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Non - Residential New Build 4.2.4 Flat Roofs August 2008: Issue 1

Non - Residential New Build 4.2.4 Flat Roofscms.esi.info/Media/documents/Knauf_flatroofs_ML.pdf · 2016. 6. 21. · BS 6399: Part 2: 1997. Drainage Guidance on the number and size

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  • Non - Residential New Build4.2.4 Flat Roofs

    August 2008: Issue 1

  • 4.0Non-residential new build

    Non-residential New Build

    Sales 0844 800 0135 Technical Advisory Centre 01744 766666 www.knaufinsulation.co.uk

    Introduction find online pageSolution optimiser and pathfinder 336Design considerations 338

    Design Details 540

    Flat Roof - Contents

    find online pageWarm deck single ply membraneRocksilk Krimpact Flat Roof Slab Fl01 540

    Warm deck single ply membranePolyfoam Roofboard Fl02 542

    Warm deck built-up felt/mastic asphalt Fl03 544

    Protected membrane Fl04 546

    Car park roof Fl05 548

    Rocksilk Krimpact Cut-To-Falls Fl06 550

    Polyfoam Cut-To-Falls Fl07 552

    Existing warm roof cut-to-falls upgrade Fl08 554

    Existing warm roof upgrade Fl09 556

  • Flat roofsSolution optimiser and pathfinder

    Sales 0844 800 0135 Technical Advisory Centre 01744 766666 www.knaufinsulation.co.uk336

    4.2.4 Non-residential new build: Roofs

    Flat roofs are defined as roofs with a pitch not exceeding10º that have a continuously supported weatherproof finish.The choice of weatherproof finish includes single ply membranes, mastic asphalt and built-up roofing.

    However, material choice is only one factor in the long-termperformance of flat roofing. Experience has shown that thequality of design and workmanship play a critical role in thedurability of flat roofs.

    Advantages of flat roofsAlthough many older flat roofs have oftensuffered a short life and high maintenancecosts, if properly designed, using qualitymaterials and installed by competentcontractors flat roofs can offer a wide range ofbenefits that cannot be achieved with atraditional pitched roof:

    • Flexibility of design

    • Opportunities for recreational use and/or car parking

    • The option of installing a green roof

    • Accommodation of and access to plant

  • 337

    4.2.4Non-residential new build: Roofs

    Cut-to-fallsProduct*: Rocksilk Krimpact Cut-To-Falls systemDescription: Warm deck flat roof with a compression-resistant rock mineral wool cut-to-falls insulation systemPage No: 550

    Warm deck car park roofProduct*: Polyfoam Floorboard ExtraDescription: Car park roof withultrastrong XPS insulation abovewaterproofing layer

    Page No: 548Fl05

    Fl06

    Cut-to-falls Product*: Polyfoam Cut-To-Falls systemDescription: Warm deck flat roof with ultra strong XPS cut-to-falls insulation system

    Page No: 552Fl07

    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

    Warm deck built-up felt/mastic asphaltProduct*: Rocksilk Krimpact Flat Roof Slab Description: Warm deck flat roof with compression-resistant rock mineral woolinsulation and built-up roofing or mastic asphalt waterproofing Page No: 544

    Fl03

    Protected membrane Products*: Polyfoam Slimline systemDescription: Protected membrane roof with ultra strong XPS insulation and watershedding system

    Page No: 546Fl04

    Elemental U-value requirementFlat roofsConstruction compatibility with Part L2A

    Knauf Insulation solution

    Area weighted average

    max U-value England and

    Wales and Northern Ireland

    Typical U-value for

    compliance England and

    Wales and Northern Ireland

    Warm deck single ply membraneProduct*: Polyfoam RoofboardDescription: Warm deck flat roof with ultrastrong XPS insulation and bonded or mechanically fixed single ply membrane

    Page No: 542

    Warm deck single ply membraneProduct*: Rocksilk Krimpact Flat Roof SlabDescription: Warm deck flat roof with compression-resistant rock mineral woolinsulation and mechanically fixed single ply membrane

    Page No: 540Fl01

    Fl02

    U-values 0.26 0.25 0.24 0.23 0.22 0.21 0.20 0.19 0.18 0.170.29 0.28 0.270.32 0.300.31 0.15 0.140.16

    Sales 0844 800 0135 Technical Advisory Centre 01744 766666 www.knaufinsulation.co.uk

  • Flat roofsF lat roof design

    Sales 0844 800 0135 Technical Advisory Centre 01744 766666 www.knaufinsulation.co.uk338

    4.2.4 Non-residential new build: Roofs

    CondensationThermal insulation and the flow of heat andwater vapour through a construction areinextricably linked. The position of thermalinsulation, vapour control layer and the need forventilation must all be considered together. The likelihood of condensation occurring willdepend on the U-value of the construction, the relative humidity and temperature of theinternal environment and whether an effectivevapour control layer has been provided. Toprevent surface condensation, the roof must bekept above the dew point of the internal air withan appropriate thickness of insulation, correctlylocated. To prevent interstitial condensation, an effective vapour control layer must beprovided on the warm side of the insulation.

    Warm and cold roofsThe position of the thermal insulation related tothe structural roof deck has created two basiccategories of roof design:

    • Warm roofs

    • Cold roofs

    A warm roof has the insulation above thestructural deck, which is thus kept warm. The waterproof covering is above the insulationand a vapour control layer is placed below theinsulation.

    An inverted/protected membrane roof is a formof warm roof in which the insulation is placedabove the waterproof covering (which also actsas a vapour control layer).

    A cold roof has the insulation placed below thestructural deck, which thus remains cold. Thisconstruction relies on a vapour barrier workingeffectively in tandem with a continuous flow ofventilation air to disperse the water vapourbefore it reaches the cold deck.

    This section only considers warm roofs as follows:

    • Warm roof with built-up felt or mastic asphalt roof covering

    • Warm roof with single ply membrane

    • Inverted/protected membrane roof

    For practical and cost reasons, flat roofs are a common type of roof construction for most non-residential buildings. A range of flat roof construction methods are availablewhich provide thermal performance along with bothacoustic and fire protection.

    Knauf Insulation provide solutions for a wide range of flat roof systems, giving options that will comply with theBuilding Regulations and the required level of thermalperformance. These systems include Single Ply, Built-Up Felt, Inverted/Protected Membrane and Cut-To-Falls and can be used with timber, metal and concrete decks.

    Roof loadingsThe roof structure must be capable of supportingall of the associated loadings.In addition, the wind pressure acting on the roofshould be assessed in accordance with BS 6399: Part 2: 1997.

    DrainageGuidance on the number and size of rainwateroutlets can be obtained from BS EN 12056-Part 3: 2000. The drainage and edge detailsshould be installed as per the waterproofingmembrane manufacturer’s instructions.

    design detail finderKnauf Insulation solutions for these types of construction can be found on pages 540-557

  • Sales 0844 800 0135 Technical Advisory Centre 01744 766666 www.knaufinsulation.co.uk 339

    4.2.4Non-residential new build: Roofs

    1. Warm deck – built-up roof

    The three types of warm deck considered in this section

    Built-up roof

    Insulation

    Filtration water shedding layer

    Vapour control layer

    Insulation

    Mastic asphalt waterproofing

    Isolating layer (Type 4a Felt)

    Screed to falls

    Concrete deck

    Gravel ballast

    Non-woven polyester fleece

    Timber deck

    2. Warm deck – single ply membrane

    Single ply membrane

    Insulation

    Vapour control layer

    Metal deck

    3. Inverted/protected membrane roof – mastic asphalt waterproofing

  • Flat roofsF lat roof design

    Sales 0844 800 0135 Technical Advisory Centre 01744 766666 www.knaufinsulation.co.uk340

    4.2.4 Non-residential new build: Roofs

    Built-up felt/mastic asphalt Concrete, timber and metal deck flat roofs can allbe designed as warm roofs with a built-up felt ormastic asphalt roof covering. Installation of theroof covering should be in accordance with themanufacturer’s instructions with due considerationbeing taken of fixing methods and wind uplift.

    An integral part of a warm deck flat roofingsystem is the installation of the vapour controllayer on the warm side of the insulation.

    Single plyConcrete, metal and timber deck flat roofs can allbe designed as flat roofs with a single ply roofcovering. Installation of the roof covering shouldbe in accordance with the manufacturersinstructions with due consideration being taken offixing methods and wind uplift.

    An integral part of a warm deck flat roofingsystem is the installation of the vapour controllayer on the warm side of the insulation.

    When insulation is placed over the deck, an insulant with a low rate of thermal expansionshould be selected with adequate mechanicalstrength to resist the compressive and tensileloads during installation and in service.Differential movement can be avoided by layinga single ply waterproof membrane andmechanically fixing it through the insulation to thedeck, using an approved fully bonded system orleaving the membrane loose and covering withballast.

    Refer to the Single Ply Roofing Association (SPRA)Design Guide for Single Ply Roofing for advice onalternative fixing methods.

    Fixing of insulation/singlemembraneWhere the insulation is mechanically fixed ratherthan bonded to the roof deck, the wind upliftcapability of the roof finish depends entirely onthe mechanical fixing.

    When mechanically fixed, the roof membranemay be temporarily lifted by wind suction.

    It is advisable with mechanically fixedmembranes, to ensure that all boards are fixed tothe structural deck to avoid the boards movingout of place.

    When mechanically fixing or fully bonding themembrane the systems should be designed towithstand the wind loadings calculated inaccordance with BS 6399:2:1997.

    Suitable mechanical fixings and adhesives arereadily available for use with all types of deck.

    PVC single ply membranesWhere extruded polystyrene insulation boardsare used with a PVC membrane, a separatinglayer must be placed between the PVC membraneand the insulation to prevent plasticiser migrationout of the membrane. This may take the form of aglass fibre or polyester fleece with a minimumdensity of 100 g/m2, or a foil facing to the insulation board. Analternative is to use a membrane with anintegrally bonded fleece backing. EPDM andpolyolefin membranes do not require aseparating layer.

    Vapour control layersThe vapour control layer may take the form of a bitumen bonded felt, a nailed felt layer ora reinforced polyethylene sheeting. If in doubtplease contact our Technical Advisory Centre on 01744 766666.

    Protection of insulation during installationTo prevent moisture entrapment on or in theinsulation boards it is essential to protect themduring laying, before the application of the roofwaterproofing, or to lay the roof covering at thesame time as the board.

    StandardsBS 6229:2003 is the code of practice for flatroofs with continuously supported coverings. It recommends these are inspected at least twice a year in spring and autumn as a minimumand also after events which may have had a detrimental effect on the roofcovering, such as violent storms Workmanship iscovered by BS 8000: Part 4: 1989.

    design detail finderKnauf Insulation solutions for these types of construction can be found on pages 540-557

  • Sales 0844 800 0135 Technical Advisory Centre 01744 766666 www.knaufinsulation.co.uk 341

    4.2.4Non-residential new build: Roofs

    Specify SPRAThe Single Ply Roofing Association (SPRA)represents membrane manufacturers,associated component manufacturers and specialist sub contractors and aimsto ensure the delivery of best value single

    ply roofing systems, through a quality assuredpartnership.

    By specifying products and specialistinstallation by SPRA members you can beassured that all parties meet strict qualitycriteria. Compliance with these criteria andwith the Code of Conduct is assessed atapplication, by annual audit and by randomspot checks. For further information and toobtain copies of the SPRA Design Guide and other documents visit www.spra.co.uk

    Example details for warm deck single ply roofs

    Abutment detail

    Metal capping

    Perimeter fixing

    Polyfoam Roofboard

    Vapour control layer

    Metal deck

    Outer cladding

    Single ply membrane

    Metal deck

    Rooflight kerb detail

    Rooflight

    Capping

    Insulated rooflight kerb

    Single ply membrane

    Metal angle bolted back to structure

    Polyfoam Roofboard

    Vapour control layer

    Metal deck

    Metal closure to opening

    Steel structure

    Drain outlet detail

    Outlet guard

    Single ply membrane

    Polyfoam Roofboard

    Vapour control layer

    Profiled metal deck

    Rainwater outlet

  • Flat roofsF lat roof design

    Sales 0844 800 0135 Technical Advisory Centre 01744 766666 www.knaufinsulation.co.uk342

    4.2.4 Non-residential new build: Roofs

    Roof loadingsInverted/protected membrane roofs can beconstructed on concrete, timber or metal decks.The structure must be capable of supporting theweight of the loading layer to the satisfaction ofthe structural engineer.

    The loading layer can be provided by washed,graded and rounded gravel of nominal diameter20-40mm free from fines, or by dense concretepaving slabs or by a green/garden roof system.

    A loading layer is necessary to prevent theinsulation boards being lifted by high winds orfloating as water drains from the roof. It alsoprotects the insulation from the effects of UV lightand contributes towards the roof fire rating. Forheavily trafficked areas, concrete paving slabsshould be used to form the loading layer.

    Where gravel ballast is used paving slabs arerequired at exposed edges (i.e. edges withoutupstands or abutments) to negate the risk of winduplift or wind scour (as shown in the designdetails overleaf).

    Ballast depths can vary according to theinsulation used in some systems. Table 3 sets out typical loadings for roofs insulated with thePolyfoam Slimline system.

    For further details on dead and imposed loadsrefer to BS 6399-1: 1996. For wind loads refer toBS 6399-2: 1997.

    Protected membrane/inverted roofsWith insulation placed above the waterproofmembrane the latter is protected from extremes oftemperature and thus shielded from excessivethermal stress, this will normally result in anextended life. An inverted/protected membraneroof places additional requirements on thethermal insulation which needs to have thefollowing properties:

    • Low water absorption in service (includingfreeze/thaw cycles)

    • High compressive strength to withstand ballastload and support surface traffic

    BS 6229:2003 recommends a minimum finishedfall of 1:60 or 1:80 dependent on thewaterproofing covering. In the absence ofdetailed analysis a fall equal to twice that of theminimum finished fall should be assumed fordesign purposes.

    For roofs with slopes below 1:80 the asphaltwaterproofing must be tanking grade and aseparating membrane placed between thewaterproofing and the insulation.

    Where the filter membrane above the insulationalso forms a water resistant layer, as in thePolyfoam Slimline system, there is an increase in run-off of surface water above the insulation.Care should be taken to ensure that the capacityand location of gulleys and outlets is sufficient.Further details can be found inBS EN 12056: Part 3.

    Because the roof structure and membrane areboth kept warm in an inverted/protectedmembrane roof, the risk of condensation isvirtually eliminated. Nevertheless, condensationmight occur on the underside of the deck if the deck is thin and has beencooled by water run-off during heavy andcontinuous rain or melting snow. Thiscondensation will disperse when the heatingsystem overcomes the temperature difference.

    To help prevent the condensation from occurringensure that the deck has a minimum R-value of0.15 m2K/W. If the deck has a high thermalcapacity it will not be rapidly cooled byrainwater. The proposed design should beassessed for condensation risk using themethods and information given in BS 6229:1982 and BS 5250: 2002.

    The Polyfoam Slimline system will shed the rainwater to thegutters before it can penetrate through the insulation layer tothe waterproofed deck, therefore the condensation risk isconsiderably reduced if this system is adopted.

    Filter layerA filter layer should be placed between theinsulation and ballast layer to prevent fine gritbeing washed down to the waterproofmembrane. The incorporation of the PolyfoamSlimline membrane layer improves theperformance of the roofing system by restrictingthe flow of water below the insulation. Thisimproves the thermal performance and has theadded benefit of reducing the potential forinsulation flotation which allows the thickness ofthe ballast layer to be reduced, thus reducing theoverall weight of the roof.

    Roof maintenanceAs with all other types of roof the inverted/protected membrane roof will benefit from aregular schedule of inspection and routinemaintenance. Areas of special concern are themembrane, rainwater outlets, gutters, flashingsand other detail work.

    The inspection should also include checks toensure that the insulation and its loading layerare still positioned as installed. Weed growthshould be eradicated with a water based weed killer.

    Table 3: Weight and thickness of ballast with Polyfoam Slimline system

    Ballast type Thickness Weight(mm) (kg/m2)

    Gravel 50 80

    Concrete slabs 50 125

    Control of condensation in protected membrane roofs

    design detail finderKnauf Insulation solutions for these types of construction can be found on pages 540-557

  • Sales 0844 800 0135 Technical Advisory Centre 01744 766666 www.knaufinsulation.co.uk 343

    4.2.4Non-residential new build: Roofs

    U-value calculations for inverted roofs must becorrected to allow for the impact of rainwaterflowing between the insulation and thewaterproofing membrane. This correction shouldbe applied as set out in BS EN ISO 6946 AnnexD.

    The following procedures are applicable only toinsulation made from extruded polystyrene(XPS). Refer to ‘Symbols and units’ for anexplanation of the components considered in thefollowing formula.

    Correction due to water flowing between theinsulation and the waterproofing membrane:

    ΔU = pfx (Ri)2

    (Rt)2

    ΔU is calculated to two decimal places.

    ΔU less than 0.01 is considered as zero.

    The correction is applied to the U-value which iscalculated according to the conventions as setout in BR443 ‘Conventions for U-valuecalculations’ BRE 2006 by subtracting the �ΔU-value from the calculated U-value.

    For the Polyfoam Slimline system using a singlelayer of insulation above the membrane with anopen covering such as gravel f·x = 0.001.

    This value is the tested and certified value of the PolyfoamSlimline system, any other solution would require materialand system specific results to have comparable performance.Otherwise a value of 0.04 for f·x should be used for a singlelayer of insulation with open covering.

    The Polyfoam Slimline system is third party certified by theBritish Board of Agrément.

    Symbols and unitsf Drainage factor giving the fraction of p reaching the

    waterproofing membrane

    p Average rate of rain during the heating season, based upon data relevant for the location, eg, weather station, or given through local, regional or national regulation (unit: mm/day)

    x Factor for increased heat loss caused by rainwater flowing on the membrane (unit: (W·day)/(m2K·mm)

    Ri Thermal resistance of the layer of Polyfoam insulation above the waterproofing membrane (unit: m2K/W)

    Rt Total thermal resistance of the construction(unit: m2K/W)

    ΔU Correction to the calculated U value of the construction, to take into account the extra heat loss caused by rainwater flowing through joints in the insulation and reaching the waterproofing membrane(unit: W/m2K)

    Aluminium or GRP coping system

    Polyfoam High Impact and Upstand Board held back to upstand

    Polyfoam Slimline membrane turned up behind Polyfoam

    High Impact and Upstand Board

    Gravel and paving slabs as ballast

    Polyfoam Roofboard

    Mastic asphalt waterproofing

    Wall insulation

    Concrete deck

    Polyfoam Slimline membrane turned up behind Polyfoam High

    Impact and Upstand Board

    Gravel or paving slabs as ballast

    Polyfoam Roofboard

    Single ply waterproofing

    Screed to falls

    Concrete deck

    3. Edge detail

    Paving slab at edge of roof to contain ballast

    Polyfoam Slimline membranedressed over edge flashing

    Polyfoam Roofboard

    Polyfoam High Impact and Upstand Board to slab edge

    4. Drain outlet detail

    Gravel guard

    Polyfoam Slimline membrane dressed over

    upper drainage outlet

    Polyfoam Roofboard

    Waterproof membrane bonded to lower outlet

    Screed to falls

    Concrete deck

    U-value calculations of inverted/protected membrane roofs

    Polyfoam Slimline System

    1. Parapet detail 2. Abutment detail

    Example details for protected membrane roofs

  • Flat roofsWarm deck single ply membrane

    Sales 0844 800 0135 Technical Advisory Centre 01744 766666 www.knaufinsulation.co.uk540

    6.1.3 Design details: Flat roofs

    Structural deck

    Compressive resistanceRocksilk Krimpact Flat Roof Slab has acompressive strength in excess of 75 kPa.

    Thermal performance The thermal conductivity of Rocksilk KrimpactFlat Roof Slab is 0.038 W/mK.

    Table 20 gives U-values for typical constructionsinsulated with Rocksilk Krimpact Flat Roof Slab.

    Fire performanceRocksilk Krimpact Flat Roof Slab is classified asA1 to BS EN ISO 13501-1, the best fireperforming insulation. Rocksilk Krimpact FlatRoof Slab has a melting point of over 1000°C.In the event of fire it will emit negligiblequantities of smoke and fumes. The heatemission from the products is insignificant.

    InstallationThe vapour control layer should be laid over the structural deck and all joints lapped andbonded. Rocksilk Krimpact Flat Roof Slab is then laid in a staggered pattern from onecorner of the roof. The orientation of the slabs is unimportant provided the constraints onspanning metal profiled decks are followed. The slabs and membrane should bemechanically fixed to the deck using specialistfixings such as those available from Ejot*.Typically two fixings equally spaced along the length and in the centre of each slab arerequired to secure the system in place.*For information on EJOT fixings, contact 01977 687040

    PerformanceStandards Rocksilk Krimpact Flat Roof Slab has beentested to the UEAtc Technical Guidelines MOATNo 50: 1992, Thermal insulation systemsintended for supporting waterproofingmembranes on flat and sloping roofs. It isclassified B for mechanical performance – roofonly accessible for purpose of maintenance andmay be used without any restrictions.

    Rocksilk Krimpact Flat Roof Slab mechanicallyfixed to metal deck

    ProductsRocksilk Krimpact Flat Roof Slab is a highstrength, consistent density, rigid, glass tissuefaced rock mineral wool slab manufacturedusing Krimpact technology and specificallydesigned for use in flat roofing.

    Rocksilk Krimpact Flat Roof Slab has sufficientcompressive strength to be used whereoccasional loading and impact resistance isrequired.

    Typical constructionRocksilk Krimpact Flat Roof Slab is suitable foruse on all types of roof deck. The slabs are laidover a vapour control membrane andmechanically fixed to the deck. The insulation isoverlaid with a single ply membrane which ismechanically fixed.

    Rocksilk Krimpact Flat Roof Slab is compatiblewith most PVC, EPDM and other types ofmechanically fixed single ply waterproofingmembrane systems. The advice of the single plymembrane manufacturer should be sought toconfirm compatibility with specific membranes.

    Advantages� Compatible with all single ply

    membranes

    � No requirement for separating layer with PVC single ply membranes

    � Significantly improves acoustic performance of timber and metal decks and reduces the drumming effect of rainwater on lightweight roofs

    � Non-combustible product with highest Euroclass A1 rating, enhancing the fire performance of the roof

    � Interlocking nature of mineral wool ensures slabs knit together at joints ensuring no loss of thermal performance

    Fl01

    Single ply waterproofing systemmechanically fixed tothe deck

    Vapour control layer

    Rocksilk Krimpact Flat Roof Slab

  • 541

    6.1.3Design details: Flat roofs

    Sales 0844 800 0135 Technical Advisory Centre 01744 766666 www.knaufinsulation.co.uk

    Single ply waterproofing system mechanically fixed to the deck

    Vapour control layer

    Structural deck

    Rocksilk Krimpact Flat Roof Slab mechanically fixed to metal deck

    Typical specificationThe vapour control membrane and RocksilkKrimpact Flat Roof Slab, thickness ......mm to be mechanically fixed to the roof deck.(*delete as required)

    The single ply membrane should be appliedover the insulation in accordance with the

    appropriate manufacturer’s recommendedspecification.

    Alternatively, consult the NationalBuilding Specifications (NBS)based on Standard Version J42,it contains a set of proprietaryclauses, which are editedversions written by KnaufInsulation.

    Flat roofsThe profiles of metal deck roofs need to providesufficient support for the insulation. The greater the thickness of insulation, the greater the spanit can accommodate on profiled metal decks.Where the butt joint of Krimpact Flat Roof Slabsoccurs along the top of the profiles then themaximum allowable span is (a), as shown in thetable. Where the butt joint occurs over thetroughs of the profiles then the maximumallowable span is (b), as shown in the table.Note: Polyfoam solutions will perform at least as well asRocksilk Krimpact Flat Roof Slab.

    Typical section

    Table 20: Typical U-values of warm deck single ply membrane roofs productProduct U-values (W/m2K)

    150mm concrete Profiled 19mm chipboardThickness 40mm screed metal timber joists

    (mm) 13mm plaster deck 12.5mm plasterboardRocksilk Krimpact 245 (145 + 100) 0.15 0.15 0.15Flat Roof Slab 230 (130 + 100) 0.16 0.16 0.15

    225 (150 + 75) 0.16 0.17 0.16210 (130 + 80) 0.17 0.18 0.17200 (2 x 100) 0.18 0.19 0.17

    195 (145 + 50) 0.16 0.19 0.18180 (100 + 80) 0.20 0.21 0.19

    160 0.22 0.23 0.21150 0.23 0.25 0.22145 0.24 0.25 0.23130 0.26 0.28 0.25

    Note: The U-values have been calculated to BS EN ISO 6946:1997. For project specific calculations contact our Technical Advisory Centre on 01744 766666.

    Insulation slabs butt along tops of profiles

    Insulation slabs butt over troughs

    Table 20a: Maximum allowable spanInsulation Max span Max span

    thickness (mm) a (mm) b (mm)

    140 400 280120 360 240100 300 20070 170 14050 170 120

  • Flat roofsWarm deck single ply membrane

    Sales 0844 800 0135 Technical Advisory Centre 01744 766666 www.knaufinsulation.co.uk542

    6.1.3 Design details: Flat roofs

    Advantages� Compressive strength of Polyfoam

    Roofboards offer future usepotential for roof

    � Rebated edges provide supportacross spans in profiled roof decks

    � Rigid support of the water proofing membrane, reduces the risk of puncture on site

    Structural deck

    InstallationThe vapour control layer should be laid over thestructural deck and all joints lapped andbonded. If a PVC membrane is being used,Polyfoam Foil Faced Roofboard, or a suitableseparating fleece layer, should be used.

    The boards are then laid in a staggered pattern from one corner of the roof.

    In a bonded membrane system, each layer ofPolyfoam Roofboard must be bonded as well asthe waterproof membrane itself. A polyurethanebased adhesive is recommended.

    When a mechanically fixed membrane isbeing used, the Polyfoam Roofboard should bemechanically fixed to the deck with twocentrally placed fixings in each board to securethe boards in place before the membrane isfixed.

    When installing double layers of PolyfoamRoofboard, the second layer should be installedtransversely to the first layer in order tominimise the number of coincident jointsbetween the insulation boards. If required, onecentrally placed mechanical fixing can beinstalled in the first layer prior to the installationand final fixing of the second layer. Bothinsulation layers should be laid in a staggeredstretcher brick bond pattern.

    When using partially or fully bonded membranesystems, Polyfoam Roofboards should bemechanically fixed to the deck to withstand the calculated wind load. The waterproofmembrane may then be bonded to theinsulation using a polyurethane based adhesivein accordance with the membranemanufacturer’s instructions. The advice of thewaterproofing membrane manufacturer will berequired for the precise fixing specification.

    When using mechanically fixed membranes,Polyfoam Roofboards should be mechanicallyfixed to the deck.

    Polyfoam Roofboards are suitable for use with most PVC (provided there is aseparation layer between the board andmembrane), EPDM and other types of single plywaterproof membrane systems. The advice ofthe single ply membrane manufacturer shouldbe sought to confirm compatibility with specificmembranes. Polyfoam Foil Faced Roofboardhas been developed to eliminate the risk ofplasticiser migration when a PVC membrane isused. It also provides protection for theinsulation when solvent or heat weldedmembrane systems are used.

    Single ply waterproofing system

    ProductsPolyfoam Roofboard Standard is 100% ozonefriendly, extruded polystyrene, rigid boardinsulation it is lightweight, yet has excellentstructural strength and long term effectiveness. Itis supplied with interlocking rebated edges andis suitable for lightly trafficked flat roofs.

    Polyfoam Foil Faced Roofboard is supplied foilfaced on one side, for use where separationfrom the membrane is necessary.

    Polyfoam Roofboard Extra is for use in mediumtrafficked flat roofs and in green and garden roofs - see pages 588-561.

    Typical constructionPolyfoam Roofboards and Polyfoam Foil FacedRoofboards are suitable for use on all types ofroof deck. The boards are laid over a vapourcontrol layer and either mechanically fixed orbonded to the vapour control layer.

    The insulation is overlaid with a single plymembrane which can be fully adhered to theinsulation or mechanically fixed to the deck.

    Fl02

    Polyfoam Roofboard

    Vapour control layer

    Polyfoam Roofboard

  • 543

    6.1.3Design details: Flat roofs

    Sales 0844 800 0135 Technical Advisory Centre 01744 766666 www.knaufinsulation.co.uk

    Typical specificationThe vapour control layer and Polyfoam Roofboard Standard*/PolyfoamRoofboard Extra/ Polyfoam Foil FacedRoofboard*, ......mm thick, to bemechanically fixed*/adhered* to the roof deck(*Delete as appropriate)

    The single ply membrane should be appliedover the insulation in accordance with theappropriate manufacturer’s recommendedspecification.

    Alternatively, consult the National Building Specifications(NBS) based on StandardVersion J42 It contains a set of proprietary clauses, which are edited versions written byKnauf Insulation.

    Table 21: Typical U-values of warm deck single ply membrane roofs

    Product U-values (W/m2K)

    150mm concrete Profiled 19mm chipboardThickness 40mm screed metal timber joists

    (mm) 13mm plaster deck 12.5mm plasterboard

    Polyfoam Roofboard Standard/Extra and Polyfoam Foil Faced Roofboard

    200 0.15 0.15 0.14

    190 0.15 0.16 0.15

    180 0.16 0.17 0.16

    170 0.17 0.18 0.17

    160 0.18 0.19 0.18

    150 0.19 0.20 0.19

    140 0.20 0.22 0.20

    130 0.22 0.23 0.21

    120 0.22 0.23 0.22

    110 0.24 0.25 0.23Note: The U-values have been calculated to BS EN ISO 6946: 1997.

    Performance

    Thermal performancePolyfoam Roofboard Extra, Polyfoam RoofboardStandard and Polyfoam Foil Faced Roofboardhave a thermal conductivity of 0.029W/mK upto a thickness of 120mm and 0.031W/mKabove this. The actual performance in use isoutlined in table 21.

    Compression resistancePolyfoam Roofboards are highly resistant tocompression and withstand both occasionaland long term static loads.

    Knauf Insulation recommends a factor of safetyof 3 for occasional loading (5 for long termstatic loads) is applied to the compressivestrength of the product.

    Moisture resistanceIn many applications, Polyfoam Roofboards areinstalled above the waterproofing layer and thusexposed to rainwater, either in service or duringconstruction. Polyfoam Roofboards are highlyresistant to moisture and can be laid in standingwater or up against wet concrete with negligibleimpact on the performance of the product.

    Fire performanceWhen Polyfoam Roofboards are installed in aroof construction they will not contribute to thedevelopment stages of a fire.

    Polyfoam Foil Faced Roofboard below a mechanically fixed single ply membrane

    PVC single ply waterproofing system

    Polyfoam Foil FacedRoofboard mechanicallyfixed to metal deck

    Vapour control layer

    Structural deck

  • Vapour control layer

    Mastic asphalt waterproofing

    Isolating felt

    Rocksilk Krimpact Flat Roof Slab bonded to vapour control layer

    Flat roofsWarm deck built-up felt/mastic asphalt

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    6.1.3 Design details: Flat roofs

    Advantages� Improves acoustic performance

    � Non-combustible product withhighest Euroclass A1 rating

    � Robust, consistent density solution

    � Consistent compressive strength

    Performance

    StandardsRocksilk Krimpact Flat Roof Slab has beentested to the UEAtc Technical Guidelines MOATNo 50: 1992, Thermal insulation systemsintended for supporting waterproofingmembranes on flat and sloping roofs. It isclassified B for mechanical performance – roofonly accessible for purpose of maintenance andmay be used without any restrictions.Thermal performanceThe thermal conductivity of Rocksilk KrimpactFlat Roof Slab is 0.038 W/mK.

    Table 22 gives U-values for typical constructionsinsulated with Rocksilk Krimpact Flat Roof Slab.

    Compressive resistanceRocksilk Krimpact Flat Roof Slab has acompressive strength in excess of 75 kPa.

    Fire performanceRocksilk Krimpact Flat Roof Slab is classified asEuroclass A1 to BS EN ISO 13501-1. Rocksilkproducts have a melting point of over 1000°C.In the event of fire they will emit negligiblequantities of smoke and fumes. The heatemission from the products is insignificant.

    InstallationThe vapour control layer and Rocksilk KrimpactFlat Roof Slab are both fully bonded in hotbitumen and then waterproofed.

    Built-up felt membranesHigh performance bitumen membrane systemsare fully bonded in hot bitumen to the tissuefaced Rocksilk Krimpact Flat Roof Slab usingtraditional roll and pour methods. RocksilkKrimpact Flat Roof Slab is not suitable for thedirect application of torch-on roofing felts.

    Mastic asphalt surfaceRocksilk Krimpact Flat Roof Slab provides astable base for mastic asphalt. The slabs shouldbe overlaid with a 12mm layer of bitumenimpregnated fibreboard. A bitumen felt (lowgrade is satisfactory) should be loose laid andbonded to the fibre board prior to theapplication of the mastic asphalt.

    ProductsRocksilk Krimpact Flat Roof Slab is a highstrength, consistent density, rigid, glass tissuefaced rock mineral wool slab manufacturedusing Krimpact technology and specificallydesigned for use in flat roofing.

    Rocksilk Krimpact Flat Roof Slab has sufficientcompressive strength to be used whereoccasional loading and impact resistance isrequired.

    Typical constructionRocksilk Krimpact Flat Roof Slab is suitable foruse on all types of roof deck. The insulationslabs are laid staggered bond, butt jointed andbonded to the deck. The insulation is overlaidwith a waterproof membrane consisting ofeither a fully bonded built-up bitumen roofingsystem, or mastic asphalt. When used withmastic asphalt, the insulation is overlaid with12mm bitumen impregnated fibreboard and anisolating felt.

    Fl03

    12mm bitumen impregnated fibreboard

    Sand cement screed laid to falls Concrete roof deck

    Rocksilk Krimpact Flat Roof Slab

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    6.1.3Design details: Flat roofs

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    Mastic asphalt waterproofing

    Rocksilk Krimpact Flat Roof Slab bonded to vapour control layer

    Sand cement screedlaid to falls

    Vapour control layer

    Isolating felt

    12mm bitumen impregnated fibreboard

    36/6 Polyfoam High Impact and Upstand Boardseparated from mastic asphaltby polyester fleece .

    Flashing

    Cavity tray

    Typical specificationThe vapour control layer and RocksilkKrimpact Flat Roof Slab,......mm thick to befully bonded, with hot bitumen. (*Delete asappropriate) The waterproof membraneshould be applied in accordance with theappropriate manufacturer’s recommendedspecification.

    Alternatively, consult the National Building Specifications(NBS) based on StandardVersion J42, it contains a set of proprietary clauses, which are edited versions written byKnauf Insulation.

    Typical parapet

    Table 22: Typical U-values of flat roofs insulated with Rocksilk Krimpact Flat Roof Slab

    U-values (W/m2K)

    150mm concrete Profiled 19mm chipboardThickness 40mm screed metal timber joists

    (mm) 13mm plaster deck 12.5mm plasterboard

    230 (130 + 100) 0.15 0.15 0.15

    220 (145 + 75) 0.16 0.16 0.15

    210 (130 + 80) 0.16 0.17 0.16

    200 (2 x 100) 0.17 0.18 0.17

    195 (145 + 50) 0.18 0.18 0.17

    180 (100 + 80) 0.19 0.19 0.18160 0.22 0.23 0.21150 0.23 0.25 0.22145 0.24 0.25 0.23130 0.26 0.28 0.25

  • Flat roofsProtected membrane

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    6.1.3 Design details: Flat roofs

    Advantages� Polyfoam Slimline System achieves superior

    thermal performance compared to systemswith a standard filtration membrane

    � Protected membrane flat roofs using thePolyfoam Slimline system are lighter asless ballast is required

    � Protects waterproofing membrane from UVdegradation and temperature extremesincreasing the membrane’s in-service life

    � Polyfoam Slimline System’s thermalperformance is unaffected by moisture

    � Highly cost effective solution with highcompressive strength, Extra grade able tosupport loading of paving slab supports

    � Allows the creation of patios, roof terraces and balconies

    � Polyfoam High Impact and Upstand Boardsupports this system with a simple, one-piece, easy cut upstand insulation solution

    The insulation boards should be laid in astaggered pattern from the point of accessacross the roof. It is important that all jointsbetween boards are tight fitting and there areno gaps at the junctions with rooflights,upstands etc.

    The Polyfoam Slimline membrane is loose laidover the insulation, at right angles to the slope,with 300mm side laps. At all upstands andpenetrations, turn the membrane up so itfinishes above the ballast level.

    Gravel ballast is laid (using 20-40mm diametergravel at 50mm depth) to prevent wind uplift. Tocreate a roof terrace/patio area, paving slabsat 50mm thick are an alternative to gravelballast – Polyfoam Roofboard Extra should beused for this application.

    Each layer is laid on an advancing front inorder to protect the membrane from mechanicaldamage as the materials are transported across the roof.

    At upstands, fix Polyfoam High Impact andUpstand Board to the abutment using a suitablemechanical fixing or adhesive. Ensure the topexposed edge of insulation is protected from UV degradation using a suitable UV resistantflashing.

    InstallationThe waterproofing membrane is laid on the roof deck in accordance with manufacturersinstructions. The waterproofing membrane can be either reinforced bitumen membrane,polymeric single ply membrane, mastic asphalt or hot melt waterproofing system.The waterproof membrane must be free of loose gravel and grit before the insulationboards are laid.

    On existing roofs, any existing chippings shouldbe covered with a polyethylene cushion layer,such as Floorfoam.

    For all mastic asphalt applications, a separatingnon woven polyester fleece – as defined in BS 8218:1998, and for PVC single plymembranes, a similar fleece or other approvedseparating layer, should be laid immediatelybelow the insulation and turned up at allupstands to the top of any upstand insulation toisolate the Polyfoam from the waterproofinglayer. If in doubt regarding the compatibility ofthe insulation and membrane contact KnaufInsulation Technical Advisory Centre or themembrane manufacturer.

    ProductsPolyfoam Roofboard is a range of 100% ozonefriendly, extruded polystyrene, rigid insulationboards that are lightweight, yet have excellentstructural strength and moisture resistance.

    Polyfoam Slimline membrane is a highperformance, non woven polypropylenegeotextile membrane that prevents the passageof water and is vapour permeable.

    Polyfoam High Impact and Upstand Board is a laminate of Polyfoam, extruded polystyrene,rigid board insulation and a tough, weatherresistant fibre reinforced cement facing board.It provides a tough faced solution suitable forexterior use. Polyfoam High Impact andUpstand Board is square edged.

    Typical constructionProtected membrane roof with ballast of gravelor paving slabs and the Polyfoam Slimlinemembrane in place of the standard filtrationmembrane. Polyfoam Slimline membrane:

    • is water resistant, preventing cold rainwaterreaching the waterproof membrane and soimproving thermal performance

    • allows water vapour from below to evaporatethrough the membrane

    • reduces flotation, less ballast is required

    Fl04

    Mastic asphalt waterproofmembrane

    Screed laid to falls

    Concrete roof deck

    Polyfoam Slimline System

    36/6mmPolyfoam High Impact and UpstandBoard

    Flashing

    Polyfoam Slimline membrane

    Polyfoam Roofboardon separating fleece/isolating layer

    Paving slabballast

    Spacer supports

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    6.1.3Design details: Flat roofs

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    Mastic asphalt waterproof membrane on isolating layer

    36/6mm Polyfoam High Impact and Upstand Board

    Concrete paving slabs

    Polyfoam Roofboard Extra onseparating fleece/isolating layer

    Polyfoam Slimline membrane

    Screeds laid to falls

    Concrete roof deck

    Spacer supports

    Typical specificationThe whole of the roof area, lined with a waterproof membrane to be insulated withPolyfoam Roofboard Standard*/Extra*/Super*, ......mm thick. The insulation to beoverlaid with Polyfoam Slimline membraneand covered with gravel ballast.*/ minimum50mm thick paving slabs on spacers*.

    The gravel to be washed, rounded andgraded, free from sand and grit with anominal diameter of 20 to 40mm and aminimum of 50mm deep.

    Alternatively, consult the National Building Specifications(NBS) based on StandardVersion J21, J41 or J42.It contains a set of proprietaryclauses, which are editedversions written by KnaufInsulation.

    Table 24: Typical U-values of protected membrane roofs using Polyfoam Slimline System

    Product U-values (W/m2K)

    150mm concrete Thickness 40mm screed

    (mm) 13mm plasterPolyfoam Roofboard Standard 170 (120 + 50) 0.16Polyfoam Roofboard Extra 160 (110 + 50) 0.17

    150 (2 x 75) 0.18140 0.19130 0.21120 0.22110 0.24

    Note: The U-values have been calculated to BS EN ISO 6946: 1997. For project specific calculations contact our Technical Advisory Centre on 01744 766666.

    PerformanceCompression resistancePolyfoam Roofboards are highly resistant tocompression and withstands both occasionaland long term static loads.

    Knauf Insulation recommends a factor of safetyof 3 for occasional loading (5 for long termstatic loads) is applied to the compressivestrength of the product.

    The facing material of Polyfoam High Impactand Upstand Board is highly resistant to impactdamage, offering an excellent robust lining.

    Polyfoam Roofboard Extra or Super must beused in trafficked areas and where paving slabs are laid on spacers.

    Moisture resistancePolyfoam Roofboards are highly resistant tomoisture and can be laid in standing water orup against wet concrete with negligible impacton the performance of the product.

    The facing material of Polyfoam High ImpactBoard is moisture resistant.

    Typical detail with concrete paving ballast

    Thermal performancePolyfoam Roofboard Standard has a thermalconductivity of 0.029 W/mK.

    Polyfoam Roofboard Extra up to 120mm thickhas a thermal conductivity of 0.029 W/mK,and 0.031 W/mK above this.

    Fire performanceWhen Polyfoam Roofboards are installed in a roof construction they will not contribute to the development stages of a fire.

    Polyfoam High Impact and Upstand Board isfaced with a 6mm fibre reinforced cementboard which offers excellent fire performanceas a facing material and Polyfoam insulationwhich contains a flame retardant to inhibitlocalised ignition.

    The facing board is classified as Class 1 SurfaceSpread of Flame to BS 476: Part 7: 1987.

  • Flat roofsWarm deck car park roof

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    6.1.3 Design details: Flat roofs

    Advantages� Ultra strong Polyfoam Roofboard

    Super Insulation has thecompressive strength to support theloads associated with a car parkroof

    � Protects waterproofing membraneduring concrete casting, increasingits in-service life

    � Thermal performance of Polyfoam Roofboard Super is unaffected by moisture

    � Polyfoam Roofboard Super is lightweight so adds minimal weight to the roof

    Asphalt and felt layer

    Thermal performanceThe thermal conductivity of Polyfoam RoofboardSuper varies from 0.034 to 0.036 W/mKdepending on thickness.

    The actual performance in use is outlined in Table 25 (opposite).

    Fire performanceWhen Polyfoam Roofboard Super is installed ina roof construction it will not contribute to thedevelopment stages of a fire.

    PerformanceCompression resistanceAll materials are compressed under load. If theroof is going to be transformed from a limitedaccess waste of space into a useful space theinsulation must be capable of accommodatingapplied loads.

    Polyfoam Roofboard Super is highly resistant tocompression and withstands both occasionaland long term static loads.

    Knauf Insulation recommends a factor of safetyof 3 for occasional loading (5 for long termstatic loads) is applied to the compressivestrength of the product.

    Moisture resistanceIn many applications, Polyfoam RoofboardSuper is installed above the waterproofing layerand thus exposed to rainwater, either in serviceor during construction.

    The board is highly resistant to moisture andcan be laid in standing water or up against wetconcrete with negligible impact on theperformance of the product.

    Reinforced castconcrete slab

    ProductsPolyfoam Roofboard Super is a 100% ozonefriendly, extruded polystyrene, rigid boardinsulation. It is lightweight, yet has excellentstructural strength and long term effectiveness. It is supplied with interlocking rebated edges

    Typical constructionA structural concrete deck designed as a carpark roof is to be waterproofed. PolyfoamRoofboard Super sits on top of the waterprooflayer and is then covered with a structuralreinforced concrete slab to withstand heavyloading and traffic.

    InstallationCover the whole of the roof deck with awaterproofing layer. Lay Polyfoam RoofboardSuper onto this layer (using a non wovenpolyester fleece separation layer if thewaterproofing layer is PVC based or asphalt).Stagger the joints of the boards and ensure theinterlocking rebates are tightly pushed together.

    Cover the insulation with a slip layer and areinforced cast concrete slab designed towithstand the expected load of vehicle traffic.

    Finish slab as required for car park deck.

    Fl05

    Slip layer

    Polyfoam Roofboard Super

    Polyfoam Roofboard

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    Waterproofing layer

    Reinforced cast concrete slab

    Polyfoam Roofboard Super

    Non woven polyester fleece betweeninsulation and waterproofing layer

    Concrete roof deck

    Typical specificationThe whole of the roof area covered with awaterproofing layer to be insulated usingPolyfoam Roofboard Super ....mm thick. The insulation to be covered with a .....mmreinforced concrete slab. Finish slab asrequired for car park deck.

    Alternatively, consult the National Building Specifications(NBS) based on StandardVersion J21, J41 or J42. Itcontains a set of proprietaryclauses, which are editedversions written by KnaufInsulation.

    Table 25: Typical U-values of car park roofs productProduct U-values (W/m2K)

    150mm concrete Thickness 40mm screed

    (mm) 13mm plasterPolyfoam Roofboard Super

    225 (3 x 75) 0.15200 (2 x 100) 0.17

    175 (100 + 75) 0.19150 (2 x 75) 0.21

    125 (75 + 50) 0.25100 0.31

    Note: 100mm Cast concrete slab finish assumed. The U-values have been calculated toBS EN ISO 6946: 1997. For project specific calculations contact our Technical Advisory Centre on 01744 766666

    Typical section

  • Flat roofsCut-To-falls

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    Advantages� Provides for a fall either where deck

    was designed to be flat, or does notprovide the designed fall when constructed.

    � Ideal method for upgrading roofs with ponding problems

    � Significantly improves acoustic performance of timber and metal decks and absorbs ‘rainwater drumming’ noise

    � Non-combustible product withhighest Euroclass A1 rating

    � Supported by specialist design service and installation advice

    � Bespoke system designed to meet the needs of each individual project

    Vapour control layer

    Typical example of cut-to-falls plan

    Performance

    StandardsRocksilk Krimpact Cut-To-Falls has been tested tothe UEAtc Technical Guidelines MOAT No 50:1992, Thermal insulation systems intended forsupporting waterproofing membranes on flatand sloping roofs. It is classified B formechanical performance – roof only accessiblefor purpose of maintenance and may be usedwithout any restrictions.

    Compressive resistanceRocksilk Krimpact Cut-To-Falls has a compressivestrength in excess of 75 kPa.

    Timber decksThe vapour barrier can be either nailed to thetimber deck as defined in BS 8217: 1994, orbitumen bonded using traditional techniques.

    Built-up felt membranesWhere Rocksilk Cut-To-Falls is used in a bondedmembrane system, tissue faced slabs should beused. High performance bitumen membranesystems are fully bonded in hot bitumen to thetissue faced Rocksilk Cut-To-Falls slabs usingtraditional roll and pour methods.

    Mastic asphalt surfaceRocksilk Cut-To-Falls slabs provide a stable basefor mastic asphalt. The slabs should be overlaidwith a 12mm layer of bitumen impregnatedfibreboard. A bitumen felt (low grade issatisfactory) should be loose laid withoutbonding onto the fibreboard prior to theapplication of the mastic asphalt.

    Single ply membranesThese should be fixed in accordance with themanufacturer’s recommendations.

    Built-up bitumen roofing system bonded in hot bitumen

    ProductsRocksilk Krimpact Cut-To-Falls is a system oftapered, pre-cut, compression resistantinsulation slabs made from rock mineral wool.The slabs are supplied pre-cut to the requiredfalls, normally 1:60 or 1:40 (BS 6229 requiresa minimum fall of 1:80 to be achieved on built-up roofs, so normal practice is to design at agreater fall to allow for deflection of the deck or other site problems).

    Typical constructionRocksilk Krimpact Cut-To-Falls is suitable for use on all types of roof deck. The insulationslabs are laid over and fully bonded to avapour control layer which is bonded to theroof deck. The insulation is overlaid with awaterproof membrane consisting of either a fully bonded built-up bitumen roofing system, a single ply membrane or mastic asphalt. When used with mastic asphalt, the insulation is overlaid with 12mm bitumen impregnatedfibreboard and an isolating felt.

    InstallationRocksilk Krimpact Cut-To-Falls slabs arenumbered and supplied with a laying schemefor their application. These will be produced byKnauf Insulation from scale drawings suppliedby the client. Rocksilk Krimpact Cut-To-Falls isnot just a product but a comprehensive servicefrom design to delivery.

    Fl06

    Rocksilk Krimpact Cut-To-Falls bonded to vapour control layer

    Plywood, chipboard or OSB deck Timber roof construction

    Roof drainageoutlets

    Rocksilk Krimpact Flat Roof Slab

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    Built-up bitumen roofing system bonded in hot bitumen

    Vapour control layer

    Rocksilk Krimpact Cut-To-Falls bonded to vapour control layer

    Void fully filled with insulation to provide continuity between wall and roof insulation

    Insulation extends toedge of roof

    Ceiling fixed first and sealed against wall to minimise air leakage

    Typical specificationThe vapour control layer and RocksilkKrimpact Cut-To-Falls ......mm thick to be fullybonded, with hot bitumen. Rocksilk KrimpactCut-To-Falls should be laid in accordance withthe laying scheme supplied. The waterproofmembrane should be applied in accordancewith the appropriate manufacturer’srecommended specification.

    Alternatively, consult the National Building Specifications(NBS) based on StandardVersion J41. It contains a set of proprietary clauses, which are edited versions written byKnauf Insulation.

    Table 26: Typical U-values of flat roofs

    Product U-values (W/m2K)

    150mm concrete Profiled 19mm chipboardThickness 40mm screed metal timber joists

    (mm) 13mm plaster deck 12.5mm plasterboard

    Rocksilk Krimpact Cut-To-Falls

    245 0.15 0.15 0.14

    230 0.16 0.16 0.15

    215 0.17 0.17 0.16

    205 0.17 0.18 0.17

    190 0.19 0.19 0.18

    180 0.20 0.21 0.19

    170 0.21 0.22 0.20

    160 0.22 0.23 0.21

    150 0.23 0.24 0.22

    145 0.24 0.25 0.23Note: U-value calculations based on the installation of a single ply membrane and are calculated for the specific indicated thickness of Rocksilk Krimpact Cut-to-Falls Slab. For project specific calculations contact our Technical Advisory Centre on 01744 766666.

    Thermal performanceThe thermal conductivity of Rocksilk KrimpactCut-To-Falls is 0.038 W/mK.

    Table 26 (right) shows the U-values achieved fortypical constructions insulated with variousthicknesses of Rocksilk Cut-To-Falls Slabs.Because the thickness of insulation varies acrossthe entire roof in cut to falls schemes, the U-value varies across the whole roof, being bestand worse where the greatest and leastthickness of insulation occurs, respectively.Every scheme is different and the average U-value for the entire roof can only be calculatedwhen the scheme of falls has been designed.The cut to falls scheme designers will then setthe minimum thickness so that the average U-value for the entire roof meets the designers orBuilding Regulations requirements. This table isa useful reference to determine what the highestpossible minimum thickness of insulation wouldbe to achieve a specific U-value, in reality it willbe less. The thermal performance of a cut-to-fallsroof is based on the overall U-value of the roofsystem, which is a function of the individualtapers and the respective areas as detailed inBS 6946:1997

    Typical verge detail

    Fire performanceRocksilk Cut-To-Falls is classified as Euroclass A1 to BS EN ISO 13501-1, this is the highestfire rating possible for an insulation product to achieve. Rocksilk products have a meltingpoint of over 1000°C. In the event of fire theywill emit negligible quantities of smoke andfumes. The heat emission from the products isinsignificant.

    For general technical enquiries on cut to fallsroofing, contact the Knauf Insulation TechnicalAdvisory Centre on 01744 766666. For aquotation on a specific project please contactKnauf Insulation Sales on 0844 800 0135.

  • Flat roofsCut-To-falls

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    6.1.3 Design details: Flat roofs

    Advantages� Provides for a fall either where deck

    was designed to be flat, or does notprovide the designed fall whenconstructed.

    � Ideal method for upgrading roofs with ponding problems

    � For a purpose-designed trafficked warm roof, Polyfoam Cut-To-Falls is the ideal robust insulant

    � Supported by specialist design service with installation advice

    � Bespoke system designed to meet the needs of each individual project

    Each component will be marked on the diagramand should be laid as indicated starting at, and working away from, the drainage outlet.

    In a bonded membrane system, each layer of the Polyfoam Cut-To-Falls scheme must be bonded as well as the waterproof membrane itself.

    When a mechanically fixed membrane is being used, the Polyfoam Cut-To-Falls boardsshould be mechanically fixed to the deck withtwo centrally placed fixings in each board to secure the boards in place before themembrane is fixed.

    PerformanceCompression resistancePolyfoam Cut-To-Falls is highly resistant tocompression and can be specified to withstandboth occasional and long term static loads.

    Moisture resistancePolyfoam Cut-To-Falls boards are resistantto moisture absorption and can be laid instanding water or up against wet concretewith negligible impact on the performance of the product.

    Thermal performancePolyfoam Cut-To-Falls has a thermal conductivityof 0.029 W/mK.

    The waterproof membrane may then be bondedto the insulation using a polyurethane basedadhesive in accordance with the membranemanufacturer’s instructions. The advice of thewaterproofing membrane manufacturer will berequired for the precise fixing specification.

    When using mechanically fixed membranes,Polyfoam Cut-To-Falls boards should bemechanically fixed to the deck.

    Polyfoam Cut-To-Falls is suitable for use withmost PVC membranes (providing there is aseparation layer between the board and themembrane), EPDM and other types of single plywaterproof membrane systems. The advice ofthe single ply membrane manufacturer shouldbe sought to confirm compatibility with specificmembranes. Polyfoam Foil Faced Cut-To-Falls hasbeen developed to eliminate the risk of plasticisermigration when a PVC membrane is used. It also provides protection for the insulationwhen solvent or heat welded membrane systems are used.

    InstallationThe vapour control layer should be laid over the structural deck and all joints lapped and bonded. Polyfoam Cut-To-Falls boards arenumbered and supplied with a laying schemefor their application.

    Single ply membrane

    ProductsPolyfoam Cut-To-Falls is a specially designedsystem of pre-cut, tapered, 100% ozonefriendly, extruded polystyrene rigid boardinsulation. Typical board sizes are 1200 x 600mm and cut to suit any fall scheme, though mostare either 1:40 or 1:60 (BS 6229 requires aminimum fall of 1:80 to be achieved on built-uproofs, so normal practice is to design at agreater fall to allow for deflection of the deck orother site problems).The boards are straight edged and can besupplied with a foil facing to suit PVC single plymembrane applications.

    Typical constructionPolyfoam Cut-To-Falls boards are suitable for useon all types of roof deck.

    The boards are laid over a vapour control layerand mechanically fixed or bonded to the deck.

    The insulation is overlaid with a single plymembrane which can be fully adhered to theinsulation or mechanically fixed to the deck.

    When using partially or fully bonded membranesystems, Polyfoam Cut-To-Falls boards should bemechanically fixed to the deck to withstand the calculated wind load.

    Fl07

    Polyfoam Cut-To-Falls mechanically fixed to deck

    Vapour control layer

    Timber roof construction

    Plywood, chipboard or OSB deck

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    6.1.3Design details: Flat roofs

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    Vapour control layer

    Insulation upstand to extend thermalbridge to minimum of 300mm high

    300m

    m m

    in

    Vapour control layer to bond with weatherproof membrane

    Polyfoam Cut-To-Falls

    Typical specificationThe vapour control layer and Polyfoam Cut-To-Falls to be mechanically fixed*/ adhered*to the roof deck. (*delete as required)

    Polyfoam Cut-To-Falls should be laid inaccordance with the laying scheme supplied.

    The waterproof membrane should be appliedin accordance with the appropriatemanufacturer’s recommended specification.

    Alternatively, consult the NationalBuilding Specifications (NBS)based on Standard Version J42.It contains a set of proprietaryclauses, which are editedversions written by KnaufInsulation.

    Table 27: Typical U-values of flat roofs insulated with Polyfoam Cut-To-Falls

    Product U-values (W/m2K)

    150mm concrete Profiled 19mm chipboardThickness 40mm screed metal timber joists

    (mm) 13mm plaster deck 12.5mm plasterboard

    Polyfoam Cut-To-Falls

    190 0.14 0.15 0.14

    180 0.15 0.16 0.15

    170 0.16 0.17 0.16

    160 0.17 0.18 0.17

    150 0.18 0.19 0.18

    140 0.19 0.20 0.19

    130 0.21 0.22 0.20

    120 0.22 0.23 0.21

    110 0.24 0.25 0.23Note: For project specific calculations contact our Technical Advisory Centre on 01744 766666

    Table 27 (right) shows the U-value achieved fortypical constructions insulated with variousthicknesses of Polyfoam Cut-To-Fallsproducts. Because the thickness of insulationvaries across the entire roof in cut to fallsschemes the U-value varies across the wholeroof, being best and worse where the greatestand least thickness of insulation occursrespectively. Every scheme is different and theaverage U-value for the entire roof can only becalculated when the scheme of falls has beendesigned. The cut-to-falls scheme designers willthen set the minimum thickness so that theaverage U-value for the entire roof meets thedesigners or Building Regulations requirements.This table is a useful reference to determinewhat the highest possible minimum thickness ofinsulation would be to achieve a specificU-value, in reality it will be less.The thermal performance of a cut-to-falls roofis based on the overall U-value of the roofsystem, which is a function of the individualtapers and the respective areas as detailedin BS 6946:1997.

    Typical abutment detail with concrete deck

    For general technical enquiries on cut-to-fallsroofing, contact the Knauf Insulation TechnicalAdvisory Centre on 01744 766666. For aquotation on a specific project please contactKnauf Insulation Sales on 0844 800 0135.

    Fire performanceWhen Polyfoam Cut-To-Falls is installed in a roof construction it will not contribute to thedevelopment stages of a fire. When overlaidwith a single ply membrane the performance of the finished roof will depend on the membraneused. Please consult the membrane supplier forfurther details.

  • Flat roofsExisting warm roof cut-to-falls upgrade

    Sales 0844 800 0135 Technical Advisory Centre 01744 766666 www.knaufinsulation.co.uk554

    6.1.3 Design details: Flat roofs

    Advantages� Ideal method for upgrading roofs

    with ponding problems

    � Significantly improves acoustic performance of timber and metal decks

    � Non-combustible product withhighest Euroclass A1 rating

    � Supported by specialist design and installation advice

    � Bespoke system designed to meet the needs of each individual project

    Performance

    StandardsRocksilk Krimpact Cut-To-Falls Slab has beentested to the UEAtc Technical Guidelines MOATNo 50: 1992, Thermal insulation systemsintended for supporting waterproofingmembranes on flat and sloping roofs. It isclassified B for mechanical performance – roofonly accessible for purpose of maintenance andmay be used without any restrictions.

    Compressive resistanceRocksilk Krimpact Cut-To-Falls Slab has acompressive strength in excess of 75 kPa.

    Thermal performanceThe thermal conductivity of Rocksilk KrimpactCut-To-Falls Slab is 0.038 W/mK.

    Table 28 shows the U values achieved fortypical constructions insulated with variousthicknesses of Rocksilk Krimpact Cut-To-FallsSlab. Because the thickness of insulation variesacross the entire roof in cut to falls schemes theU-value varies across the whole roof, being bestand worse where the greatest and leastthickness of insulation occurs respectively. Everyscheme is different and the average U-value forthe entire roof can only be calculated when thescheme of falls has been designed. The cut to

    InstallationThe insulation slabs are laid over and fullybonded to either the existing roof membrane, or to a new vapour control layer. The insulationis overlaid with a waterproof membraneconsisting of either a fully bonded built-upbitumen roofing system, single ply membrane or mastic asphalt.

    Built-up felt membranesWhere Rocksilk Krimpact Cut-To-Falls Slab isused in a bonded membrane system, tissuefaced slabs should be used. High performancebitumen membrane systems are fully bonded inhot bitumen to the tissue faced RocksilkKrimpact Cut-To-Falls slabs using traditional rolland pour methods.

    Mastic asphalt surfaceRocksilk Krimpact Cut-To-Falls Slabs provide astable base for mastic asphalt. The slabs shouldbe overlaid with a 12mm layer of bitumenimpregnated fibreboard. A bitumen felt (lowgrade is satisfactory) should be loose laidwithout bonding onto the fibreboard prior to the application of two layers of mastic asphalt.

    Single ply membranesThese should be fixed in accordance with themanufacturer’s recommendations.

    ProductsRocksilk Krimpact Cut-To-Falls is a system of pre-cut, tapered, high density insulation slabsmade from rock mineral wool. The slabs aresupplied pre-cut to the required falls, normally1:60 or 1:40 (BS 6229 requires a minimum fall of 1:80 to be achieved on built-up roofs, so normal practice is to design at a greater fall to allow for deflection of the deck or othersite problems).

    Typical constructionRocksilk Krimpact Cut-To-Falls can be used toboth upgrade the thermal insulation of anexisting roof and also provide improveddrainage. A survey of the existing roof shouldestablish whether the existing waterproofmembrane and thermal insulation are in asuitable condition for retention, or if they needto be completely replaced. The existing roofstructure should be checked to ensure that theadditional loads can be supported safely. KnaufInsulation recommends that condensationanalysis is carried out where any existingthermal insulation is retained.

    Fl08

    Existing vapour control layer

    New buil t-up bitumen roofing system bonded in hot bitumen

    Rocksilk Krimpact Cut-To-Falls bondedto existing waterproof membrane

    Existing weatherproof membrane

    Structural deckExisting thermal insulation

    Rocksilk Krimpact Flat Roof Slab

  • 555

    6.1.3Design details: Flat roofs

    Sales 0844 800 0135 Technical Advisory Centre 01744 766666 www.knaufinsulation.co.uk

    Structural deck

    New buil t-up bitumen roofing system bonded in hot bitumen

    Rocksilk Krimpact Cut-To-Falls slab bonded to existing waterproof membrane

    Existing waterproof membrane and thermal insulation

    Vapour control layer

    Typical specificationRocksilk Krimpact Cut-To-Falls ......mm thick tobe fully bonded, with hot bitumen to theexisting waterproof membrane*/ vapourcontrol layer*. (*delete as required) RocksilkKrimpact Cut-To-Falls should be laid inaccordance with the laying scheme supplied.

    The new waterproof membrane should beapplied in accordance with the appropriatemanufacturer’s recommended specification.

    Alternatively, consult the NationalBuilding Specifications (NBS)based on Standard Version J21or J41, it contains a set ofproprietary clauses, which areedited versions written by KnaufInsulation.

    Table 28: Typical U-values of flat roofs where existing warm roof is upgraded

    Product U-values (W/m2K)

    150mm concrete Profiled 19mm chipboardThickness 40mm screed metal timber joists

    (mm) 13mm plaster deck 12.5mm plasterboard

    Rocksilk Krimpact Cut-To-Falls

    245 0.15 0.15 0.14

    230 0.16 0.16 0.15

    215 0.17 0.17 0.16

    205 0.17 0.18 0.17

    190 0.19 0.19 0.18

    180 0.19 0.20 0.19

    170 0.21 0.22 0.20

    160 0.22 0.23 0.21

    150 0.23 0.24 0.22

    145 0.24 0.25 0.23Note: U-value calculations based on the installation of a single ply membrane and the existing insulation layer is deemed to beRocksilk Flat Roof Slab Extra. The U-values have been calculated to BS EN ISO 6946:1997. For project specific calculations contact our Technical Advisory Centre on 01744 766666.

    falls scheme designers will then set the minimumthickness so that the average U-value for theentire roof meets the designers or BuildingRegulations requirements. This table is a usefulreference to determine what the highest possibleminimum thickness of insulation would be toachieve a specific U-value, in reality it will beless. The U-values shown are calculatedassuming the existing insulation has the samethermal performance as Rocksilk Krimpact FlatRoof Slab. The U-value will be achieved if thetotal thickness of insulation matches thethickness indicated. If the existing insulation isnot Rocksilk Krimpact Flat Roof Slab contactKnauf Insulation Technical Advisory Centre forspecific U-value calculations.

    Fire performanceRocksilk Krimpact Cut-To-Falls Slab is classifiedas Euroclass A1 to BS EN ISO 13501-1, this isthe highest fire rating possible for an insulationproduct to achieve. Rocksilk products have anextremely high melting point of over 1000°C. In the event of fire they will emit negligiblequantities of smoke and fumes. The heatemission from the products is insignificant.

    Typical section

    For general technical enquiries on cut to fallsroofing, contact the Knauf Insulation TechnicalAdvisory Centre on 01744 766666. For aquotation on a specific project please contactKnauf Insulation Sales on 0844 800 0135

  • Flat roofsExisting warm roof upgrade

    Sales 0844 800 0135 Technical Advisory Centre 01744 766666 www.knaufinsulation.co.uk556

    6.1.3 Design details: Flat roofs

    Advantages� Ideal method for upgrading roofs

    with ponding problems

    � Significantly improves acoustic performance of timber and metal decks

    � Non-combustible product withhighest Euroclass A1 rating

    � Supported by specialist design service and installation advice

    � Bespoke system designed to meet the needs of each individual project

    PerformanceStandardsRocksilk Krimpact Flat Roof Slab has beentested to the UEAtc Technical Guidelines MOATNo 50: 1992, Thermal insulation systemsintended for supporting waterproofingmembranes on flat and sloping roofs. It isclassified B for mechanical performance - roofonly accessible for purpose of maintenance andmay be used without any restrictions.

    Compressive resistanceRocksilk Krimpact Flat Roof Slab has acompressive strength in excess of 75 kPa.

    Thermal performanceThe thermal conductivity of Rocksilk KrimpactFlat Roof Slab is 0.038 W/mK. The U-Values for typical constructions insulatedwith Rocksilk Krimpact Flat Roof Slab are givenin table 29. These are calculated assuming theexisting insulation has the same thermalperformance as Rocksilk Krimpact Flat RoofSlab. The U-value will be achieved if the totalthickness of insulation matches the thicknessindicated. If the existing insulation is notRocksilk Krimpact Flat Roof Slab contact KnaufInsulation Technical Advisory Centre for specificU-value calculations.

    InstallationThe insulation slabs are laid over and fullybonded to either the existing roof membrane, or to a new vapour control layer. The insulationis overlaid with a waterproof membraneconsisting of either a fully bonded built-upbitumen roofing system, single ply membrane or mastic asphalt.

    Built-up felt membranesHigh performance bitumen membrane systemsare fully bonded in hot bitumen to the tissuefaced Rocksilk Krimpact Flat Roof Slab usingtraditional roll and pour methods. Highperformance bitumen membrane systems arefully bonded in hot bitumen to the tissue facedRocksilk Krimpact Flat Roof Slabs usingtraditional roll and pour methods.

    Mastic asphalt surfaceRocksilk Krimpact Flat Roof Slabs provide astable base for mastic asphalt. The slabs shouldbe overlaid with a 12mm layer of bitumenimpregnated fibreboard. A bitumen felt (lowgrade is satisfactory) should be loose laidwithout bonding onto the fibreboard prior to theapplication of two layers of mastic asphalt.

    Single ply membranesThese should be fixed in accordance withthe manufacturer’s recommendations.

    ProductsRocksilk Krimpact Flat Roof Slab is a highstrength, consistent density, rigid, glass tissuefaced rock mineral wool slab manufacturedusing Krimpact technology and specificallydesigned for use in flat roofing.

    Typical constructionRocksilk Krimpact Flat Roof Slabs can be usedto upgrade the thermal insulation of an existingroof. A survey of the existing roof shouldestablish whether the existing waterproofmembrane and thermal insulation are in asuitable condition for retention, or if they needto be completely replaced. The existing roofstructure should be checked to ensure that theadditional loads can be supported safely.Knauf Insulation recommends that condensationanalysis is carried out where any existingthermal insulation is retained.

    Fl09

    Existing vapour control layer

    New buil t-up bitumen roofing system bonded in hot bitumen

    Rocksilk Krimpact Flat Roof Slab bondedto existing waterproof membrane

    Existing weatherproof membrane

    Structural deckExisting thermal insulation

    Rocksilk Krimpact Flat Roof Slab

  • 557

    6.1.3Design details: Flat roofs

    Sales 0844 800 0135 Technical Advisory Centre 01744 766666 www.knaufinsulation.co.uk

    Structural deck

    New buil t-up bitumen roofing system bonded in hot bitumen

    Rocksilk Krimpact Flat Roof Slab bonded to existing waterproof membrane

    Existing waterproof membrane and thermal insulation

    Vapour control layer

    Typical specificationRocksilk Krimpact Flat Roof Slab, thickness......mm thick to be fully bonded, with hotbitumen to the existing waterproofmembrane*/ vapour control layer*. (*delete as required) The new waterproofmembrane should be applied in accordancewith the appropriate manufacturer’srecommended specification.

    Alternatively, consult the NationalBuilding Specifications (NBS)based on Standard Version J21or J41, it contains a set ofproprietary clauses, which areedited versions written by KnaufInsulation.

    Table 29: Typical U-values of flat roofs where existing warm roof is upgraded

    Product U-values (W/m2K)

    150mm concrete Profiled 19mm chipboardThickness 40mm screed metal timber joists

    (mm) 13mm plaster deck 12.5mm plasterboard

    Rocksilk Krimpact Flat Roof Slab

    245 (145+100) 0.15 0.15 0.15

    230 (130+100) 0.16 0.16 0.15

    225 (150+75) 0.16 0.17 0.16

    210 (130+80) 0.17 0.18 0.17

    200 (2x100) 0.18 0.19 0.17

    195 (145+50) 0.16 0.19 0.18

    180 (100+80) 0.20 0.21 0.19

    160 0.22 0.23 0.21

    150 0.23 0.25 0.22

    145 0.24 0.25 0.22

    130 0.26 0.28 0.25Note: U-value calculations based on the installation of a single ply membrane and the existing insulation layer is deemed to beRocksilk Flat Roof Slab Extra. The U-values have been calculated to BS EN ISO 6946:1997. For project specific calculations contact our Technical Advisory Centre on 01744 766666.

    Fire performanceRocksilk Krimpact Flat Roof Slab is classified asEuroclass A1 to BS EN ISO 13501-1. Rocksilkproducts have a melting point of over 1000°C.In the event of fire they will emit negligiblequantities of smoke and fumes. The heatemission from the products is insignificant.

    Typical section

  • www.knaufinsulation.co.uk

    www.thinkinsulation.com

    Knauf Insulation Ltd.PO Box 10Stafford RoadSt HelensMerseysideWA10 3NS

    Customer Service (Sales)Tel: 0844 800 0135Fax: 01744 612 007email: [email protected]

    Technical Advisory Centre (TAC)Tel: 01744 766666Fax: 01744 766667email: [email protected]

    LiteratureTel: 08700 668 660Fax: 0870 400 5797email: [email protected]

    August 2008: Issue 1

    Ref: KB57508

    Front CoverContentsSolution optimiser and pathfinderDesign considerationsWarm deck singly ply membrane Rocksilk Krimpact Flat Roof SlabWarm deck single ply membrane Polyfoam RoofboardWarm deck built-up felt/mastic asphaltProtected membraneCar park roofRocksilk Krimpact Cut-To-FallsPolyfoam Cut-To-FallsExisting warm roof cut-to-falls upgradeExisting warm roof upgradeBack Cover