aia convention 2015 bryan - third level design

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Designing High Performance Walls for Cold Climates www.third-level.com

Designing High Performance Wallsfor Cold Climates (like ours)

Dave Bryan AIA, LEED APThird Level DesignRolf Jacobson LEED AP, CPHCSkandia Design & Consulting


Learning Objectives:Attendees will may be able to:o Outline the major building science topics that must be considered

when designing a highly insulated envelope.o Categorize the major options and trade-offs for insulating high R-

value frame wall assemblies.o Explain the basics of hygrothermal modeling and the need for it.o Recognize assembly characteristics that affect moisture risk.


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2005 2010 2015 2020 2025 2030

Estimated Energy Use Reduction relative to the2006 Energy Code (ASHRAE 90.1 2004 & IECC 2006)

Architecture 2030 2030 Target w/o 15% PV ASHRAE 90.1 & IECC

2012 IECC adoption in MN


Typical reductions from: Mitigating CO2 Emissions from Energy Use in the World's Buildings, Urge-Vorsatz, Harvey, Mirasagedis, Levine, 2007

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R‐value Requirementsfor Wall Assemblies Climate Zone 6

Previous MN ASHRAE 90.1 2010 Increase from IECC 2012Commercial : Energy Code IECC 2012 IECC 2006 PrescriptiveWalls, metal-framed R11.9 R15.6 31% R13 + 7.5 ciWalls, metal-framed, R R17.5 47% R13 + 7.5 ciWalls, wood-framed R11.2 R19.6 75% R13 + 7.5 ci

or R20 + 3.8 ci

Previous MN Minnesota 2015 Increase from MinnesotaResidential : Energy Code Residential Energy Code IECC 2006 Prescriptive Walls, metal-framed R15.6 R20.8 33% R13 + 8.9ci, etc.Walls, wood-framed R15.6 R20.8 33% R20, R13 + 5 ci

U and R values are “clear wall” numbers


How do we achieve R30 plus walls?


Generic Wall Components & Functions


Moisture Movement Mechanisms

from: “Insulations, Sheathings and Vapor Diffusion Retarders”, Building Science Corporation 2003

Higher air pressure Lower air pressure

Air flow through visible cracks and holesWater vapor is carried by the air

Higher water vapor concentration

Lower water vapor concentration

No air flowWater vapor flow through tiny pores

Control with Air BarrierSmall holes & seams must be sealed.

Continuity important

Control with Vapor RetarderSmall holes & seams not too important if

there is a good air barrier

Both Air Barrier and Vapor Retarder are important

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Forces Creating Air Movement

From Air Leakage Control in Multi-Unit Residential Buildings, RDH


Convective Air Loops Reduce Effective Insulation Value

Building Science Corporation, BSD-011 Thermal Control


Alternative Air Barrier Locations

From Building Science Corp, BSI-084,40 Years of Air Barriers


Air Barrier Strategies – Interior1. Sealed polyethylene Approach• Caulk polyethylene vapor barrier to framing at

perimeter and joints• Seal at electrical boxes and other penetrations• Maintaining continuity between floors and at

partition walls is difficult• Unsuitable for taller buildings because of wind

loads and lack of support by cavity insulation• Easily damaged during construction

2. Airtight Drywall Approach• Caulk gypsum board to framing or vapor

barrier at perimeter and joints• Seal at electrical boxes and other penetrations• Maintaining continuity between floors and at

partition walls is difficult• Accessible and easy to repair during blower

door testing

3. Sealing sheathing from inside stud cavity• Closed cell or open cell spray foam insulation• Provides both insulation and air barrier• Airtightness is susceptible to building movement

and long term foam shrinkage• Spray foam cannot seal small gaps at framing• Flexible spray sealants can seal gaps up to 3/8”

without using backer rod• To seal leaks, blower door testing can be

performed without drywall and cavity insulation

Knauf Ecoseal Plus

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Air Barrier Strategies – Exterior4. Taped synthetic house wrap sheeting• Difficult to avoid wind damage to mechanically

attached sheeting during construction• If not sandwiched between sheathing and

cladding or exterior insulation, may pump in wind.

• Possible damage by brick ties• Not recommended for high rise use• Relatively inexpensive

5. Taped exterior insulation• Compatible tapes are available• Concerns about long-term adhesion with

insulation movement and aging• Is a water barrier still needed?

6. Adhesive-backed weather/air barriers• Vapor permeable membranes are available• Resistant to fastener damage• Relatively expensive

7. Liquid or fluid-applied air/weather barriers• Includes material to bridge sheathing joints• Vapor permeable coatings are available• Compatible with EIFS• Relatively expensive

8. Sealed sheathing joints• Compatible sealants and tapes are available• Less expensive than liquid/fluid-applied or

adhesive-backed systems• Need additional water barrier unless sheathing is

coated for water resistance


From a MN BEC presentation by Graham Finch at RDH


Worst Case Air Leakage Scenario

High Damage PotentialLow Damage Potential

Fraunhofer Institute

1. air permeable cavity insulation

2. major vapor retarder and/or air barrier failure

3. moist room air reaches cold, moisture sensitive sheathing


Window Location and Control Layers Must Be Coordinated

from Thermal Bridges Redux, Building Science Corp. 2012

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Blower Door Infiltration Targets

Description Residential CommercialACH @ 50 Pascals CFM/Sq Ft Surface @ 75 Pascals

Typical Existing Building 24 (6 since1993) 1.40

Energy Code 3.0 .40 (testing is optional)

Army Corps of Engineers .25

Readily achieved with reasonable care 3.0 .15

Reliably achieved with significant effort 1.5

Passive House 0.6

Residential equivalent of .4 cfm/ft2 at 75 Pa ~ 3 to 5 air changes/hour at 50 Pa


Class 1 Vapor Barriers Class 2 Vapor Retarders Class 3 Vapor Retarders0 to .1 perms .1 to 1 perms 1 to 10 perms

Polyethylene Sheet Vapor Barrier Paint Latex Paint

Aluminum Foil Oil-based Paint, 3 coats Oil-based Paint, primer +1coat

most Bituminous Sheet Closed-cell Polyurethane Closed-cell PolyurethaneMaterials spray foam, thicker than 2” spray foam, less than 1”

Vinyl Wall Covering, Extruded Polystyrene, Extruded Polystyrene, un-perforated unfaced, thicker than 1” unfaced, less than 1”

Hot Asphalt Roofing Kraft Paper (nominal) Kraft Paper (NAHB measured)

Smart Vapor Retarders Open-cell Polyurethane (Membrain, Intello) spray foam (Icynene)

Building codes generally require Class I or Class II vapor retarders for Climate Zones 5 through 8

Vapor Permeability of Selected Building Materials


Smart Vapor Retarder Performance

Certainteed


Diameter of the circle is proportional to water vapor content of the air

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JAN FEB MAR APR MAY JUN JUL AUG SEP OCT NOV DEC

Indoor Air: 40% winter RH to 60% summer RHIndoor Air: 40% winter RH to 50% summer RHMinneapolis, MNMiami, Fl

Dewpo

int, F.

Differential between Interior and Exterior Dewpoints




Extrud

ed polystyrene

, con

tinuo

us

Expa

nded

polystyrene

, con

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Mineral W

ool, 8 lbs/ft3, con

tinuo

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Polyisocyanu

rate, con

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cell spray fo

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ood stud

s

Fibe

rglass batt, woo

d stud

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lown, woo

d stud

s

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rglass, sprayed

, woo

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cell spray fo

am, m

etal stud

s

Fibe

rglass batt, metal stud

s

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lose, b

lown, m

etal stud

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Fibe

rglass, sprayed

, metal stud

s

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Insulation and Assembly Type

Installed Co

st per Effe

ctive R‐value

Relative Cost Effectiveness of Wall Insulation

Exterior Insulation Between Wood Studs Between Metal Studs


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enho

use

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Sav

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Extr

uded

Pol

ysty

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l Pol

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house Gas, 50 yr

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Savings are for reducing natural gas use by adding R10 insulation to a base R15 wall

Greenhouse Gas Savings and Emissionsfor Exterior Insulation in Climate Zone 6

60 % of Savings

37 % of Savings

Based on “Total Climatic Impact of Insulation”, David White, 2011

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General Approaches to Frame Wall Insulation


What can we achieve with only stud cavity insulation?


Nominal Correction Actual Insulation Type R-value Factor R-value Cavity Insulation 7.25” x R4 /inch = 30.0 ?? ??Other Materials 2.5 1.0 2.5

Clear Wall R-value ??

Wood studs, 2x8, 16” o.c.

Nominal Correction Actual Insulation Type R-value Factor R-value Cavity Insulation 7.25” x R4 /inch = 30.0 ?? ??Other Materials 2.5 1.0 2.5

Clear Wall R-value ??

Metal studs, 1 5/8” x 7.25”, 16” o.c



Advanced Framing

Conventional framing with 2x6’s 16” o.c.Framing factor: 25%Clear wall R-value: 17.9

Conventional framing with 2x6’s 24” o.c.Framing factor: 20%Clear wall R-value: 18.3

Advanced framing:Framing factor: 15%Clear wall R-value: 19.0

Less labor, less lumber, higher R-values

Building Science Corp, BSI-030 Advanced Framing

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Stud Spacing, in.

Stud Cavity Insulation Effectiveness for full cavity fill, from EZFRAME, California Energy Commission

2x4 wood studs 2x6 wood studs 2x8 wood studs2x4 metal studs, 20 Ga. 2x6 metal studs, 20 Ga. 2x8 metal studs, 20 Ga.

See ASHRAE 90.1, Tables A3.3 & A3.4


Nominal Correction Actual Insulation Type R-value Factor R-value Cavity Insulation 7.25” x R4 /inch = 30.0 81% 24.3Other Materials 2.5 1.0 2.5

Clear Wall R-value 26.9




Metal studs, 1 5/8” x 7.25”, 16” o.c



How do we design energy efficient building enclosures that avoid problems with mold, rot and corrosion?

How we used to do it:Consider examples of local buildingsConsult best practices checklistComply with building codesGuess the rest !


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Condensation Analysis Shortcomings

Requires guessing an appropriate static outdoor temperature

Does not address:o Moisture storage capacity or permeability of materialso Seasonal variation in indoor and outdoor temperature and humidityo Time dependent nature of wetting and drying cycleso Driving rain penetrationo Relative tightness or leakiness of assemblieso Vapor barrier typeo Solar radiation and surface orientationo Condensation versus frost

Assumes implicitly that damage does not occur until liquid water is present


Damage Threshold Criteria

Structural damage of wood products:o Limit moisture content of wood products to 18% peak (80% to 85% R.H.)

Corrosion of metals: o Keep the surface of metals < 80% R.H.

for any 30 day period (unless specific material information is available)

Identify moisture sensitive materials and critical components

Corrosion Rates vs RH, Harriman, 2003

Structural damage of gypsum products:o Limit moisture content of fiberglass-faced gypsum to 90% to 95% R.H.

Mold Growth (ASHRAE 160):o 30 day running surface temp average

< 80% RH when between 41 and 104 F.


Sorption Curve for Common Building Materials

www.buildingscience.com


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An analytical tool for designing building assemblies to:

o Control moisture o Reduce the risk of mold, rot and corrosion

Allows fine-tuning assemblies for longevity and cost-effectiveness

Allows sensitivity analysis to determine critical variables:o Vapor retarder typeo Insulation quantity, type and locationo Sheathing typeo Air-tightness of assemblieso Water and Air barrier permeabilityo Natural ventilation of wall and roof cavitieso Interior relative humidity

HYGROTHERMAL MODELING with WUFI


Designing High Performance Walls for Cold Climates www.third-level.com Designing High Performance Walls for Cold Climates www.third-level.com

Wind-Driven Rain and Building Envelopes

Perfect building assemblies exist only on paper

Most wall claddings and many types of roof claddings leak

Moisture-tolerant enclosures must be designed to deal with water that penetrates the cladding

ASHRAE Standard 160 Criteria for Moisture Control in Buildings requires walls to withstand 1% of wind-driven rain penetrating the cladding

Modeled and Measured Drainage, Storage and Drying behind Cladding Systems, Straube, 2007

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Minneapolis

Driving Rain Varies Tremendously by Region

BostonMontpelier

Zone 6 Zone 6 Zone 5

Exterior Climate


5/8”

gyp

sum

boa

rd

with

late

x p

aint

Example of WUFI Wall Section Input


Interior Climate


Fraunhofer Institute, Holzkirchen, Germany: Building Mold and Fungi Studies

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Initial construction moisture in interior gypsum board dries gradually over a three year cycle

Interior gypsum board annually cycles back into the mold growth danger zone

Good RH/Temp Data Points Bad RH/Temp Data Points

Time Sequence of Data Points: yellow to green to black


WUFI Limitations

Results are sensitive to material propertieso The requisite material properties are very detailed o Complete data rarely available from manufacturerso Must use standard WUFI library and modify as needed

Results are very sensitive to indoor relative humidityo Varies by building use, airtightness, climate and user activity

No local active group or third party operation & reference manualo Must rely on personal research of available literature and WUFI forums

Materials meeting the same specifications can exhibit significant variation in physical properties (i.e. brick)

Most assemblies aren’t homogeneous and the WUFI version in common use is one-dimensional


WUFI 2D Stud Wall ComparisonWood Stud Wall Metal Stud Wall

WUFI 1D center of sheathingSame both cases







Metal studs, 1 5/8” x 7.25”, 16” o.c


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Legacy 2x8 Wallfiberglass insulation, plywood sheathing, polyethylene vapor barrier,

20% winter RH, poor air barrier

Sheathing moisture content


Sheathing relative humidity and temperature

Legacy 2x8 Wallfiberglass insulation, plywood sheathing, polyethylene vapor barrier,

20% winter RH, poor air barrier


2x8 Wall – current conditionsfiberglass insulation, plywood sheathing, polyethylene vapor barrier

40% interior winter RH andpoor air barrier

40% interior winter RH andresidential code-compliant

barrier


Double Stud Wall

Building America High–R Walls Case Study Analysis

For R30 clear wall:3” gap for wood studs4” gap for steel studs

High R with no foam

Could also be behind gyp.bd.Air barrier location?

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Double Stud Wall



High R with no foam

Why?Lower GWPFewer air pollutantsNo cantilevered claddingNo thermal bridge at studs

But: Uses extra floorspaceNo thermal break at floorsNeed good moisture control

Could also be behind gyp.bd.Air barrier location?


Hollis, New Hampshire Montessori School

12” thick double stud walls with dense pack cellulose, R41. 15% energy consumption of comparable code-compliant schools. Meets Passive House standards.10% additional construction costs with 3 year payback.


Double Stud Wall


High R with no foam

40% to 60% interior RH9” dense pack celluloseSmart vapor retarderFiberboard sheathing3 ach @ 50 Pa infiltrationTyvek water barrierFiber cement siding



Double Wall Sheathing Conditionsfor 9” cellulose, Tyvek, fiberboard sheathing, smart vapor retarder, unvented

ASHRAE 160: 30 day mold criteria failure hours/year:

3933 (45% of hours)

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Modeled and Measured Drainage, Storage and Drying behind Cladding Systems, Straube, 2007

WUFI allows simulation of the effectiveness ofNaturally-Ventilated Wall and Roof Cavities


Double Wall Sheathing Conditionsfor 9” cellulose, Tyvek, fiberboard sheathing, smart vapor retarder, vented


355 (4.1% of hours)


Foam insulation or mineral wool board

“Perfect Wall”


• NFPA 285‐06, Evaluation of Flammability Characteristics of Exterior, Nonload‐bearing Wall Assemblies Containing Combustible Components (IBC 2603.5.5) .

• Applies to non‐combustible buildings (Type I, II, III, IV)Typically this means buildings larger than 25,000 square feet

• Requires expensive fire testing of the exact assembly proposed in the design

• Some foam insulation manufactures have tested assembliesDow and Hunter, for example

• Must follow manufacturer’s detailsXPS and EPS require fire blocking around openings and don’t play well with metal cladding. Polyisocyanurate is more forgiving.

• Also applies to WRB and combustible cladding in buildings over 40 feet tallhigh pressure laminates, fiber reinforced polymers, metal composites

Exterior Foam InsulationFire Considerations

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Design an R30 metal stud wall (2x6’s,16”o.c.)

Nominal Correction Actual Poliso (R5.4)Insulation Type R-value Factor R-value ThicknessStud Air Space .8 1.0 .8Other Materials 2.5 1.0 2.5“Continuous” Exterior Insulation 26.7 1.0 26.7 ~5” (too thick?)

Total Wall R-value 30.0

Alternative: 8” thick EPS (expanded polystyrene) SIP panels

EIFS: 4” max. expanded polystyrene = ~ R18 (not compliant with residential code)

Case 1: Assume stud cavity has no insulation

The “Actual R-value” is the “clear wall” R-value for this assembly


Vertical Furring Strips on Rigid Insulation

Pros:o Thermal bridging of insulation by fasteners onlyo Cost effectiveo Provides drainage and cladding supporto Can be metal or woodo Offers the opportunity to ventilate the furring

cavity

Cons:o Limitations to insulation thickness defined by

cladding systemo Not suitable for heavy claddingo Need horizontal furring strips for vertical

cladding systems – drainage?

Image by BSC Corp.

Align furring strips with studs


Thickness limitations are greater with higher wind loads, heavier claddings and metal studs


Design an R30 metal stud wall (2x6’s,16”o.c.) for light cladding

Nominal Correction Actual Poliso (R5.4)Insulation Type R-value Factor R-value ThicknessFiberglass Cavity Insulation 21.0 ??? ?Other Materials 2.5 1.0 2.5“Continuous” Exterior Insulation ? 1.0 ? ?


Case 1: Assume stud cavity is filled with fiberglass insulation

The “Actual R-value” is the “clear wall” R-value for this assembly

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Nominal Correction Actual Poliso (R5.4)Insulation Type R-value Factor R-value ThicknessFiberglass Cavity Insulation 21.0 .37 7.8Other Materials 2.5 1.0 2.5“Continuous” Exterior Insulation 19.7 1.0 19.7 3.6



Design an R30 metal stud wall (2x6’s,16”o.c.) for light cladding

Note: if the studs were wood, the framing correction factor would be ~ .8 and only about 2” of exterior insulation would be needed


Base Wall Materials R = 2.5R21 Fiberglass (2x6) x .37 R = 7.83.5” x R5.4 Polyisocyanurate R = 18.9Cost /SF per actual R = $0.21 Total = 29.2

Base Wall Materials R = 2.5R13 Fiberglass (2x6) x .37 R = 4.84” x R5.4 Polyisocyanurate R = 21.6Cost /SF per actual R = $0.20 Total = 28.9

Base Wall Materials R = 2.5No Cavity Insulation (2x6) R = 0.85” x R5.4 Polyisocyanurate R = 27.0Cost /SF per actual R = $0.22 Total = 30.3

`

Alternative Assemblies for Rmin = 30

Costs include insulation and furring strips

For 2 x6 steel studs, 16” o.c.

Image by BSC Corp.


Base Wall Materials R = 2.5R21 Fiberglass (2x6) x .37 R = 7.83.5” x R5.4 Polyisocyanurate R = 18.9Cost /SF per actual R = $0.21 Total = 29.2

Base Wall Materials R = 2.5R13 Fiberglass (2x6) x .37 R = 4.84” x R5.4 Polyisocyanurate R = 21.6Cost /SF per actual R = $0.20 Total = 28.9

Base Wall Materials R = 2.5No Cavity Insulation (2x6) R = 0.85” x R5.4 Polyisocyanurate R = 27.0Cost /SF per actual R = $0.22 Total = 30.3

`

Alternative Assemblies for Rmin = 30

Costs include insulation and furring strips

Image by BSC Corp.

40% to 60% interior RHSmart vapor retarderFiberglass-faced gypsum sheathing15 perm water / air barrierFiber cement siding


Furred Wall Case 1 Sheathing Conditionsfor 3.5” fiberglass-faced polyisocyanurate, 6” fiberglass, smart vapor retarder


2180 (25% of hours)

Rout / Rin ~ .8

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Furred Wall Case 2 Sheathing Conditionsfor 4” fiberglass-faced polyisocyanurate, 3.5” fiberglass, smart vapor retarder


(0 hours)

Rout / Rin ~ 1.7


Furred Wall Case 1 Sheathing Conditionsfor 3.5” fiberglass-faced polyisocyanurate, 6” fiberglass, polyethylene vapor retarder

Rout / Rin ~ .8


4887 (56% of hours)


Furred Wall Case 1 Sheathing Conditionsfor 3.5” foil-faced polyisocyanurate, 6” fiberglass, smart vapor retarder

Rout / Rin ~ .8


3461 (40% of hours)


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0.2 0.4 0.6 0.8 1.0 1.2 1.4 1.6 1.8 2.0 2.2

Foil‐faced polyisocyanurate exterior insulation, Class 3 vapor retarderFoil‐faced polyisocyanurate exterior insulation, Smart vapor retarderFiberglass‐faced polyisocyanurate exterior insulation, Smart vapor retarder

R‐value Outside of Sheathing / R‐value Inside of Sheathing

Gypsum Sheathing, 15 perm Weather BarrierR30 walls with steel studs or R40 walls with wood studs, Climate Zone 6

Sheathing Pe

ak Relative Hum

idity

Effect of R‐value Ratio on Wall Moisture

Vapor Permeable Exterior MaterialsSmart vapor retarder

Vapor Impermeable Exterior MaterialsClass 3 vapor retarder

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0.2 0.4 0.6 0.8 1.0 1.2 1.4 1.6 1.8 2.0 2.2

Fiberglass‐faced polyisocyanurate exterior insulation Smart vapor retarderFoil‐faced polyisocyanurate exterior insulation Smart vapor retarderFoil‐faced polyisocyanurate exterior insulation, Class 3 vapor retarder

R‐value Outside of Sheathing / R‐value Inside of Sheathing

Plywood Sheathing, 15 perm Weather BarrierR30 walls with steel studs or R40 walls with wood studs, Climate Zone 6

Sheathing Pe

ak Relative Hum

idity

Smart vapor retarder

Vapor Impermeable Exterior MaterialsClass 3 vapor retarder

Effect of R‐value Ratio on Wall Moisture


Hybrid Wall Insulation for Heavy CladdingStucco with Exterior Insulation (Rigid Foam Up to 2” Thick)


Design an R30 metal stud wall (2x6’s,16”o.c.) for stucco

Nominal Correction Actual Poliso (R5.4)Insulation Type R-value Factor R-value ThicknessFiberglass Cavity Insulation 21.0 .37 7.8Other Materials 2.5 1.0 2.5“Continuous” Exterior Insulation 19.7 1.0 19.7 3.6




Stucco with Exterior Insulation For Exterior Insulation Greater Than 2” Thick

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Exterior Insulation Framing Alternatives

Morrison Hershfield


Intermittent Z-girtsUsing Fiberglass Clips





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Exterior Insulation R-value between Steel Z-girts

The Real R-value of Exterior Insulated Wall AssembliesBased on ASHRAE 1365-RP

Wood Studs 16" o.c., 25% framing factor Intermittent Vert. Z-girts 16" o.c.Hoiz. & Vert. Z-girts 24" o.c. Horizontal Z-girts 24" o.c.Vertical Z-girts 16" o.c.


Design an R30 metal stud wall (2x6’s,16”o.c.) for stucco

Nominal Correction Actual Poliso (R5.4)Insulation Type R-value Factor R-value ThicknessFiberglass Cavity Insulation 21.0 .37 7.8Other Materials 2.5 1.0 2.5“Continuous” Exterior Insulation 29.0 .67 20.0 5.5”



The correction factor is for intermittent vertical clips on Z-girts


Wall Assemblies Alternatives for R 30Heavy Cladding with intermittent fiberglass Z-clipsBase Wall Materials R = 2.5R21 Fiberglass (2x6) x .37 R = 7.85.5” x R5.4 Polyisocyanurate x .67 R = 20.0

Cost /SF per actual R = $0.34 Total = 30.3

83

Light Cladding with furring and steel screwsBase Wall Materials R = 2.5R21 Fiberglass (2x6) x .37 R = 7.84” x R5.4 Polyisocyanurate x .90 R = 19.4

Cost /SF per actual R = $0.23 Total = 29.7

For this example, the need for exterior cladding supports:Increases cost/SF per actual R ~ 50%Increases wall assembly costs ~ $3 to $4 / SFIncreases building cost ~$1 to $2 / SF ??


Service Life of Wall Components*Vinyl Siding 25 yrsEIFS 25 to 50 yrs ? Wood Siding 25 to 100 yrsCement Siding 50 to 100 yrsSimulated Stone 100 yrs or moreStucco 100 yrs or moreBrick 100 yrs or more

Brick Ties 25 yrs (hot-dipped galvanized)Brick Ties 50 yrs (epoxy-coated)Brick Ties 100 yrs or more (stainless steel)

Flashing 25 yrs (polyethylene)Flashing 25 yrs (galvanized sheet metal)Flashing 100 yrs or more (copper, 18 ga.)Flashing 100 yrs or more (stainless steel, 24 ga.)

* A drainage plane is assumed to be present in all casesExcerpted from “Increasing the Durability of Building Components”, BSD-144, Joe Lstiburek

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Apartment building in Margate by Alex Chinneck


Service Life of Wall Components*Water Barriers Non-ventilated & Non-ventilated & Under Rigid

Non-backprimed Backprimed Insulation

Building Papers 25 yrs 50 yrs 100 yrs or moreHousewraps 25 yrs 50 yrs 100 yrs or more

Cladding Non-ventilated & Non-ventilated & Ventilated & Non-backprimed Backprimed Backprimed

Wood Siding 25 yrs 50 yrs 100 yrs or moreCement Siding 50 yrs 75 yrs 100 yrs or more

* A drainage plane is assumed to be present in all cases

Excerpted from “Increasing the Durability of Building Components”, BSD-144, Joe Lstiburek


Proo Low moisture risko Conceptually simple – a vapor impermeable air/water/vapor barrier can be usedo Thermal break at framing members and floor lineCono Relatively expensiveo Most foam insulation has relatively high environmental impacto Exterior insulation may need to be interrupted with framing to support cladding


Proo Relatively inexpensive if single wall. Can also be high-R double wallo Most cavity insulations have low environmental impacto Simple to constructCono Increased risk of moisture damage as permeable cavity insulation becomes thickero Thermal bridging at framing members and floor line for single wall constructiono Convective looping more likely with cold sheathing – need dense insulation

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A Compromise Solutiono Intermediate costo Intermediate environmental impacto Construction difficulty varieso As the R-value ratio of exterior to cavity insulation increases, moisture risk decreaseso Thermal bridging is reduced


Avoid foam insulations with HFC blowing agents:o Use expanded polystyrene, polyisocyanurate, cellulose, mineral wool or fiberglass

products instead of closed cell spray foam (ccSPF) and extruded polystyrene (XPS).

Assume that the wall cladding will not be watertight:o Provide a drainage plane between cladding and water barrier. o It can be as small as 1 mm but 3/8” or thicker is better.o Consider ventilating the drainage gap for additional drying.

Ventilate and control indoor moisture to keep RH between 30% and 60%.

Design walls to dry to the inside as well as the outside when conditions permit:o For interior winter RH greater than 40%, use a Class I vapor retarder like polyethylene.o For normal moisture loads (40% maximum RH in winter), use a “smart vapor retarder”.

Detail a continuous whole building air barrier. Test and seal it during construction.

For walls with both exterior insulation and vapor-permeable cavity insulation, pay attention to the (R out / R in) ratio: Higher is Drier.

Recommendations for Zone 6 Frame Walls


aia convention 2015 bryan - third level design

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