Determining how weathering affects the reflectance and emittance of metal roofs is of paramount importance for accelerating the market penetration of metal roofing in both residential and commercial applications. Ultraviolet radiation, atmospheric pollution, microscopic growths, acid rains, temperature cycling caused by sunlight and sudden thunderstorms, moisture penetration, condensation, wind, hail, and freezing and thawing all contribute to the weathering of a roof's exterior surface. However, data describing the impact of weathering are extremely sparse simply because of the time and patience required to collect and interpret the data. Temperature, heat flow, reflectance, and emittance field data have been electronically cataloged for a full two years for 12 different painted and unpainted metal roofs exposed to weathering on an outdoor test facility. A white-painted metal surface, having a moderate reflectance and high emittance, showed the best thermal performance for predominantly cooling-load climates. For predominantly heating-load climates, a painted metal surface having moderate reflectance and low emittance showed excellent balance for reducing heat gain in the summer and heat loss in the winter.

Authors: Scott A. Kriner; William A. Miller, Ph.D., P.E.; Andre O. Desjarlais, P.E.

Citation: Thermal Performance of the Exterior Envelopes of Buildings VIII

Keywords: December, Florida, 2001