timber frame isometric view

Timber FrameIsometric cut-away view

This example should be read in conjunction with the guidance in the introduction to this document. It illustrates the reductionof unwanted infiltration in buildings and provides a Psi value for this junction situation which can be used in calculationprovided the principles outlined and any identified component specification are followed.

Detail 3.00

Structural timber frame

Vapour control layer

Insulation

Wall ties

Cavity

Outer leaf (brick shown)

Sheathing board

Breather membrane

Timber batten /service void (option)

Rigid insulation /plasterboard composite

LegendInsulation zone

Air tightness barrier(note: this can alsoact as a vapourcontrol layer)

Guidance on thermalcontinuity

Blue text

Guidance on airtightness

Red text

General guidance notes

Alternative constructions1. The rigid insulation / plasterboard

construction can be replaced otherfinishes but this will require that thickerinsulation is used in the wall. Ensurethat the thermal conductivity of thisinsulation is equal or less than thatused in the cavity of the timber frame,to prevent interstitial condensationproblems.

2. Different constructions can be used toprovide an outer leaf but check thatthere is sufficient ventilation provisionto prevent moisture from being trappedwithin the wall.

Sealing membrane junctions3. All membranes should be taped,

stapled or bedded in adhesive asidentified by manufacturer. Repair alltears in membranes beforecommencing next stage of work.

Psi-value calculations4. For details of all thermal conductivity

values of materials used in thepsi-value calculations, see Appendix Bof the Introduction.

Material ?-values usedin calculations(W/mK)

Plasterboard 0.21Insulation (generic) 0.04Plywood sheathing 0.13Brick outer leaf 0.77Mineral wool insulation 0.044Concrete block(dense) protected

1.13

Concrete block(lightweight, high strength)

0.19

Timber frame 0.13Concrete floor beam 2.3Concrete screed 1.15Render (cement/sand) 1.0Gypsum plaster(1000kg/m3)

0.4

Concrete roof tiles 1.5EPDM membrane 0.25Timber battens 0.13Timber flooring 0.13Chipboard 0.13Floor joists 0.13Aluminium 160Steel 50Stainless steel 17Glass 1Sarking felt 0.23Insulation board 0.022

Values used in psi calculations

Timber FramePitched Roof: Ventilated Roofspace - EavesPsi value = 0.0464W/mK

Thermal continuity checklist

1. Ensure that insulation layers in roof arefitted perpendicularly, to cover junctions

2. Ensure that roof insulation fully laps timberframe insulation

3. Install cavity barrier at the top of the wall.

Detail 3.01

Proprietary cross flowventilator to maintainminimum 25mm air gap

Ventilation gap equivalent to10mm minimum continuousopening is required where???????????????????????orventilation gap equivalent to25mm minimum continuousopening is required where???????????????????????????

Vapour control layer inwall and ceiling

Ventilation gap equivalent to 5mmminimum continuous opening at ridgeis required where the roof pitch is????????????????????????????????????more than 10m

Insulation between the studsmust be tightly fitted leaving no

gaps

Cavity barrier giving 30 minutefire resistance - ensure cavitybarrier is not breeched byinappropriate rigid sheathinginsulation material

Timber batten to providefixing for plasterboard sheet

HEAT 2.7 software image of isothermsthrough junction detail.

For illustrative purposes only.


Design advice

Minimising condensation risk1. Check ventilation paths are clear before

installing insulation above the ceiling

Thermal Resistance of insulation used indetails:

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Note: See detail numbers 3.02 and 3.21 forother junctions using this roof construction

20x38mm timber battens /services void (optional)

Composite rigid insulation /plasterboard

Air tightness checklist

1. Check that any air tightness barrier usedin the wall overlaps and is robustly joinedto the barrier in the ceiling

Timber FramePitched Roof: Ventilated Roofspace - GablePsi value = 0.1006W/mK Detail 3.02

Loft insulation continued upto outer face of the rigidsheathing

Cavity barrier giving 30minute fire resistance -ensure cavity barrier is notbreeched by inappropriaterigid sheathing insulationmaterial


Cavity ventilator

Timber runner to provide fixingfor plasterboard sheet

Insulation between thestuds must be tightly fitted

leaving no gaps




Design advice




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1. Check that any air tightness barrier usedin the wall overlaps and is robustly joinedto the barrier in the ceiling



2. Ensure that roof insulation butts against the timber sheathing in the wall


Full depth dwang required tosecure roof bracing at a levelabove the rafter ties.Alternative batten and bracingdetails can also be used

Timber FramePitched Roof: Ventilated Rafter Void - GablePsi value = 0.0472W/mK Detail 3.03


1. Ensure that insulation is fitted tightly withinthe timber frame

2. Ensure that insulation layers in roof arefitted perpendicularly to cover junctions



1. Check that any air tightness barrier usedin the wall overlaps with the barrier in theceiling

Masonry built upbetween ladder legs



Cavity ventilator

Timber runner to provide fixingfor plasterboard sheets


leaving no gaps

Minimum 50mm ventilation path over insulation

Where two insulation types areused together see

supplementary guidance




Design advice




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Note: See detail numbers 3.04, 3.05 and 3.22for other junctions using this roof construction

Note: this construction istypically used where thereare habitable rooms withinthe roof construction

Timber FramePitched Roof: Ventilated Batten Void (warm roof) - EavesPsi value = 0.0284W/mK Detail 3.04



Rigid insulation used as sarking.Insulation to be vapour permeable

Proprietary overfascia ventilator


Cavity barrier giving 30 minutefire resistance - ensure cavity

barrier is not breeched byinappropriate rigid sheathing

insulation materialInsulation between the

studs must be tightlyfitted leaving no gaps

Timber batten to provide fixingfor plasterboard sheets

Ventilation tobatten void

Vapour permeable membrane(with a vapour resistance ofnot more than 0.6MN.s/g)

Lap roof and wall insulationminimum 150mm thickness atnarrowest point

Ventilation gap equivalent to5mm minimum continuousopening is required at ridgeto batten space




Design advice




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2. Ensure that roof insulation overlaps with the top of the timber frame wall, with minimum 50mm overlap at the narrowest point

3. Install cavity barrier at the top of the wall

Alternative position forplasterboard ceiling


Timber FramePitched Roof: Ventilated Batten Void (warm roof) - GablePsi value = 0.0431W/mK Detail 3.05





Cavity ventilator

Insulation between the studs mustbe tightly fitted leaving no gaps


Where two insulation types areused together see


Vapourpermeablemembrane(with a vapourresistance ofnot more than0.25 MN.s/g)




Design advice




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Compressible filler


1. Ensure that insulation layers are fittedperpendicularly, to cover junctions



Timber runner to provide fixingfor plasterboard sheets


Timber FrameTimber Flat RoofPsi value = 0.0536W/mK Detail 3.06



Verge - tightly fit insulationinto void over wall andunder deck (not shown)


Vapour control layer in wall

Cavity ventilator Timber batten to be provided tocover over junction between

plasterboard sheets


leaving no gaps

Compressible filler

Eaves - fix full height blockingpiece and tightly fit insulation intovoid and under deck

Vapour control layer turned up edgeof roof insulation, lapped with roofwaterproofing layer and sealed

Membrane roof construction

Vapour control layer in ceiling




Design advice


installing insulation above the ceiling2. A vapour barrier is required at ceiling

level, to prevent moisture from enteringinto the roof construction

3. The option shown here includes a vapourcontrol layer and insulation as part of amembrane roof construction. Similardetails could be used for a profiled metaldecking roof but consult withmanufacturer regarding ventilationrequirements.


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Timber FrameTimber Flat Roof with ParapetPsi value = 0.0299W/mK Detail 3.07



Cavity barriergiving 30 minutefire resistance -ensure cavitybarrier is notbreeched byinappropriate rigidsheathinginsulation material


Insulation between the studs must betightly fitted leaving no gaps

Compressible fillerRoofing membrane to be taken minimum

150mm above finished roof level

Vapour control layer turned up edgeof roof insulation, lapped with

breather membrane from cavity wall

Tightly fit compressible insulant between the wallstuds above the level of the roof deck





Design advice


installing insulation above the ceiling2. A vapour barrier is required at ceiling

level, to prevent moisture from enteringinto the roof construction

3. The option shown here includes a vapourcontrol layer and insulation as part of amembrane roof construction. Similardetails could be used for a profiled metaldecking roof but consult withmanufacturer regarding ventilationrequirements.


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2. Ensure that roof insulation butts against the timber wall sheathing with a minimum of 50mm overlap at narrowest point

3. Install cavity barrier at the top of the wall

Timber FrameLintel at Window HeadPsi value = 0.121W/mK


1. Check that there is no debris in the cavity2. Install cavity barrier around opening


1. Install window to overlap with outer leaf ofwall finish.

Alternative:If window lines through with the bottom ofthe opening in the external finish, somemeans of preventing a direct line of airinfiltration will be required

2. Install air tightness seal between theinside face of the window and thestructural finish of the window opening

Insulation between thestuds must be tightly

fitted leaving no gaps

30 minute fireresistingproprietaryinsulating cavitybarrier withintegral DPC

Detail 3.08

Insulate the window reveal

Sealant to back of frame

Sealant at window frame

Weep Hole

Air tightness tape

Compressible fill

Use approved lintoldetails from timber

frame supplier


Cavity tray withminimum upstandof 140mm andstop ends




Design advice

Minimising condensation risk1. Alternative internal finish at window

reveal - use insulation backedplasterboard


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If position of window head islower than or level with theunderside of the lintol, a largercompressible filler will berequired to stop up a potentialair infiltration route

Timber FrameWindows and Doors - Jambs and Cills

Psi value (jamb)=0.0328W/mK Psi value (cill) = 0.0934W/mK


1. Check that there is no debris in the cavity2. Install cavity barrier around opening


1. Install window to overlap with outer leaf ofwall finish.

Alternative:If window lines through with the bottom ofthe opening in the external finish, somemeans of preventing a direct line of airinfiltration will be required

2. Install air tightness seal between theinside face of the window and thestructural finish of the window opening

Detail 3.09


Air tightness tape andsealant to back of frame

Sealant at window frame

30 minute fire resisting cavitybarrier with integral DPC

Vapour controllayer in wall

Insulation between thestuds must be tightly

fitted leaving no gaps

DPC lappedbehind cill andbelow window

Solid cill acts as cavitycloser. If pressed cill isused, a 30 minute firerated thermally insulatedcavity closer will berequied


Air tightness tape andsealant to back of frame

Compressiblefiller betweenwindow and cill





Design advice

Minimising condensation risk1. Alternative internal finish at window

reveal - use insulation backedplasterboard


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Cill detail

Jamb detail

Timber FrameGround Bearing Floor: Insulation Above SlabPsi value = 0.1145W/mK

20mm strip of perimeterinsulation with thermal

conductivity (? value) notexceeding 0.025 W/mK around

slab and any screed

Detail 3.10


1. Use a lightweight loadbearing concreteblock where the wall abuts the concreteslab to minimise thermal bridging

2. Use a perimeter strip of insulation wherethe concrete slab abuts the concreteblockwork wall


1. Ensure that any air tightness barrier usedin the wall overlaps onto the floor slab

External ground level

Seal between the wall and floormembrane with a flexible sealant orseal the gap between skirting board

and floor using a flexible sealant


Damp proof membraneabove or below slab

Vapour control layer belowtimber floor finish




Design advice

Minimising condensation risk1. Check that concrete slab is level and

clear of debris before fitting the insulationat floor level

2. If a screed finish is used instead of a timber floor, use a strip of perimeter insulation with a minimum R value of ??????????????????????????????????????

Alternative detail3. Using lightweight blockwork (e.g. with ?

value of 0.19W/mK) to improve thethermal performance at the junction wherethe external wall and ground floorconstructions meet will change the psivalue


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Timber FrameGround Bearing Floor: Insulation Below SlabPsi value = 0.1733W/mK Detail 3.11

50mm strip of perimeterinsulation with thermal

conductivity (? value) notexceeding 0.025 W/mK around

slab and any screed


1. Use a lightweight loadbearing concreteblock where the wall abuts the concreteslab to minimise thermal bridging

2. Use a perimeter strip of insulation wherethe concrete slab abuts the concreteblockwork wall


1. Check that any air tightness barrier usedin the wall overlaps onto the floor slab





Damp proof membrane




Design advice

Minimising condensation risk1. If a screed finish is used instead of a

timber floor, use a strip of perimeter insulation with a minimum R value of ??????????????????????????????????????

Alternative detail2. Using lightweight blockwork (e.g. with ?

value of 0.19W/mK) to improve thethermal performance at the junctionwhere the external wall and ground floorconstructions meet will change the psivalue


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Timber FrameTimber Suspended Ground FloorPsi value = 0.0423W/mK Detail 3.12

Sub floor ventilation should be?????????????????????????

per run of external wall or???????????????????????????


1. Ensure that floor insulation butts againstthe insulation in the external wall


1. Check that any air tightness barrier usedin the wall overlaps with the barrier in thefloor


Add timber batten to cover the floor/wall junction. Useair tightness tape at junction of air barrier in wall and

floor. Seal between the wall and floor membrane with aflexible sealant or seal the gap between skirting board



Damp proof membrane

Air tightness barrier belowtimber floor finish

Insulation directly under flooringsupported on netting draped over

joists and stapled at required depths

Solum




Design advice

Minimising condensation risk1. Check that all ventilation paths are clear

before installing the floor insulationAlternative detail2. Using lightweight blockwork (e.g.

with ? value of 0.19W/mK) to improvethermal performance at the junctionwhere the external wall and ground floorconstructions meet will change the psivalue

3. If there are concerns about damaging theair tightness membrane in the floor finishduring construction, an additional servicesvoid can be created using timber battenson top of the floor joists


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Timber FrameSeparating WallPsi value = 0.0725W/mK


1. Check that there is no debris in the cavity2. Install cavity barrier at junction of wall

Detail 3.13


1. Check that any air tightness barrier usedin the internal wall overlaps with thebarrier in the external wall

Cavity barriers giving 30 minutefire resistance - ensure cavitybarriers are not breeched by

inappropriate insulation materialin the timber frame

For more information onacoustic details see

guidance in Section 5 ofthe Technical Standards





Design advice

Minimising condensation risk1. Check that insulation is fitted between

timber studs at corner junctions


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Plan view

Timber FrameTimber Separating FloorPsi value = 0.0353W/mK


1. Check that there is no debris in the cavity2. Install cavity barrier in line with floor

construction

Detail 3.14


1. Check that any air tightness barrier usedin the external wall overlaps with thebarrier in the floor

Cavity barriergiving 30 minutefire resistance -ensure cavitybarrier is notbreeched byinappropriate rigidsheathinginsulation material Vapour control layer in wall

Cavityventilator

Insulation between the studs must betightly fitted leaving no gaps

Seal between the wall and floormembrane with a flexible sealant or sealthe gap between skirting board and floor

using a flexible sealant


Separating floors to comply withSection 2: Fire and Section 5:

Noise




Design advice

Minimising condensation risk1. Check that insulation is tightly fixed to the

timber studs adjacent to the floor junction,leaving no gaps


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Timber FrameIntermediate Floor / External WallPsi value = 0.0574W/mK


1. Check that there is no debris in the cavity2. Install cavity barrier as necessary

Detail 3.15


1. Check that any air tightness barrier usedin the external wall overlaps with thebarrier in the floor

Vapour control layer in wallInsulation between the

studs must be tightlyfitted, leaving no gaps







Design advice

Minimising condensation risk1. Check that insulation is tightly fixed to the

timber studs adjacent to the floor junction,leaving no gaps


?????????????????????????????????????????????????????????

Install air tightness barrier aroundjoists, then lap membrane from

walls over it and tape junction

Timber FrameGround Floor/Separating Wall Junction- timber suspended floorPsi value = 0.0713W/mK


1. Ensure that insulation is tightly fittedbetween the timber floor joists

2. Install cavity barrier as necessary

Detail 3.16


1. Check that any air tightness barrier usedin the internal wall overlaps with thebarrier in the floor

Sub floor ventilation should be?????????????????????????

per run of external wall or???????????????????????????

Damp proof membrane

Use air tightness tape at junction of air barrier in walland floor. Seal between the wall and floor membrane

with a flexible sealant or seal the gap between skirtingboard and floor using a flexible sealant

Vapour contol layer in wall

Air tightness barrier belowtimber floor finish

Insulation directly under flooring -supported on netting draped over

joists and stapled at required depths

Solum




Design advice

Minimising condensation risk1. Check that all ventilation paths are clear

before installing the floor insulationAlternative Detail2. Lightweight thermal blockwork can be

used in the separating wall to improve thethermal performance but this will alsoreduce the acoustic performance of thewall. If this alternative is used thenadditional elements will be required tomeet Section 5 of the TechnicalStandards.


?????????????????????????????????????????????????

Timber FrameConcrete Ground Floor/ Separating Wall: Insulation Below SlabPsi value = 0.2765W/mK


1. Ensure that insulation is tightly fittedagainst the separating floor

Detail 3.17


1. Check that any air tightness barrier usedin the internal wall overlaps onto the floorslab




Damp proof membrane

Lightweight loadbearing concreteblockwork to minimise thermal bridging




Design advice

Minimising condensation risk1. If a screed finish is used instead of a

timber floor, use a strip of perimeter insulation with a minimum R value of ??????????????????????????????????????

Alternative Detail2. Heavyweight thermal blockwork can be

used in the separating wall below slablevel but this will reduce the thermalperformance of this junction. Additionalconstruction elements may be requiredalong with lightweight blockwork in orderto meet the acoustic requirements ofSection 5 of the the Technical Standards


?????????????????????????????????????????????????

Timber FrameConcrete Ground Floor/ Separating Wall: Insulation Above SlabPsi value = 0.0146W/mK


1. Ensure that insulation is tightly fittedagainst the separating floor

Detail 3.18


1. Check that any air tightness barrier usedin the internal wall overlaps onto the floorslab




Damp proof membrane




Design advice

Minimising condensation risk1. Check that concrete slab is level and

clear of debris before fitting the insulationat floor level

2. If a screed finish is used instead of a timber floor, use a strip of perimeter insulation with a minimum R value of ??????????????????????????????????????

Alternative Detail3. Lightweight thermal blockwork can be

used in the separating wall to improve thethermal performance but this will alsoreduce the acoustic performance of thewall. If this alternative is used thenadditional elements will be required tomeet Section 5 of the TechnicalStandards.


?????????????????????????????????????????????????

Seal air tightnessmembrane to floor slab

Vapour barrier in floor

Timber FrameSeparating Floor / Wall JunctionPsi value = 0.0241W/mK


1. Ensure that insulation is tightly fitted

Detail 3.19


1. Check that any air tightness barrierused in the internal wall overlaps withthe barrier in the floor

Alternative:Ensure that a continuous air tightnessbarrier from the wall wraps around theend of the floor construction, leavingno gaps


Insulation between the studsmust be tightly fitted

Vapour control layer in ceiling




Vapour control layer belowtimber floor finish

Separating floors requireadditional layers and components

to comply with Section 2: Fireand Section 5: Noise

Cavity barrier




Design advice

Minimising condensation risk

See general guidance notes


?????????????????????????????????????????????????

Timber FrameIntermediate FloorPsi value = 0.0333W/mK


1. Ensure that insulation is tightly fitted

Detail 3.20






Cavity barrier




Design advice

Minimising condensation risk s

See general guidance notes


?????????????????????????????


1. Check that any air tightness barrierused in the internal wall overlaps withthe barrier in the floor

Alternative:Ensure that a continuous air tightnessbarrier from the wall wraps around theend of the floor construction, leavingno gaps

Install air tightness barrier aroundjoists, then lap membrane from

walls over it and tape junction

Timber FramePitched Roof: Cold Roof / Separating Wall junctionPsi value = 0.0132W/mK


1. Install a cavity barrier at the top of the wall2. Ensure that insulation layers in the roof are

fitted perpendicularly, to cover junctions


1. Check that there are no gapsbetween the top of the masonry andthe underside of the roof

2. Check that the air tightness barrier inthe wall overlaps with the barrier inthe ceiling



Where two insulation typesare used together see





Design advice




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Separating walls requireadditional layers and componentsto comply with Section 2: Fireand Section 5: Noise

Detail 3.21

Cavity barrier is used in line withceiling insulation to prevent thermalbypass.Use dense insulation orproprietary cavity barrier in sleeve

Timber FramePitched Roof: Ventilated Batten Void / Separating Wall JunctionPsi value = 0.0481W/mK Detail 3.22


Vapour control layerin wall and ceiling


Where two insulation typesare used together see





Design advice




????????????????????????????????????????????????




1. Install a cavity barrier at the top of the wall2. Ensure that insulation layers in the roof are

fitted perpendicularly, to cover junctions


1. Check that there are no gapsbetween the top of the masonry andthe underside of the roof

2. Check that the air tightness barrier inthe wall overlaps with the barrier inthe ceiling

Separating walls requireadditional layers and componentsto comply with Section 2: Fireand Section 5: Noise

Note: this construction istypically used where thereare habitable rooms within

the roof construction

Timber FrameWall JunctionPsi value = 0.0179W/mK


1. Check that there is no debris in the cavity2. Install cavity barrier

Detail 3.23


1. Ensure that any air tightness barrier usedin the external wall overlaps at the corner

Plan view

Cavity barrier giving 30 minutefire resistance - ensure cavity

barrier is not breeched byinappropriate insulation

material

Insulation betweenthe studs must betightly fitted leavingno gaps

Vapour controllayer




Design advice

Minimising condensation risk1. Check that insulation is tightly fixed to

the timber studs at the corner junction,leaving no gaps


?????????????????????????????????????????????????????????

timber frame isometric view

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