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Water-Vapor Measurements of Low-Slope Roofing Materials.

pdf icon Water-Vapor Measurements of Low-Slope Roofing Materials. (1594 K)
Burch, D. M.; Desjarlais, A. O.

NISTIR 5681; 32 p. July 1995.

Available from:

National Technical Information Service
Order number: PB95-251617


moisture; moisture transfer; sorption isotherm; water vapor permeability; water vapor transfer; moisture property


New measurement methods recently developed at the National Institute of Standards and Technology were used to measure the sorption isotherm and permeability of several low-slope roofing materials at a mean temperature of 24 deg C (75 deg F). The materials included: fiberboard, perlite board, exterior-grade plywood, polyisocyanurate board insulation with glass-matt facers, and glass-fiber board insulation with a facer. For the sorption isotherm measurements, the materials were placed in various ambient relative humidities ranging from a dry to a saturated state. The equilibrium moisture content plotted versus ambient relative humidity at 24 deg C (75 deg F) gave the sorption isotherm. Separate sorption isotherms were obtained for specimens initially dry (adsorption isotherm) and specimens initially saturated (desorption isotherm). For the permeability measurements, a series of cup measurements was performed, and the permeability was plotted as a function of the mean relative humidity across the specimen. The measurements revealed that the moisture properties of building materials are often significantly dependent on average relative humidity. Standard measurement methods currently in use in the United States do not adequately account for the effect of relative humidity on moisture properties.