When Toronto's city council passed a bylaw May 27 mandating green roofs on new commercial, industrial, institutional and high-rise residential construction, its proponents hailed it as a major step toward preserving the environment.
The city would be the first in North America to make roofs planted with greenery a must on almost everything except the smallest structures.
The development industry, however, warns that the laws of unanticipated consequences may start kicking in and that a city-ordered focus on green roofs may actually slow the steady march toward energy conservation and environmental preservation.
"What the bylaw does is limit our options for future buildings," says Stephen Upton, vice-president for development at Tridel Corp., one of the city's major high-rise condominium developers. "Council has decided on this path without investigating any other options or even creating pilot projects to work out details and measure results."
The mandate for green roofs may impede acceptance of other technologies, says Keith Major, senior vice-president for property management at Bentall LP, which manages office towers such as 200 King St. West. As he explains, budgets for new developments may include room for only eight items directed toward energy conservation and environmental protection.
"Now that green roofs are mandated, that will bring the number of line items we can include down to seven," he says. "Decisions have to be made on cost-benefits analysis - getting the biggest bang for the buck. We may not be able to go with another technology which would deliver greater benefits because we must build green roofs."
The new bylaw says that new commercial and institutional structures larger than 2,000 square metres in total floor space and built after Jan. 31, 2010, must devote a portion of their roofs to green plantings with the size of that green space escalating from 20 per cent to 60 per cent depending on the size of the roof. Industrial buildings of the same size need devote only 10 per cent of roof space to greenery and they will get an extra year's grace to start incorporating it into designs.
Residential structures are affected if they are more than 20 metres or about six storeys tall. There is also a clause, however, that allows developers to opt out by making a payment to a new fund that will be used to promote retrofitting existing structures with green roofs.
"I think one of the main concerns about the bylaw is that it is just one more thing the development industry has to deal with, one more cost, one more demand to face at a time when they are already being squeezed by recessionary pressures," says Scott Addison, executive managing director, Toronto, for Colliers International, a major real estate broker.
"On the office and industrial side you already have tenants pressing for lower rents; construction costs are rising; there is fierce competition for development in surrounding municipalities."
Industrial developers are especially concerned about health problems, he adds. A large chunk of Toronto's industrial buildings are devoted to the food industry, and green roofs would seem a natural habitat for rodents and insects.
"It was an easy win for the city because it is hard to argue against anything that helps preserve the environment, but green roofs have all kinds of implications that don't seem to have been considered and worked out," Mr. Addison says.
One of those implications is the towering heights new residential and commercial towers are reaching in Toronto, says Lyle Scott, director of sustainable design at Cohos Evamy Integrated Design Inc., which has created green roofs on such Toronto projects as Minto Midtown condominiums at Yonge and Eglinton.
"What has been forgotten in the process is the height Toronto buildings are reaching," he says. "Many recent structures top 70 storeys. I can't think of another city where green roofs have been tried on buildings that reach so high in the air."
