Green Roofs Have Positive Effect on Sewer Systems

Green roofs like the one atop a Con Edison building in Long Island City, Queens can be a cost-effective way to keep water from running into sewer systems and causing overflows, Columbia University researchers have found.

The Con Edison Green Roof, which is home to 21,000 plants on a quarter acre of The Learning Center, retains 30 percent of the rainwater that falls on it. The plants then release the water as vapor, the researchers said in the study (http://www.coned.com/greenroofcolumbia).

If New York City’s 1 billion square feet of roofs were transformed into green roofs, it would be possible to keep more than 10 billion gallons of water a year out of the city sewer system, according to the study led by Stuart Gaffin, research scientist at Columbia’s Center for Climate Systems Research.

The study concluded that based on the cost of building and maintaining a green roof it costs as little as 2 cents a year to capture each gallon of water.

Con Edison built the green roof and formed its research partnership with Columbia in 2008.