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The impact of green roofs in Toronto

Natalie Thomas, reporter
June 28, 2012 — When it gets hot, it can get even warmer in a big city. One way to lessen the impact of Urban Heating, or the Urban Heat Island Effect, is by creating green roofs.

Green roofs are becoming more common in the city of Toronto
Green roofs are becoming more common in the city of Toronto

Toronto’s green roof bylaw came into effect in 2009, and requires new developments of a certain size to construct their roofs using measures which will reduce their climate impact.

"As you see behind me, one of those ways is a green roof which is vegetation on a roof which helps absorb the water, helps reduce the heat island effect by not having just huge expanses of rough roof," says Peter Milczyn, Toronto City Councillor, Ward 5. 

The Heat Island Effect Councillor Milczyn refers to happens in cities like Toronto where you have a huge concentration of black surfaces and pavement that absorb heat. Green roofs help to mitigate that effect. 

Cities like Chicago and San Francisco have been a great inspiration in the green roof initiative. But here in Toronto with all of the buildings that continue to go up, we're quickly becoming the North American leader. 

"So in a city like Toronto that's growing so dramatically, each year there can be dozens of new buildings that can incorporate this technology so over the next decade or so it's going to start having a dramatic impact on our city," Milczyn says.

The weather is considered when creating a green roof
The weather is considered when creating a green roof

Subhi Alsayed with the Tridel Group, says you can’t just create any old green roof – you have to keep the weather in mind.

"Now that we're seeing higher and higher multi-unit residential buildings being built in the city of Toronto, locating a vegetated green roof at those altitudes, when you're talking about 75 to 80 story buildings, it has its own challenges," Alsayed explains. "Wind uplift and wind pressure at that altitude is higher than wind pressure at a lower elevation. So when you install something like a green roof there, you want to make sure it's structurally intact, and it would be able to resist higher than normal wind uplift pressure." 

Subhi says the builder has to decide whether they should go with a vegetated green roof at those altitudes, or go with something that may not look as nice, but will be more beneficial for the building occupants and the community. 

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