by Allan Chen

Roofs and the rainbow of colors used in roofing materials are getting cooler, thanks to research by scientists in the Lawrence Berkeley National Laboratory Environmental Energy Technologies Division (EETD). "Cooler" roofs reflect more solar radiation, and in warm climates, this means lower interior temperatures and smaller cooling loads, saving energy and money.

Traditional cool roofs are white because light surfaces absorb less solar radiation than dark ones. EETD research has demonstrated that raising the solar reflectance of a roof from about 20 percent (dark gray) to about 55 percent (weathered white) can reduce a building's cooling energy use by 20 percent.

Although light-colored materials may find acceptance on flat-roofed commercial buildings, U.S. homeowners typically demand darker roofs for aesthetic reasons. EETD researchers, working with industry, have found that nonwhite cool roofs can be manufactured using colorants (pigments) that reflect the invisible, "near-infrared" radiation that accounts for more than half of the energy in sunlight.

"Our research estimates that the potential net energy savings in the United States achievable by applying white roofs to commercial buildings and cool colored roofs to houses is valued at more than $750 million per year," says Hashem Akbari, head of the Heat Island Group at Berkeley Lab.

The group's research has shown that widespread regional application of cool roofs can reduce ambient air temperatures and retard smog formation. Cool roofs can also reduce peak electricity demand in summer, which helps reduce strain on the aging electricity grid when relief is most needed. The lower temperatures of cool roofs may also increase the roofs' serviceable lives.   >>>

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Testing cool-colored roof materials at Oak Ridge National Laboratory on the Envelope Systems Research Apparatus. Photo: Oak Ridge National Laboratory Cool colors are formulated to reflect more sunlight at near-infrared wavelengths. Image: Lawrence Berkeley National Laboratory   Click on thumbnail images to view full-size pictures.