A major source of stormwater runoff in urban areas comes from rooftops. A green roof is a rooftop surface with plants and a soil medium that helps to capture rainwater from storms before it can enter the stormwater system. Green roofs can also absorb air toxins, provide habitat and food, cool the building and save energy, and extend the roof lifespan by two to three times.
A number of municipalities have enacted bylaws to reduce the impacts of rooftop runoff, including downspout disconnect bylaws, rain barrel programs, and green roofs. The City of Toronto has a Green Roof Bylaw that requires the installation of a green roof on most new buildings and some additions, and mandates standards for construction and maintenance of green roofs.
ESRI Canada: This business occupies two floors of a 9-storey, 18,794-square metre suburban commercial office building overlooking Toronto’s Don Valley Parkway. As the result of a Ryerson University study that showed widespread greening of building roofs in Toronto could reduce Toronto’s ambient air temperatures up to 2° Celsius, Esri oversaw the transformation of a 704 square metre roof that now
- diverts an estimated 393,353 litres of of stormwater from the municipal system per year
- reduces an estimated 88kg of CO2 equivalent per year
- reduces heating and cooling costs, while providing better weather and sound insulation