Post on 10-May-2020
Non - Residential New Build4.2.3 Pitched Roofs - Rafter Level
August 2008: Issue 1
4.0Non-residential new build
Non-residential New Build
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Introduction find online pageSolution optimiser and pathfinder 330Design considerations 334
Design Details 512
Pitched Roof - Rafter Level Contents
find online pageBetween rafters only(Crown Room in Roof Roll 37) Pr01 512
Between rafter only (Crown Rafter Roll 32) Pr02 514
Between engineered timber rafters Pr04 516
Between and below rafter with(Crown Rafter Roll 32 or 37 and PIR) Pr05 518
Between and below rafter (Crown RafterRoll 32 or 37 and Polyfoam Linerboard) Pr06 520
Between and below rafters withcounter battens Pr07 522
Between rafters with service duct below Pr08 524
Between rafters with Multifoil below Pr09 526
Between and above rafters (PolyfoamPitched Roofboard with Raftersqueeze) Pr10 528
Between and above rafters(Rocksilk Pitched Roof Slab) Pr11 530
Between, above and below rafter Pr12 532
Refurbishment detailsUpgrading ceiling level insulation/HR underlay Pr13 534
General details 536
Pitched roofs – rafter levelSolution optimiser and pathfinder
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4.2.3 Non-residential new build: Roofs
The thermal efficiency required by the Building Regulations,coupled with the desire to create interesting and attractiveinterior working spaces, can make the specification ofinsulation for this application a complex issue. Insulationplaced in the plane of the roof pitch creates a warm roof space.
Single layer sloping ceiling• Uses void in structure as insulation zone
• Semi rigid mineral wool products can be friction fitted with no special fixings, speeding up installation
• Simple installation from within sealed roof
• Utilises Euroclass A1 insulation throughout
• Using mineral wool insulation will significantly improve the acousticperformance of the roof
Rafter levelsloping ceiling• Use when low U-values are required
and internal lining would restrict head room in the room in roof
• Rafters are within the insulated envelope and kept warm, removing the risk of condensation forming on them
• Using mineral wool will significantly improve the acoustic performance of the roof
Double layer sloping ceiling• Systems can achieve low U-values even
with shallow rafters
• Minimises thermal bridging through timber rafters
• Systems with Low emissivity air layers provide service void
• Using mineral wool will significantly improve the acoustic performance of the roof
This option allows the designer to omit a flatceiling and use the space within the roof volumeas a functioning area of the property withoutsignificantly altering the building envelope.Where cables and piped services are to beinstalled within the heated envelope, theplasterboard lining may be battened out toprovide a suitable duct.
These types of construction require the installationof insulation at rafter level, following the pitch ofthe roof. Knauf Insulation products provide anumber of insulation options for this type ofconstruction, maximising both space and thermalefficiency.
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4.2.3Non-residential new build: Roofs
Between and below rafters with counterbattensProduct*: Crown Room-in-Roof Roll 32 or 37 (2 layers)Description: Glasswool friction fitted between rafters, counter battens below infilled with glasswool Page No: 522
Pr07
Between rafters onlyProduct*: Rocksilk Flexible SlabDescription: Rock mineral wool friction fitted between rafters
Page No: 514
Between rafters onlyProduct*: Crown Room-in-Roof Roll 32 or 37Description: Glasswool friction fitted between rafters
Page No: 512Pr01
Pr02/3
Between engineered timber raftersProduct*: Crown Room-in-Roof Roll 32 or 37 Description: Glasswool friction fitted between engineered timber rafters
Page No: 516Pr04
Between and below rafterProduct*: Crown Rafter Roll 32 or Crown Room-in-Roof Roll 32 or 37 Description: Glasswool friction fitted between rafters, PIR fixed below rafters
Page No: 518
Between and below rafters with insulated plasterboardProducts*: Crown Room-in-Roof Roll 32 or 37, Polyfoam Liner BoardDescription: Glasswool friction fitted between rafters, insulated plasterboard fixed below rafters Page No: 520
Elemental U-value requirement
Pitched roof with insulation at rafter levelConstruction compatibility with Part L2A
Knauf Insulation solution U-values 0.23 0.22 0.21 0.20 0.19 0.18 0.17 0.16 0.15 0.130.14 0.12 0.110.26 0.25 0.24 0.10
KeyU-values achievable by constructions within this document.
* Recommended Knauf Insulation product(s). Other products may be applicable.
Find online. Visit www.knaufinsulation.co.uk and key in construction code to find the most up to date information on your chosen solution.
Pb01
Area weighted average max
U-value England and Wales
and Northern Ireland
Typical U-value for compliance
England and Wales and Northern Ireland
Pr05
Pr06
continued overleaf
Between rafters with MultifoilProducts*: Crown Rafter Roll 32 or 37, Thinsulex multifoil/service voidDescription: Glasswool friction fitted between rafters, Thinsulex Multifoiland counter battens belowPage No: 526
Between rafters with service voidProduct*: Crown Room in Roof Roll 32 or 37Description: Glasswool friction fitted between rafters, Low E VCL and counter battens creating service void
Page No: 524
Between and above raftersProducts*: Polyfoam Pitched Roofboard,Polyfoam RaftersqueezeDescription: XPS board over rafters, compressible XPS board friction fitted between rafters Page No: 528
Between and above raftersProducts*: Rocksilk Krimpact Pitched Roofboard, Crown Room in Roof Roll 32 or 37, or Crown Rafter Roll Description: Rigid rock mineral wool board over rafters, friction fitted glasswool between rafters Page No: 530
Pr11
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4.2.3 Non-residential new build: Roofs
Pitched roofs – rafter levelSolution optimiser and pathfinder
KeyU-values achievable by constructions within this document.
* Recommended Knauf Insulation product(s). Other products may be applicable.
Find online. Visit www.knaufinsulation.co.uk and key in construction code to find the most up to date information on your chosen solution.
Pb01
Elemental U-value requirement
Pitched roof with insulation at rafter levelConstruction compatibility with Part L2A
Knauf Insulation solution
Pr08
Pr09
Pr10
U-values 0.23 0.22 0.21 0.20 0.19 0.18 0.17 0.16 0.15 0.130.14 0.12 0.110.26 0.25 0.24 0.10
Area weighted average max
U-value England and Wales
and Northern Ireland
Typical U-value for
compliance England and
Wales and Northern Ireland
continued from overleaf
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4.2.3Non-residential new build: Roofs
Pitched roofs – rafter levelInsulation at rafter level design
Utilising the loft area as a working spaceMany designers of commercial and publicbuildings (especially offices and schools) use theheight offered in the pitch of the roof to createlight, attractive interiors with high level slopingceilings which include light wells and roofwindows. The thermal efficiency required by theBuilding Regulations, coupled with the desire tocreate interesting and attractive interiors, canmake the specification of insulation for thisapplication a complex issue.
Pitched roofs – rafter levelInsulation at rafter level design
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4.2.3 Non-residential new build: Roofs
Rafter level insulationInsulation between the rafters can be designed intwo ways:
• ‘Breathing’ roof with LR underlay
• Ventilated design with HR underlay
Rafter level insulation with LR underlayWith this option, insulation fully fills the rafterspace without an airspace between the insulationand type LR underlay. Counterbattens are neededto ensure wind driven rain drains freely to thegutter.
The space created by the counterbattens allowsthe dispersion of any moisture that passesthrough the breather underlay. Where the roofcovering is very tight fitting, eaves ventilationabove the underlay is recommended.
A combined airtight/vapour control layer shouldbe placed on the warm side of the insulation. Thisnot only makes the ceiling convection tight, butalso restricts the amount of water vapour passing through the ceiling.
Where cables and piped services are to beinstalled, the plasterboard lining may be battenedout to provide a suitable servicesduct. The services should be routed on the warmside of the vapour control layer to avoid any puncturing.
Over rafter insulation with LR underlayInsulation over the rafters provides a completelyinsulated external envelope to the roofconstruction, and allows the maximum usablespace within the roof enclosure.
The insulation boards are laid across the rafters.It is important that there should be no gaps in theinsulation layer and no ventilation between theoutside and the attic space. A LR underlay mustbe provided to allow moisture vapour to diffusethrough the entire roof construction.
Counterbattens are fixed through the insulationboards and vapour permeable underlay into therafters. Where the over rafter insulation is over50mm thick, consideration should be given to thefixing of the counterbattens.
Further insulation is placed between the rafters toachieve the desired entire performance.If the insulation board over the rafters has a highvapour resistance, the use of mineral woolbetween the rafters is not recommended unlessthe designer is confident that an effective vapourcontrol layer can be provided to the underside ofthe rafters.
The rafters should be faced with 12.5mmplasterboard, or similar, to provide fireprotection.
Rafter level insulation with HR underlayWith this design, a 50mm ventilated airspace isrequired between the top of the insulation and thetiling underlay. Should the rafter depth beinsufficient to accommodate both the requiredthickness of insulation and the 50mm ventilatedairspace, an insulation/plasterboard laminate isrecommended. This has the added benefit ofminimising thermal bridging.
Ventilation openings should be provided at eachand every roof void at both low and high level.At the eaves, ventilation openings should beequivalent to a 25mm continuous gap. At theridge the ventilation opening should be theequivalent of a 5mm continuous gap each side ofthe ridge.
Care is needed where rooflights and dormerwindows interrupt the ventilation path. Ventilationto the outside must be provided at the top andbottom of each space between the rafters.
It is usual for the HR underlay to drape at least10mm between the rafters to avoid the need forcounterbattens.
A vapour control layer must be applied to thewarm side of the insulation.
Flanking sound
Rafter level insulation with LR underlay
The roof and wall insulation should be tightly butted with no gaps to avoid air leakage and thermal bridging
Ventilation space created by counter battensGaps between tiles and slates allow watervapour to escape (for tight fitting slates,eaves ventilation is recommended).
Snow and rain driven through tilingcan drain safely to gutter Vapour control layer to
underside of insulation
UV resistant eaves tray to dress into gutter
Continuous diffusion of moisture
Insect guard
Continuous diffusion of moisture
BS 5250 provides guidance for pitched roofswith two types of tiling underlay:
• Type HR (high water vapour resistance), such as traditional sarking felt
• Type LR (Low water vapour resistance – less than 0.25 MN s/g)
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4.2.3Non-residential new build: Roofs
Roofs insulated at rafter level that adjoin masonryseparating walls between ‘rooms for residentialpurposes’ can act as a flanking path for soundtransmission between the rooms. Using glasswoolroof space insulation will restrict the passage ofsound from the roof space into the rooms below,reducing the effect of flanking soundtransmission. The excellent acoustic properties ofmineral wool are also beneficial at rafter level inreducing the noise from road traffic andairplanes as well as rainfall drumming on theroof.
The ceiling and dwarf walls should be lined withtwo layers of plasterboard with a combinedminimum mass of 16 kg/m2 . Normally thiswould be achieved using two layers of 12.5mmPlasterboard, but could also be achieved using a layer of 9.5mmplasterboard and a layer of 15mm plasterboard.
Warm roof construction details to restrict flankingtransmissions and external noise
Two layers of plasterboard to underside of rafters and to dwarf
stud walls
Section A-A
Flexible closer between junction of separating wall and roof
12.5mmplasterboard(minimum mass8kg/m2)
Section through roof
100mm mineral wool (density of 10 kg/m3)
design detail finderKnauf Insulation solutions for these types of construction can be found on pages 512-539
Pitched roofs – rafter levelBetween rafters only
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6.1.2 Design details: Pitched roofs
Advantages Uses void in structure as insulation
zone
Semi-rigid mineral wool products can be friction fitted with no special fixings, speeding up installation
Simple installation from within sealed roof
Utilises Euroclass A1 insulation throughout
Using Crown Room-in-Roof Roll 37 will significantly improve the acoustic performance of the roof – reducing airborne noise
Crown Room-in-Roof Roll 37 canbe used along with an extra layer ofplasterboard to satisfy the requirementsof Robust Details to restrict flankingsound around separating walls
Low cost option
Long rolls with greater coverage per roll than other equivalent products
Knauf Breatheline
InstallationKnauf Breatheline is pulled taught and laiddirectly over the rafters. 50x32mm counterbattens are nailed into the rafters with minimumpenetration of 38mm into the rafter.Alternatively, helical fixings can be used with aminimum penetration of 35mm into the rafter.Tiling battens are nailed into the counterbattens. Finally, the roofing tiles or slates arefixed to the manufacturer’s recommendations.
Crown Room-in-Roof Roll 37 is simply frictionfitted to fully fill the space between the rafters,with all joints closed, and is normally fitted frombelow once the roof is weathertight.
The roof insulation should be cut to shape to linkwith the wall insulation to avoid a thermalbridge at the eaves.
IntroductionThe most satisfactory method of insulating atpitch level within a roof is when the requiredthermal performance can be achieved withinthe depth of the rafters. This is because it doesnot increase the depth of the roof build up,special fixings are not required and allinsulation work can be carried out from withinthe sealed roof space.
Typical constructionA pitched roof of timber rafters with tiles orslates on battens and counter battens on KnaufBreatheline. The space between the rafters isfully insulated with Crown Room-in-Roof Roll 37.
ProductsCrown Room-in-Roof Roll 37 is made from glass mineral wool and formed into rolls whichare dimensioned to fit tightly between rafters at600mm centres. The rolls are lightweight,flexible, resilient and non-combustible, and arefaced with a low emissivity vapour control layer.The facing is wider than the roll to overlap therafters to aid fixing, and create a vapourcontrol layer. Its manufacture has a very lowimpact on the environment and is classified asZero ODP and Zero GWP*
* Ecohomes and Code for Sustainable Homes classification
Robust DetailsIn order to comply with the Robust Detailsrequirements for masonry separating walls androof junctions, the complete ceiling area shouldcontain at least 100mm of mineral wool(10 kg/m3 min) between the rafters andinstalled so that it is flush with the soffit of therafters. Any dwarf walls which are adjacent tothe separating wall where there are rooms inthe roof should also contain at least 100mm ofmineral wool (10 kg/m3 min).
Knauf Breatheline
Crown Room-in-RoofRoll 37
Plasterboard lining
Counter battens
Vapour control layer
Pr01
513
6.1.2Design details: Pitched roofs
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Typical specificationThe whole area of the pitched roof to beinsulated with Crown Room-in-Roof Roll37…mm thick, friction fitted between therafters. The insulation to be pushed over thewall plate at the eaves to link up with thewall insulation.
Alternatively, refer to NBS clauses: P10/140and 320
Typical section
Table 7: Typical U-values of roofs with insulation between rafters
Product Thickness U-values
(mm) (W/m2K)
Crown Room-in-Roof Roll 37 200 0.20
160 0.25Notes: Rafter sizes assumed to be 38mm wide at 600mm centres (6.3% bridging) and the same depth as the insulation. The U-values have been calculated in accordance with BS EN ISO 6946:1997.
PerformanceThermal performanceCrown Room-in-Roof Roll 37 has a thermalconductivity of 0.037 W/mK.
Table 7 gives U-values for typical constructionswith insulation between the rafters.
Fire performanceCrown Room-in-Roof Roll 37 is classified asEuroclass A1 to BS EN ISO 13501-1.
Vapour resistanceKnauf Breatheline has a vapour resistanceof 0.22 MNs/g.
Refurbishment of existing roofsThis is a valid solution for the refurbishment of an existing roof where the roof tiles and roof tile underlay are not being removed. In thesecircumstances a continuous 50mm gap must be maintained between the insulation and the roof tile underlay which is vented at theeaves and ridge.
The U-values achieved are as shown in Table 7.
Plasterboard lining
Counter battens
Knauf Breatheline
Vapour control layer
Crown Room-in-Roof Roll 37
Pitched roofs – rafter levelBetween rafters only
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6.1.2 Design details: Pitched roofs
InstallationKnauf Breatheline is pulled taught and laiddirectly over the rafters. 50x32mm counterbattens are nailed into the rafters with minimumpenetration of 38mm into the rafter.Alternatively, helical fixings can be used with aminimum penetration of 35mm into the rafter.Tiling battens are nailed into the counterbattens. Finally, the roofing tiles or slates arefixed to the manufacturer’s recommendations.
Crown Rafter Roll 32 is simply friction fitted (inlayers if necessary) to fully fill the spacebetween the rafters. All layers should be closelybutt jointed, and are usually installed frombelow once the roof is weathertight.
If installed in layers, ensure joints arestaggered.
The roof insulation should be cut to shape to linkwith the wall insulation to avoid a thermalbridge at the eaves.
A continuous vapour control layer should befixed to the underside of the rafters with alljoints sealed.
IntroductionThe most satisfactory method of insulating atpitch level in a roof is when the requiredthermal performance can be achieved withinthe depth of the rafters. This is because it doesnot increase the depth of the roof build up,special fixings are not required and allinsulation work can be carried out from withinthe sealed roof space.
Typical constructionA pitched roof of timber rafters with tiles orslates on battens and counter battens on KnaufBreatheline. The space between the rafters isfully insulated with Crown Rafter Roll 32.
ProductsCrown Rafter Roll 32 is made from glassmineral wool and formed into rolls which arelightweight, flexible, resilient and non-combustible. Its manufacture has a very lowimpact on the environment and is classified asZero ODP and Zero GWP*
Knauf Breatheline is a breathable membranewith a polypropylene non-woven coating onboth sides – see also page 534.
Rocksilk Flexible Slab is a semi-rigid rockmineral wool slab. In this construction RocksilkFlexible Slab can be used as an alternative toCrown Rafter Roll 32. See Table 9.
* Ecohomes and Code for Sustainable Homes classification
Robust DetailsIn order to comply with the Robust Detailsrequirements for masonry separating walls androof junctions, the complete ceiling area shouldcontain at least 100mm of mineral wool(10 kg/m3 min) between the rafters andinstalled so that it is flush with the soffit of therafters. Any dwarf walls which are adjacent tothe separating wall where there are rooms inthe roof should also contain at least 100mm ofmineral wool (10 kg/m3 min).
Advantages Uses void in structure as insulation
zone
Mineral wool products can be frictionfitted with no special fixings, speeding up installation
Simple installation from within sealed roof
Utilises Euroclass A1 insulation throughout
Using Crown Rafter Roll 32 willsignificantly improve the acousticperformance of the roof – reducingairborne noise
Crown Rafter Roll 32 can be used alongwith an extra layer of plasterboard tosatisfy the requirements of Robust Detailsto restrict flanking sound aroundseparating walls.
Long rolls with greater coverage per roll than other equivalent products
Pr03Knauf Breatheline
Pr02
Knauf Breatheline
Crown Rafter Roll 32
Plasterboard lining
Counter battens
Vapour control layer
PerformanceThermal performanceCrown Rafter Roll 32 has a thermalconductivity of 0.032 W/mK.
Rocksilk Flexible Slab has a thermal conductivityof 0.035 or 0.037 W/mK.
Tables 8 and 9 give U-values for typicalconstructions with insulation between the rafters.
Fire performanceCrown Rafter Roll 32 and Rocksilk Flexible Slabare classified as Euroclass A1 to BS EN ISO 13501-1.
Vapour resistanceKnauf Breatheline has a vapour resistanceof 0.22 MNs/g.
Refurbishment of existing roofsThis is a valid solution for the refurbishment of an existing roof where the roof tiles and roof tile underlay are not being removed. In thesecircumstances a continuous 50mm gap must be maintained between the insulation and the roof tile underlay which is vented at theeaves and ridge.
The U-values achieved are as shown inTables 8 and 9.
515
6.1.2Design details: Pitched roofs
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Typical specificationThe whole area of the pitched roof to beinsulated with Crown Rafter Roll 32/RocksilkFlexible Slab*…mm thick, friction fittedbetween the rafters. The insulation to bepushed over the wall plate at the eaves tolink up with the wall insulation. (*Delete as appropriate)
Alternatively, refer to NBS clauses: P10/140and 320
Table 8: Typical U-values of roofs with insulation between rafters
Product Thickness U-values
(mm) (W/m2K)
Crown Rafter Roll 32 200 (100+100) 0.18
185 (100+85) 0.19
175 (100+75) 0.20
165 (100+65) 0.22Notes: Rafter sizes assumed to be 38mm wide at 600mm centres (6.3% bridging) and the same depth as the insulation. The U-values have been calculated in accordance with BS EN ISO 6946:1997.
Plasterboard lining
Counter battens
Knauf Breatheline
Vapour control layer
Crown Rafter Roll 32/Rocksilk Flexible Slab
Typical section
Table 9: Typical U-values of roofs with insulation between rafters
Product Thickness U-values
(mm) (W/m2K)
Rocksilk Flexible Slab 200 (2x100) 0.20
190 (100+90) 0.21
180 (2x90) 0.22
170 (100+70) 0.23
160 (90+70) 0.25
150 (90+60) 0.26Notes: Rafter sizes assumed to be 38mm wide at 600mm centres (6.3% bridging) and the same depth as the insulation. The U-values have been calculated in accordance with BS EN ISO 6946:1997.
Pr03
Pr02
Advantages Makes excellent use of the deep
rafter depth
Using Crown Rafter Roll 32 will significantly improve the acoustic performance of the roof restricting airborne noise
Crown Rafter Roll 32 can be used along with an extra layer of plasterboard to satisfy the requirements of Robust Details to restrict flanking sound around separating walls
Pitched roofs – rafter levelBetween engineered timber rafters
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6.1.2 Design details: Pitched roofs
ProductsCrown Rafter Roll 32 is made from glassmineral wool and formed into rolls which arelightweight, flexible, resilient and non-combustible. Its manufacture has a very lowimpact on the environment and is classified asZero ODP and Zero GWP*
Knauf Breatheline is a breathable membranewith a polypropylene non-woven coating onboth sides – see also page 534.
* Ecohomes and Code for Sustainable Homes classification
Typical constructionA pitched roof of engineered timber rafters withtiles or slates on battens. 8mm plywood sarkingfixed to the top of the rafters with KnaufBreatheline laid across the plywood. Insulatedwith Crown Rafter Roll 32 between the rafterssupported by plywood fixed to the upper edgeof the lower flange of the engineered timberrafter and lined internally with a vapour controllayer and plasterboard.
Install the vapour control layer to the lower faceof the plywood support pieces and across thelower edge of each engineered timber flangetaping all joints to ensure its integrity ismaintained. After first fix services have beeninstalled finish using standard dryliningtechniques.
If the insulation is fitted from below then theplywood sarking board, Knauf Breatheline,counter battens, tilling battens and slates or tilesare fixed as above. Friction fit Crown Rafter Roll32 (in layers if necessary) between the rafters.The insulation should be butt jointed andcontinuous with the wall insulation to avoidthermal bridging. Install the insulation supportpieces and fix the vapour control layer to thelower face of the plywood support pieces andacross the lower edge of each engineeredtimber flange taping all joints to ensure itsintegrity is maintained. After first fix serviceshave been installed finish using standarddrylining techniques.
InstallationThe insulation is fitted from above or belowonce the roof is watertight.
If fitting from above fix the ply wood supportpieces to the upper edge of the lower flange ofthe engineered timber rafter making sure thetimber fits tightly to the sides of the web of therafters. Friction fit Crown Rafter Roll 32 betweenthe web and upper flange of the engineeredtimber rafter to the full depth, in layers ifnecessary. The insulation should be but jointedand continuous with the wall insulation to avoidthermal bridging.
Fix the 8mm plywood sarking board to the topof the rafters. Knauf Breatheline is laid directlyover the plywood sarking board and 50x32mmcounter battens placed on top of the KnaufBreatheline directly above the rafters and nailedinto the rafters with minimum penetration of38mm into the rafter – alternatively, helicalfixings can be used with a minimum penetrationof 35mm into the rafter. Tiling battens arenailed into the counter battens and the roofingtiles or slates are fixed to the manufacturer’srecommendations.
Knauf Breatheline
Pr04
Knauf Breatheline
Crown Rafter Roll 32
Plasterboard
Counter battens
8mm plywood support for insulation
8mm plywood sarking
517
6.1.2Design details: Pitched roofs
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Knauf Breatheline
Vapour control layer
Crown Rafter Roll 32between rafters
8mm ply sarking
Counter battens
Service void formed in depthof lower flange
12.5mm plasterboard
Typical specificationThe whole area of the pitched roof to beinsulated with Crown Rafter Roll 32, ofthickness ...... mm friction fitted between theengineered rafters. The width of theinsulation should be appropriate to thespacing of the rafters.
Staple a vapour control layer to theunderside of the rafters and seal all joints.
Nail 50x25mm timber battens to the raftersto form a service void. Nail foil backedplasterboard to the timber battens.
Alternatively, refer to NBSclauses.
Table 10: Typical U-values for roofs with Crown Rafter Roll 32 between engineered rafters
Insulation U-values (W/m2K)Product Thickness Service void Low E service void
(mm)
Crown Rafter Roll 32 200 (2x100) 0.16 0.15
Note: Rafters assumed to be 58mm wide, 241mm deep with 9.5mm web, spaced at 600 centres, with no bracing betweenthe rafters. The U-values have been calculated in accordance with BS EN ISO 6946: 1997
Typical section
PerformanceThermal performanceCrown Rafter Roll 32 has a thermal conductivityof 0.032 W/mK.
Table 10 gives U-values for typical constructionswith insulation between the rafters.
Acoustic performanceCrown Rafter Roll 32 meets the specification fora mineral wool insulation required for thecontrol of flanking sound as described inAppendix A of Robust Details.
Fire performanceCrown Rafter Roll 32 is classified as Euroclass A1 to BS EN ISO 13501-1.
Vapour resistanceKnauf Breatheline has a vapour resistance of 0.22 MNs/g.
Pitched roofs – rafter levelBetween and below rafters
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6.1.2 Design details: Pitched roofs
Knauf Breatheline
Advantages System achieves low U-value even
with shallow rafters
Crown Rafter Roll 32 or Crown Room-in-Roof Roll 32/37 are compressible so it is easy to friction fit the product tight to the sides of rafters ensuring that there is no cold air penetration at junction between the insulation and rafters
Using Crown Rafter Roll 32 or Crown Room-in-Roof Roll 32/37 will significantly improve the acoustic performance of the roof restricting airborne noise
Crown Rafter Roll 32 or Crown Room-in-Roof Roll 32/37 can beused along with an extra layer ofplasterboard to satisfy the requirementsof Robust Details to restrict flankingsound around separating walls
ProductsCrown Room-in-Roof Roll 32/37 is made from glass mineral wool and formed into rolls whichare dimensioned to fit tightly between rafters at600mm centres. The rolls are lightweight,flexible, resilient, non-combustible, and arefaced with a low emissivity vapour control layer.The facing is wider than the roll to overlap therafters to aid fixing, and create a vapourcontrol layer. Their manufacture has a very lowimpact on the environment and is classified asZero ODP and Zero GWP*
Crown Rafter Roll 32 is made from glassmineral wool and formed into rolls which arelightweight, flexible, resilient and non-combustible - its manufacture has a very lowimpact on the environment and is classified asZero ODP and Zero GWP*
Knauf Breatheline is a breathable membranewith a polypropylene non-woven coating onboth sides – see also page 534.
* Ecohomes and Code for Sustainable Homes classification
Typical constructionA pitched roof of timber rafters with tiles orslates on battens. Either with counter battens if Knauf Breatheline is pulled taught andinsulation is to the full depth of the rafters,
or alternatively without counter battens if it isdraped and the insulation stops at least 10mmbelow the top of the rafters. Insulated withCrown Rafter Roll 32 or Crown Room-in-RoofRoll 32/37 between the rafters and linedinternally with rigid foam insulation board.
InstallationKnauf Breatheline is pulled taught and laiddirectly over the rafters. 50x32mm counterbattens are nailed into the rafters with minimumpenetration of 38mm into the rafter -alternatively, helical fixings can be used with aminimum penetration of 35mm into the rafter.Tiling battens are nailed into the counterbattens. Finally, the roofing tiles or slates arefixed, to the manufacturer’s recommendations.
Friction fit Crown Rafter Roll 32 or Crown Room-in-Roof Roll 32/37 between the rafters.The insulation should be butt jointed andcontinuous with the wall insulation to avoidthermal bridging.
Finally, the PIR/PUR plasterboard laminate isnailed or screwed to the underside of the raftersat maximum 300mm centres at least 12mm infrom the board edge.
The fixings should be long enough to penetrateat least 25mm into the timber. The boards arefinished using standard drylining techniques.
With service voidWhere a service void is provided, nail a foilfaced PIR/PUR board to the rafters and tape allthe board joints and joints where the boardabuts walls, roof windows and other intrusionswith self-adhesive aluminised tape to completethe vapour control layer. The vapour controllayer formed by the PIR/PUR insulation boardand the tape should form a complete, unbroken,barrier to the warm side of the insulation. Thevapour control layer should be linked to the airbarrier in the external walls
Nail 50mm wide timber battens through thePIR/PUR board into the rafters. The battens tobe a minimum of 25mm deep but to suit therequired depth of the service void. Afterinstalling first fix services, nail plasterboard tothe timber battens. The boards are finishedusing standard drylining techniques.
PerformanceThermal performanceCrown Rafter Roll 32 has a thermal conductivityof 0.032 W/mK.
Crown Room-in-Roof Roll 32 has a thermalconductivity of 0.032 W/mK.
Crown Room-in-Roof Roll 37 has a thermalconductivity of 0.037 W/mK.
Pr05
Knauf Breatheline
Crown Rafter Roll 32 or Crown Room-in-Roof Roll 32/37
PIR/PUR insulation board
519
6.1.2Design details: Pitched roofs
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Knauf Breatheline
Foil faced PIR/PUR insulation board
Crown Rafter Roll 32 or
Crown Room-in-Roof Roll 32/37
25mm service duct formed withtimber battens nailed to rafters
12.5mm plasterboard
The PIR/PUR is assumed to have a thermalconductivity of 0.023 W/mK.
Table 11 gives U-values for typical constructionswith insulation between and below the rafters.
Acoustic performanceCrown Rafter Roll 32 and Crown Room-in-RoofRoll 32/37 meet the specification for a mineralwool insulation required for the control offlanking sound as described in Appendix A of Robust Details.
Fire performanceCrown Rafter Roll 32 and Crown Room-in-RoofRoll 32/37 are classified as Euroclass A1 to BS EN ISO 13501-1.
Vapour resistanceKnauf Breatheline has a vapour resistance of0.22 MNs/g.
Refurbishment of existing roofsThis is a valid solution for the refurbishment of an existing roof where the roof tiles and roof tile underlay are not being removed. In thesecircumstances a continuous 50mm gap must be maintained between the insulation and the roof tile underlay which is vented at theeaves and ridge.
The U-values achieved are as shown in Table 11.
Typical specificationThe whole area of the pitched roof to beinsulated with Crown Rafter Roll 32/CrownRoom-in-Roof Roll 32/37*, friction fittedbetween the rafters. The width of theinsulation should be appropriate to thespacing of the rafters. (*Delete as appropriate)
PIR/PUR plasterboard laminate of thickness......mm with integral 12.5mm plasterboardnailed or screwed to the rafters at maximum300mm centres and finished using standarddrylining techniques.
Alternatively, refer to NBSclauses.
Table 11: Typical U-values with insulation between and below rafters
U-values (W/m2K)Thickness PIR/PUR Insulation Board 25mm services void with PIR/PUR Insulation
thickness (mm) Board, thickness (mm)
(mm) 20 30 40 20 30 40
Crown Room-in-Roof Roll 32
100 0.26 0.23 0.21 0.24 0.22 0.20
Crown Room-in-Roof Roll 37
200 0.17 0.16 0.15 0.16 0.15 0.14
160 0.20 0.19 0.17 0.19 0.17 0.16
100 0.28 0.25 0.23 0.26 0.23 0.21
Crown Rafter Roll 32
200 (2x100) 0.15 0.14 0.13 0.15 0.14 0.13
170 (2x85) 0.17 0.16 0.15 0.16 0.15 0.14
150 (2x75) 0.19 0.18 0.16 0.18 0.17 0.16
130 (2x65) 0.21 0.20 0.19 0.20 0.18 0.17
100 0.26 0.23 0.21 0.24 0.21 0.20
85 0.29 0.26 0.23 0.26 0.23 0.21
Notes: Rafters assumed to be 38mm wide at 600mm centres (6.3% bridging). The U-values have been calculated inaccordance with BS EN ISO 6946:1997 and BR443. The service void is assumed to have an R value of 0.34 m2K/W as is specified in BR443. The U-values are valid for service voids at least 25mm deep
Typical section
Pitched roofs – rafter levelBetween and below rafters with insulated plasterboard
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6.1.2 Design details: Pitched roofs
Advantages System achieves low U-value even
with shallow rafters
Can be used with taught or draped LR underlay
Polyfoam Linerboard provides thermal and lining functions in one application
Robust nature of Polyfoam in Polyfoam Linerboard supports the plasterboard, improving its impact resistance
Using Crown Room-in-Roof Roll 32/37 willsignificantly improve the acousticperformance of the roof restrictingairborne noise
Crown Room-in-Roof Roll 32/37 can beused along with an extra layer ofplasterboard to satisfy the requirementsof Robust Details to restrict flankingsound around separating walls
Long rolls with greater coverage per roll than other equivalent products
Crown Room-in-Roof Roll 32/37 or PolyfoamRaftersqueeze are friction fitted (in layers ifnecessary) between the rafters. They should bebutt jointed and continuous with the wallinsulation to avoid thermal bridging.
Finally, Polyfoam Linerboard is nailed or screwed to the underside of the rafters atmaximum 300mm centres at least 12mm infrom the board edge. The fixings should be longenough to penetrate at least 25mm into thetimber. The boards are finished using standarddrylining techniques.
PerformanceThermal performanceCrown Room-in-Roof Roll 32 has a thermalconductivity of 0.032 W/mK.
Crown Room-in-Roof Roll 37 has a thermalconductivity of 0.037 W/mK.
Polyfoam Raftersqueeze and the insulation inPolyfoam Linerboard has a thermal conductivityof 0.030 W/mK.
Table 12 gives U-values for typical constructionswith insulation between and below the rafters.
Typical constructionA pitched roof of timber rafters with tiles orslates on battens. Either with counter battens if Knauf Breatheline is pulled taught andinsulation is to the full depth of the rafters orwithout counter battens if it is draped and theinsulation stops at least a 10mm below the topof the rafters. Insulated with Crown Room-in-Roof Roll 32/37 or Polyfoam Raftersqueezebetween the rafters and lined internally withPolyfoam Linerboard.
InstallationKnauf Breatheline is pulled taught and laiddirectly over the rafters. 50x32mm counterbattens are nailed into the rafters with minimumpenetration of 38mm into the rafter.Alternatively, helical fixings can be used with aminimum penetration of 35mm into the rafter.Tiling battens are nailed into the counterbattens. Finally, the roofing tiles or slates arefixed, to the manufacturer’s recommendations.The insulation is fitted from below once the roofis weathertight.
ProductsCrown Room-in-Roof Roll 32/37 is made from glass mineral wool and formed into rolls whichare dimensioned to fit tightly between rafters at600mm centres. The rolls are lightweight,flexible, resilient, non-combustible, and arefaced with a low emissivity vapour control layer.The facing is wider than the roll to overlap therafters to aid fixing, and create a vapourcontrol layer. Its manufacture has a very lowimpact on the environment and is classified asZero ODP and Zero GWP*
Polyfoam Raftersqueeze is 100% ozonefriendly, extruded polystyrene insulation.It consists of a flexible infill piece of insulationthat fits between rafters, and allows for sometimber variation.
Polyfoam Linerboard is a laminate of Polyfoamextruded polystyrene and 9.5mm tapered edgeplasterboard.
Knauf Breatheline is a breathable membranewith a polypropylene non-woven coating onboth sides – see also page 534.
* Ecohomes and Code for Sustainable Homes classification
Pr06Knauf Breatheline
Knauf Breatheline
Crown Room-in-Roof Roll 32/37 orPolyfoam Raftersqueeze
Polyfoam Linerboard
521
6.1.2Design details: Pitched roofs
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Knauf Breatheline
Roof insulation to link with wall insulation
Polyfoam Linerboard
Crown Room-in-Roof Roll 32/37 orPolyfoam Raftersqueeze
Sealant to reduce air leakage
Air barrier
Typical specificationThe whole area of the pitched roof to beinsulated with Crown Room-in-Roof Roll32/37*/ Polyfoam Raftersqueeze ......mmthick, friction fitted between the rafters. Thewidth of the insulation should be appropriateto the spacing of the rafters.(*Delete as appropriate)
Polyfoam Linerboard of thickness ......mmwith integral 9.5mm plasterboard nailed orscrewed to the rafters at maximum 300mmcentres and finished using standard dryliningtechniques.
Alternatively, refer to NBS clauses: P10/140 and 320, and K10/245
Acoustic performanceCrown Room-in-Roof Roll 32/37 meets thespecification for a mineral wool insulationrequired for the control of flanking sound asdescribed in Appendix A of Robust Details.
Compression resistanceThe rigidity of the Polyfoam in PolyfoamLinerboard offers an excellent support to thefinished internal lining and assists in theresistance of impact, helping to prolong itsservice life.
Fire performanceCrown Room-in-Roof Roll 32/37 are classified as Euroclass A1 to BS EN ISO 13501-1.
Polyfoam insulation contains a flame retardantspecifically designed to inhibit localisedignition. The boards will melt if brought intocontact with high temperature sources.However, the use of the boards will not affectthe fire rating obtained by tiled roofs whenevaluated by assessment or tested to BS 476: Part 3: 2004.
Polyfoam Linerboard is faced with 9.5mmplasterboard which offers excellent fireperformance.
Table 12: Typical U-values of roofs with insulation between and below rafters
U-values (W/m2K)Product Thickness Polyfoam Linerboard Thickness (mm)
(mm) 25.5/9.5 36/9.5 45.5/9.5
Crown Room-in-Roof Roll 32 100 0.26 0.24 0.22
Crown Room-in-Roof Roll 37 200 0.17 0.16 0.15
160 0.20 0.19 0.18
100 0.29 0.26 0.24
Polyfoam Raftersqueeze 150 (2x75) 0.19 0.17 0.17
140 (65+75) 0.20 0.18 0.17
125 (50+75) 0.21 0.20 0.19
100 (2x50) 0.25 0.23 0.22
Notes: Rafter sizes assumed to be 38mm wide at 600mm centres (6.3% bridging) and the same depth as the insulation. The U-values have been calculated in accordance with BS EN ISO 6946:1997.
Typical section
Vapour resistanceKnauf Breatheline has a vapour resistance of 0.22 MNs/g.
Pitched roofs – rafter levelBetween and below rafters with counter battens
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6.1.2 Design details: Pitched roofs
Advantages Can be used with taught or draped
LR underlay
Using Crown Rafter Roll 32/CrownRoom-in-Roof Roll 32/37 willsignificantly improve the acousticperformance of the roof restrictingairborne noise
Crown Rafter Roll 32/Crown Room-in-Roof Roll 32/37 can be usedalong with an extra layer ofplasterboard to satisfy therequirements of Robust Details torestrict flanking sound aroundseparating walls
Long rolls with greater coverage per roll than other equivalent products
rafters and to any dwarf walls. Lap all joints inthe vapour control layer. Using a self adhesivealuminised tape seal all joints and staplepunctures in the air barrier; junctions betweenthe air barrier and any walls abutting the roofand any penetrations through the roof, such asroof windows. The vapour control layer shouldbe linked to the air barrier in the external walls.Nail plasterboard to the rafters and finish usingstandard drylining techniques.
PerformanceThermal performanceCrown Rafter Roll 32 has a thermal conductivityof 0.032 W/mK.
Crown Room-in-Roof Roll 32 has a thermalconductivity of 0.032 W/mK.
Crown Room-in-Roof Roll 37 has a thermalconductivity of 0.037 W/mK.
Table 14 gives U-values for typical constructionswith insulation between the rafters.
Acoustic performanceCrown Rafter Roll 32 and Crown Room-in-RoofRoll 32/37 meet the specification for mineralwool insulation required for the control offlanking sound as described in Appendix A ofRobust Details.
10mm below the top of the rafters. Insulatedwith Crown Rafter Roll 32 and Crown Room-in-Roof Roll 32/37 between the rafters. A layer ofCrown Rafter Roll 32 is installed above theCrown Room in Roll 32/37 if required and12.5mm plasterboard forms the internal lining.This is an ideal solution where the depth ofshallow rafters can be increased toaccommodate an increased thickness ofinsulation.
InstallationKnauf Breatheline is pulled taught and laiddirectly over the rafters. 50x32mm counterbattens are nailed into the rafters with minimumpenetration of 38mm into the rafter.Alternatively, helical fixings can be used with aminimum penetration of 35mm into the rafter.Tiling battens are nailed into the counterbattens. Finally, the roofing tiles or slates arefixed, to the manufacturer’s recommendations.
Friction fit, if required, a layer of Crown RafterRoll 32 into the rafter space leaving sufficientdepth to accommodate the Crown Room-in-RoofRoll 32/37 when this is installed between therafters. The insulation should be butt jointed andcontinuous with the wall insulation to avoidthermal bridging. Staple the laps of the integralvapour control layer to the underside of the
ProductsCrown Room-in-Roof Roll 32/37 is made fromglass mineral wool and formed into rolls whichare dimensioned to fit tightly between rafters at600mm centres. The rolls are lightweight,flexible, resilient, non-combustible and arefaced with a low emissivity vapour control layer.The facing is wider than the roll to overlap therafters to aid fixing, and create a vapourcontrol layer. Their manufacture has a very lowimpact on the environment and is classified asZero ODP and Zero GWP*
Crown Rafter Roll 32 is made from glassmineral wool and formed into rolls which arelightweight, flexible, resilient and non-combustible. Its manufacture has a very lowimpact on the environment and is classified asZero ODP and Zero GWP*
Knauf Breatheline is a breathable membranewith a polypropylene non-woven coating onboth sides – see also page 534.
* Ecohomes and Code for Sustainable Homes classification
Typical constructionA pitched roof of timber rafters set out at600mm centres with tiles or slates on battens.Either with counter battens if Knauf Breathelineis pulled taught and insulation is to the fulldepth of the rafters or without counter battens ifit is draped and the insulation stops at least
Knauf Breatheline
Pr07
Crown Room-in-Roof Roll 32/37
Knauf Breatheline
12.5mm plasterboard
523
6.1.2Design details: Pitched roofs
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Knauf Breatheline
Crown Room-in-Roof Roll32/37 with integral vapourcontrol layer
Crown Room-in-Roof Roll32/37 with integral vapourcontrol layer
Counter battens a 600mmcentres (as rafters)
Crown Room-in-Roof Roll 32/37
12.5mm plasterboard
12.5mm plasterboard
Typical specificationThe whole area of the pitched roof to beinsulated with Crown Rafter Roll 32/CrownRoom-in-Roof Roll 32/37*, friction fittedbetween the rafters. The width of theinsulation should be appropriate to thespacing of the rafters.
Timber battens to be nailed to the undersideof the rafters. A vapour control layer to bestapled to the timber battens.(*Delete as appropriate)
12.5mm plasterboard nailed or screwed tothe timber battens at maximum 300mmcentres and finished using standard dryliningtechniques.
Alternatively, refer to NBS clauses.
Fire performanceCrown Rafter Roll 32 and Crown Room-in-RoofRoll 32/37 are classified as Euroclass A1 to BSEN ISO 13501-1.
Vapour resistanceKnauf Breatheline has a vapour resistance of0.22 MNs/g.
Refurbishment of existing roofsThis is a valid solution for the refurbishment of an existing roof where the roof tiles and roof tile underlay are not being removed. In thesecircumstances a continuous 50mm gap must be maintained between the insulation and the roof tile underlay which is vented at theeaves and ridge.
The U-value achieved is as shown in Table 13.
Table 13: Typical U-values of roofs with insulation between rafters and battens
Product Thickness U-values (W/m2K)
Between rafters Crown Rafter Roll 32
(mm) 50 65 75 85 100
Crown Room-in-Roof Roll 32 100 0.24 0.21 0.20 0.19 0.17
Crown Rafter Roll 32
(mm) 50 65 75 85 100
Crown Room-in-Roof Roll 37 200 0.16 0.15 0.14 0.13 0.12
160 0.19 0.17 0.16 0.15 0.15
100 0.26 0.22 0.21 0.20 0.18
Rafters assumed to be 38mm wide at 600mm centres (6.3% bridging). The U-values have been calculated in accordancewith BS EN ISO 6946:1997.
Typical section
Timber battens at 600mmcentres
Advantages Can be used with taught or draped
LR underlay
Using Crown Rafter Roll 32/CrownRoom-in-Roof Roll 32/37 willsignificantly improve the acoustic performance of the roof restricting airborne noise
Crown Rafter Roll 32/Crown Room-in-Roof Roll 32/37 can be usedalong with an extra layer ofplasterboard to satisfy therequirements of Robust Details torestrict flanking sound aroundseparating walls
Using a low emissivity vapour control layer increases the thermal resistance of the service void, thus improving the U-value of the construction
Pr08
Pitched roofs – rafter levelBetween rafters with service void
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6.1.2 Design details: Pitched roofs
ProductsCrown Room-in-Roof Roll 32/37 is made from glass mineral wool and formed into rolls whichare dimensioned to fit tightly between rafters at600mm centres. The rolls are lightweight,flexible, resilient, non-combustible, and are isfaced with a low emissivity vapour control layer.The facing is wider than the roll to overlap therafters to aid fixing, and create a vapourcontrol layer. Their manufacture has a very lowimpact on the environment and is classified asZero ODP and Zero GWP*
Crown Rafter Roll 32 is made from glassmineral wool and formed into rolls which arelightweight, flexible, resilient and non-combustible. Its manufacture has a very lowimpact on the environment and is classified asZero ODP and Zero GWP*Knauf Breatheline is a breathable membranewith a polypropylene non-woven coating onboth sides – see also page 534.* Ecohomes and Code for Sustainable Homes classification
Knauf Breatheline
Typical constructionA pitched roof of timber rafters set out at 600mm centres with tiles or slates on battens. Either with counter battens if Knauf Breathelineis pulled taught and insulation is to the full depth of the rafters or without counter battens ifit is draped and the insulation stops at least10mm below the top of the rafters. Insulatedwith Crown Rafter Roll 32 and Crown Room-in-Roof Roll 32/37 between the rafters. A layer ofCrown Rafter Roll 32 is installed above theCrown Room in Roll if required. The integrallow emissivity vapour control layer has laps thatfix to the rafter and face onto a services voidformed with timber battens nailed along the lineof the rafters. 12.5mm plasterboard forms theinternal lining.InstallationKnauf Breatheline is pulled taught and laiddirectly over the rafters. 50x32mm counterbattens are nailed into the rafters withminimum penetration of 38mm into the rafter.Alternatively, helical fixings can be used with aminimum penetration of 35mm into the rafter.Tiling battens are nailed into the counterbattens. Finally, the roofing tiles or slates arefixed, to the manufacturer’s recommendations.
Friction fit, if required, a layer of Crown RafterRoll 32 into the rafter space leaving sufficientdepth to accommodate the Crown Room-in-RoofRoll 32/37 when this is installed between the rafters. The insulation should be butt jointed and continuous with the wall insulation to avoid thermal bridging. Staple the laps of the integral vapour control layer to the underside of the rafters and to any dwarf walls. Lap all joints in the vapour control layer. Using a self adhesive aluminised tape seal all joints and staple punctures in the air barrier; junctions betweenthe air barrier and any walls abutting the roof and any penetrations through the roof, such as roof windows. The vapour control layer should be linked to the air barrier in the external walls.Nail 50mm wide timber battens along the lineof the rafters. The battens to be a minimum of 25mm deep butto suit the required depth of the service void.After installing first fix services, nailplasterboard to the timber battens. Finish theplasterboard using standard dryliningtechniques.
Knauf Breatheline
Crown Rafter Roll 32 / Crown Room-in-Roof Roll 32/37
Counter battens
Integral low emissivity vapourcontrol layer
12.5mm plasterboardTimber battens to form service void
Typical specificationThe whole area of the pitched roof to beinsulated with Crown Rafter Roll 32 andCrown Room-in-Roof Roll 32*/37*,… mmthick friction fitted between the rafters. Thewidth of the insulation should be appropriateto the spacing of the rafters.(*Delete as appropriate)The integral low-emissivity vapour control layer to be stapled to the rafters with alljoints well sealed. 50x25mm timber battens nailed along the line of the rafters to form a service void.12.5mm plasterboard nailed or screwed tothe timber battens at maximum 300mmcentres and finished using standard dryliningtechniques.
Alternatively, refer to NBSclauses.
525
6.1.2Design details: Pitched roofs
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PerformanceThermal performanceCrown Rafter Roll 32 has a thermalconductivity of 0.032 W/mK.
Crown Room-in-Roof Roll 32 has a thermal
conductivity of 0.032 W/mK.
Crown Room-in-Roof Roll 37 has a thermalconductivity of 0.037 W/mK.
Table 14 gives U-values for typical constructionswith insulation between the rafters.
Acoustic performanceCrown Rafter Roll 32 and Crown Room-in-RoofRoll 32/37 meet the specification for a mineralwool insulation required for the control offlanking sound as described in Appendix A ofRobust Details.Fire performanceCrown Rafter Roll 32 and Crown Room-in-RoofRoll 32/37 are classified as Euroclass A1 to BSEN ISO 13501-1.Vapour resistanceKnauf Breatheline has a vapour resistance of0.22 MNs/g.
Knauf Breatheline
Integral low emissivityvapour control layer
Crown Rafter Roll 32 /
Crown Room-in-Roof Roll 32/37
25mm service void
12.5mm plasterboard
Table 14: Typical U-values with insulation between rafters with service void
Product Thickness U-values (W/m2K)
Between rafters Crown Rafter Roll 32
(mm) 50 65 75 85 100
Crown Room-in-Roof Roll 32 100 0.22 0.19 0.18 0.18 0.16
Crown Rafter Roll 32
(mm) 50 65 75 85 100
Crown Room-in-Roof Roll 37 200 0.15 0.14 0.13 0.13 0.12
160 0.18 0.16 0.15 0.15 0.14
100 0.24 0.21 0.20 0.19 0.17
Note: Rafters assumed to be 38mm wide at 600 centres (6.3 % bridging). The U-values have been calculated in accordancewith BS EN ISO 6946: 1997.
Low emissivity airspace is assumed to have a thermal resistance of 0.34m2K/W
12.5mm plasterboard
Typical section
Refurbishment of existing roofsThis is a valid solution for the refurbishment ofan existing roof where the roof tiles and roof tileunderlay are not being removed. In thesecircumstances a continuous 50mm gap must be maintained between the insulation and theroof tile underlay which is vented at the eavesand ridge.
The U-values achieved are shown in Table 14.
Advantages Using Crown Rafter Roll 32/Crown
Room-in-Roof Roll 37 willsignificantly improve the acousticperformance of the roof restrictingairborne noise
Crown Rafter Roll 32/Crown Room-in-Roof Roll 37 can be usedalong with an extra layer ofplasterboard to satisfy therequirements of Robust Details torestrict flanking sound aroundseparating walls
Long rolls with greater coverage perroll than other equivalent products
Pr09Knauf BreathelineThinsulex
Pitched roofs – rafter levelBetween rafters with Multifoil
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6.1.2 Design details: Pitched roofs
ProductsCrown Room-in-Roof Roll 37 is made from glass mineral wool and formed into rolls whichare dimensioned to fit tightly between rafters at600mm centres. The rolls are lightweight,flexible, resilient, non-combustible, and arefaced with a low emissivity vapour control layer.The facing is wider than the roll to overlap therafters to aid fixing, and create a vapourcontrol layer. Its manufacture has a very lowimpact on the environment and is classified asZero ODP and Zero GWP*
Crown Rafter Roll 32 is made from glassmineral wool and formed into rolls which arelightweight, flexible, resilient and non-combustible. Its manufacture has a very lowimpact on the environment and is classifiedas Zero ODP and Zero GWP*
Thinsulex™ Multi-foil is an insulation productcomprising multilayers of insulation separatedby multiple layers of sheets of reflectivesurfaces.
Knauf Breatheline is a breathable membranewith a polypropylene non-woven coating onboth sides – see also page 534.
* Ecohomes and Code for Sustainable Homes classification
Typical constructionKnauf Breatheline is pulled taught and laiddirectly over the rafters. 50x32mm counterbattens are nailed into the rafters with minimumpenetration of 38mm into the rafter -alternatively, helical fixings can be used with aminimum penetration of 35mm into the rafter.Tiling battens are nailed into the counterbattens. Finally, the roofing tiles or slates arefixed, to the manufacturer’s recommendations.
With Crown Rafter Roll 32 or Crown Room-in-Roof Roll 37 between the rafters. ThinsulexMulti-foil is stapled to the underside of therafters with 12.5mm foil backed plasterboardas the internal lining.
The full thermal performance of Thinsulex is only achieved when there is an airspace onboth sides of the insulation.
25mm deep cross battens are nailed throughthe Thinsulex into the rafters to create anairspace below the Thinsulex.
InstallationKnauf Breatheline is pulled taught and laiddirectly over the rafters. Counter battens arenailed into the rafters. Tiling battens are nailedinto the counter battens and the roofing tiles or slates are fixed, to the manufacturer’srecommendations.
The insulation is fitted from below once the roofis weathertight. Friction fit Crown Room-in-RoofRoll 37 between the rafters. Alternatively frictionfit Crown Rafter Roll 32 between the rafters (inlayers if necessary). The insulation should bebutt jointed and continuous with the wallinsulation to avoid thermal bridging.
Staple Thinsulex Multi-foil to the underside of therafters. Tape all joints with aluminised tape.
Nail 32x25mm timber cross battens at 600mmcentres into the rafters. After installing first fixservices, nail foil backed plasterboard to thetimber battens. Finish the plasterboard usingstandard drylining techniques.
PerformanceThermal performanceCrown Rafter Roll 32 has a thermal conductivityof 0.032 W/mK.
Crown Room-in-Roof Roll 37 has a thermalconductivity of 0.037 W/mK.
Thermal resistance of Thinsulex Multi-foilincluding air layers and bridging is 1.37 m2K/W (1 airspace)1 and 1.69 m2K/W (2 airspaces)2.
Table 15 gives U-values for typical constructionswith insulation between the rafters andThinsulex Multifoil, with either one or twoairspaces, below the rafters.
Knauf Breatheline
Crown Rafter Roll 32
Crown Room-in-Roof Roll 37
Counter battens
Thinsulex™ Multi-foil
12.5mm foil backed plasterboard Service void
Typical specificationThe whole area of the pitched roof to beinsulated with Crown Rafter Roll 32 or Crown Room-in-Roof Roll 37, friction fittedbetween the rafters.(*Delete as appropriate)
The width of the insulation should beappropriate to the spacing of the rafters.
Thinsulex Multi-foil to be stapled to theunderside of the rafters, with all joints taped with aluminised tape.
32x25mm timber cross battens to be nailedinto the rafters at 600mm centres. 12.5mmfoil backed plasterboard to be nailed orscrewed to the timber battens at maximum300mm centres and finished using standarddrylining techniques.
Alternatively, refer to NBSclauses.
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6.1.2Design details: Pitched roofs
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Knauf Breatheline
Thinsulex Multi-foil insulation
Crown Rafter Roll 32 orCrown Room-in-Roof Roll37 between rafters
32x25mm cross battens at 600mm centres
12.5mm foil backed plasterboard
Counter battens
Acoustic performanceCrown Rafter Roll 32 and Crown Room-in-RoofRoll 32/37 meet the specification for a mineralwool insulation required for the control offlanking sound as described in Appendix A of Robust Details.
Fire performanceCrown Rafter Roll 32 and Crown Room-in-RoofRoll 32/37 are classified as Euroclass A1 to BS EN ISO 13501-1.
Thinsulex Multi-foil will not contribute to thedevelopment stages of a fire or present a smoke or toxic hazard.
Vapour resistanceKnauf Breatheline has a vapour resistance of0.22 MNs/g.
Refurbishment of existing roofsThis is a valid solution for the refurbishment of an existing roof where the roof tiles and roof tile underlay are not being removed. In thesecircumstances a continuous 50mm gap must be maintained between the insulation and the roof tile underlay which is vented at theeaves and ridge.
The U-value achieved is as shown in Table 15.
Table 15: Typical U-values for roofs with insulation between and below rafters, with a service void
Product Thickness Thinsulex (2 air spaces)2 Thinsulex (1 air spaces)1
(mm) U-values (W/m2K) U-values (W/m2K)
Crown Rafter Roll 32 200 (2x100) 0.14 0.15
170 (2x85) 0.16 0.16
150 (2x75) 0.17 0.18
130 (2x65) 0.19 0.20
100 0.22 0.23
Crown Room-in-Roof Roll 37 200 0.15 0.16
160 0.18 0.19
100 0.23 0.25
Note: Rafters assumed to be 48mm wide at 600 centres (8% bridging). The U-values have been calculated in accordancewith BS EN ISO 6946: 1997
Typical section
Knauf Breatheline
Polyfoam Pitched Roofboard
Counter battens
Polyfoam RaftersqueezePlasterboard
Vapour control layer
Pitched roofs – rafter levelBetween and above rafters
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6.1.2 Design details: Pitched roofs
Advantages Polyfoam Pitched Roofboard can
be used with any rafter spacing
Vertical joints do not need to occur at rafters, making installation quick and simple
Polyfoam is lightweight yet very strong, making it easy to handle on the roof
Polyfoam Raftersqueeze fits tightlyto the sides of rafters
Once Polyfoam Pitched Roofboard is fixed inplace, Polyfoam Raftersqueeze is friction fittedbetween the rafters. If rafter centres are otherthan 600mm (e.g. 450mm, 300mm etc) cut theboard slightly oversize to fit and use theremaining squeeze on one edge to push fitbetween rafters. They boards should be pushedup to the underside of the Polyfoam PitchedRoofboard, so there are no gaps. A timberbatten or noggin fixed into the rafter below thePolyfoam Raftersqueeze (optional) can be usedto hold the board in position.
There is an alternative fixing method for counterand tiling battens which is described in BritishBoard of Agrément Certificate 06/4386.
InstallationA timber stop rail is fixed to the ends of therafters. Polyfoam Pitched Roofboard is fittedstarting from the timber stop rail, with all boardstightly butted.
The board is not suitable to be walked on, asdefined in HSE33, except when covered withsupporting timbers.
Knauf Breatheline, is pulled taught and laiddirectly over the insulation.
50 x 32mm counter battens are nailed throughthe Knauf Breatheline and Polyfoam PitchedRoofboard and into the rafters using spiralfixings such as Helifix Inskew 600 or BuildexRG, with minimum penetration into the rafter of35mm. Tiling battens are laid across the roofand nailed into the counter battens. Tiles shouldbe stacked so that they bear directly over therafters. Finally, the roofing tiles or slates arefixed to the manufacturer’s recommendations.
ProductsPolyfoam Pitched Roofboard is a 100% ozonefriendly, extruded polystyrene, rigid boardinsulation system. It is lightweight with shiplapedge details that do not have to meet directlyon top of rafters, making installation very quickand simple.
Polyfoam Raftersqueeze is a 100% ozonefriendly, extruded polystyrene, rigid boardinsulation – it is lightweight and consists of aflexible infill piece of insulation that fits betweenrafters, and allows for some timber variation.
Knauf Breatheline is a breathable membranewith a polypropylene non-woven coating onboth sides – see also page 534.
Typical constructionA pitched roof of timber rafters with tiles orslates on battens and Knauf Breatheline.Insulated with Polyfoam Pitched Roofboard laidover rafters and Polyfoam Raftersqueeze fittedbetween rafters.
Knauf BreathelinePolyfoam Pitched Roofboard
Pr10
529
6.1.2Design details: Pitched roofs
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Typical specificationInsulation laid over rafters to be PolyfoamPitched Roofboard, ......mm thick. KnaufBreatheline is then pulled taught and laiddirectly over the insulation and held in placeby 50 x 32mm counter battens nailedthrough the boards, into the rafters. The tilingbattens to be nailed into the counter battens.
Insulation between the rafters to be PolyfoamRaftersqueeze, supported on battens nailedto the side of the rafters (optional).
Alternatively, refer to NBS clauses: K11/670 and P10/140 and 320
PerformanceThermal performancePolyfoam Pitched Roofboard has a thermalconductivity of 0.029 W/mK.
Polyfoam Raftersqueeze has a thermalconductivity of 0.030 W/mK.
Table 16 gives U-values for typicalconstructions.
Table 16: Typical U-values of pitched warm roofs insulated above and between raftersU-values (W/m2K) of Polyfoam Pitched
Insulation between rafters Thickness Roofboard thickness over rafters (mm)
(mm) 35 50 60 75
Polyfoam Raftersqueeze 150 (75+75) 0.17 0.16 0.15 0.14
125 (75+50) 0.20 0.18 0.17 0.15
100 (50+50) 0.23 0.21 0.19 0.17
75 0.28 0.24 0.22 0.20Notes: Rafter sizes assumed to be 38mm wide at 600mm centres (6.3% bridging). The U-values have been calculated in accordance with BS EN ISO 6946:1997.
Compression resistanceThe rigidity of Polyfoam Pitched Roofboardmakes the board easy to handle and less proneto site damage than less robust materials.
Moisture resistancePolyfoam Pitched Roofboard is highly resistantto moisture absorption and will perform asstated if exposed to moisture in use.
Fire performanceThe boards contain a flame retardantspecifically designed to inhibit localisedignition. The boards will melt if brought intocontact with high temperature sources.However, the use of the boards will not affectthe fire rating obtained by tiled roofs whenevaluated by assessment or tested to BS 476:Part 3: 2004. The underside of the raftersshould be faced with 12.5mm plasterboard to provide fire protection.
Counter battens
Knauf Breatheline
Roof insulation to link with wall insulation
Polyfoam Raftersqueeze
Sealant to reduce air leakage
Polyfoam Pitched Roofboard over rafters
Vapour control layer
Air barrier
Typical section
Timber Stop Rail
Pitched roofs – rafter levelBetween and above rafters
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6.1.2 Design details: Pitched roofs
Advantages Non-combustible insulation gives
fire safe solution
No ventilation required at eaves orroof voids
A breathable and vapour permeablesystem
Significantly improves the acousticperformance of the roof
Crown Rafter Roll 32 and Crown Room-in-Roof Roll 37 can be used along with an extra layer of plasterboard to satisfy the requirements of Robust Details to restrict flanking sound around separating walls
Long rolls with greater coverage per roll than other equivalent products
Counter battens should be fixed through theRocksilk Pitched Roof Slab boards using spiralfixings such as Helifix Inskew 600 or BuildexRG, with a minimum penetration into the rafterof 35mm.
The fixings are to be installed at no greater than 400mm centres along the battens.
From below, Crown Room-in-Roof Roll 37 orCrown Rafter Roll 32 is simply friction fittedbetween the rafters. The insulation should befriction fitted between the rafters so that it is indirect contact with the Rocksilk Pitched RoofSlab, with no air gaps between the two layersof insulation.
To avoid a thermal bridge at the eaves, RocksilkPitched Roof slabs should be cut to shape to linkthe roof and wall insulation.
A continuous vapour control layer should befixed to the underside of the rafters.
Knauf Breatheline is a breathable membranewith a polypropylene non-woven coating onboth sides – see also page 534.
* Ecohomes and Code for Sustainable Homes classification
Typical constructionA pitched roof of timber rafters with tiles orslates on battens and counter battens and KnaufBreatheline. Insulated with Rocksilk Pitched RoofSlab laid over the rafters and Crown Room-in-Roof Roll 37 or Crown Rafter Roll 32, frictionfitted between the rafters.
InstallationA timber stop rail is fixed to the ends of therafters. Rocksilk Pitched Roof Slab is fittedstarting from the timber stop rail, with all slabstightly butted.
Rocksilk Pitched Roof Slab should be laid acrossthe finished rafters with staggered joints. Theslabs should be cut to length to match thespacings of the rafters.
Knauf Breatheline can be installed either belowthe counter battens (as shown above), or abovethe counter battens. When installed above thecounter battens Knauf Breatheline should bedraped by no less than 10mm.
ProductsCrown Room-in-Roof Roll 37 is made from glass mineral wool and formed into rolls whichare dimensioned to fit tightly between rafters at600mm centres. The rolls are lightweight,flexible, resilient, non-combustible, and arefaced with a low emissivity vapour control layer.The facing is wider than the roll to overlap therafters to aid fixing, and create a vapourcontrol layer. Its manufacture has a very lowimpact on the environment and is classified asZero ODP and Zero GWP*
Crown Rafter Roll 32 is made from glassmineral wool and formed into rolls which arelightweight, flexible, resilient and non-combustible. Its manufacture has a very lowimpact on the environment and is classifiedas Zero ODP and Zero GWP*
Rocksilk Pitched Roof Slab is a compressionresistant, water repellent, rock mineral woolslab specifically developed for over rafter(sarking) insulation. Its manufacture has a verylow impact on the environment and is classifiedas Zero ODP and Zero GWP*
Pr11Knauf Breatheline
Knauf Breatheline
Rocksilk Pitched Roof Slab
Counter battens
Crown Rafter Roll 32 or Crown Room-in-Roof Roll 37 12.5mm plasterboard
Vapour control layer
531
6.1.2Design details: Pitched roofs
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Typical specificationInsulation laid over rafters to be RocksilkPitched Roof Slab, ......mm thick, locatedover the rafters. All boards tightly butted andwith staggered joints. Knauf Breathelineshould then be laid over the insulation withthe edges lapped.
The insulation and underlay to be held inplace by 50 x 32mm counter battens fixedthrough the boards, into the rafters. The tilingbattens to be nailed into the counter battens.
Crown Room-in-Roof Roll 37 or Crown RafterRoll 32......mm thick, to be friction fittedbetween the rafters. The width of the insulation should beappropriate to the spacing of the rafters.
Alternatively, refer to NBS clauses: K11/670 and P10/140 and 320
PerformanceThermal performanceRocksilk Pitched Roof Slab has a thermalconductivity of 0.038 W/mK.
Crown Rafter Roll 32 has a thermal conductivityof 0.032 W/mK.
Crown Room-in-Roof Roll 37 has a thermalconductivity of 0.037 W/mK.
Table 17 gives U-values for typicalconstructions.
Acoustic performanceCrown Rafter Roll 32 and Crown Room-in-RoofRoll 37 meet the specification for mineral woolinsulation required for the control of flankingsound as described in Appendix A of RobustDetails.
Fire performanceCrown Rafter Roll 32, Crown Room-in-Roof Roll37 and Rocksilk Pitched Roof Slab are classifiedas Euroclass A1 to BS EN ISO 13501-1.
Table 17: Typical U-values of pitched roofs with insulation between and over rafters
U-values (W/m2K)Insulation Thickness Rocksilk Pitched Roof Slab (mm)
(mm) 50 70
Crown Room-in-Roof Roll 37 200 0.16 0.14
160 0.18 0.17
100 0.25 0.22
Crown Rafter Roll 32 200 (2x100) 0.14 0.14
170 (2x85) 0.16 0.15
150 (2x75) 0.18 0.16
130 (2x65) 0.20 0.18
100 0.23 0.21Notes: Rafter sizes assumed to be 38mm wide at 600mm centres (6.3% bridging) and the same depth as the insulation. The U-values have been calculated in accordance with BS EN ISO 6946:1997.
Counter battens
Knauf Breatheline
Roof insulation to link with wall insulation
Crown Room-in-Roof Roll 37or Crown Rafter Roll 32
Sealant to reduce air leakage
Rocksilk Pitched Roof Slab
Vapour control layer
Air barrier
Typical section
Pitched roofs – rafter levelBetween and below rafters – existing roof
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6.1.2 Design details: Pitched roofs
Advantages Robust nature of Polyfoam in
Linerboard supports the plasterboard, improving its impact resistance
Crown Rafter Roll 32/Crown Room-in-Roof Roll 32/37 andPolyfoam Raftersqueeze friction fit tightly to rafters
Using Crown Rafter Roll 32/Crown Room-in-Roof Roll 32/37 will significantly improve the acousticperformance of the roof restrictingairborne noise
Suitable for upgrading existing roof
Long rolls with greater coverage per roll than other equivalent products
Alternatively, Polyfoam Raftersqueeze is fittedbetween the rafters. If rafter centres are otherthan 600mm (e.g. 450mm, 300mm etc) cut theboard slightly oversize to fit and use theremaining squeeze on one edge to push fitbetween rafters.
Finally, Polyfoam Linerboard is nailed orscrewed to the underside of the rafters atmaximum 300mm centres at least 12mm infrom the board edge. The fixings should be longenough to penetrate at least 25mm into thetimber. The boards are finished using standarddrylining techniques.
Typical constructionA pitched roof of timber rafters with tiles orslates on battens on an HR type underlay.Insulated with Crown Room-in-Roof Roll 32/37,Crown Rafter Roll 32 or PolyfoamRaftersqueeze between the rafters and linedinternally with Polyfoam Linerboard.
There must be a continuous 50mm gap abovethe insulation which is vented at the eaves andridge. This is the most popular method forinsulating an existing roof when a loft isconverted to habitable accommodation.
InstallationCrown Room-in-Roof Roll 32/37 or CrownRafter Roll 32 is friction fitted (in layers ifnecessary) between the rafters, taking care toleave a 50mm gap above the insulation. The rolls should be butt jointed and continuouswith the wall insulation to avoid thermalbridging.
Polyfoam Linerboard
ProductsCrown Room-in-Roof Roll 32/37 is made from glass mineral wool and formed into rolls whichare dimensioned to fit tightly between rafters at600mm centres. The rolls are lightweight,flexible, resilient, non-combustible, and arefaced with a low emissivity vapour control layer.The facing is wider than the roll to overlap therafters to aid fixing, and create a vapourcontrol layer. Their manufacture has a very lowimpact on the environment and is classified asZero ODP and Zero GWP*
Crown Rafter Roll 32 is made from glassmineral wool and formed into rolls which arelightweight, flexible, resilient and non-combustible. Its manufacture has a very lowimpact on the environment and is classifiedas Zero ODP and Zero GWP*
Polyfoam Raftersqueeze is a 100% ozonefriendly, extruded polystyrene insulation. Itconsists of a flexible infill piece of insulation thatfits between rafters, and allows for some timbervariation
Polyfoam Linerboard is a laminate of Polyfoamextruded polystyrene and 9.5mm tapered edgeplasterboard
* Ecohomes and Code for Sustainable Homes classification
Optional timber spacer battens to maintain ventilation space above insulationInsulation between rafters
Polyfoam Linerboard
Pr12
50mm clear ventilation space between membrane and insulation
Crown Rafter Roll 32 or Crown Room-in-Roof Roll 32/37or Polyfoam Raftersqueeze
HR type underlay drapedbetween rafters
533
6.1.2Design details: Pitched roofs
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50mm ventilation path
Roof insulation to link with wall insulation
Polyfoam Linerboard
Sealant to reduce air leakage
Air barrier
Typical specificationThe whole area of the pitched roof to beinsulated with Crown Room-in-Roof Roll32/37*/Crown Rafter Roll 32/PolyfoamRaftersqueeze* ......mm thick, friction fittedbetween the rafters, with a continuous 50mmventilation space above the insulation. Thewidth of the insulation should be appropriateto the spacing of the rafters.
Polyfoam Linerboard of thickness .....mm withintegral 9.5mm plasterboard nailed orscrewed to the rafters at maximum 300mmcentres and finished using standard dryliningtechniques.(*Delete as appropriate)
Alternatively, refer toNBS clauses: P10/140and 320, and K10/245
PerformanceThermal performanceCrown Room-in-Roof Roll 32 has a thermalconductivity of 0.032 W/mK.
Crown Room-in-Roof Roll 37 has a thermalconductivity of 0.037 W/mK.
Crown Rafter Roll 32 has a thermal conductivityof 0.032 W/mK.
Polyfoam Raftersqueeze and the insulation inPolyfoam Linerboard has a thermal conductivityof 0.030 W/mK.
Table 18 (opposite) gives U-values for typicalconstructions with insulation between and belowthe rafters.
Compression resistanceThe rigidity of the Polyfoam in PolyfoamLinerboard offers an excellent support tothe finished internal lining and assists inthe resistance of impact, helping to prolongits service life.
Fire performanceCrown Room-in-Roof Roll 32/37 and CrownRafter Roll 32 are classified as Euroclass A1 toBS EN ISO 13501-1.
Table 18: Typical U-values of roofs with insulation between and below rafters
U-values (W/m2K)Product Thickness Polyfoam Linerboard Thickness (mm)
(mm) 25.5/9.5 36/9.5 45.5/9.5
Crown Room-in-Roof Roll 32 100 0.26 0.24 0.22
Crown Rafter Roll 32 200 (2x100) 0.15 0.15 0.14
160 (75+85) 0.19 0.17 0.17
100 0.26 0.24 0.22
Crown Room-in-Roof Roll 37 200 0.17 0.16 0.15
160 0.20 0.19 0.18
100 0.28 0.26 0.24
Polyfoam Raftersqueeze 150 (2x75) 0.20 0.18 0.17
140 (65+75) 0.21 0.19 0.18
125 (50+75) 0.22 0.21 0.20
100 (2x50) 0.26 0.24 0.22Notes: Rafter sizes assumed to be 38mm wide at 600mm centres (6.3% bridging) and the same depth as the insulation.The U-values have been calculated in accordance with BS EN ISO 6946:1997.
Typical sectionCrown Room-in-Roof Roll 32/37 or
Crown Rafter Roll 32or Polyfoam Raftersqueeze
Polyfoam insulation contains a flame retardantspecifically designed to inhibit localisedignition. The boards will melt if brought intocontact with high temperature sources andare classed as combustible.
However, the use of the boards will not affectthe fire rating obtained by tiled roofs whenevaluated by assessment or tested to BS 476:Part 3: 2004.
Polyfoam Linerboard is faced with 9.5mmplasterboard which offers excellent fireperformance.
Pitched roofsVapour permeable underlays
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6.1.2 Design details: Pitched roofs
ProductsKnauf Breatheline is a breathable membranewith a polypropylene non-woven coating onboth sides. It is classified as a type LR roof tile underlay according to the specification inBS 5250.
Typical constructionKnauf Breatheline can be used in both warmand cold pitched roofs.
In cold pitched roofs, Knauf Breatheline isnormally draped about 10-15mm between therafters to allow wind driven rain and snow todrain below the tiling battens into the gutter. At the eaves, Knauf Breatheline should not beexposed to the long term effects of sunlight –a type 5U felt underlay or eaves carrier shouldbe used and dressed into the gutter.
In warm pitched roofs, where the insulationstops short of the top of the rafters, it can bedraped 10-15mm between the rafters.
In warm pitched roofs where the membrane isfully supported by insulation or sarking boards,counter battens are required.
Knauf Breatheline
Advantages Low vapour resistance – Knauf
Breatheline is classified as an LR underlay as defined in BS5250
Allows the continuous diffusion of moisture from the whole area of the pitched roof under all wind conditions
Waterproof to wind driven rain and snow
Excellent nail tear and tensile strength
Can be laid directly over insulation or sarking boards as there is no capillary action through the underlay
When installed in accordance with the BBA Certificate there is no requirement for ventilation of the roof space
InstallationAlways use non-ferrous staples or nails to fixKnauf Breatheline at 300mm centres.
Use the dotted lines printed on the underlay to indicate the size of laps when layingsubsequent lengths of underlay.
Unsupported underlaysKnauf Breatheline is laid parallel to the eavesand draped between the rafters as traditionaltiling underlays.
Knauf Breatheline underlays can also be draped over counter battens in boarded andwarm roofs.
Supported underlaysWhenever rigid insulation or timber boarding is fixed directly onto the rafters, counter battensmust be used.
Counter battens can either be fixed directly onto the boarding with Knauf Breathelinedraping between the counter battens or it canbe laid directly over the boarding or insulationand the counter battens fixed on top.
PerformanceVapour resistanceKnauf Breatheline has a vapour resistance of 0.22 MNs/g.
Knauf Breatheline
Pr13
Table 19: Ventilation requirements for LR underlays
LR underlay approval type of Size of ventilation openings at:ceiling eaves high level
No technical approval Normal 7mm 5mm
No technical approval Well sealed* 3mm 5mm
With technical approval Normal 7mm 5mm
With technical approval Well sealed* Not required Not required
*See page 152 for definition of well sealed ceiling.
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6.1.2Design details: Pitched roofs
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Alternative positions for Knauf Breatheline
Cold roof
Warm roof – insulation stops short of top of rafters
Warm roof – fully supported
Warm roof – draped over counter battens
Typical specification
Fully supported underlayKnauf Breatheline should be laid horizontallyacross the roof slope, pulled taught, with thebottom edge lapping the eaves tray by150mm. Fix with non-ferrous nails or staplesto each rafter at maximum 300mm centres.Nail counter battens along the line of therafters. Nail the tiling battens to the counterbattens at centre required by the roof finish.Use the battens as footholds to position andfix the next roll. Specification should bebased on, and referenced to BBA Certificate03/4014. Horizontal and vertical laps to bein accordance with BS 5534: 2003.
Unsupported underlayKnauf Breatheline should be laid horizontallyacross the roof slope, with the bottom edgelapping the eaves carrier by 150mm. Drapethe underlay 10-15mm between rafters. Fixwith non-ferrous nails or staples to each rafterat maximum 300mm centres. Nail the tilingbattens to the rafters*/counter battens* atcentre required by the roof finish. Use thebattens as footholds to position and fix thenext roll. Specification should be based on,and referenced to BBA Certificate 03/4014.Horizontal and vertical laps to be inaccordance with BS 5534: 2003.
Knauf Breatheline draped between rafters
Knauf Breatheline draped between rafters
Insulation between raftersstops 10-15mm short of top ofrafters
Knauf Breatheline fully supported
Counter batten
Insulation fully fills space between rafters
Tiling batten
Knauf Breatheline draped overcounter battens
Vapour control layer
Vapour control layer
Counter batten
Pitched roofsTypical eaves details
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6.1.2 Design details: Pitched roofs
Eaves detail with boxed eaves
Knauf Breatheline pulled taught over Polyfoam Pitched Roofboard laid over rafters
Polyfoam Raftersqueeze between rafters
Vapour control layer behind plasterboard
Crown DriTherm to provide continuity insulation and minimise air leakage into the roof space
Wall plate bedded on a continuous mortar bed
Ceiling/drylining junction sealed with plaster, adhesive or sealant to reduce air leakage
Double nogging with vapour control layer between sealed to provide continuous air barrier
Scottish eaves detail with exposed rafter feet
Knauf Breatheline fully supported on sarking boards
Roof and wall insulation butted togetherto ensure continuity of insulation
Crown Room-in-Roof Roll 32/37 between rafters
Wall plate bedded on a continuous mortar bed
Ceiling/drylining junction sealed with plaster,adhesive or sealant to reduce air leakage
Flat ceiling installed first and junctionsealed with plaster, adhesive or sealantto reduce air leakage
Polyfoam Linerboard
537
6.1.2Design details: Pitched roofs
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Pitched roofsTypical verge details
Polyfoam Pitched Roofboard over rafters
Vapour control layer
Polyfoam Raftersqueeze between rafters
Crown DriTherm Cavity Slab taken up to top of wall
Typical overhanging verge detail with insulation over and between rafters
Fully fill the void between the wall head and the over rafter insulation
Install compressible insulation between last rafter and wall
Ceiling/drylining junction sealed with plaster, adhesive or sealant to reduce air leakage
Typical overhanging verge detail with insulation between and under rafters
Crown Room-in-Roof Roll 32/37 between rafters
Polyfoam Linerboard
Crown DriTherm Cavity Slab taken up to top of wall
Dry verge
Ceiling/drylining junction sealed with plaster,adhesive or sealant to reduce air leakage
Crown Room-in-Roof Roll 32/37 over the top of thewall, within the gable ladder
10mm drape in Knauf Breatheline
Pitched roofsTypical ceiling level details
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6.1.2 Design details: Pitched roofs
Detail with exposed eaves
Knauf Breatheline pulledtaught over rafters to providewindproof layer
100mm Crown Loft Roll 44 has an R-value of 2.25 m2K/W
Tiling battens on counter battens
Gutter skirt dressed into gutter
Insulation pushed up tight against Knauf Breatheline andcontinuous with wall insulation
Space between rafters well sealed toprevent air infiltration into loft space
Crown Loft Roll 40 or 44in two layers
Crown Loft Roll 40 or 44 intwo layers
Boxed eaves
Knauf Breatheline pulled taught overrafters to provide windproof layer
100mm Crown Loft Roll 44 has an R-value of 2.25 m2K/W
Tiling battens on counter battens
Gutter skirt dressed into gutter
Fully enclosed boxed eaves with noprovision for ventilation
Insulation pushed up tight against Knauf Breatheline andcontinuous with wall insulation
Scottish example with exposed rafter feetSlates nailed directly to sarkingboard
Knauf Breatheline fully supported onsarking boards
Space between rafters well sealed toprevent air infiltration into loft space
Crown Loft Roll 40 or 44in two layers
Insulation pushed up tight against sarkingboard and continuous with wall insulation
100mm Crown Loft Roll 44 hasan R-value of 2.25 m2K/W
Gutter skirt dressed into gutter
539
6.1.2Design details: Pitched roofs
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Crown Room-in-Roof Roll 32/37between rafters
Crown DriTherm Cavity Slabscut to shape to link wall androof insulation
PolyfoamLinerboard butted withsealant at junction
Longitudinal tie
Counter battens fixed to rafters
Knauf Breatheline pulled taught over rafters
Foil facing
Ceiling/drylining junction sealed withplaster, adhesive or sealant to reduceair leakage
Double nogging with vapourcontrol layer between andsealed to provide continuousair barrier
Vapour control layer tolink Polyfoam Linerboardand wall air barrier
Crown Room-in-Roof Roll 32/37 between studs
Seal betweenvapour control layer and PolyfoamLinerboard
PolyfoamLinerboard forms air barrier
Gutter skirt dressedinto gutter
Crown Loft Roll 40 or 44 intwo layers
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Knauf Insulation Ltd.PO Box 10Stafford RoadSt HelensMerseysideWA10 3NS
Customer Service (Sales)Tel: 0844 800 0135Fax: 01744 612 007email: sales@knaufinsulation.com
Technical Advisory Centre (TAC)Tel: 01744 766666Fax: 01744 766667email: tech@knaufinsulation.com
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