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Two recent studies add data to the ongoing quest for the best sustainable roofing design strategies. A German analysis indicates that solar cells have a 6% higher electrical output if they are combined with a green (planted) roof, compared with a more standard bitumen roof. A similar study, conducted in New York City, indicated a 3% boost in solar panel output when a green roof is used. Green roof systems lead to higher water retention, high evaporation and cooling, and minimum surface discharge. http://bit.ly/XerQJ7

However, an Arizona State University study indicates that finding the "greenest" roof design is far from a simple proposition. Light-colored roofs, widely lauded as "cool roofs" that will reduce urban heat island effects, may reduce the evapotranspiration of urban vegetation enough to unintentionally cut rainfall. The roofs cut building energy costs but also lead to a measurable decrease in precipitation. The research team cautions that the findings need more study before accurate conclusions can be made about the use of light vs. dark roofing materials. http://bit.ly/PyG0RX

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