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Feb 26, 2009

Researcher Hashem Akbari believes he has found a simple and cost-effective way to help cool the planet.

By Amy Van Vechten

Could you help to combat global warming by painting your roof white?
Dr. Hashem Akbari, a researcher at the Lawrence Berkeley National Laboratory in California, thinks so.
Dark colors—including asphalt and other dark roof materials—absorb heat. According to Akbari, if all the rooftops in America were “cool”—either painted white or, ideally, surfaced with materials designed to maximize reflectivity—the country’s air conditioning bill could be reduced by 20 percent. 
“The idea is not to simply change the color of every roof with a brush of paint,” Akbari explains. “Every roof, whether residential or commercial, has to be repaired or resurfaced every ten to 20 years. When the time comes, you select the right color, and in addition, the reflective surfaces.”
During the summer months, 12 hours of sunlight a day can heat roof temperatures to 200 degrees Fahrenheit. White roofs and new cool roof surfacing materials can reduce that temperature by more than half.
Because hot roofs increase indoor temperatures, more air conditioning is required to cool buildings that have dark roofs. The hotter the roof material gets, the more damage it sustains and the more often it has to be replaced.
Akbari doesn’t claim that re-roofing alone would make the climate change problem disappear. It could, however, lower the temperature of urban areas such as Los Angeles and Phoenix by 5 to 10 degrees on summer days.
It’s not just roofs that can benefit from cooler colors. “The car air conditioner operates at a very, very low efficiency,” Akbari says.
Therein lies potential savings for California, a state currently struggling with its budget. “Cool-colored cars would save the state about 2 percent of the fuel used by vehicles, a statewide savings close to 300 million dollars a year.”
As usual, California is taking a lead in introducing new environmental practices. Since 2005, the state has required new flat roofs to be white in the state. In 2008, it also demanded “cool colored” materials, which are more reflective than regular roofs, for new steep slope roofs.
“I think getting white roofs accepted by states nationwide is probably about a five-year project,” says Art Rosenfeld, one of the five commissioners on the California Energy Commission. “The asphalt manufacturers are a nuisance, but they’re really swimming against the tide.”


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