Whiter Roofs Mean Lower Cooling Bills

A new study by the Florida Solar Energy Center (FSEC) demonstrates that high-reflectivity coatings can dramatically reduce air conditioning costs. Two houses—one with a pitched asphalt-shingle roof and R-11 attic insulation, and the other with a flat tar-paper roof and no insulation—were used in the study. The roofs of both were painted with a commercially available white elastomeric roof coating that reflects 70% of the sunlight striking it. Air conditioning loads were reduced 25% in the first house (pitched roof, R-11 insulation), and 43% in the second. For the Florida housing stock in general, FSEC estimates that such treatments would reduce cooling costs by 10% to 40%. These results correspond with data from similar tests at Lawrence Berkeley Laboratory in Berkeley, California, which show even higher savings in some cases.

Researchers at FSEC say there are a number of ways to achieve high-reflectivity roof surfaces, both in new construction and for older houses. White anodized sheet-metal roofing, white metal tile panels, white cement/composite shingles, aluminum shingles, and white EPDM roll roofing all provide high reflectivity. Sur-prisingly, white asphalt shingles aren’t that much more reflective than dark ones (25% reflectivity, compared with 20% for gray and 5% for black), which may be due to exposed asphalt on even the white shingles, according to FSEC. Staff members of the Building Design Assistance Center at FSEC are discussing their findings with shingle manufacturers in hopes of encouraging the development of high-reflectivity shingles for southern markets.