Photo courtesy Terry McGlade, Gardens in the Sky Inc.

If a new bylaw passes, Toronto green roofs like this one will become an increasingly common sight.

Depending on the outcome of a meeting held today, Toronto could be the first major municipality in North America with a mandatory green roof bylaw.

Vegetated roofing assemblies have been acclaimed for their ability to improve insulation and durability, absorb greenhouse gases (GHGs), and help control the urban heat island (UHI) effect. Three years ago, Toronto City Council adopted a "Green Roof Strategy" to encourage these systems to be included in both public and private buildings through an array of incentives and development approvals. Now, the proposed Green Roof Bylaw would outright require such roofs on the majority of new buildings. (The bylaw would also regulate standards for green roof design and construction.)

The new rules would require green roofs on most projects exceeding 5000 m² (53,820 sf); depending on building size, a range of 30 to 60 per cent of the roof area would need to be vegetated. (The total roof area excludes space designated for renewable energy devices, non-vegetative areas required in the Toronto Green Roof Construction Standard, and private terraces.) Structures exempted from the bylaw include schools, industrial projects, residential buildings lower than 23 m (75.5 ft), and affordable housing.

According to the municipal government's website, Section 108 of the 2006 City of Toronto Act provides the council with the authority to pass such a bylaw. This is an outlined exception to the 1992 Building Code Act, which otherwise generally prohibits municipal bylaws to exceed the requirements of the Ontario Building Code (OBC).

Some developers have cited concerns regarding costs, esthetics, and usable space restrictions. Others have said the green roof requirement does not go far enough by excluding certain building types. The city's Planning and Growth Management Committee is deferring the draft until a public meeting on May 6 to allow enough time for public review. (Visit www.toronto.ca/greenroofs/index.htm.)

Toronto has a long history associated with the vegetated assemblies—international industry group Green Roofs for Healthy Cities (GRHC) is headquartered in the city and the World Green Roof Infrastructure Conference will be coming to the provincial capital in October.