The green roof installed last year by the American Society of Landscape Architects (ASLA) retained thousands of gallons of stormwater, reduced building energy costs by hundreds of dollars a month and significantly lowered outdoor air temperature, according to a report the association released last week. The report examined various components of ASLA’s green roof demonstration project, ranging from water and temperature monitoring to individual plant performance.
“The findings show that our green roof delivered significant economic and environmental benefits,” says Nancy Somerville, Executive Vice President and CEO of ASLA of the green roof the association installed on its headquarters as a demonstration project to measure the impact green roofs can have on their communities.
“Collectively, green roofs can save billions of dollars in urban infrastructure costs, which is why more and more cities are encouraging them through tax and other incentives,” Somerville says.
From July 2006 to May 2007, ASLA’s green roof:
• Prevented 27,500 gallons of stormwater – nearly 75 percent of all precipitation on the roof – from flowing into Washington’s overburdened sewer and stormwater system. Except during repeated heavy rains, the roof only created runoff during rainfalls that exceeded one inch. The water runoff itself contained fewer pollutants than typical water runoff.
• Lowered air temperature by as much as 32 degrees in the summer when compared to a neighboring tarred roof, helping mitigate the urban heat island effect.
• Reduced the building’s energy costs – especially in the winter. Engineering analysis showed that the green roof’s extra insulation lowered energy usage in the winter by 10 percent with a potential of two to three percent in the summer.
Related Links
Details and performance data on ASLA’s green roof project – www.asla.org/greenroof