Types of Cool Roofs
Cool roofs for commercial and industrial buildings fall into one of three categories: roofs made from inherently cool roofing materials, roofs made of materials that have been coated with a solar reflective coating, or green planted roofs.
Inherently cool roofs
White vinyl roofs, which are inherently reflective, achieve some of the highest reflectance and emittance measurements of which roofing materials are capable. A roof made of thermoplastic white vinyl, for example, can reflect 80 percent or more of the sun’s rays and emit at least 70% of the solar radiation that the building absorbs. An asphalt roof only reflects between 6 and 26% of solar radiation, resulting in greater heat transfer to the building interior and greater demand for air conditioning.
Coated roofs
An existing (or new) roof can be made reflective by applying a solar reflective coating to its surface. The reflectivity and emissivity ratings for over 1000 reflective roof products can be found in the CRRC (Cool Roofs Rating Council) website.
Green roofs
Green roofs provide a thermal mass layer which helps reducing the flow of heat into a building. The solar reflectance of green roofs varies depending on the plant types (generally 0.3-0.5). Because of the lower solar reflectance, green roofs reflect less sunlight and absorb more solar heat than white roofs. The absorbed heat in the green roofs is trapped by the greenhouse effect and then cooled by evapotranspiration.
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