b'ABSTRACTEFFECTOFINSULATION The effects of solar heating on the weathering characteristics of smooch-surfaced, built-uproofings applied over insulation arediscussed.DaraarepresentedgivingthetemperaturesOnTheWeatheringOf attained at the underside of smooth-surfaced, built-up roofings placed either overinsulationor directlyon aconcretedeck. Photographs are given showing the differences in che weathering between the insulated and non-insulated roofings observedSmooth-Surfaced in the laboratory and in the field.The data show that roofings placed over insulation are subjected co much higher maximumBUILT-,UPROOFS temperatures,morerapidtemperaturechanges,andgreater sub-cooling on clear nights than similar roofings placed directly on concrete decks.Exposed To by WILLIAMC.CULLENandSOLARHEATING WILLIAMH.APPLETON or are accelerated byboth thermal movements and stresses and PARTONEchangingair and/or vapor pressures whichin tum arerelated to temperature and temperature changes. OFSERIESIr is to be expected that the presence or absence of roof insulation affectsthetemperature attainedbytheroofmembrane. 1.IntroductionTherefore, an investigation was made to measure the temperatures attained by the roofings applied directly to the deck or over Insulation in many forms has been usedto separate the roofinsulation under summer conditions and to observe their effects membrane from the roof deck during the past 25 years or more.on the deterioration of the roofings. Thishasbeentheacceptedpracticeforseveralreasons,but primarily for its thermal insulating properties which ultimately2.Background contribute to the comfort of the building occupants.Anumber of investigationsrelatingtothemechanisms. of As early as193Rogers [l )1 stated that all roofs should be 5,degradationofroofingasphaltscarriedoutattheNational insulated and that normally on a flatroof the insulation shouldBureau of Standards have shown that a chemical reaction occurs be placed above the roof deck.He further indicated that above within a bitumen during the weathering process. Greenfeld [2), deck insulation, thoroughlywaterproofedat allpoints,retardson thebasisof extensive laboratorytests,hasestablishedthat the flow of absorbed solar heat to the roof deck so that the latterwhen asphalts are exposed to light (ultraviolet), heat, and water, radiates less heat within the structure.numerous and complex changes take place.Other investigators The use of insulation above deck alsoreduces the maximum[3,4,5)connectedwiththesestudiesdescribeindetailthe temperature reached by the deck and thus reduces the chances ofvariouschemicalandphotochemicalreactionswhichoccur structural cracking of a concrete deck due to temperature changes. In addition, insulation is often used for reasons of economy;during weathering. less power is needed to cool the interior during the summer andLike other chemical changes, these reactions are accelerated by less fuel is used to heat the structure in the winter.Further, theincreased temperatures. use of insulation is necessary in many cases to provide a suitableThe effect of rise in temperature on the speed of a chemical surface for the application of a built-up roof.reaction is rather astonishing. A rise of 10C (18F) may double ,.or even triple the rate of a chemical reaction [6]. Accordingly,thetemperaturesattainedbyabuilt-upmembrane, ocher factors being similar or equal, must have a definite effect on the durability of the bitumen and felt comprising the membrane. In additiontothe chemical degradation of the bitumen, another factor must be considered in the weathering of a built-up roof, specifically thethermalmovementsand stressesproduced in the membraneandsurfacingbitumen bytheirtemperature changes. A combination of the hardening effect on the surfacing asphalt duetooxidation and the relative thermal movements and stresses due to temperature change results in the alligatoring and crackBoth samples were exposed for two years, during the same period.ing of the surface, possibly to such an extent that water eventuNote the remarkable difference in the exposed surfaces of the two.ally enters the waterproofing membrane. Therefore,twofactorsshouldbeconsideredinrelating These factors,among others,requirethattheinsulationbetemperaturetothedegradationofabuit-uproofasfollows: placedbetweentheroofingandtheroofdeckinmostcases.( 1) the acceleration of the race of degradation by increased temHowever, the question arises as to the effect of the insulation onperature, and( 2) the effect of thermal stresses and movements the weathering of the roofings due to solar heating.caused by rapid temperature changes. Blistering,buckling,wrinkle-cracking,membranerupturesLittle information has been published regarding the temperaand other defects common to built-up roofs result directly from(Continued on page 22) MARCH,196319'