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1、锚逆耢刃舯醴氨莛锰皿淘迓UseofVaporBarrierstoPreventCondensation谁束骋赏桷硪薛逵弟斟鹆预Wheneverinsulationisinstalledinawall,roof,orslab,itsresistancetotheflowofheatissomuchgreaterthanthatoftheotherelementsoftheconstructionthatthedewpointandresultingcondensationmayoccurwithintheinsulation.竽芤狂腱夫彻暹谰爆碴螗铆
2、Sincewatervaporflowsfromregionsofhightemperaturetoregionsoflowtemperature,asimplesolutiontocondensationistostoptheflowofwatervaporbymeansofsomesurfacematerialimpervioustomoisture---providedthissurfaceiscalledavaporbarrier.Itmustalwaysbeappliedonthewarmside.症希贡围馒技湛坟浣媾橘免Becausec
3、ondensationisgenerallymostsevereduringtheheatingseason,allvaporbarriersshouldbeinstalledontheinteriorsideofwallsandroofs.Fromapracticalstandpoint,thismeansthatthevaporbarriershouldbenexttoandpartoftheinsulation.窜薯悚痞窍耸歌藻篌毂拣倡Oneofthebestandmosteconomicalvaporbarriersisaluminumfo
4、il.Someinsulationcomeequippedwiththisfoilattachedtoonesurface.However,unlessreinforcedwithkraftpaperorsomeotherstrongmaterial,thefoiliseasilyripped,torn,orpunctured,andsoisoflittlevalueasabarrier.嗲臾磨努齐涉隧捍浆酚艟蝶Sincevaporbehavesasagas,avaporbarrier,tobeeffective,mustbeairtight,or
5、asnearlysoaspossible.Butthisisoftenanimpracticalrequirement.Forexample,consideraroofwiththeinsulationabovethedeckandbetweenavaporbarrierandwaterproofroofing.Unlesstheinsulationisofafirmmaterial,theinsulationtoexpand,formingbubblesunderthewaterproofing.炻饼莞韭徨茁铊绀杵汤袭繇Duringthecool
6、nessofthenight,thebubbleswillcontract.Afteraseriesofsunnydaysandcoolnights,thebendingbackandforthofthesurfacemaydestroytheroofing.Onewaytopreventthisistoside-venttheroofinsulationsothecontainedaircanfreelyexpandandcontract.Thesideventsmust,however,beprotectedfromdrivingrain.亚愀
7、澄懋汔跛玳腾著焊寰嵴Vaporbarrierscanbemadeofothermaterialsbesidesaluminumfoil.Therearealuminumpaints,plasticpaints,someplasticfilms,asphaltpaints,rubber-basepaints,asphalt,andfoil-laminatedpapers.Itmustberememberedthatwaterrepellentsurfacesarenotnecessarilyvaporbarriers,thatis,airtight.
8、胧傲苊誊鞴淅殓咦爿肠疳居Toevaluateavaporbarrier,aunitknownasthepermisused
