b'andthemembrane0Also 5theincidenceofsplit tingfailurescanbereducedbymakingcertaininnovationsinroofdesignandroofingprocedureso Inapreviousstudy(NBSTechoNewsBullo~7 9Nooll~203-205 (November1963))ofprematurefailuresinbui lt=Uproofsystems,splitting hadbeenpostulatedtoresultfromthermalshrinkageoftheroofmembraneo Therefore,inthepresentworktheeffectsofthermalshrinkagegi 0e o, contractionduetodecreasingtemperature~wereinvestigatedoTestsshowed thatthecoefficientoflinearthermalexpansionofthemembranewasgreater thanthatofthebituminoussaturated~reinforcingfeltsfromwhichit was constructed,butlessthanthatofthebitumenusedastheplyingcemento Inaddition,thelinearthermalexpansioncoefficientsofboththesaturatedfeltsandthecompositemembraneweregreaterinthe"acrossmachine" directionthaninthe"inmachine"directi onofthefelt~andthatthe tensilestrengthwasgenerallygreaterintheninmachine"directiono Relatingthermalshrinkagetostrengthpropertiesindicatesthat thermalshrinkagealonecannotproducethestressneededtosplitthe membranetalthoughitisafactorthatmustbeconsideredoTherefore, additionalstressmustcombinewiththeshrinkagest resstoproducea stressconcentrationofsufficientmagnitudetocausearuptureoField experienceindicatesthatthisaddi tionalstressmaybeproducedwhen sectionsofinsulationtowhichthemembraneissecureddrawapartoUsing thesamematerialsjstepsmaybetakentoreducethebuild=upofastress concentrationandtherebyreducesplittingo Wheninsulationisusedbetweenthedeckandthemembrane,it shouldbeplacedsothatthelongitudinal(continuous)jointisparallel totheshortdimensionoftheroofoThemembraneshouldthenbeapplied withthefelts 00 inmachine"di rectionperpendiculartothecontinuous jointoBecausethefelts 0"inmachine"directionundergoeslessthermal shrinkagethanthe"acrossmachine"dire.ction~1essstresswouldthusbe producedoverthejointandbecausethefeltsQ"inmachine"directionis stronger,theirability toresistthestresswithoutfailureisincreasedo Tapingoftheinsulationjointswouldtendtoreducethemovementbetween unitsoftheinsulationandwouldfurthereliminateareasofstressconcentrationsoverthejointsoAlso,theuseofexpansionjoints(not structural)intheroofingmembranewillreducethemagnitudeofthe stressproducedbythermalshrinkageoThereductionofstressconcentrationsoverthecontinuousjointbetweeninsulationboardsshouldreducesplitting failureso Insecuringthemembranetotheinsulation,theadhesivebond shouldbeofoptimumstrengthoItshouldbestrongenoughtowithstand exposureconditionssuchaswinduplift,butsufficientlydistributedon finiteareasofcontacttopermitdistributionofstressoverlargeareas ofthemembraneintheeventofthermalshockoThiscouldbeaccomplished byspot,sprinkle,orstripmoppingoTheuseofalaminatedbasesheet, inwhichboththeelongationoftherespecti velami nantsandthestrength oftheadhesivebondbetweenlaminantscouldbecontrolled , mayproducethe desiredeffectso'