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Article about White Roofs vs. Green Roofs

Posted by Morgan White on April 10, 2014

White Roofs Better Than Dark, Vegetated Roofs, LBNL Study Finds
BERKELEY, Calif.—Compared to traditional dark-colored roofs and green or “vegetated” roofs, white roofs offer greater ability to lower temperatures that lead to the urban heat island effect, and they do it at less cost, according to a recent report. The Lawrence Berkeley National Laboratory report states that building owners “concerned with global warming should choose white roofs, which are three times more effective than green roofs at cooling the globe.” The authors 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. Compared to black roofs, the report says, white roofs save $25/m2 ($2.30/ft2) and green roofs have an additional cost of $71/m2 ($6.60/ft2). The authors also concluded that black roofs should be prohibited in some areas. “We strongly recommend building code policies that phase out dark-colored roofs in warm climates to protect against their adverse public health externalities,” the report states.

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Excerpt:    However, unlike white roofs, green roofs do not offset climate change. White roofs are more reflective than green roofs, reflecting roughly three times more sunlight back into the atmosphere and therefore absorbing less sunlight at earth’s surface. By absorbing less sunlight than either green or black roofs, white roofs offset a portion of the warming effect from greenhouse gas emissions.

“Both white and green roofs do a good job at cooling the building and cooling the air in the city, but white roofs are three times more effective at countering climate change than green roofs,” said Rosenfeld.