Masonry: Cavity Wall Insulation: Partial FillIsometric cut-away view

Service void / protectionzone for air tightnessmembrane (optional)

Air tightness barrier

Insulation supportedwithin secondary timberstud frame

Wall ties

Cavity

Outer leaf (renderon block shown)

Inner leaf (block shown)

Insulation

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.

Plasterboard

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 thermal resistance of cavity

insulation needs to be greater than thatused in the inner leaf insulation, toreduce the risk of interstitialcondensation.

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 the psi-valuecalculations, see also Appendix B of theIntroduction.

Material λ-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

Detail 2.00

Masonry: Cavity Wall Insulation - Partial fillPitched Roof: Ventilated Roofspace - EavesPsi value = 0.0392W/mK

Thermal continuity checklist

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

2. Check that roof insulation butts against thecavity wall insulation, with minimum of50mm overlap at narrowest point

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

Air tightness checklist

1. Check that any air tightness barrierused in the ceiling overlaps with thelayer in the wall

Detail 2.01

Proprietary cross flowventilator to maintainminimum 25mm air gap

Ventilation gap equivalent to10mm minimum continuousopening is required whereroof pitch is above 15°orventilation gap equivalent to25mm minimum continuousopening is required wherethe roof pitch is below 15°

Vapour control layer in wall and ceiling

Ventilation gap equivalent to 5mmminimum continuous opening at ridgeis required where the roof pitch isgreater than 35° or the roof span ismore than 10m

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

Timber batten to provide fixingfor plasterboard sheet

HEAT 2.7 software image of isothermsthrough junction detail.

For illustrative purposes only.

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.

Design advice

Minimising condensation risk1. Check ventilation paths are clear before

installing insulation above the ceiling

Thermal Resistance of insulation used indetails:

Wall (cavity) - 2.500 (m²K)/WWall (inner leaf) - 2.272 (m²K)/WRoof - 9.500(m²K)/W

Note: See detail numbers 2.02 and 2.21 forother junctions using this roof construction

Insulation between the studsin addition to the cavity insulation.

This insulation to be tightly fittedagainst the wall, leaving no gaps

Masonry: Cavity Wall Insulation - Partial fillPitched Roof: Ventilated Roofspace - GablePsi value = 0.0918W/mK Detail 2.02

Air tightness checklist

1. Check that any air tightness barrierused in the ceiling overlaps with thelayer in the wall

Cavity insulation continuedfull height of gable or to thetop of the loft insulation

Insulation betweenthe last truss andthe gable wall

Vapour control layer in wall and ceiling

Timber batten to provide fixingfor plasterboard sheet

Insulation between the studsin addition to the cavity insulation.

This insulation to be tightly fittedagainst the wall, leaving no gaps

Thermal continuity checklist

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

2. Ensure that roof insulation butts againstthe gable wall

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

HEAT 2.7 software image of isothermsthrough junction detail.

For illustrative purposes only.

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.

Design advice

Minimising condensation risk1. Check ventilation paths are clear before

installing insulation above the ceiling

Thermal Resistance of insulation used indetails:

Wall (cavity) - 2.500 (m²K)/WWall (inner leaf) - 2.272 (m²K)/WRoof - 9.500(m²K)/W

Note: See detail numbers 2.01 and 2.21 forother junctions using this roof construction

Cavity barrier giving30 minute fireresistance - ensurecavity barrier is notbreeched byinappropriate rigidsheathing insulationmaterial

Masonry: Cavity Wall Insulation - Partial fillPitched Roof: Ventilated Rafter Void - GablePsi value = 0.0206W/mK Detail 2.03

Insulationbetween joistsand coveringcavity insulation

Cavity barriergiving 30 minutefire resistance -thin calcium silicateboard or similaracross top of wall

Vapour control layer in wall and ceiling

Timber runner to provide fixingfor plasterboard sheet

Insulation between the studs inaddition to the cavity insulation.

This insulation must be tightlyfitted, leaving no gaps

Minimum 50mm ventilation path over insulation

Where two insulation types areused together see

supplementary guidance

Air tightness checklist

1. Check that any air tightness barrierused in the ceiling overlaps with thelayer in the wall

Thermal continuity checklist

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

2. Ensure that roof insulation butts againstthe gable wall

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

HEAT 2.7 software image of isothermsthrough junction detail.

For illustrative purposes only.

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.

Design advice

Minimising condensation risk1. Check ventilation paths are clear before

installing insulation above the ceiling

Thermal Resistance of insulation used indetails:

Wall (cavity) - 2.500 (m²K)/WWall (inner leaf) - 2.272 (m²K)/WRoof - 9.500(m²K)/W

Note: See detail numbers 2.04, 2.05 and 2.22for other junctions using this roof construction

Note: thisconstruction istypically usedwhere there arehabitable roomswithin the roofconstruction

Masonry: Cavity Wall Insulation - Partial fillPitched Roof: Ventilated Batten Void (warm roof) - EavesPsi value = 0.034W/mK Detail 2.04

Rigid insulation used as sarkingInsulation to be vapour permeable

Proprietary overfascia ventilator

Vapour control layer in wall and ceiling

Insulation between thestuds in addition to thecavity insulation. This

insulation must be tightlyfitted, leaving no gaps

Timber batten toprovide fixing for

plasterboard sheetVentilation tobatten void

Vapour permeable membrane(with a vapour resistance ofnot more than 0.25MN.s/g)

Lap roof and wall insulationminimum 150mm thickness atnarrowest point

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

Thermal continuity checklist

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

2. Ensure that roof insulation butts againstthe cavity wall insulation, with minimum of50mm overlap at narrowest point

3. Install cavity barrier at the top of the wall

Air tightness checklist

1. Check that any air tightness barrierused in the ceiling overlaps with thelayer in the wall

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

Alternative air barrier- parge coat of plaster

finish on blockwork

HEAT 2.7 software image of isothermsthrough junction detail.

For illustrative purposes only.

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.

Design advice

Minimising condensation risk1. Check ventilation paths are clear before

installing insulation above the ceiling

Thermal Resistance of insulation used indetails:

Wall (cavity) - 2.500 (m²K)/WWall (inner leaf) - 2.272 (m²K)/WRoof - 9.500(m²K)/W

Note: See detail numbers 2.03, 2.05 and 2.22for other junctions using this roof constructionNote: this construction is

typically used where thereare habitable rooms withinthe roof construction

Masonry: Cavity Wall Insulation - Partial fillPitched Roof: Ventilated Batten Void (warm roof) - GablePsi value = 0.0552W/mK Detail 2.05

Insulation betweenjoists and inner faceof the wall

Cavity barrier giving30 minute fireresistance - ensurecavity barrier is notbreeched byinappropriate rigidsheathing insulationmaterial

Vapour control layer in wall and ceiling

Timber runner to provide fixingfor plasterboard sheet

Insulation between the studs inaddition to the cavity insulation.

This insulation must be tightlyfitted, leaving no gaps

50mm ventilation path over insulation

Where two insulation types areused together see

supplementary guidance

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

Air tightness checklist

1. Check that any air tightness barrierused in the ceiling overlaps with thelayer in the wall

Thermal continuity checklist

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

2. Ensure that roof insulation butts againstthe gable wall

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

HEAT 2.7 software image of isothermsthrough junction detail.

For illustrative purposes only.

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.

Design advice

Minimising condensation risk1. Check ventilation paths are clear before

installing insulation above the ceiling

Thermal Resistance of insulation used indetails:

Wall (cavity) - 2.500 (m²K)/WWall (inner leaf) - 2.272 (m²K)/WRoof - 9.500(m²K)/W

Note: See detail numbers 2.03, 2.04 and 2.22for other junctions using this roof construction

Note: this constructionis typically used wherethere are habitablerooms within the roofconstruction

Masonry: Cavity Wall Insulation - Partial fillTimber Flat RoofPsi value = 0.0695W/mK Detail 2.06

Verge option - tightly fitinsulation into void overwall and under deck tomaintain thermalcontinuity

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

Vapour control layer

Timber runner to provide fixingfor plasterboard sheet

Insulation between the studs inaddition to the cavity insulation.

This insulation must be tightlyfitted, leaving no gaps

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

Vapour controllayer in ceiling

Air tightness checklist

1. Check that any air tightness barrierused in the ceiling overlaps with thelayer in the wall

Thermal continuity checklist

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

2. Ensure that roof insulation butts against the gable wall

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

HEAT 2.7 software image of isothermsthrough junction detail.

For illustrative purposes only.

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.

Membrane roof construction

Design advice

Minimising condensation risk1. Check ventilation paths are clear before

installing insulation above the ceiling2. A vapour control layer is required at

ceiling level, to prevent moisture fromentering into 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.

Thermal Resistance of insulation used indetails:

Wall (cavity) - 2.500 (m²K)/WWall (inner leaf) - 2.272 (m²K)/WRoof - 9.500(m²K)/W

Masonry: Cavity Wall Insulation - Partial fillTimber Flat Roof with ParapetPsi value = 0.0811W/mK Detail 2.07

Insulation between the studs in additionto the cavity insulation. This insulation must

be tightly fitted, leaving no gaps

Compressible filler

Roofing membrane to be taken minimum150mm above finished roof level

Vapour control layer turned up edgeof parapet, lapped over top of

blockwork and sealed

Vapour control layer inwall and roof

Membrane roof construction

Air tightness checklist

1. Check that any air tightness barrierused in the ceiling overlaps with thelayer in the wall

Thermal continuity checklist

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

3. Ensure that roof insulation butts against the gable wall

4. Install cavity barrier at the top of the wall

HEAT 2.7 software image of isothermsthrough junction detail.

For illustrative purposes only.

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.

Design advice

Minimising condensation risk1. Check ventilation paths are clear before

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.

Thermal Resistance of insulation used indetails:

Wall (cavity) - 2.500 (m²K)/WWall (inner leaf) - 2.272 (m²K)/WRoof - 9.500(m²K)/W

Masonry: Cavity Wall Insulation - Partial fillLintel at Window HeadPsi value = 0.1302W/mK

Thermal continuity checklist

1. Check that there is no debris in the cavity2. Install cavity barrier around opening3. Install insulation in the window reveal

Air tightness checklist

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 tobe tightly fixed

back to innerleaf of wall30 minute fire

resistingproprietaryinsulating cavitybarrier withintegral DPC -ensure cavitybarrier is notbreeched byinappropriaterigid sheathinginsulationmaterial

Detail 2.08

Insulate the window reveal

Sealant to back of frame

Sealant at window frame

Air tightness tape

Compressiblefill

Lintol -any type

Vapour controllayer

Cavity tray withminimumupstand of140mm andstop ends

HEAT 2.7 software image of isothermsthrough junction detail.

For illustrative purposes only.

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.

Design advice

Minimising condensation risk1. Alternative internal finish at window

reveal - use insulation backedplasterboard

General notes2. The window head and jamb details

shown have used a plywood box liningaround the window opening in the internalleaf of the wall, to allow for windowfixings. Alternative details are possiblebut the continuity of insulation and airtightness should be considered.

Thermal Resistance of insulation used indetails:

Wall (cavity) - 2.500 (m²K)/WWall (inner leaf) - 2.272 (m²K)/WInsulated plasterboard - 1.591(m²K)/W

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

Detail shows window fixed to plywoodframe set into window opening

Note: the timber batten in window reveal is shown smallerthan actual size, to allow the membrane corner strip to be seen

Masonry: Cavity Wall Insulation - Partial fillWindows and Doors - Jambs and Cills

Psi value (jamb) =0.2224W/mK Psi value (cill) =-0.02W/mK

Thermal continuity checklist

1. Check that there is no debris in the cavity2. Install cavity barrier around opening3. Install insulation in the window reveal

Air tightness checklist

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

Alternative:If window lines through with the externaljamb, some means of preventing a directline of air infiltration will be required

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

Detail 2.09

Insulate the window reveal

Air tightness tape andsealant to back of frame

Sealant at window frame

30 minute fire resistingproprietary insulating cavitybarrier with integral DPC

Vapour control layer in wall

Insulation between the studs inaddition to the cavity insulation.

This insulation must be tightlyfitted, 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 berequired

Insulate the window reveal

Air tightness tape andsealant to back of frame

Compressible fillerbetween window and cill

Air tightness barrier in wall

30 minute firerated thermallyinsulatedcavity barrier

HEAT 2.7 software image of isothermsthrough junction detail.

For illustrative purposes only.

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.

Design advice

Minimising condensation risk1. Alternative internal finish at window

reveal - use insulation backedplasterboard

General notes2. The window head and jamb details

shown have used a plywood box liningaround the window opening in the internalleaf of the wall, to allow for windowfixings. Alternative details are possiblebut the continuity of insulation and airtightness should be considered.

Thermal Resistance of insulation used indetails:

Wall (cavity) - 2.500 (m²K)/WWall (inner leaf) - 2.272 (m²K)/WInsulated plasterboard - 1.591(m²K)/W

Cill detail

Jamb detail

Detail shows window fixedto plywood frame set intowindow opening

Note: the timber battens inthe window reveal and cill are

shown smaller than actualsize, to allow the membrane

corner strip to be seen

Masonry: Cavity Wall Insulation - Partial fillGround Bearing Floor: Insulation Above SlabPsi value = 0.0744W/mK

20mm strip of perimeterinsulation with thermal

conductivity (λ value) notexceeding 0.025 W/mK around

slab and any screed

Detail 2.10

Thermal continuity checklist

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

2. Ensure that insulation level in externalwall overlaps with the insulation at thefloor slab

Air tightness checklist

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

The wall insulation installedbelow the wall dpc must befit for purpose with regardsto water absorption

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

Vapour control layer

Damp proof membraneabove or below slab

Vapour control layer belowtimber floor finish

HEAT 2.7 software image of isothermsthrough junction detail.

For illustrative purposes only.

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.

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 atimber floor, use a strip of perimeterinsulation with a minimum R value of0.75 m²/KW for the depth of the screed

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

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

Thermal Resistance of insulation used indetails:

Wall (cavity) - 2.500 (m²K)/WWall (inner leaf) - 2.272 (m²K)/WInsulated perimeter strip - 0.455 (m²K)/WFloor - 3.864 (m²K)/W

Masonry: Cavity Wall Insulation - Partial fillGround Bearing Floor: Insulation Below SlabPsi value = 0.175W/mK Detail 2.11

Thermal continuity checklist

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

2. Ensure that insulation level in externalwall overlaps with the insulation at thefloor slab

20mm strip of perimeterinsulation with thermal

conductivity (λ value) notexceeding 0.025 W/mK around

slab and any screed

The wall insulation installedbelow the wall dpc must befit for purpose with regardsto water absorption

External ground level

Seal between the wall andfloor membrane with a flexible

sealant or seal the gap betweenskirting board and floor using a

flexible sealant

Vapour control layer

Damp proof membrane

Air tightness checklist

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

HEAT 2.7 software image of isothermsthrough junction detail.

For illustrative purposes only.

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.

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 0.75 m²/KW for the depth of the screed

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

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

Thermal Resistance of insulation used indetails:

Wall (cavity) - 2.500 (m²K)/WWall (inner leaf) - 2.272 (m²K)/WInsulated perimeter strip - 1.136 (m²K)/WFloor - 3.864 (m²K)/W

Masonry: Cavity Wall Insulation - Partial fillTimber Suspended Ground FloorPsi value = 0.0978W/mK Detail 2.12

Sub floor ventilation should beprovided, minimum 1500mm²

per run of external wall or500mm² per m² of floor area

External ground level

Use air tightness tape at junction of airbarrier in wall and floor. Seal between the

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

Vapour control layer

Air tightness barrierbelow timber floor finish

Solum

Damp proof membrane

Insulation directly under flooring -supported on netting draped over joists

and stapled at the required depths

Minimum 50mm strip ofinsulation with thermalconductivity (λ value) notexceeding 0.025 W/mKshould be installed betweenwall and the last joist

Floor joist ends supported on joisthangers or using scarcement wall

Thermal continuity checklist

1. Use a perimeter strip of insulationbetween the floor joists and blockworkwall

2. Ensure that insulation level in externalwall overlaps with the insulation at thefloor construction

Air tightness checklist

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

HEAT 2.7 software image of isothermsthrough junction detail.

For illustrative purposes only.

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.

Design advice

Minimising condensation risk1. Check that all ventilation paths are clear

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

with λ 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

Thermal Resistance of insulation used indetails:

Wall (cavity) - 2.500 (m²K)/WWall (inner leaf) - 2.272 (m²K)/WInsulated perimeter strip - 1.136 (m²K)/WFloor - 5.455 (m²K)/W

Masonry: Cavity Wall Insulation - Partial fillSeparating WallPsi value = 0.0508W/mK

Thermal continuity checklist

Design stage1. Install thermally insulated cavity barrier in

line with separating wall2. Check that there is no debris in the cavity

Detail 2.13

Air tightness checklist

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

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

inappropriate insulation material

For more informationon acoustic details see

guidance in Section 5 ofthe Technical Standards

Vapour control layer

HEAT 2.7 software image of isothermsthrough junction detail.

For illustrative purposes only.

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.

Design advice

Minimising condensation risk1. Check that insulation is fitted tightly to

concrete block wall at corner junctions

Thermal Resistance of insulation used indetails:

Wall (cavity) - 2.500 (m²K)/WWall (inner leaf) - 2.272 (m²K)/W

Air tightness layer,13mm plaster shown

Minimum specification of8kg/m2 gypsum based

plasterboard required if13mm plaster not used, to

comply with acousticrequirements

Masonry: Cavity Wall Insulation - Partial fillConcrete Separating FloorPsi value = 0.0541W/mK

Thermal continuity checklist

1. Check that there is no debris in the cavity

Detail 2.14

Air tightness checklist

Design stage1. Check that any air tightness barrier used

in the external wall is secured onto thefloor slab

2. If plaster is use as an air tightness barrierseal over junction at floor with barrier tape

Vapour control layer

Insulation between the studs in additionto the cavity insulation. This insulationmust be tightly fitted, leaving no gaps

Vapour control layer

Vapour control layerbelow timber floor finish

HEAT 2.7 software image of isothermsthrough junction detail.

For illustrative purposes only.

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.

Design advice

Minimising condensation risk1. Check that insulation is tightly fixed into

the studs adjacent to the floor junction,leaving no gaps

Thermal Resistance of insulation used indetails:

Wall (cavity) - 2.500 (m²K)/WWall (inner leaf) - 2.272 (m²K)/W

Vapour control layer lappedover corner junction and taped to

underside of floor construction

Separating floors requireto comply with Section 2:Fire and Section 5: Noise

Vapour barrier lapped overcorner junction and taped tosurface of floor construction

Alternative air barrier - parge coatof plaster finish on blockwork

Masonry: Cavity Wall Insulation - Partial fillTimber Intermediate FloorPsi value = 0.0109W/mK Detail 2.15

Vapour control layer in wall

Insulation between the studs in additionto the cavity insulation. This insulationmust be tightly fitted, leaving no gaps

Air tightness barrier to becontinuous behind joists

Thermal continuity checklist

1. Check that there is no debris in the cavity

Minimum 50mmstrip of rigidinsulation withthermal conductivity(λ value) notexceeding 0.025W/mK should beinstalled betweenjoists

HEAT 2.7 software image of isothermsthrough junction detail.

For illustrative purposes only.

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.

Design advice

Minimising condensation risk1. Check that insulation is tightly fixed into

the studs adjacent to the floor junction,leaving no gaps

Thermal Resistance of insulation used indetails:

Wall (cavity) - 2.500 (m²K)/WWall (inner leaf) - 2.272 (m²K)/WInsulated infill strip - 1.136(m²K)/W

Air tightness checklist

1. Check that any air tightness barrier usedin the internal wall overlaps with the layerin the floor or ceiling

Alternative:If the air tightness barrier is installed ontothe face of the blockwork wall and runscontinuously through the floorconstruction, infill any gaps where floorfixing is made to external wall

Air tightness barrier cornerstrip lapped over top ofjoists and joist hangers

Vapour control layer lappedover corner junction and taped

to air tightness barrier

Joists shown supportedon joist hangers

Alternative air barrier - parge coatof plaster finish on blockwork

Masonry: Cavity Wall Insulation - Partial fillGround Floor / Separating Wall junction - Timber susp. floorPsi value = 0.2365W/mK Detail 2.16

Sub floor ventilation should beprovided, minimum 1500mm²

per run of external wall or500mm² per m² of floor area

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

Air tightness barrier in wall (plaster option shown)

Damp proof membrane

Air tightness layer belowtimber floor finish

Solum

Insulation directly under flooring -supported on netting draped over joists

and stapled at the required depths

Air tightness checklist

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

2. Consider gluing joints between floorboards

Thermal continuity checklist

1. Ensure that insulation is tightly fitted to theback of the masonry wall

HEAT 2.7 software image of isothermsthrough junction detail.

For illustrative purposes only.

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.

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.

Thermal Resistance of insulation used indetails:

Internal Wall - 1.136 (m²K)/WFloor - 5.455 (m²K)/W

Masonry: Cavity Wall Insulation - Partial fillConcrete Ground Floor/ Separating Wall: Insulation Below SlabPsi value = 0.2736W/mK Detail 2.17

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

and floor using a flexible sealant

Air tightness barrier in wall (plaster shown)

Damp proof membrane

Thermal continuity checklist

1. Ensure that insulation is tightly fittedagainst the separating wall

Air tightness checklist

1. Check that there are no gaps between thewall and floor constructions

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

HEAT 2.7 software image of isothermsthrough junction detail.

For illustrative purposes only.

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.

Minimum 50mm strip of insulationwith thermal conductivity (λ value)

not exceeding 0.025 W/mK should beinstalled between wall and the slab

Design advice

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

timber floor, use a strip of perimeterinsulation with a minimum R value of0.75 m²/KW for the depth of the screed

Alternative 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.

Thermal Resistance of insulation used indetails:

Insulated infill strip - 1.136 (m²K)/WFloor - 3.864 (m²K)/W

Tape corner strip of airtightness membraneover wall / floor junction Vapour control layer in floor

Masonry: Cavity Wall Insulation - Partial fillConcrete Ground Floor/ Separating Wall: Insulation Above SlabPsi value = 0.2822W/mK Detail 2.18

Air tightness checklist

1. Check that there are no gaps between thewall and floor constructions

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

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

and floor using a flexible sealant

Air tightness barrier in wall (plaster option shown)

Damp proof membrane

Thermal continuity checklist

1. Ensure that insulation is tightly fittedagainst the separating wall

HEAT 2.7 software image of isothermsthrough junction detail.

For illustrative purposes only.

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.

Minimum 20mm strip of insulationwith thermal conductivity (λ value)

not exceeding 0.025 W/mK should beinstalled between wall and the slab

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 atimber floor, use a strip of perimeterinsulation with a minimum R value of0.75 m²/KW for the depth of the screed

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.

Thermal Resistance of insulation used indetails:

Internal Wall - 1.136 (m²K)/WInsulated infill strip - 0.455 (m²K)/WFloor - 3.864 (m²K)/W

Tape corner strip of airtightness membraneover wall / floor junction

Vapour control layer in floor

Masonry: Cavity Wall Insulation - Partial fillConcrete Separating Floor / Separating Wall junctionPsi value = 0.0133W/mK Detail 2.19

Air tightness barrier inwall (plaster shown)

Air tightness barrier lappedover corner junction

5mm minimum resilient flankingstrip to be used at floor junction. See

Technical Standards GuidanceNotes for Section 5 for details

Air tightness barrier in wall(plaster option shown)

Separating floors requireadditional layers and components

to comply with Section 2: Fireand Section 5: Noise

Air tightness checklist

1. Check that any air tightness barrier usedin the internal wall overlaps with the layerin the floor or ceiling

Thermal continuity checklist

1. Ensure that there are no gaps betweenfloor slabs or between the top of the walland the underside of the floor slab.

2. Ensure that the insulation is tightly fitted tothe top of the floor slab.

HEAT 2.7 software image of isothermsthrough junction detail.

For illustrative purposes only.

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.

Design advice

Minimising condensation risk1. Check that concrete slab is level and

clear of debris before fitting the insulationat floor level

If membrane used, seal onto top ofscreed. If render or plaster used as

airtightness layer, add a corner stripof membrane to cover junction

before applying finish

Cavity barrier isused in toprevent thermalbypass.Usedense insulationor proprietarycavity barrier insleeve

Masonry: Cavity Wall Insulation - Partial fillTimber Intermediate Floor / Separating Wall junctionPsi value = 0.1053W/mK Detail 2.20

Air tightness barrier in to becontinuous behind joists

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

and floor using a flexible sealant

Air tightness barrier inwall (plaster shown)

Thermal continuity checklist

1. Check that there are no gaps between thefloors and the separating wall.

Air tightness checklist

1. Check that any air tightness barrier usedin the internal wall overlaps with the layerin the floor or ceiling

Alternative:If the air tightness barrier is installed ontothe face of the blockwork wall and runscontinuously through the floorconstruction, infill any gaps where floorfixing is made to the wall

Air tightness barrier inwall (plaster shown)

HEAT 2.7 software image of isothermsthrough junction detail.

For illustrative purposes only.

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.

Design advice

Minimising condensation risk

See general guidance notes

Masonry: Cavity Wall Insulation - Partial fillPitched Roof: Cold Roof / Separating Wall junctionPsi value = 0.2008W/mK Detail 2.21

Thermal continuity checklist

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

fitted perpendicularly, to cover junctions

Air tightness checklist

1. Check that there are no gaps betweenthe top of the masonry wall and theunderside of the roof

2. Check that the air tightness barrierused in the ceiling overlaps with thelayer in the wall

HEAT 2.7 software image of isothermsthrough junction detail.

For illustrative purposes only.

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.

Vapour control layer inwall and ceilingMinimum 50mm strip of

rigid insulation withthermal conductivity (λvalue) not exceeding0.025 W/mK should beinstalled between walland the last joist

Design advice

Minimising condensation risk1. Check ventilation paths are clear before

installing insulation above the ceiling

Thermal Resistance of insulation used indetails:

Roof - 9.500(m²K)/W

Note: See detail numbers 2.01 and 2.02 forother junctions using this roof construction

For more informationon acoustic details see

guidance in Section 5 ofthe Technical Standards

Cavity barrier is used in toprevent thermal bypass.Uselow or soft density insulationwrapped in plastic ormembrane

Masonry: Cavity Wall Insulation - Partial fillPitched Roof: Ventilated Batten Void/ Separating Wall junctionPsi value = 0.2247W/mK Detail 2.22

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

Air tightness barrier inwall and ceiling (plaster

shown on wall)

Minimum 50mm ventilation path over insulation

Where two insulation types areused together see

supplementary guidance

Thermal continuity checklist

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

perpendicularly, to cover junctions

Air tightness checklist

1. Check that there are no gaps betweenthe top of the masonry wall and theunderside of the roof

2. Check that the air tightness barrierused in the ceiling overlaps with thelayer in the wall

HEAT 2.7 software image of isothermsthrough junction detail.

For illustrative purposes only.

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.

Design advice

Minimising condensation risk1. Check ventilation paths are clear before

installing insulation above the ceiling

Thermal Resistance of insulation used indetails:

Internal Wall - 2.045 (m²K)/WRoof - 9.500(m²K)/W

Note: See detail numbers 2.03, 2.04 and 2.05for other junctions using this roof construction

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

Cavity barrier is used in toprevent thermal bypass.Use lowor soft density insulationwrapped in plastic or membrane

Masonry: Cavity Wall Insulation - Partial fillWall JunctionPsi value = 0.0607W/mK Detail 2.23

Plan view

Vapour control layer

Insulation between thestuds in addition to thecavity insulation. Thisinsulation must betightly fitted, leaving nogaps

Thermal continuity checklist

1. Check that there is no debris in the cavity.2. Check that there are no gaps in insulation

fitted at the corner junction in the cavity

Air tightness checklist

1. Check that any air tightness barrier usedin the external walls overlaps at thecorner

HEAT 2.7 software image of isothermsthrough junction detail.

For illustrative purposes only.

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.

Design advice

Minimising condensation risk1. Check that insulation is tightly fixed into

the studs at the corner junction, leavingno gaps

Thermal Resistance of insulation used indetails:

Wall (cavity) - 2.500 (m²K)/WWall (inner leaf) - 2.272 (m²K)/W

Masonry: Cavity Wall Insulation - Partial fillWall Junction - Inward Corner Psi value = -0.0826W/mK Detail 2.24

Plan view

Vapour control layer

Insulation betweenthe studs in addition to

the cavity insulation.This insulation must be

tightly fitted, leavingno gaps

Thermal continuity checklist

1. Check that there is no debris in the cavity

Air tightness checklist

1. Check that any air tightness barrier usedin the external walls overlaps at thecorner

HEAT 2.7 software image of isothermsthrough junction detail.

For illustrative purposes only.

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.

Design advice

Minimising condensation risk1. Check that insulation is tightly fixed into

the studs at the corner junction, leavingno gaps

Thermal Resistance of insulation used indetails:

Wall (cavity) - 2.500 (m²K)/WWall (inner leaf) - 2.272 (m²K)/W