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All new residential, commercial and institutional buildings with more than 2,000 square meters of floorspace in the City of Toronto will soon require a vegetated area, known as a green roof, on a portion of the rooftop. Toronto says it is the first municipality to pass a mandatory green roof bylaw, effective February 2010.

"The City of Toronto’s leadership on all things green took another major step by making it obligatory to have green roofs for all types of new buildings," says deputy mayor Joe Pantalone. "This bylaw is a major part of the solution to climate change, the creation of green jobs, and it represents a whole new mindset on how our cities approach the 20 per cent or so of surface area that are roofs."

Steven Peck, president of the not-for-profit industry group Green Roofs for Healthy Cities says Toronto’s bylaw "breaks new ground on how to structure a mandatory green roof requirement and the construction standard also contains important best practices that may prove to be a model for other cities."

Green roofs offer environmental benefits such as reducing storm water runoff, cutting energy consumption, lowering the temperature in urban areas, providing opportunities for local food production and adding to the esthetics of large buildings. A study commissioned by the city in 2005 says it will also save money by reducing expenditures on infrastructure for storm water runoff, erosion control measures, pollution control and energy costs.

However, many in the development industry opposed the bylaw. Stephen Upton, vice-president for development at Tridel Corp., a major condominium developer, told Reuters that green roofs could add $200,000 to the cost of a new building, and will be more expensive to maintain. At a time when few new projects are finding financing, adding more expense could slow the amount of development in the city.

Other critics of the bylaw say that green roofs are only one environmental solution, and that other options such as solar roof panels, which might produce greater energy benefits, will no longer be considered by designers.

Industrial buildings will get an extra year before they must start complying with the bylaw, but builders are concerned that since many industrial buildings house the food service industry, green roofs could cause problems with insects and rodents. There are also concerns that green roofs have not been tested on very tall buildings.

City Council passed the bylaw based largely on the study by Ryerson University, which says the widespread greening of Toronto’s roofs could reduce local temperatures from 0.5 to two degrees C. The study said green roofs would result in improved air quality, and more energy savings from better solar reflectivity and insulation.

Green roofs include a waterproof membrane, layers for root resistance, drainage and a filter, a growing medium and vegetation. Intensive or active green roofs have a deep growing medium and can be used for recreational spaces. Toronto’s Manulife Centre has a green roof that was built over a parking garage about 25 years ago, and now has trees that are three storeys high.

An extensive green roof has a shallower growing medium and the landscape is designed to be more self-sustaining, says the city. They are lighter than intensive systems and require less structural support and not as much maintenance. An example of this kind of roof is the Mountain Equipment Co-op building in Toronto.

Modular systems, which are ideal for existing roofs, are grown off-site in large trays or containers, and placed on the roof. They come in a variety of designs. There are also systems that are grown on farms like sod turf, then rolled up and transported to the rooftop, where they are rolled out.

Green Roofs for Healthy Cities says that Chicago leads North America in the number of green roofs in place, but that "the mandatory bylaw in Toronto may change that, resulting in approximately 50 to 75 new projects annually."

The city also offers an incentive program for owners of existing buildings, providing funds of up to $50 per square meter (maximum $100,000) for eligible projects. Details of the Eco-Roof program are available at the Live Green Toronto website.

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