How do they differ from conventional roofing products?
Unlike most North American asphalt roofs, cool roofs are specially engineered to reflect much of the sun’s radiant energy back into space instead of transferring it as heat into the building below. The two basic characteristics that determine the performance of a cool roof are solar reflectance and thermal emittance. Both properties are rated on a scale from 0 to 1, where 1 is the most reflective or emissive. Although there is no industry-wide definition of a cool roof, the EPA’s Energy Star Roof Products Program has established a minimum standard, requiring that cool roof products have an initial reflectance of at least 0.65, and a reflectance of at least 0.5 after three years of weathering. By contrast, conventional asphalt roofs have a reflectivity of between 0.06 and 0.26, resulting in large amounts of heat transfer into the building’s interior. The use of cool roof products offers the following benefits: • increased lifetime of roofing materials. Cool roofs do not experience therm
