White roofs can be more effective at reducing the urban heat-island effect than darker roofs and roofs covered with plants, according to a report by the Lawrence Berkeley National Laboratory. White roofs also cost less.
The report, Economic Comparison of White, Green, and Black Flat Roofs In the United States,says that white roofs are three times more effective than green roofs at “cooling the globe.” Researchers analyzed 22 commercial flat roof projects in the U.S. and performed a 50-year life cycle cost analysis.
They assumed a 20-year service life for black roofs and white roofs, and 40 years for green roofs. White roofs save $25 per square meter compared to black roofs and green roofs cost $71 per square meter more compared to black roofs, the report says.
Green roofs provide benefits that white roofs do not offer, however, such as controlling runoff and curbing air pollution.