In May of this year, Toronto catapulted to the top of the list when its city council adopted the most comprehensive and stringent green roof bylaw of any city in North America. 

“This is a highly commendable act for a city that presently does not even rank in the top 10 of North American cities — with Chicago in #1 spot — in terms of square footage of green roofs installed in 2008,” said Steven Peck, president of Green Roofs for Healthy Cities as he praised council for “exercising leadership” on a tool to fight climate change.

The rules — requiring up to 50 percent green roof coverage on multi-unit residential dwellings over 2,000 square meters (21,500 sq. ft.) and higher than six stories — kick in on January 31, 2010.  

Newly constructed schools, commercial and industrial buildings were given a reprieve until January 31, 2011, at which time they will have to set aside either 10 percent of their roofs, or 2,000 square meters, whichever is less, for sod and other plant material.

Toronto’s deputy mayor, Joe Pantalone, noted that roofs make up 21 percent of Toronto’s surface area, raising the temperature of the urban environment and pushing up demand for electricity in summer months.  “Garden roofs,” he said, “help conserve rainfall, reduce energy demand and add to the beauty of the city.  This bylaw, one part of the solution to climate change, will create new ‘green’ jobs and represents a whole new mindset on how cities make their rooftops work for them and the environment.”

It comes as no surprise that developers warn “the new measures will add to costs,” and green-roof advocates say “the new measures do not go far enough.”

If the European model is anything to go by — for example, more than a decade ago Germany started giving tax credits to buildings with green roofs — green roof technology and know-how will become a fast-growing segment of the horticulture industry.