Research Shows White Roof Energy BenefitsBy Derrill Holly | ECT Staff Writer Published: April 22nd, 2014
When it comes to cutting cooling costs and reducing the negative environmental effects of development, not all roofs are created equal. A recent study found that white roofs beat planted green roofs on flat buildings, and both trumped traditional black roofs that were deemed inefficient and outdated.
Those are among the findings in Economic Comparison of White, Green and Black Flat Roofs in the United States, a newly released report by government researchers examining the economics of roof replacement in urban areas where flat roofs for commercial and retail structures are common.
“Both white and green roofs do a good job at cooling the building and cooling the air in the city,” said Art Rosenfeld, a principle researcher at Lawrence Berkeley National Laboratory, was one of four researchers for the project. “White roofs win, based on the purely economic factors we included, and black roofs should be phased out. White roofs are three times more effective at countering climate change than green roofs.”
Researchers looked at 22 commercial flat roof projects across the United States in which two or more roof types were considered. Using 50-year life cycle cost data, they assumed that white and black roofs would have service lives of 20 years, while green roofs would last 40.
In recent years, black, or dark roofing materials have drawn criticism as a major contributor to the “urban heat island” effect responsible for elevating temperatures higher in central cities compared to their surrounding rural areas.
While green, or vegetated roofs, are becoming more popular for a number of aesthetic or environmental reasons, they cost about $7 a square foot more than black roofs over a 50-year period.
White roofs—those composed of light-colored materials—reflect about three times more sunlight back into the atmosphere than green roofs. According to researchers, lower sunlight absorption rates than either green or black roofs offset a portion of the warming effect attributed to greenhouse gas emissions.
Researchers compared the least expensive type of green roof, a utilitarian surface covered with local grasses, to a comparable surface using white roof technology. Their analysis identified $2 in cooling savings per square foot over black roofs, and $9 per square foot projected savings compared to green roofs, citing lower installation and maintenance costs.
“The relative costs and benefits do vary by circumstance,” said Benjamin Mandel, co-author of the study. “Other factors may make green roofs more attractive or more beneficial options in certain scenarios.”
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