Toronto, Canada’s most populous metropolitan area, sits anchored on the northwestern shore of Lake Ontario. The city is incredibly diverse. The roughly 2.7 million people here speak over 160 languages. The city rests on a broad sloping plateau crossed with rivers and ravines, though the skyline is marked by skyscrapers and high-rise buildings.
The city is famous for being one of the most multicultural and cosmopolitan cities in the world. However, it’s also making waves for its innovative developments; in particular for choosing to go with green roofs.
What is a green roof?
A green roof is a roof of a building that is partially or completely covered with plants. At a minimum, a roof should include a root repellent and drainage system, ﬁltering layer, growing medium and plants. It should be built on a waterproof layer.
Making green roofs law
Toronto is the ﬁrst City in North America to have a bylaw that requires and governs green roofs on new developments. Since 2010, new developments bigger than 2 000 m² must include between 20% and 60% green roof space.
Published with the bylaw, green roof construction standards and guidelines provide people with best practices and instructions. It provides information, for example, on the depth of growth media and plants to choose from. These are usually native or adaptive from the Southern Ontario area, appropriate for the local climate and building exposure. Plants that do well in drought are usually recommended and the list results in a variety of species to be grown across the city.
Why should you choose green roofs?
Green roofs have many beneﬁts. They help to cool cities. In the process, energy bills that would have been racked up to do this with electricity are reduced. By soaking up rainwater, they help to reduce ﬂooding. Plus, less pollutants and litter now enter the stormwater system. It’s a prime example of what we are working towards when we talk about sustainable stormwater systems. Plants improve air quality, the city is left looking more beautiful and with more biodiversity.
Yet, one of the biggest reasons for Toronto to push for the implementation of green roofs, is money.
Green roofs make financial sense
The city’s 2006 Green Roof Strategy follows on results of a study that showed that widespread green roofs would provide signiﬁcant economic beneﬁts.
According to Shayna Stott, environmental planner at the City of Toronto, the study estimated beneﬁts based on 4 984 ha of potential green roof implementation. The financial benefits are staggering.
Stormwater beneﬁts amounted to an estimated infrastructure saving between $2.8 and $79 million. A pollutant reduction beneﬁt of $14 million could be achieved, and savings from erosion control measured $25 million. The total stormwater beneﬁt was estimated to range from $41.8 to $118 million.
Since the bylaw was passed, permits for approximately 420 green roofs for a total of approximately 400 000 m² of green roof area have been passed, says Stott. At the time of the interview, a triple bottom line analysis on costs and beneﬁts was in the pipeline.
Green roofs against climate change
Except for the ﬁnancial beneﬁts and other mentioned above, Stott says that “green roofs are part of the toolkit required to make Toronto more resilient to the impacts of climate change, which will include hotter, wetter and more intense climate”.
As such, green roofs are always factored into the required stormwater analysis for development applications to the city. “They are a key strategy in meeting our requirements for water to be retained onsite,” she says. While an analysis of the collective beneﬁts of green roofs in the city was in the pipeline, the existing beneﬁts were already so clear that the programme was being expanded.
“Because our requirements apply to new development only they are helping to mitigate impacts on those buildings,” says Stott. Yet, there are still stormwater issues related to the vast majority of buildings that existed prior to the requirement. “We are in the process of increasing stormwater requirements and as such green roofs will play an even more important role in meeting the higher standards.”
- All photos were kindly provided by the City of Toronto
- As mentioned, green roofs are an excellent example of sustainable stormwater management. This again, is where the whole movement of water resilient cities started. Don’t know exactly what this is? Read this – it’s an overview of everything you should know.
- Wondering why all of this matters? This is why we must save water.
- Thank you again to the Water Research Commission (WRC) in South Africa, who published the book Water Resilient Cities, where this blog was first published
- Toronto City website
- City of Toronto Guidelines for Biodiverse Green Roofs