Green roof study demonstrates environmental benefits

A green roof system on the headquarters building of the American Society of Landscape Architects (ASLA), Washington, D.C., has shown economic and environmental advantages, according to the Engineering News-Record. Installed in 2006, the 3,000-square-foot roof system also included monitoring equipment for stormwater runoff, water quality and temperature.

ASLA released the first analysis of the green roof system—which was designed by Michael Van Valkenburgh Associates Inc., New York—on Sept. 20. The report states that from July 2006 to May 2007 the roof system prevented almost 75 percent of all precipitation on the roof system (about 27,500 gallons of stormwater) from flowing into the city's sewer and stormwater runoff system.

In addition, the roof system reduced energy costs by 10 percent during the heating season and ASLA plans to reduce it even more next year by keeping thermostats at a higher temperature during the cooling season. The urban heat island effect was alleviated because the roof system lowered roof air temperature by as much as 32 degrees Fahrenheit during the summer when compared with a neighboring asphalt roof system.

Higher amounts of heavy metals, which may come from roofing materials, or settled particulate matter or pollutants, were reported in the runoff. Higher levels of some nutrients, such as phosphorous, also were found in the runoff; Nancy Somerville, ASLA executive vice president and chief executive officer, says research shows that higher amounts of nutrients can be typical for "young" green roof systems. Water quality will be tested again in two years.

Date : 11/1/2007