Every year, Americans spend about $40 billion to keep buildings air-conditioned, and, in doing so consume about one-sixth of all electricity generated in the U.S. While more efficient air-conditioning units can help to bring down homeowners’ summer utility bills, an even more effective solution is to reduce the need for AC in the first place through the installation of “cool roofs.”
Different from green roofs, which use vegetation to cool roof surfaces, cool roof products can resemble conventional roofing materials; they can be used on normal residential sloped roof surfaces, and are often easily incorporated into new construction and roof retrofitting. The best part? They can cost the same as their conventional counterparts.
How Does a Cool Roof Work?
Heat from the sun’s rays is absorbed at the roof surface and then transferred to the rest of the building. Two properties determine the “coolness” of a roof: its solar reflectance, or the ability to reflect the sun’s rays; and its thermal emittance, or the ability to emit thermal radiation. Conventional black asphalt roofs have very low solar reflectance and thermal emittance; as a result they absorb a lot of heat. Cool roof materials, which often use lighter colors or incorporate metallic and polymer materials that increase the surface’s reflectivity and emittance, can reduce roof surface temperatures by almost 100 degrees.
Saving Energy and Money
Analysis conducted by the American Council for an Energy-Efficient Economy (ACEEE) of a Sacramento Municipal Utility District program found that homes could save as much as $179 per year on energy bills as a result of a cool roof installation. While a slight increase in heating might be necessary during winter months, it is insignificant when compared to the savings accrued from reduced air-conditioning during the summer. Households in warmer climates that use air-conditioning more often than homes in cooler regions will benefit the most from cool roof energy savings.
Installing a Cool Roof
There are currently several financial incentives available for homeowners and homebuilders who install cool roof materials in existing or new homes. The American Recovery and Reinvestment Act provides a 30 percent tax credit (up to $1,500) for the installation of certain metal and asphalt roofing products that meet ENERGY STAR requirements in existing homes during 2009 and 2010. Additionally, certain utility companies offer rebates (as much as $300 for an average 3,000 square foot roof) for the installation of cool roofing materials in new construction and/or roof retrofits.