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August 11, 2008, 02:36 PM ET
Study of Green Roofs Finds Some Perform Better Than Others
Green roofs can vary widely in their performance characteristics, researchers at the University of Texas at Austin found in a study comparing six manufacturers’ products. For the study, the researchers created 24 experimental roof samples that used varying mixes of 16 types of plants.
The study was conducted in 2006 and 2007 by the university’s Lady Bird Johnson Wildflower Center, and some results were described in a university news release. The researchers published a full account of their findings on the Web site of the journal Urban Ecosystems.
All of the green roofs, which rely on native Texas plants, outperformed traditional roofs in lessening the need for air-conditioning. At noon today, for instance, the center reported on its Web page that the outdoor air temperature was 84.9 degrees Fahrenheit. The surface temperature of a black-topped roof was 101.5 degrees, while the temperature below it was 101.6. The surface temperature of a white-topped roof was 89.2, while the temperature below it was 97.0. The surface temperature of a green roof was 82.2, and the temperature below was 89.4.
Where the green roofs differed significantly, however, was in how much rainwater they captured during storms, preventing the water from becoming runoff. The best roofs captured all of the water during a light rain and about half the water from a downpour, the researchers reported, whereas the least-effective roofs captured only a quarter of the water from a light rain and less than 10 percent of what fell during a deluge.
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