What are Cool Roofs?
Cool Roofs use roofing materials that are highly reflective (also called high albedo roofs) of the sun's radiant heat. They may also have a high thermal eminence value. Eminence is a measure of how much absorbed radiant energy is given off into the atmosphere - keeping the surface cooler as a result.
One issue given enormous attention in the last few years is the usage of Cool Roofs to mitigate the Urban Heat Island effect. The Urban Heat Island effect is the creation of higher ambient temperatures in densely compacted urban areas than the surrounding suburban areas. It is a result from reduced vegetative growth as well as a higher incidence rate of black or dark colored pavement and roofing. Typically, Cool Roofs are those with a solar reflectance value of 0.65 or higher when new. That means 65% of the total radiant heat energy is reflected back into the atmosphere.
As much as 40% of a city's impervious area is composed of roof area.
Why is an urban heat island significant?
Because it means that more cooling energy is needed for occupied spaces in these urban areas. There is also a higher incidence rate of air pollution created that includes the production of ozone.
Cool roof studies
Studies have shown that if cities were to install only Cool Roofs, significant energy savings would result as well as an improvement in urban air quality. These studies have led to local and state-mandated commercial roof regulations. They are rapidly proliferating to other locales that see cool roofing as an inexpensive means to reduce overall energy consumption. Such programs as Title 24 in California and regulations in the State of Georgia, Salt Lake City, Chicago and other urban northeastern cities are examples of trends being adopted nationwide.