non - residential new build 4.2.1 built-up metal roofs · built-up metal roofs solution optimiser...

Non - Residential New Build4.2.1 Built-up Metal Roofs

August 2008: Issue 1

4.0Non-residential new build

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

Introduction find online pageSolution optimiser and pathfinder 320Design considerations 322

Design Details 562

Built-up Metal Roofs Contents

Non-residential New Build

find online page

Rail and bracket systems Bu01 562

Standing seam Bu02 564

Built-up metal roofsSolution optimiser and pathfinder

Sales 0844 800 0135 Technical Advisory Centre 01744 766666 www.knaufinsulation.co.uk320

4.2.1 Non-residential new build: Roofs

Profiled metal roofing systems have longbeen successfully used throughout the UK as a lightweight, fast and simple method ofconstruction which can reduce both structural steel and foundation costs. Such systemstypically consist of a low profile metal innerliner sheet, separated from an outer, higherprofile, metal weather sheet. The cavity isfilled with a layer of insulation to providehigh levels of thermal performance. Thisinsulation is normally a glass mineral woolquilt, a high performance, lightweightinsulant with A1 fire resistance.

Built-up metal roofing systems are typicallyassembled on site with the design andcomponents usually forming part of aproprietary system.

Knauf Insulation provide products with arange of thermal conductivities to be used in roof systems for modern commercial,industrial and warehouse buildings.

Photograph courtesy of Corus Building Systems

Elemental U-value requirement

Sales 0844 800 0135 Technical Advisory Centre 01744 766666 www.knaufinsulation.co.uk 321

4.2.1Non-residential new build: Roofs

Standing seam systemProduct*: Crown FactoryClad range and Rocksilk Universal SlabDescription: Glasswool and rock mineral wool insulation in standing seam system

Page No: 564

Rail and bracket systemProduct*: Crown FactoryClad rangeDescription: Glasswool insulation between twin skin profile metal sheeting

Page No: 562Bu01

Bu02

Built-up metal roofs**Construction compatibility with Part L2A

Knauf Insulation solution

Area weighted average

max U-value England and

Wales and Northern Ireland

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 0.300.33 0.31 0.15

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.

**Note: The above table shows typical U-values for built-up metal systems. Generic rail andbracket U-value calculations can be provided by our Technical Advisory Centre, however, forproprietary rail and bracket systems and all standing seam systems the system manufacturershould be consulted for project specific U-value calculations

Pb01

0.16

Built-up metal roofsBuilt-up metal roof design


4.2.1 Non-residential new build: Roofs

Benefits• Fast method of construction

• Lightweight construction

• High levels of fire resistance (when using mineral wool) with potentially lower insurance premiums compared to foam composite panels

• Secure and weatherproof at an early stage in the build programme

• Cost effective and energy efficient

• Easy to install

Thermal insulationIt is possible to achieve very high standards ofthermal insulation using built-up metal systems,but due to the complex nature of heat flowthrough these systems due to the spacer systems itis not possible to calculate U-values using thenormal simplified methods.

The Knauf Insulation Technical Advisory Centrecan calculate the thickness of insulation needed toachieve specific U-values, including the effect ofthermal bridging for simple rail and bracketsystems but normally one would consult thesystem manufacturer, similarly for standing seamsystems one should in the first place consult thesystem manufacturer.

Air permeabilityThe uncontrolled infiltration or leakage of airfrom a building has a significant impact on itsenergy efficiency. With good detailing and carein the construction phase it is possible to achievevery high standards of air tightness in built-upmetal constructions. This will of course restrictuncontrolled air infiltration and leakage andimprove the energy efficiency of the building.Building Regulations require a measurement ofthe air permeability to be included in the SBEM‘whole building’ calculation used for compliance.Problem areas include at the junction of buildingelements such as the wall roof junction orpenetrations through the system such asrooflights.

Thermal bridging There are two categories of thermal bridging thatoccur in built-up Metal systems, the repeatingthermal bridges inherent in the spacer system andthe thermal bridges at junctions and openings inthe construction. The effect of the repeatingthermal bridges is included in theU value calculation for the roof. Thermal bridgesat junctions and openings must be calculatedseparately and the heat losses at these pointsincluded in the SBEM calculation. This value isincluded by multiplying the length of eachthermal bridge by the calculated psi value.

Acoustic performanceBuildings with built-up metal roofs may need toincorporate noise control measures not only tomeet building regulation requirements, but alsoHealth and Safety and Environmental HealthRegulations regulations as well as the buildingoccupiers specific requirements. These measurescan be grouped into two categories, soundinsulation and sound absorption.

Sound insulationA poorly designed built-up metal roof willtransmit a significant amount of sound, whether itbe airborne sound or rain noise (the drummingsound that heavy rainfall can cause), which willlead to the building failing to provide anacceptable level of protection either to theoccupants of the building (in the case of eithernoise outside the building or rain noise) or to

IntroductionProfiled metal roofing systems typically consist of a low profile metal inner liner sheet, separated from an outer, higher profile,metal weather sheet. The cavity is filled with alayer of insulation to provide maximum thermalperformance. This insulation is normally a glassmineral wool quilt, a high performance,lightweight insulation properties with A1 fireresistance. Built-up metal roofing systems aretypically assembled on site with the design andcomponents used forming part of a proprietarysystem.

Amongst the considerations the designer will have to include when designing a buildingwith a built-up metal roof the following bothinfluence and are influenced by the insulationmaterials in the system:

• Thermal insulation

• Air permeability

• Thermal bridging

• Acoustic performance

• Fire safety

• Control of condensation

• Environmental impact of the materials.

Photograph courtesy of Ash and Lacy Building Systems

Sales 0844 800 0135 Technical Advisory Centre 01744 766666 www.knaufinsulation.co.uk 323

4.2.1Non-residential new build: Roofs

people living close to the building from noisegenerated within the building.

One of the most effective methods of improvingsound insulation is to increase the mass of thestructure. Built up metal roofs are generallylightweight, however they are able to provide a high level of separation between the two sidesof the roof and also include glass and rockmineral wool within the structure which providevery high levels of sound absorption. When the effects of separation and sound absorptionare combined in a built-up metal roof it ispossible to achieve outstanding levels of sound insulation.

Building regulations impinge primarily on roofs inrespect of schools where it is a requirement thatthe building should meet the standards set out inSection 1 of Building Bulletin 93 ‘The AcousticDesign of Schools’. This sets specific upper limitsfor indoor ambient noise levels.

Factors affecting the performance required by theroof will include noise from road, rail and airtraffic, industrial and commercial premises. Theperformance required in other types of buildingsmay be controlled by government requirementssuch as Hospitals under HTM 2045, or specificclient requirements. Environmental HealthRegulations may require specific sound insulationperformance in roofs where high levels of noiseare generated, such as industrial buildings, sportsand concert halls to stop sound breaking out ofthe building and thus prevent noise nuisance toneighbours.

Sound absorptionThe control of the indoor acoustic environment isimportant to maintain health and safety forworkers and occupants of buildings. It is possibleusing perforated metal liner sheets with soundabsorbing lining, usually glass or rock mineralwool, to control reverberation of sound whichwould otherwise be problematic.

Rain noiseAcoustic performance has traditionally notfeatured high on the list of design priorities butguidance now states that it is essential that rainnoise is considered in the design of built-up metalsystems as it can significantly increase the indoorambient noise level. Addressing this issue hascreated focus on the governmental BuildingSchools for the Future programme. Futureintention is that rain noise will be consideredwithin BB93. Until this time, it is appropriate fordesign teams to provide evidence to the BuildingControl Body that the built-up metal system hasbeen designed to minimise rain noise whererequired.

Fire protection It is a requirement of the Building Regulations thatexternal cladding elements shall resist the spreadof fire from one building to another. The degree of fire resistance which the external roofing element must provide willdepend upon the size and use of the building andit's distance from any boundary. Furtherperformance information will be available from the cladding system manufacturer.

Built-up metal roofs have the advantage of usingnon-combustible glass and rock mineral woolinsulation.

Control of condensationCondensation could potentially occur either onthe underside of the liner sheet if there weresignificant thermal bridges through the system orwithin the structure of the system if there was asignificant break in the vapour control layer.

The spacer system used to support the outercladding sheet is a potential thermal bridge andthus could be a point for localised condensationon the liner sheet, however the modern spacersystems all include a significant thermal break, asa necessity for the achievement of the overall U-value, and as such the chance of condensationwhere the spacer system is fixed to the liner isnegligible. If there are significant gaps in theinsulation layer then it would be possible thatlocalised condensation would occur.

To control condensation within the built-up metalroof structure it is normal to create an effectivevapour barrier at the level of the liner sheet. Thisis done by sealing all joints in the liner sheet andwhere there are any penetrations through theliner sheet. Where a perforated liner sheet isused then a separate vapour barrier must beinstalled.

The likelihood of either problem occurring is verylow however extra care needs to be taken inbuildings with high levels of humidity such asswimming pools or certain industrial processes.

Photographs courtesy of Corus Building Systems


6.1.5 Design details: Built-up metal roofs

Built-up metal roofsRail and Bracket System

Advantages� Strong and easy to assemble

Quick and economical to install

Speeds up building programme

Lightweight

Building is secure and weatherproof at an early stage in the programme

Non-combustible liner

Rain impact noise and flanking sound:Proprietary System manufacturers haveachieved significant impact noise reductionsby incorporating mineral wool insulation.Thermal performanceCrown FactoryClad 40 has a thermalconductivity of 0.040 W/mK

Crown FactoryClad 37 has a thermalconductivity of 0.037 W/mK



Thickness of Crown FactoryClad required toachieve U-values is shown on Table 32.

PerformanceFireCrown FactoryClad is classified as EuroclassA1 to BS EN ISO 13501-1Vapour ResistivityCrown FactoryClad has a vapour resistivityof 7.00 MN.s.g.m.Acoustic performanceSound absorption: Achieved by installing aperforated metal liner sheet andincorporating a ‘soft’ absorbing insulationmaterial behind it. Different combinations of perforations and levels of insulation willgive varying results of sound absorption.See pages 556-7.Airborne sound reduction: A standardinsulated roof construction will have anapproximate weighted sound reduction (Rw)of 33dB with an aluminium trapezoidal linerand 36dB with a steel trapezoidal liner. Thesound reduction performance can beincreased by varying the number and thedensities of the insulation layers as well asadding additional mass into the construction.

ProductsCrown FactoryClad Rolls are a range of flexible,lightweight rolls of resilient, non-combustibleglass mineral wool with exceptionally high tearstrength. They are produced in a range of fourdifferent thermal conductivities.They have a very low impact on theenvironment and are classified as zero ODPand zero GWP*.

* Ecohomes and Code for Sustainable Homes classification

Typical constructionCrown FactoryClad is used for the thermal and acoustic insulation in profiled metal cladroofing systems.

InstallationCrown FactoryClad is located between profiled metal outer cladding sheets and innerlining sheets. The lining sheets are fixed on topof the supporting purlins. The inner and outermetal cladding sheets are separated by rail and bracket systems or preformed insulatedspacer systems.

To maintain continuity of the insulation whererail and bracket systems are used, the insulationis tucked under the rails, with all quilt edgestightly butted. There is no continuous airspace in the construction other than that created by the cladding profile.

Bu01

Profiled metalouter sheet

Rail and bracket

Vapour controllayer

CrownFactoryClad Roll Profiled metal liner sheet

563

6.1.5Design details: Built-up metal roofs


Typical specificationLiner panels to be positioned over purlins anda metal spacer system secured to the linerand purlin to ensure the full thickness ofinsulation is maintained between the linerand cladding sheets. Crown FactoryClad40*/37*/35*/32* ......mm thick, to be laidover the lining sheets and installed accordingto system manufacturer’s instructions, with alljoints closely butted. Cladding sheets to besecurely fixed in position. (*Delete asappropriate)

Alternatively, refer to NBS clause H31/50 and 271

Table 32: Typical U-values for built-up metal roofs - rail and bracket systems

Product Rails at 1.20 metre spacings Thickness (mm) U-value

Crown FactoryClad 40 200 0.22180 0.24160 0.27

Crown FactoryClad 37 200 (2x100) 0.20180 0.23160 0.26

Crown FactoryClad 35 200 (2x100) 0.19

180 (2x90) 0.22Crown FactoryClad 32 200 (2x100) 0.18

180 (2x90) 0.20170 (80+90) 0.21

Notes: The U-values are based on SCI P312. Knauf Insulation recommend that the system designer/manufacturer is contacted forU-values specific to their systems.

Crown FactoryClad RollProfiled metalouter sheet

Profiled metalliner sheetVapour control layer

Typical section


6.1.5 Design details: Built-up metal roofs

Built-up metal roofsStanding seam system

Advantages� Euroclass A1 fire classification

Exceptionally high tear strength

Combines thermal and acoustic insulation

Cost effective

Easy to install

Lightweight and easy to handle

Thickness of Crown FactoryClad required toachieve U-values is shown in Table 33.

Vapour resistivityCrown FactoryClad has a vapour resistivity of7.00 MN.s.g.m.

Acoustic performanceSound absorption: Achieved by installing aperforated metal liner sheet and incorporating a ‘soft’ absorbing insulation material behind it.Different combinations of perforations andlevels of insulation will give varying results ofsound absorption.

Airborne sound reduction: A standard insulatedroof construction will have an approximateweighted sound reduction (Rw) of 33dB with an aluminium trapezoidal liner and 36dB witha steel trapezoidal liner. The sound reductionperformance can be increased by varying thenumber and the densities of the insulation layersas well as adding additional mass into theconstruction.

Rain impact noise and flanking: Proprietorysystem manufacturers have achieved significantrain impact noise reductions by incorporatingmineral wool insulation within their systems.

InstallationCrown FactoryClad is used for the thermal andacoustic insulation in profiled metal clad roofingsystems. With Euroclass A1 fire classification, itsuse can potentially reduce insurance premiumswhen compared to foam composite panels.Crown FactoryClad is manufactured 1200mmwide and in long lengths, making it particularlysuitable for use in standing seam roofs.

Performance

Thermal:





Rocksilk Universal Slab RS100 has a thermalconductivity of 0.035 W/mK

FireCrown FactoryClad and Rocksilk Universal SlabRS100 are classified as Euroclass A1 to BS ENISO 13501-1.

ProductsCrown FactoryClad Rolls are a range of flexible,lightweight rolls of resilient, non-combustibleglass mineral wool with exceptionally high tearstrength. They are produced in a range of fourdifferent thermal conductivities.They have a very low impact on theenvironment and are classified as zero ODPand zero GWP*.

* Ecohomes and Code for Sustainable Homes classification

Rocksilk Universal Slab is a multi purpose rockmineral wool slab which has a very low impacton the environment and is classified as zeroODP and zero GWP*.

Typical constructionStanding seam profiles are able to meet themost demanding construction and designrequirements to create a roof which combinesfunctionality with aesthetics. Profiled metalsystems typically consist of a low profile metalinner liner sheet, separated from an outer,higher profile, metal weather sheet. The cavityis filled with a layer of insulation to providemaximum thermal performance. Built-up roofingand cladding systems are assembled on site.The design and components used are usuallypart of a proprietary system.

Bu02

Profiled metalouter sheet

Vapour controllayer

Crown FactoryCladRoll

Perforated metal linersheet

Rocksilk UniversalSlab RS100

565

6.1.5Design details: Built-up metal roofs


Table 33: Typical U-values for standing seam systems

Product Purlin centres (m)Thickness 1.00 1.40 1.80 2.00

(mm) U-valueCrown FactoryClad 40 200 0.25 0.23 0.22 0.22

180 0.28 0.26 0.25 0.25Crown FactoryClad 37 200 0.24 0.22 0.21 0.21

180 0.25 0.24 0.23 0.23160 0.28 0.26 0.23 0.23

Crown FactoryClad 35 200 0.23 0.21 0.20 0.20180 0.25 0.23 0.22 0.22

Crown FactoryClad 32 200 0.20 0.19 0.18 0.17180 0.23 0.21 0.21 0.20170 0.24 0.22 0.21 0.21

Notes: The U-values are based on SCI P312. Knauf Insulation recommend that the system designer/manufacturer is contacted forU-values specific to their systems.

Typical section

Crown FactoryClad RollProfiled sheeting Vapour controllayer

Rocksilk UniversalSlab RS100

Typical specificationLiner panels to be positioned over purlins anda metal spacer system secured to the linerand purlin to ensure the full thickness ofinsulation is maintained between the linerand cladding sheets. Crown FactoryClad40*/37*/35*/32* ......mm thick, to be laidover the lining sheets and installed accordingto system manufacturer’s instructions, with alljoints closely butted. Cladding sheets to besecurely fixed in position. (*Delete asappropriate)

Alternatively, refer to NBS clause H31/50 and 271

Acoustic systemPerforated metal liner sheets to be positionedover purlins and support brackets fixed to thepurlins. Rocksilk Universal Slab RS100,......mm thick, to be laid over the liningsheets and overlaid with a vapour controllayer. Secure a metal spacer system throughthe vapour control layer to the supportbracket to ensure the full thickness of thermalinsulation is maintained between the vapourcontrol layer and cladding sheets. CrownFactoryClad 40*/37*/35*/32* ......mmthick, to be laid over the vapour control layerand tucked under the metal spacer as eachtier is completed with all joints closely butted.Cladding sheets to be securely fixed inposition. (*Delete as appropriate) Insulationto be installed according to systemmanufacturer’s instructions.

Alternatively, refer to NBS clause H31/254

www.knaufinsulation.co.uk

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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: KB57208

non - residential new build 4.2.1 built-up metal roofs · built-up metal roofs solution optimiser...

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