BENEFITS
Storm Water Management
Green roofs are ideal for Low Impact Development (LID) because it renders impermeable surfaces permeable and therefore can positively influence the quantity and quality of storm water runoff.
Green roofs reduce and delay storm water runoff, helping reduce combine sewage overflows (CSOs). CSOs result when storm water floods a city's sewage system and discharges raw sewage into the local watershed. (Osmundson, 1999)
Extensive green roofs can retain an average of 75% annual rainfall and delay runoff by 3 to 4 hours. (Susan K. Weiler, 2009)
In addition, green roofs filter pollutants from rainwater, roofing materials, and atmospheric deposition. (Kingsbury, 2008)
A study conducted by Environment Canada found that if Toronto covered 6% of available roof space with green roofs, it could retain 127 million cubic feet of rain water per year. The storage tank needed to hold the same amount of rainwater would cost $60 million while the green roofs needed would cost $45 million.
The 10.4 acre green roof on the Ford Dearborn Truck Plant retains approximately 4 million gallons of rainwater each year. (XeroFlor)
The 18,000 square foot green roof atop Radio City Music Hall will prevent approximately 566,000 gallons of water from entering New York City's sewage system. (environmentalleader.com, 2007)
