image source httpwwwtheblazecomblog20130124finally‐the‐answer‐sort‐of‐for‐what‐came‐first‐the‐chicken‐or‐the‐egg

Section 3 ndash Using psi values in PHPP

50

EavesMost details will have negative psi value

Rim joistAlmost always positive psi value ‐MODEL

Wall to slabfootingOnly well‐designed details will have negative psi value ‐MODEL

Footing below bearing wall or postOnly well‐designed details will have psi value lt 001 WmK‐MODEL

Roof ridgeMost details will have negative psi value

Section 3 ndash Using psi values in PHPP

51

RakeMost details will have negative psi value

Windowdoor sill on slab MODEL BUThellipCan be entered as a window sill TB + wall‐to‐slab TB (requires two separate psi values)

Window sillAlmost always positive psi value since overinsulationis difficult ndashMODEL

Window headIf overinsulated probably no need to model If not ndashMODEL

Section 3 ndash Using psi values in PHPP

52

Exterior cornerMost details will have negative psi value

Interior cornerAlmost always positive psi value ndashMODEL

Window jambIf overinsulated probably no need to model If not ndashMODEL

Wall junctionIf insulation layers are interrupted ‐MODEL

Section 3 ndash Using psi values in PHPP

53

Other places to keep in mind for possible thermal bridgesbull Plumbing stacksbull Rain pipes (interior)bull ERV vent penetrations (to the exterior)bull Sump pumpsbull Radon remediation pipes (if interior to the building)

Section 3 ndash Using psi values in PHPP

54

Section 3 ndash Using psi values in PHPP

55

Section 3 ndash Using psi values in WUFI Passive

56

Section 3 ndash Using psi values in PHPP

49

How do I know which thermal bridges need to be modeled and entered in PHPP

PHI requires 1 of 2 paths1) Model all thermal bridges enter psi values for both + and ‐2) Model and enter only thermal bridges with psi values over 001 WmK

Path 2 begs the question ndash how do I know which TBs will be over 001 WmK before Irsquove modeled them

Image source httpwwwtheblazecomblog20130124finally‐the‐answer‐sort‐of‐for‐what‐came‐first‐the‐chicken‐or‐the‐egg

Section 3 ndash Using psi values in PHPP

50

EavesMost details will have negative psi value

Rim joistAlmost always positive psi value ‐MODEL

Wall to slabfootingOnly well‐designed details will have negative psi value ‐MODEL

Footing below bearing wall or postOnly well‐designed details will have psi value lt 001 WmK‐MODEL

Roof ridgeMost details will have negative psi value

Section 3 ndash Using psi values in PHPP

51

RakeMost details will have negative psi value

Windowdoor sill on slab MODEL BUThellipCan be entered as a window sill TB + wall‐to‐slab TB (requires two separate psi values)

Window sillAlmost always positive psi value since overinsulationis difficult ndashMODEL

Window headIf overinsulated probably no need to model If not ndashMODEL

Section 3 ndash Using psi values in PHPP

52

Exterior cornerMost details will have negative psi value

Interior cornerAlmost always positive psi value ndashMODEL

Window jambIf overinsulated probably no need to model If not ndashMODEL

Wall junctionIf insulation layers are interrupted ‐MODEL

Section 3 ndash Using psi values in PHPP

53

Other places to keep in mind for possible thermal bridgesbull Plumbing stacksbull Rain pipes (interior)bull ERV vent penetrations (to the exterior)bull Sump pumpsbull Radon remediation pipes (if interior to the building)

Section 3 ndash Using psi values in PHPP

54

Section 3 ndash Using psi values in PHPP

55

Section 3 ndash Using psi values in WUFI Passive

56

Section 3 ndash Using psi values in PHPP

50

EavesMost details will have negative psi value

Rim joistAlmost always positive psi value ‐MODEL

Wall to slabfootingOnly well‐designed details will have negative psi value ‐MODEL

Footing below bearing wall or postOnly well‐designed details will have psi value lt 001 WmK‐MODEL

Roof ridgeMost details will have negative psi value

Section 3 ndash Using psi values in PHPP

51

RakeMost details will have negative psi value

Windowdoor sill on slab MODEL BUThellipCan be entered as a window sill TB + wall‐to‐slab TB (requires two separate psi values)

Window sillAlmost always positive psi value since overinsulationis difficult ndashMODEL

Window headIf overinsulated probably no need to model If not ndashMODEL

Section 3 ndash Using psi values in PHPP

52

Exterior cornerMost details will have negative psi value

Interior cornerAlmost always positive psi value ndashMODEL

Window jambIf overinsulated probably no need to model If not ndashMODEL

Wall junctionIf insulation layers are interrupted ‐MODEL

Section 3 ndash Using psi values in PHPP

53

Other places to keep in mind for possible thermal bridgesbull Plumbing stacksbull Rain pipes (interior)bull ERV vent penetrations (to the exterior)bull Sump pumpsbull Radon remediation pipes (if interior to the building)

Section 3 ndash Using psi values in PHPP

54

Section 3 ndash Using psi values in PHPP

55

Section 3 ndash Using psi values in WUFI Passive

56

Section 3 ndash Using psi values in PHPP

51

RakeMost details will have negative psi value

Windowdoor sill on slab MODEL BUThellipCan be entered as a window sill TB + wall‐to‐slab TB (requires two separate psi values)

Window sillAlmost always positive psi value since overinsulationis difficult ndashMODEL

Window headIf overinsulated probably no need to model If not ndashMODEL

Section 3 ndash Using psi values in PHPP

52

Exterior cornerMost details will have negative psi value

Interior cornerAlmost always positive psi value ndashMODEL

Window jambIf overinsulated probably no need to model If not ndashMODEL

Wall junctionIf insulation layers are interrupted ‐MODEL

Section 3 ndash Using psi values in PHPP

53

Other places to keep in mind for possible thermal bridgesbull Plumbing stacksbull Rain pipes (interior)bull ERV vent penetrations (to the exterior)bull Sump pumpsbull Radon remediation pipes (if interior to the building)

Section 3 ndash Using psi values in PHPP

54

Section 3 ndash Using psi values in PHPP

55

Section 3 ndash Using psi values in WUFI Passive

56

Section 3 ndash Using psi values in PHPP

52

Exterior cornerMost details will have negative psi value

Interior cornerAlmost always positive psi value ndashMODEL

Window jambIf overinsulated probably no need to model If not ndashMODEL

Wall junctionIf insulation layers are interrupted ‐MODEL

Section 3 ndash Using psi values in PHPP

53

Other places to keep in mind for possible thermal bridgesbull Plumbing stacksbull Rain pipes (interior)bull ERV vent penetrations (to the exterior)bull Sump pumpsbull Radon remediation pipes (if interior to the building)

Section 3 ndash Using psi values in PHPP

54

Section 3 ndash Using psi values in PHPP

55

Section 3 ndash Using psi values in WUFI Passive

56

Section 3 ndash Using psi values in PHPP

53

Other places to keep in mind for possible thermal bridgesbull Plumbing stacksbull Rain pipes (interior)bull ERV vent penetrations (to the exterior)bull Sump pumpsbull Radon remediation pipes (if interior to the building)

Section 3 ndash Using psi values in PHPP

54

Section 3 ndash Using psi values in PHPP

55

Section 3 ndash Using psi values in WUFI Passive

56

Section 3 ndash Using psi values in PHPP

54

Section 3 ndash Using psi values in PHPP

55

Section 3 ndash Using psi values in WUFI Passive

56

Section 3 ndash Using psi values in PHPP

55

Section 3 ndash Using psi values in WUFI Passive

56

Section 3 ndash Using psi values in WUFI Passive

56