appropriate selection of metal thickness for use in ... · 3.0 nominal thickness/gauge 4 3.1 steel...

APPROPRIATE SELECTION OF METAL THICKNESS FOR USE IN WALLING AND ROOFING APPLICATIONS

CI/SfB

Rh2(4-)

SEPTEMBER 2010

MCRMA Technical Paper No. 20

Contents

Page

Foreword 2

1.0 Summary 2

2.0 Introduction 3

3.0 Nominalthickness/gauge 4

3.1 Steel 4

3.2 Aluminium 4

4.0 Normalrangeofthicknesses 4

5.0 Commonlyusedcoilwidths 5

6.0 Yieldstrengths–constructionpurposes 5

7.0 Tolerancespecification–potentialfornon-compliance 6

7.1 Steel 6

7.1.1 Roofingweathersheet 6

7.1.2 Wallingweathersheet 6

7.2 Aluminiumweathersheet 7

7.3 Flashings 7

7.4 Linersheet 8

8.0 Measuringthethicknessofacoilorsheet 9

9.0 CEMarking–ensuringthatthecorrectmaterialisdelivered 10

10.0 Safeworkingloadasafunctionofmaterialthickness 10

11.0 Useofloadspantables 11

11.1 Nonfragility 11

11.2 Walkability 11

11.3 Useofloadspantables 11

12.0 Profileshape 12

13.0 Fixingregime 13

14.0 Fireperformance 13

14.1 Roofingapplications 13

14.2 Wallingapplications 13

15.0 Interactionwithotherbuildingcomponents 14

16.0 Conclusions 14

17.0 Bibliography 15

©TheMetalCladding&RoofingManufacturersAssociationLimitedandEngineeredPanelsinConstructionLimited.September2010

Foruptodateinformationonmetalroofandwallcladding,includingdownloadableconstructiondetails,visitwww.mcrma.co.uk.

Theeffectofthickness(gauge)ontheperformanceofmetalsystemsinbuildingapplicationscannotbeunder-estimatedandtheresponsibilityfornotonlyensuringthatappropriatematerialsarespecified,butselectedandusedcorrectlyisplaceduponallpartieswithinthesupplychain.

Withregardtotheselectionofcoilorsheetforuseinroll-formingapplicationsitisofparticularimportancethatthematerialselectedandusedcompliesfullywiththeappropriatestandardsoftoleranceondimensionandshape:BSEN10143:2006forpre-finishedsteelandBSEN485Part4forcoldrolledaluminiumwithnormaltoleranceasaminimumrequirement.

Forthosespecifyingandusingmaterialsthekeypointsmustbe:-

• Tostatethestandardthatistoapply.• Ensurethatthematerialtobeorderedandused:-

• Meetstherequirementsofthestandard.• Isdeliveredcorrectly.

• Ensurethatthestructuralcalculationsusedarespecifictotheprofileproposedandthenominalthicknessofthematerialproposed.

• Ensurethatthereactiontofireperformanceisvalidforthenominalthicknessofthematerialproposed.

Theuseofmetalforroofingandwallingapplicationshas,throughstructuralcalculationandoveraperiodofsuccessfulperformanceinservice,determinedthosethicknessesofmaterialwhicharenormallyspecified.

Theperformanceofthesematerialsinuse(includingtheconstructionphase)isdeterminedbyloadingarisingfrompositiveandnegativeforces,wind,deadweightandpointloadorimpact,withthemainrequirementsbeing:-

• Safetyinuse.• Weatherproofing

• Waterpenetration• Airtightness• Robustdetails

• Appearanceandabilitytomaintaininthelongterm.

Usingmaterialswhichvarybeyondthelimitsofthetolerancesallowedintroducesthepossibilitythatthebuildingdesignperformancewillnotbemetand,althoughthismayresultinshorttermsavings,couldaddconsiderablytothewholelifecostsofthebuildingthroughpoorperformanceandpotentialforremedialworksorworse.

TheMetalCladdingandRoofingManufacturersAssociationrepresentsleadingmanufacturersinthemetalroofingandcladdingindustryandseekstofosteranddevelopabetterunderstandingamongstspecifiersandendusersalikeofthemosteffectiveuseofmetalbuildingproducts,componentsandsystems.

TheAssociationhastwomainobjectives:-

1. TomakesurethatpublishedstandardsintheUKandEuropeformetalroofandwallcladdingareinaccordancewithbestpracticesoastoensureaEuropean-widestandardofproductexcellencewhichcanbewrittenintoproductspecifications.

2. Toprovideabasisfortechnicalexcellenceencompassingproductdevelopment,componentanddetaildesign,improvedmanufacturingandco-operationoninstallationtechniquesandstandards

2

Foreword 1.0 Summary

3

ItistheclearlystatedpositionoftheMCRMAanditsmembersthatthebestassuranceofcompliancewiththeappropriatestandardsandperformanceexpectationistosourcesystemsandproductsfromreputablemanufacturerswhocandemonstratethepedigreeofthematerialsusedandsupportdesignrequirementswithjobspecificdata.

Metalcladdingsystemsprovideanefficient,attractiveandreliablesolutionforawidevarietyofexternalbuildingenvelopes.Overtheyearstheyhaveevolvedfromthesingle-skinmetalcladdingoftenassociatedwithagriculturalbuildingstosophisticatedsystemswhichareusedinindustrial,retailandleisureapplicationsthroughouttheUnitedKingdom.

However,aswithallconstructioncomponents,theabilityofthecladdingtosatisfyitsfunctionalrequirementsisdependentonitscorrectspecificationandinstallationand,equallyasimportant,onitsinteractionwiththeotherelementsofthebuildingenvelopeandstructure.

Inthecontinuingquestforimprovedcosteffectivenessinallformsofbusinessgenerallyandconstructioninparticular,combinedwiththeneedtomeetbudgetaryconstraints,theconsiderationofalternativemethodsandchoiceofmaterialstomeetaspecifieddesiredoutcomeisavalidandnecessaryprocessthatmustbeundertaken.Thecompletedcostofconstructionisdirectlyimpactedbythecostsofmaterialsusedwithintheconstructionprocess.

Itiskey,however,ineachstepofthisprocesstounderstandthatanyonechoiceofamaterialtypeorcomponentdoesnotexistinisolationandhaspotentiallywiderreachingimplicationsonotheraspectsoftheperformanceofthecompletedwhole.

Theindividualcomponentsthatmakeupthecladdingsystemareoftenspecifiedandsuppliedseparately,withthepotentialforinsufficientattentionbeingpaidtothewayinwhichtheyinteract.

Thispaperwillfocusonthepotentialeffectsofseekingtoreducetheeffectivegaugeofasteelsheetusedinthemanufactureofanexternalcladdingsystem.

Itwillconsiderthefollowing:-

• Nominalthicknessandadherencetotherelevantstandards.

• Tolerancespecificationandthepotentialfornon-compliancewithinanormaldistribution.

• Safeworkingloadasafunctionofmaterialgauge.• Useofappropriateloadspantablesasguides

tocladdingperformanceincorporatingbendingmoments.

• Potentialimpactsonperformanceandothercomponentsinthebuildingsystem.

2.0 Introduction

WhilstthethicknessofmetalselectedforusewillvarydependingonproductandapplicationthenominalvaluesinTable1aregenerallyacceptedasbeingnormallyusedintheUK.

Table 1

Millimetres (mm) Steel Aluminium

RoofWeatherSheet 0.7 0.8to1.2

WallWeatherSheet 0.5 0.8to1.2

Flashings 0.7 0.9

LinerSheet 0.4 0.5

StructuralLinerSheet 0.7 0.9

Whensheetmetalismanufacturedatthemillitisproducedtoatargetor‘nominal’thickness.However,aswithallmanufacturingprocessesitisinevitablethatthereisavariationintheproductionprocessand,assuch,variationsinthefinalthicknessofthefinishedmaterialisunavoidable.

3.1 SteelWithregardtotheselectionofsteelforuseinmetalroofingandcladdingapplicationsgaugetolerancesforhotdippedproductsaredeterminedfromthestandardBSEN10143:2006,Continuouslyhot-dipcoatedsteelsheetandstrip:tolerancesondimensionsandshape,andtheallowedpositiveornegativevariance(tolerance)comparedwiththenominalthicknessofthematerialvarieswiththenominalthickness,coilwidthandthegradeofsteel(asdeterminedbyitsminimumspecifiedyieldstrength).

UndernormalcircumstancesthesteelcoilusedinUKmarketsistypicallywithinthefollowingranges:-

• Nominalsteelthicknessesofbetween0.4mmand0.7mm.

• Coilwidthsof:-• lessthan1200mm• greaterthan1200mmandlessthanorequal

to1500mm• Minimumspecifiedyieldstrengthsof:-

• lessthan260MPa(260MN/mm2)

3.2 AluminiumThestandardfromwhichthetolerancesonthicknessofaluminiumsheetmaybedeterminedisasfollows:-

• BSEN485:Aluminiumandaluminiumalloys,sheet,stripandplate.Part4–tolerancesonshapeanddimensionsforcold-rolledproducts

ThetolerancespositiveornegativevaryaccordingtotheAlloyGroup(IorII)whichrelatetothechemicalcompositionofthematerialsandaredeterminedaccordingtoBSEN573:3.MaterialbelongingtoAlloyGroupIisnormallyusedforrollformingandconstructionpurposesintheUK.

4

3.0 Nominal thickness/gauge 4.0 Normal range of thickness

5

FromtheUKandEuropeanperspectivethekeyissueintermsofperformanceunderloadrelatestothebendingmomentofanyforceapplied.

Typically,theyieldstrengthofsteelsuppliedforthemanufactureofwallorroofprofilesisintherangelessthan260MPaandisgenerallyofyieldstrength220MPa.

Asoutlinedabove,aluminiumusedforrollformedproductsisinAlloyGroupIandusuallyfromseries3000and5000alloysforwhichthemaximumspecifiedmagnesiumandmanganesecontentsareeachnogreaterthan1.8%andtheirsumnogreaterthan2.3%.

Withreferencetothestandardsapplyingthetolerancesonthickness(inmillimetres)allowableforsteelmaterialswiththesetypicalcharacteristicsareasbelow:-

Theprofileofthefinishedproductwilltendtodictatetherequirementsofthemanufacturerwithregardtoselectionofthecoilwidthofthematerialinthefirstinstance.

Ingeneraltermsmostmanufacturersseektoachieveacoverwidthofthefinishedproductof1metrewithsteelroofingandwallingproducts.

• Weathersheetswithatypicalprofiledepthof31mmor32mmgenerateaneedforcoilwidthsoftheorderof1220mmto1250mm.

• Linersheetswithatypicalprofiledepthof19mmor20mmgenerateaneedforcoilwidthsoftheorderof1110mmto1150mm.

Aluminiumsheetproductsavailableinthemarkettypicallyprovidecoverwidthsofthefinishedproductofupto500mmandwouldassuchrequirecoilwidthofupto700mmalthoughcertainprofilescouldrequirecoilwidthsoflessthan500mm.

Itisworthyofnotethataluminiumprofilesmadefromcoilsofgreaterwidthareavailableinthemarket.

5.0 Commonly used coil widths

6.0 Yield strengths – construction purposes

Table 2

Nominal thickness

± Tolerance in mm for given width

Normal Tolerances Special Tolerances

Min Max ≤ 1200 1200 ≤ 1500 ≤ 1200 1200 ≤ 1500

0.2 0.4 0.040 0.050 0.030 0.035

0.4 0.6 0.040 0.050 0.035 0.040

0.6 0.8 0.050 0.060 0.040 0.045

0.8 1.0 0.060 0.070 0.045 0.050

1.0 1.2 0.070 0.080 0.050 0.060

AsummaryofthetolerancesonthicknessallowableforaluminiumfromAlloyGroupIarecontainedinthefollowingtable:-

Table 3

Specified Thickness ± Tolerance in mm for given width

Min Max ≤ 1000 1000 ≤ 1250 1250 ≤ 1600

0.2 0.4 0.020 0.040 0.050

0.4 0.5 0.030 0.040 0.050

0.5 0.6 0.030 0.050 0.060

0.6 0.8 0.030 0.060 0.070

0.8 1.0 0.040 0.060 0.080

1.0 1.2 0.040 0.070 0.090

1.2 1.5 0.050 0.090 0.100

Asmaybeseenfromtheforegoingkeypointswithregardtomaterialspecificationthereareseveralfactorstobeconsideredwhenselectingmaterial(s).

7.1 SteelIntermsofcoilwidthandyieldstrengththerangesforcompliancearerelativelywide.

Howeverintermsofthenominalthicknessofthemetalitisimportantthat:-

• Thematerialisspecifiedtotheappropriatetolerance.• Thematerialissuppliedasspecified.• Itisunderstoodwhatisbeingmeasuredandhow.

Inordertohighlightthepotentialfornon-complianceitissensibletoconsiderthecaseforeachnominalthicknessusedineverydaycircumstancesasfollows:-

7.1.1 Roofing weather sheetNormallytheoutersheetofaroofwillutiliseaprofilemanufacturedfromcoilof1250mmwidthwithnominalthicknessof0.7mmandminimumspecifiedyieldstrengthof220MPa.

FromBSEN10143:2006thetoleranceonthicknessis±0.06mm(seetablesinSection6.0)thelowerlimitonthicknessbeing0.64mmwithanupperlimitof0.76mm.

Ifweconsiderthat100%ofmaterialcanbeproducedwithinthesetolerancelimitsbytheproducingsteelmillitisreasonabletoassumethatthethicknessesmeasuredacrossawideenoughsamplewouldbenormallydistributed–i.e.followabellshapeddistributioncurveaboutthemid-pointoftherange

Figure 1

7.1.2 Walling weather sheetTheoutersheetofawallwilltypicallyutiliseaprofilemanufacturedfromcoilof1250mmwidthwithnominalthicknessof0.5mmandminimumspecifiedyieldstrengthof220MPa.


6

7.0 Tolerance specification – potential for non-compliance

0.58 0.59 0.60 0.61 0.62 0.63 0.64 0.65 0.66 0.67 0.68 0.69 0.70 0.71 0.72 0.73 0.74 0.75 0.76 0.77 0.78Actual Thickness (millimetres)

0.64 0.675 0.70

Sheets that areoutside tolerance

Sheets that are within tolerance but may notnecessarily be regarded as 0.7mm nominal

0.7mm nominal to BSEN 10143:2006

0.7mm nominal to EN 10143:1993



0.675mm nominal to BSEN 10143:2006 half tolerance

7

Figure 2

0.40 0.41 0.42 0.43 0.44 0.45 0.46 0.47 0.48 0.49 0.50 0.51 0.52 0.53 0.54 0.55 0.56 0.57Actual Thickness (millimetres)


Sheets that are withintolerance but may not

necessarily be regardedas 0.55mm nominal

0.45 0.48 0.550.50




0.48mm nominal to BSEN 10143:2006 special tolerance

0.82 0.83 0.84 0.85 0.86 0.87 0.88 0.89 0.90 0.91 0.92 0.93 0.94 0.95 0.96Actual Thickness (millimetres)




0.86 0.88 0.90

0.9mm nominal to BSEN 485-4



0.88mm nominal to BSEN 485-4 half tolerance

7.2 Aluminium weather sheetMostaluminiumweathersheetswillbemanufacturedfrommaterialoflessthan1000mmwidthwithnominalthicknessof0.9mmandfromAlloyGroupI.

FromBSEN485-4thetoleranceonthicknessis±0.04mm(seetablesinSection6.0);thelowerlimitonthicknessbeing0.86mmwithanupperlimitof0.94mm

Figure 3

7.3 FlashingsFlashingsaretypicallymadefrommetalofnominalthicknessinaccordancewiththeroofingweathersheet,i.e.0.7mminthecaseofsteel.

Themostcommonlyidentifiedeffectcausedthroughthesupplyofbelowtolerancemetalforflashingsisthetendencyoftheflashingtoboworripplepostinstallation.

Generallywhilsttherearefewguaranteesorwarrantiesappliedinthecaseofflashingsandwhilsttheremaybenomajorstructuralimplicationresultingfromthesupplyofoutoftolerancematerialtheflashingshaveamajorrolewithregardto:-

• Weathertightnessofthecompletedbuilding.• Robustdetail–theinterfacesbetweenthestructuralelements.• Aestheticappearance.

Henceitisoftheutmostimportanceinthisregard,whetherrelatingtowateringressorairtightness,thatgreatattentionispaidtothespecificationofthematerialsusedforthemanufactureofflashingssincetheimpactismostnoticeableattheinterfacebetweencomplementarysystems.

7.4 Liner sheetsThelinersheetofarooforawallinabuiltupconstructionwilltypicallyutiliseaprofilemanufacturedfromcoilof1150mmwidthwithnominalthicknessof0.4mmandminimumspecifiedyieldstrengthof220MPa.


Whilsttheforegoingrepresentswhatthestandardontoleranceforsteelwithnominal0.4mmthicknessallows,itshouldbenotedthattoensurefullcomplianceandsaferoofingsystems,MCRMAmembershaveundertakentoonlyprovidelinersheetwithactualthicknessof0.4mmorgreater.

Figure 4

Asmaybeseenfromthegraphicsitispossibletospecifyanominalthickness(thatwhilstnotnecessarilytheacceptednominalthicknessforthatparticularuse)withatolerancethatcouldbecontainedwithinthetolerancesforthenominalthicknesswhetherunderBSEN10143:2006orBSEN485-4;i.e.byspecifyinga(target)thicknesswithspecialtolerance,forexample‘halftolerance’or‘zeronegative/fullpositive’tolerance.

Itisnotpossibletospecifyalowerthannominalthicknessundernormaltolerancesandbeabletoguaranteethatthecoilwillbewithintoleranceforagenerallyacceptednominalthicknessforthatparticularuse.Thismeansthatonsomeoccasionsthecoil(duetothenormaldistributionofmanufacturingprocesses)willbebelowthelowestlevelofthicknessallowableandhenceoutoftolerance.

8

0.32 0.33 0.34 0.35 0.36 0.37 0.38 0.39 0.40 0.41 0.42 0.43 0.44 0.45 0.46Actual Thickness (millimetres)




0.36 0.38 0.40




0.38mm nominal to BSEN 10143:2006 half tolerance

9

Coatedmetalsmayhaveaprotectivecoatinganddecorativefinishtobothsides;eachofthesecoatingshasitsowntolerance.

HowtheselayersofsurfacetreatmentsandcoatingscombinetoproducethefinishedproductisshowninFigure5below.

Figure 5

AccordingtoBSEN10143:2006thethicknessofsteelsubstrateshouldbemeasuredaminimumdistanceof40mmfromthecutedge;foraluminiumunderBSEN485-4thisdistanceis10mm.

IntheUKthemostcommonlyusedexternalcoatingforsteelisplastisolof200micronsthicknesswithanembossedfinishaccompaniedbyareversesidecoatingofupto20microns,dependingontheapplication,butotherfinishesdoexistandeachhasitsown‘normal’thicknessandtolerance.Otherpaintfinishesorcoatingsmaybeappliedwhetherpolyesterorsimilarwithvaryingthicknesses,eachwiththeirowntolerancelevels.

Similarlyaluminiummayalsobesuppliedwithapaintcoating.ForexternalpurposesthemostcommonlyusedwouldbeaPVDFmaterialof25micronthicknessandforinternalpurposesof15or18micronthickness.

Manyaluminiumapplicationsretainthestandardmillfinishandforflashingsandsimilarapplyapowdercoatingtreatmentpostmanufacture.

Allcoatingsappliedaredesignedtoprovideaparticularcharacteristicintermsofthepaintsystembutdonotcontributedirectlytotheloadbearingcapabilityofthemetal.

Itisimportantinmeasuringgaugetoonlymeasurethoseelementswhichbeartheload.Thisisnecessarysinceeachcoatingthatisappliedcarriesatoleranceonthicknessandwhilstitmayappearsimplertomeasuretheexternalthicknessofthewholepaintsystemitcannotberelieduponasatrue(orindicative)measureofthethicknessofthesubstrateanditsmetalliccoating.

Forexample,inthecaseofacompletepaintsystemofupto0.25mmthickness,tolerancesofsayapproximately0.03mmarepossiblewhich,inthecaseofthesebeingpositivewherethesteelsubstratewasbelowthelowertolerancelimit,couldresultinatotalthicknessappearingtobeacceptablewithinthe“overall”measureofthickness.

Thereforeinordertoproperlymeasurethetruethicknessoftheloadbearingelementitisnecessarytoremovethepaintcoatings.Thismaysimplybeachievedthroughtheappropriateuseofaproprietarypaintstripper,takingcaretofollowtheguidanceonuse.

Thismeasurementshouldbeconductedbyuseofaproperlycalibratedmicrometerasshown…

8.0 Measuring the thickness of a coil or sheet

α α

TopcoatPrimer

Pre-treatmentMetalliccoating

SubstrateMetalliccoating

Pre-treatmentBackingcoat

10

Intuitivelyitisstraightforwardtounderstandthatasthethicknessofagivenmaterialreducessodoesitsresistancetobendingunderloadingconditions,assumingthatallothercharacteristicsofthematerialremainconstant,i.e.composition,yieldstrengthandcoilwidth.

Figure 6

Figure6showstherangeofvariationtypicallyoccurringwherespanconditionsaredifferentforthesamematerial,wherethethicknessistheactualmaterialgaugeafterallowingforcoatingsystems.

However,itshouldalsobenotedthatformaterialswhich,insomecases,maypossiblybeconsideredtobewithintolerancebutnotnecessarilycomplyingwithanominal0.7mmthickness,thesafeworkingloadcapabilitymaybereducedbyfactorsinexcessof20%,i.e.wheretheactualthicknessis0.58mmorless(seeFigure2).

TheinformationusedtoconstructtheabovegraphsistakenfromtheloadspantablesofMCRMAmembersusingCorusColorsmaterialandverifiedtoEC3methods.*

*Note: These calculations were produced for Corus Colours by the Steel Construction Institute. The profile was a typical 32/1000 which could be manufactured from one or all of Corus’s supply chain partners. The properties were calculated to EC3 using material with a minimum yield strength and using material with tolerance as defined within EN 10143:2006

TheCEmarkanditsassociatedinformationlabelhelpsdemonstratethatanyproducthasbeentestedinaccordancewiththeappropriateEuropeanstandardandinthecaseofmetalsuppliedforwallingandroofingapplicationscomplieswiththeConstructionProductsDirective.

WhereCEmarkingisinplacetheproductshouldbesuppliedwithlabelsorpackagingthatclearlyidentifythevaluesofthecharacteristicstested,allofwhicharesubjecttoexternalinspectionandchecking.

TherequirementforCEmarkingofcoilorsheetwillrequirethefollowingtobeincludedinthelabelling:-

• Standardtowhichtheproducthasbeenmanufactured

• Toleranceclass• Descriptionoftheproduct

• Coilwidth• Yieldstrength• Coatings,paintfinish(es),andcolour

• Firerating

Itshouldbenotedthatwithinthetolerancesallowedtherearethreeclassifications,asfollows:-

• Class1 Full(normal)tolerance

• Class2 Specialtolerance

• Class3 Zeronegativetolerance

Theproductspecificationandrequirementsforsupplyof‘Selfsupportingmetalsheetforroofing,externalcladdingandinternallining’arecoveredinBSEN14782:2006,whichagainallowsforthecomparisonbetweenproductssuppliedandcoverthefollowingcriteria:-

• Nominalgauge• Resistanceofroofingproductstoconcentrated

forces• Externalfireperformance• Reactiontofireperformance

9.0 CE Marking – ensuring that the correct material is delivered

10.0 Safe working load as a function of material thickness

0.58 0.60 0.62 0.64 0.66 0.68 0.70 0.72Thickness (mm)

Single spanDouble spanMulti span

Load (kN/m2)

Safe Working Load at 1.8m span for given thickness on 32/1000 profile

2.3

2.1

1.9

1.7

1.5

1.3

1.1

0.9

}

Reduction in SWLacross bottomtolerance for 0.7mmnominal thickness

11

withstandtheloadsproducedbythosepersonsconductinganysuchwork.

Thedesignloadstobemetare:-

• Generalloadof0.6kN/m2

• Pointloadof0.9kN

TheseperformancecriteriaareestablishedinaccordancewithEC3.

Anyfailuretomeetthenominalrequirementswithintherelevantstandardsmayaffectthecapabilityofthesystemorproducttomeettherequiredloadspanrequirementsandincreasethepotentialforfailure.

11.3 Use of load span tablesEachmanufacturer/supplierofprofiledmetalsheetusedforconstructionwillprovideasamatterofcourseasetofloadspantableswhichservetoassistintheselectionoftheappropriatemetalcladdingorroofingsolutionforagivensetofdesignparametersorlikelyloadingconditionsinuse.

Whatwillbenoticedisthateachmanufacturerwillidentifyslightlyvaryingfigureseitherforspan,givenasetload,orforthemaximumsafeimposedloadgivenaspecificspanrequirement.

Itisimportanttobeawareofthesedifferencessincetheyariseforavarietyofreasonsbutmaynormallybeattributedtothefollowing:-

• Choiceofmaterial• Profiledesign/shape• Fixingregime

Thechoiceofmaterial,themainsubjectofthispaperwilltosomedegreeimpactontheothertwopotentialvariants.

11.1 Non fragilityAmajorcauseforconcerninconstructionworkisthepotentialfordeathorseriousinjurycausedbyfallsfromheightandinparticularfrom,orthrough,aroof.

Itisclearlynecessarytoensurethatallworkingconditions,safesystemsofworkandmaterialsspecifiedshouldtakeaccountofthispotential.

Itisappropriatethatthefollowingpointsshouldbeaddressedinthespecification:-

• Thespecifiedconstruction/assemblyisdesignatedasbeingnon-fragile.

• Thesupplierclassifiestheroofsystemasbeingnon-fragileandcansupportthisclaimwithrelevanttestdata.

• Anyconditionaffectingthenon-fragilityoftheconstructionshouldbeclearlystated.

CompliancewiththesekeypointswillhelpensureadherencetotheACR(CP)001:2007Rev3Recommended Practice for Work on Profiled Sheet Roofs.

Howtocheckwhetheraparticularroofsystemmaybeconsiderednon-fragileiscoveredinACR(M)001:2005Test for Non-Fragility of Profiled Sheet Roof Assemblieswhichverifieswhetherthesystemcansupportwithoutcatastrophicfailuretheloadsthatwillbeappliedbyapersonfallingontoit.

11.2 WalkabilityWalkabilityisacommonlyusedword/phrasewhichtendstobeusedforthickerlinersheetsystemsbutwhichshouldnotnecessarilybeusedtodenotemetalthicknesssincethephrasemayonlybeconsideredappropriatewherethesystemiscompletelyfixedanddeemednon-fragile.

Theneedforawalkablelinersometimesarisesfromthedesiretousealinersystemasasafemethodofaccessbutwithoutthepotentialfordamagethroughlocaldistortiontothesheet.

Thelikelihoodofdeformationordamagetoanysheetthatiswalkeduponisincreasedwiththinnermaterials.Productsthathaveshallowerprofilesaremorelikelytobesusceptibletodamageordistortion.

Wheresafeaccesstoaroofforgeneralmaintenanceandrepairsarerequired,themetalsystemmustbedesignedtoaccommodateand

11.0 Resistance to loading

Aswithallrooforwallsheetingthedesignoftheprofilewillhelpdetermineitsloadbearingcapabilityinuse;allprofileswillhavetheirownvariationsdependingon:-

• Historicperspective• Rollformingequipmentused

Thedimensionsofthesheet,forexampleinatypical32/1000roofingprofilemadefromsteelwithanominal0.7mmsteelwillvaryacrosseachelementtoachievethe1000mmcoverwidthrequirement.

Variationsinthefollowingelementswillhelpdeterminehowtheprofileperformsinuse:-

• Profilepitch• Profiledepth• Crownwidth• Valleywidth• Ribwidth• Web

Figure7belowidentifieswhereeachofthesedimensionsaremeasuredandhelpsdemonstratehowtheadjustmentofoneparticulardimension(orangleoftherib/web)willaffecttheotherdimensionswithinanygivenwidthofcoil.

Figure 7

Forgreaterloadbearingcapabilitiesprofilesmaybedesignedwithadditionalstiffeningribsagain,theplacementandsizeoftheseribswillvaryfromonemanufacturertoanother.

Itshouldbenotedthateachmanufacturerpublishesitsloadspantablesbaseduponthemanufactureofitsprofileswithmaterialofnominalthickness.

Whereanydoubtexistswithregardtosafeloadbearingcapabilityforanyparticulardesignthenadviceshouldbesoughtfromthemanufactureroraqualifieddesignengineer.

Clearlywhereprofilesarepotentiallymanufacturedfrommetalthatisincorrectlyspecifiedwithregard

12

toitsthicknessandhasthepotentialtobeoutoftolerancethentheloadspantablesarenotapplicableandappropriateexpertadviceshouldbetaken.

12.0 Profile shape

Profile pitchRib widthValley width

Web

Profiledepth

Cover widthCrown width

13

Thefireperformanceofroofingandwallingsystemsareconsideredseparately.

14.1 Roofing applicationsThegenericperformanceofsteelandaluminiumsystemsinroofingapplicationshasbeenassessedaccordingtoEN1187andallocatedasfollowsunderrelevantCommissionDecisionsrelatedtothecalorificvalueofthematerialassummarisedbelow:-

Table 4

CommissionDecision

CoatingCalorificValue

Classification Notes

2000/553/EC <4MJ/m2 Satisfieswithouttheneedfortesting

2005/403/EC <8MJ/m2BROOF(1);BROOF(2),BROOF(3)

MaxDryMassof330g/m2

Bothoftheabovedecisionshaveaspecificrequirementthatthethicknessofthematerialbegreaterthan0.4mm.

14.2 Walling applicationsAswithloadbearingcapabilityitisperhapsintuitivethatmaterialthicknesshasaneffectonthefireperformanceofpre-finishedsteelinwallingapplicationswithregardtoreactiontofire;thisissupportedbyresearchthroughtheEuropeantechnicalcommittees.

Thereactiontofireperformancewhichisnormallyquotedisforsteelwhichhasgreaterthicknessthanthematerialwhichwastested.

Moststeelsheetingforwallcladdingis0.5mmorgreater.Fortheclassificationtobevalidthetestingmusthavebeenconductedonmaterialofatleast0.5mm.

WherethematerialdoesnotmeettherequirementsofBSEN10143:2006itmaynotclaimtheclassification.

Warrantiesorguaranteesofperformancereceivedfrommanufacturersaregenerallyexplicitwithregardtotheneedforfixinginaccordancewiththeirownspecificmethods,typeoffixing,frequency,maximumspacingandsoon.

Thesefixingrequirementsaremadebasedupontheuseofnominalthicknessmaterial.

Theuseofmaterialsthatarethinnerthanthetolerancelimitswilltendtoripple(seesection7.3onflashings)anddeliverimpairedperformanceregardlessofwhethertheappropriatefixingregimehasbeenapplied.

Aswithallfixingsitisnecessarythatthecorrectfastenerisusedwithregardtotheapplicationandthatthefastenersarefixedwiththecorrecttorquesetting–anyover-tighteningwilltendtocausedistortionaroundthefastenerandthiswillbecomeemphasisedwherelightergaugematerialisused.

Thepotentialforfailureinfastenersishighlightedinareasofmaximumloadingwherethinner/lightergaugematerialsareused.Importantissuestobeawareofinthesecircumstancesmaybesummarisedas:-

• Potentialforfastenerstearingorpullingthroughlightergaugecladdingsheet.

• Theneedfortorquecontrolwhenfixingtoavoidthreadstripping.

• Localdistortionwhichmayleadtopoolingonroofsandincreasedpotentialforcorrosionandfailure.

14.0 Fire performance13.0 Fixing regime

OtherMCRMAdocumentsdealmorespecificallywithissuesrelatingtointeractionsbetweenvariouscomponentswithinanybuildingsystembutitisworthyofnoteinthiscontextthatwherenominalthicknessandthepotentialtobeoutoftoleranceisapossibilitythenfurtherimpactswillneedtobeconsidered.

Fromamaterialselectionpointofviewthispaperhasidentifiedthereductioninsafeworkingloadforagivenspanasbeingsignificantasmaterialthicknessreduces.

Reductionsinsafeworkingloadofcirca20%will,towardsthelimitsofloading,compromisethestructure.

Whatshouldalsobeborneinmindisthatunderthecontinuousstressesandstrainsofnormallifeabuildinganditsenvelope(wallorroof)issubjecttoloadandre-loadovertime,whetherpositive(gravity)ornegative(suction).Itissensibletoconsiderthatwhereamaterialisbelowitstolerancelimitthenitislessabletosustaintherigoursofconstantchange.

Itisconceivablethatsuchchangesaremostlikelytoberecognisedearly(ifnotthroughcatastrophicfailure)atthosepointswherethecumulativeeffectsofanytolerancevariationaremagnified,i.e.atfixedpoints.

Inthecaseofcladdingorroofingthiswillbewherethesystemisfixedeitherbypurlinorothersupportstructuretothemainstructureandthroughthefixings.

14

Thefactthatmanufacturersrequiretolerancesagainstwhichtheymanufacturedemonstratesthatwithinanyprocessthereisthepotentialforarangeofoutcomesregardlessofthecontrolexertedduringtheprocess.

Inordertoensurethattheappropriatelevelsofsafetyaremetandadheredto,itisimperativethatinthespecification,manufactureanduseofmetalinwallingandroofingapplicationsallduecareistakenandthatthematerialssuppliedandusedarewithinthetolerancesallowedbytherelevantstandardswhetherforsteeloraluminium.

Itispossibletospecifymaterialsandspecialtolerancesthatarenotnecessarilyaddressedwithinthestandardsbutthatthesemustbecapableofbeingachievedbythemanufacturerandagreedbetweentheparties–itthenbecomestheresponsibilityofthemanufacturer/supplier(mill)tomeettheagreedspecification.

Thepotentialforadverseimpactwithregardtosafeworkingloadissignificantinthecaseofmaterialssuppliedandusedbelowtheminimumtolerancesallowed;theimportanceofappropriateprofessionaladviceonthevalidityofloadspantablesandspecificloadingconditionscannotbeoverstated.

TheMCRMA,itsmembersandassociatesremaincommittedatalltimestothecontinuingdevelopmentandsafeuseofmetalcladdingandwallingsystems.

16.0 Conclusions15.0 Interaction with other building components

15

BSEN10143:2006–Continuouslyhot-dipcoatedsteelsheetandstrip:Tolerancesondimensionsandshape

BSEN485:Aluminiumandaluminiumalloys,sheet,stripandplate.Part4:Tolerancesonshapeanddimensionsforcold-rolledproducts

BSEN573:3

BSEN14782:2006Selfsupportingmetalsheetforroofing,externalcladdingandinternallining.Productspecificationandrequirements

EC3–Eurocode3:Designofsteelstructures(EN1993)

ACR(CP)001:2007:Recommendedpracticeforworkonprofiledsheetroofs.

ACR(M)001:2005:TestforNon-Fragilityofprofiledsheetroofassemblies

EN1187:2002:Testmethodsforexternalfireexposuretoroofs

2000/553/EC:Externalfireperformanceofroofcoverings

2005/403/EC:Externalfireperformanceofroofsandroofcoverings

PermissiontoreproduceextractsfromtheBSstandardsreferredtointhisdocumentisgrantedbyBSI.BritishStandardscanbeobtainedinPDForhardcopyformatsfromtheBSIonlineshop:www.bsigroup.com/ShoporbycontactingBSICustomerServicesforhardcopiesonly:Tel:+44(0)2089969001,Email:[email protected].

17.0 Bibliography

16

MCRMA technical papers

No1 Recommendedgoodpracticefordaylightinginmetalcladbuildings

No2 Curvedsheetingmanual

No3 Secretfixroofingdesignguide

No4 Fireandexternalsteel-cladwalls:guidancenotestotherevisedBuildingRegulations,1992(out of print)

No5 Metalwallsystemsdesignguide

No6 Profiledmetalroofingdesignguide

No7 Firedesignofsteel-cladexternalwallsforbuilding:construction,performancestandardsanddesign

No8 Acousticdesignguideformetalroofandwallcladding

No9 Compositeroofandwallcladdingpaneldesignguide

No10Profiledmetalcladdingforroofandwalls:guidancenotesonrevisedBuildingRegulations1995partsL&F(out of print)

No11Flashingsformetalroofandwalls:design,detailingandinstallationguide

No12Fastenersformetalroofandwallcladding:designdetailingandinstallationguide

No13Compositeslabsandbeamsusingsteeldecking:bestpracticefordesignandconstruction

No14GuidanceforthedesignofmetalroofingandcladdingtocomplywithApprovedDocumentL2:2001

No15NewApplications:compositeconstruction

No16Guidancefortheeffectivesealingofendlapdetailsinmetalroofingconstructions

No17DesignguideformetalroofingandcladdingtocomplywithenergyrequirementsofUKBuildingRegulations(2006)

No18ConventionsforcalculatingUvalues,f-valuesand-valuesformetalcladdingsystemsusingtwo-andthree-dimensionalthermalcalculations

No19AdynamicthermalmodellingstudyofatypicalmetalcladdingbuildingtoevaluateoverheatingintheUnitedKingdom

Pleasenote:PublicationscanbedownloadedfromtheMCRMAwebsiteatwww.mcrma.co.uk

LiabilityWhilst the information contained in this design guide is believed to be correct at the time of going to press, the Metal Cladding and Roofing Manufacturers Association Limited and its member companies cannot be held responsible for any errors or inaccuracies and, in particular, the specification for any application must be checked with the individual manufacturer concerned for a given installation. The diagrams of typical constructions in this publication are illustrative only.

Metal Cladding & Roofing Manufacturers Association Ltd106 Ruskin Avenue Rogerstone Newport South Wales NP10 0BD01633 895633 | [email protected] | www.mcrma.co.ukde

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