New data collected by Green Roofs for Healthy Cities says Toronto's cutting-edge green roof by-law, which came into effect in January 2010, has resulted in 1.2 million square feet of new green space across commercial, institutional, and residential developments. Toronto's by-law requires green roofs for all new developments with gross floor area over 2,000 square meters.  According to the city, the green roof requirement is graduated, ranging from 20-60 percent of available roof space, so as buildings move up in size, the percentage area of green roof that needs to be installed also increases. If building owners can't or won't add green roofs, they can provide a cash payment instead, which gets funneled into other green roof programs in the city. In April 2012, the same regulations will apply to industrial buildings. 

Toronto provided Green Roofs for Healthy Cities with data on the impact of the by-law: More than 125 full time jobs were created, 435,000 cubic feet of stormwater was captured, 1.5 million KWH of energy were saved, and there was a "tangible reduction" in the local urban heat island effect. Other pluses: the green roofs may be improving air quality, creating wildlife habitat, and offering new rooftop recreational and food production opportunities. In addition, the organization says the new green roofs may help lengthen the lifetimes of the roofs, "saving building owners money" and reducing landwill waste over the long-term. 

Steven W. Peck, Hon. ASLA, Founder and President, Green Roofs for Healthy Cities, pointed to models run by the Canadian government, outlining the benefits if the green roof roll-out scales up: "Environment Canada modeling has demonstrated that an area covered by 10 million square feet of green roofs, the size of 10 Queens Parks, would reduce temperatures in that area by 1 to 2 degrees centigrade and will help save tens of millions in energy costs by reducing the peak load demand. Environment Canada scientists have estimated that the energy savings on heating and cooling generated by 10 million square feet of green roofs in Toronto are over 15 million KWH, the equivalent of running 29,593 60 Watt light bulbs year-round. Stormwater run-off reductions also increase to well over 3.6 million cubic feet annually."

According to their data, Toronto was just behind Chicago in terms of the total square feet of green roof added in 2010. Chicago uses a set of incentives and expedited permitting processes to promote green roof installation but unlike Toronto, has no green roof requirement.

On top of the progressive rule-making, Toronto, like Chicago, has been smart about making its green roofs public. Last year, the city added a novel green roof park to its City Hall (see image at top). The project, which was designed by local firm PLANT architects, in effect extends ground-level park land and a broader urban revitalization effort through to one of the city's most symbolic public spaces.

Learn more about Toronto's green roof by-law and "eco-incentives" program, which a number of cities are now evaluating.

Image credit: (1) Toronto City Hall Green Roof / PLANT Architects, (2) Green roof data, 2010 / Green Roofs for Healthy Cities