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Ridges in roofing have been recognized as a major factor which contributes to premature deterioration of built-up roofing. While recognized as the result of compression and flexure forces on the membrane, which frequently develop cracks that permitted ingress of water, the contribution of the components to the behavior had not been demonstrable for persistence of ridges. Eight simulated roof panels, 52 by 100 in., and many strips of conventional materials, 3 by 36 in., were subjected to wide variations in temperature, -30 to 160 F, and relative humidities from 1 to nearly 100 per cent, for varying intervals up to two years. Early observations indicated that to reach equilibrium for each condition of exposure would be impracticable, so procedures which would demonstrate the nature of motions due to temperature and humidity changes were adopted. Since the erratic motions being observed were relatable to changes in relative humidity, regardless of temperature between -20 and 160 F, a capability was developed which culminated in creating ridges at one end while removing ridges at the other end of the same insulation board at the same time. The persistence of ridges is related to characteristic changes in length of the materials used, in which interstitial water prevents removal of significant amounts of intracellular water, as is essential for ridges to recede.
roofing, ridges, splits, felts, asbestos, silica gel, humidity, moisture
Shuman, E. C.
Personal Member ASTM, Institute for Building Research, The Pennsylvania State University, University Park, Pa