I can’t believe I had never heard of this before! Apparently, in Toronto, new commercial, institutional and some residential buildings have to include green roof features. This has actually been the case since 2009.
Toronto introduced the bylaw to reduce costs associated with processing storm water runoff, and to gain energy savings from the cooling potential of vegetation cover and improve air quality from the reduction in carbon dioxide and increased production of ozone.
Up on the roof, green takes root – Globe & Mail