by KAID BENFIED, Switchboard, Natural Resources Defense Council staff blog, April 25, 2012

City Hall Podium
Source: www1.toronto.ca

In January of 2010, Toronto became the first city in North America to require the installation of green roofs on new commercial, institutional, and multifamily residential developments across the city. Next week, the requirement will expand to apply to new industrial development as well.

Simply put, a “green roof” is a rooftop that is vegetated. Green roofs produce multiple environmental benefits by reducing the urban heat island effect and associated energy demand, absorbing rainwater before it becomes runoff, improving air quality, and bringing nature and natural diversity into urban environments. In many cases, green roofs can also be enjoyed by the public much as a park can be.

Toronto’s requirements are embodied in a municipal bylaw that includes standards for when a green roof is required and what elements are required in the design. Generally speaking, smaller residential and commercial buildings (such as apartment buildings less than six stories tall) are exempt; from there, the larger the building, the larger the vegetated portion of the roof must be. For the largest buildings, 60 percent of available space on the roof must be vegetated.

For industrial buildings, the requirements are not as demanding. The bylaw will require that 10 percent of available roof space on new industrial buildings be covered, unless the building uses “cool roofing materials” for 100 percent of available roof space and has stormwater retention measures sufficient to capture 50 percent of annual rainfall (or the first five mm from each rainfall) on site. For all buildings, variances to compliance (for example, covering a lesser roof area with vegetation) may be requested if accompanied by fees (keyed to building size) that are invested in incentives for green roof development among existing building owners. Variances must be granted by the City Council.

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