Light-colored roofs lower electric bills

Electric Perspectives, Jul/Aug 2001

According to a recent study conducted by Florida Power & Light Company (FPL), the whiter your roof, the lower your electric bill. That may not be earth-shattering news to many--it may even be a statement verging on the obvious--but up until now, surprisingly, there has been little available data to back up the assertion.

In the first study of its kind, FPL sponsored a project to test the impact of six commonly used types of residential roofing materials on home cooling costs. The results of the study demonstrate that white, galvanized metal roofing saves the most energy due to its high reflectance and superior ability to cool quickly at night. On an average-size, 1,770-square-foot home, that type of roof would save $128 per year (23 percent of cooling costs) over a similar house with a dark shingle roof.

To conduct the four-month study, FPL and Habitat for Humanity built six side-by-side homes, identical except for their roofs, in Fort Myers, FL. All six homes were studied unoccupied and occupied. Also, the homes were operated identically to ensure the study's accuracy. For example, temperature controls on the air conditioning thermostats of all the houses were set at a constant 77 deg F.

The study also found that a roof with white, s-shaped cement tiles saved 20 percent over dark shingles; white, flat cement, 17 percent; white shingles, 4 percent; and terra cotta, s-shaped "Spanish" tile, 3 percent.

FPL plans to use the results of the study as the basis for a recommendation to update the energy performance calculations of the state building code. The company will also encourage homeowners to select light-colored roofs to conserve energy and save money on cooling costs.