A 40,000-square-foot green roof will be built atop a Wal-Mart in Portland, Ore. The other part of the roof, about 52,000 square feet, has a white membrane. The Green Building Research Laboratory at Portland State University will compare how well each roof type filters rainwater and whether energy use and heat-island issues can be reduced. "The data we collect will help the green building industry improve upon the many benefits provided by green roof," said David Sailor, director of the laboratory.

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