Glossary of Terms

Weathered Reflectance

The solar reflectance value of roofing after it has been installed and subjected to actual weather conditions for at least three years. Different rating programs have individual specific conditions defining weathered reflectance. Natural weathering and soiling can affect a roof's ability to maintain its high reflectance values. Depending on such variables as geographic location and climate; urban, agricultural or industrial setting; the amount and type of discharge from the building and adjacent structures; and roof slope, particles and pollutants of all kinds can accumulate and diminish the roof surface's inherent reflectivity. Although there will be some loss of reflectivity from years of exposure, the levels will continue to be significantly higher than that of traditional black materials. Even simple cleaning techniques can restore most if not all of the original reflectivity. Studies have shown that washing a weathered cool roof membrane can result in a practically complete restoration of solar reflectance. Studies have also found that most reductions in reflectivity occurred during the first year, then leveled off, with further reductions negligible by the sixth year.