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A cool roof is designed to reflect more sunlight than a conventional roof, absorbing less solar energy. This lowers the temperature of the building just as wearing light-colored clothing keeps you cool on a sunny day. Conventional roofs can reach temperatures of 150°F or more on a sunny summer afternoon, sun. Under the same conditions a reflective roof could stay more than 50°F (28 °C) cooler. This can save energy and money in buildings with air conditioning, or improve comfort and safety in buildings without air conditioning, by reducing heat flow from the roof into the occupied space. Most cool roofs have high “thermal emittance”—the ability to shed heat by giving off “thermal infrared” radiation. Nearly any type of building can benefit from a cool roof, but consider the climate and other factors before deciding to install one.
A cool roof can benefit a building and its occupants by:
Reducing energy bills by decreasing air conditioning needs
Helping older inefficient (or undersized) air conditioners provide enough cooling for today’s hotter summers
Qualifying for money-saving rebates from utilities or government programs
Making it possible to downsize new or replacement air conditioning equipment, saving money and potentially increasing cooling efficiency
Improving indoor comfort and safety for spaces that are not air conditioned
Decreasing roof temperature, which may extend roof service life
Cool roofs can also incur a winter heating penalty. That is, absorbing less sunlight at the roof reduces heat conduction into the building, increasing the need for mechanical heating in winter. Beyond the building itself, cool roofs can also benefit the environment, especially when many buildings in a community have them. Cool roofs can:
Lower local outside air temperatures, thereby lessening the urban heat island effect
Slow the formation of smog from air pollutants, which are temperature-dependent, by cooling the outside air
Reduce peak electricity demand, which can help prevent power outages
Decrease power plant emissions by reducing the demand for energy to cool buildings.
Help offset global warming by reflecting more sunlight to outer space
Cool Roof Options
There are many types of roof systems available, but the surface solar reflectance of the roofing product—the outermost layer of the roof exposed to the sun is, also known as the roof covering—determines whether the roof is cool or not. There are cool options for nearly all types of roof coverings.
Paths to a Cool Roof
Cool roofing products usually cost no more than comparable conventional roofing products. The easiest and least expensive way to make your roof cool is to choose a cool covering during new construction, or when your existing roofing covering needs to be replaced. Certain types of roofing products can also be retrofitted with cool coatings, but this will incur extra material and labor costs.
Energy efficiency is one of the easiest and most cost-effective ways to combat climate change, reduce energy costs for consumers, and improve the competitiveness of U.S. businesses.