When it rains in the forest, the rich soil and plants absorb the water and use it to grow. When it rained in the city of Toronto, the water ran fast and hard over black roofs and dirty asphalt sidewalks, then poured into a sewer system that was designed in the early 20th century to serve the city’s once-modest population.The result: A sewer system and sewer treatment plant that quickly became overloaded, spewing dirty stormwater into basements, on to public roads, or into the city’s rivers and majestic Lake Ontario.
Instead of taking on the gargantuan task of re-building the systems below ground, Toronto’s innovative problem solvers looked upwards—to roofs.
In May of 2009, Toronto’s City Council passed a law that mandates every new building constructed in the city, residential and commercial, must have a green roof. Green roofs—installing plants on all or a portion of a city roof—have been shown to decrease heating and cooling costs; absorb rainwater, thereby decreasing stormwater and alleviating water pollution and stress on sewer systems; cool the overall city temperature during the summer; improve air quality; reduce noise; protect biodiversity; and promote outdoor activity—not to mention look pretty. Though many cities around the world have been steadily taking steps to encourage green roofs, no North American city has gone as far as Toronto has in mandating them.
Here are the nitty gritties: The law applies to all new buildings 2,000 square meters (about 22,000 square feet) and over, with the percentage of the roof that must be green increasing in proportion to the size of the building. “The philosophy being the larger the building, the more likely they are able to afford a larger green roof and the larger the area you want to cover,” said Jane Welsh, the city’s project manager for Environmental Planning, at last month’s Cities Alive conference. Developers may apply for exemptions, but if they get one, they still have to pay $200 per square meter (per 11 square feet), which goes to fund Toronto’s “eco-roof incentive program” to offset the costs for residents and building owners who want to install green roofs on their existing structures.
Green roofs decrease heating and cooling costs; absorb rainwater; cool the overall city temperature; improve air quality; reduce noise; protect biodiversity; and promote outdoor activity—not to mention look pretty.
It was about 10 years ago when Toronto realized it had a real issue with stormwater management and urban heat. The problems, though, began much earlier: In 1987, Toronto was identified as a “region of concern” by an interdisciplinary commission studying pollution and degraded water quality in the Great Lakes region. In cities, where there is a big concentration of developed “impervious” surfaces—pavement, asphalt, black roofs—the lack of vegetation actually raises the temperature, a phenomenon scholars call the Urban Heat Island (UHI) effect, which also decreases air and water quality. Welsh and other city planners knew something had to be done. But what?
“It was a really involved and very iterative process working with our stakeholders—developers, architects, and engineers—to come up with what the bylaw should look like,” Welsh said.
The city partnered with non-profit advocacy organization Green Roofs for Healthy Cities to create a test case, installing more than 300 square meters of plants on a large upper “podium” area of Toronto’s City Hall, a concrete space that had once been designed as a public square but had sat unused for 10 years. The award-winning project generated a lot of public enthusiasm for the new space, which now serves as a public park.
“When that happened, green roofs weren’t really part of the vernacular,” says Jordan Richie, Education Director of Green Roofs. Now they are.
City planners expanded, putting green roofs on several other city-owned buildings, and requiring that all roofs on new city buildings, or those due to be replaced, include a green roof “where technically practical.”
The law is very detailed,covering vegetation, placement of the green roof and more, and is enforced by building inspectors. Toronto also offers an eco-roof incentive program, $75 per square meter up to $100,000, for which any existing building is eligible or any new building that is too small to fall under the bylaw (as well as any new or existing Toronto Public School building!).
Developers balked at first, arguing that green roofs would significantly increase costs to new construction—though Richie points out that they are more cost-effective over the lifespan of the building than conventional roofs.
“We want to shift the culture,” Welsh says, of the rationale behind the city taking such an active role in sustainable policy. “We want to keep raising the bar, both for our developers, and for our public.”
Since 2009, Toronto developers have installed millions of square feet of green roofs—nearly 800,000 square feet in 2014 alone, placing Toronto in second place behind D.C. in the annual survey prepared by Green Roofs for Healthy Cities.
And in third place? Philadelphia.
According to Jordan Richie, this is the result of efforts by the Philadelphia Water Department, which is at the forefront of ensuring that new developments consider sustainability and water quality in their designs. Much like Toronto, Philly’s sewer system is old—the average sewer pipe is 78 years old with some pipes dating back as far as 1824—and gets overburdened by heavy rains.
All new construction in Philadelphia that is larger than 15,000 square feet is required by the city to “manage” the water it will make dirty when the rain runs over its surface through a stormwater management practice. According to Philadelphia Water Department Civil Engineer James Pollum, the city does not tell developers which method of management to use—they can choose a rain garden or porous pavement (a set of practices ranging from using more porous materials in a manner similar to traditional asphalt to interspersing plants and paving materials in a grid structure), or a green roof.
Like Toronto, Philadelphia also has a green roof tax credit in place: After a big new building is installed with a green roof, the developer can apply for a tax credit up to $100,000 to help offset the costs. “Because of this, green roofs have become pretty popular in development in Philadelphia,” Pollum says. Indeed, in 2014 alone Philadelphia developers created nearly 600,000 square feet of green roof.
But unlike in Toronto, this tax credit is only good for commercial properties, not residential or city-owned, even though residential development makes up the largest portion of PWD customers. Nor does Philadelphia have a program like in Toronto, that lets commercial developers pay a fee rather than install a roof, which would give the city money to spread around to residents. “We can’t provide residents with financial incentives at this time,” Pollum says, “but we encourage it.”
This means that for the majority of roofs in the city—including all the new townhouse construction—it is still cost-prohibitive to install the most effective stormwater management system. Pollum says that is in part because Philadelphia has so many small row homes, on which green roofs are hard to install—though it might be possible if groups of residents were willing to join forces, or a residential developer building several adjoining homes had an additional incentive.
“When we were researching, we asked ourselves, what other alternatives are there in terms of meeting the requirements for urban heat, stormwater, and biodiversity?” Welsh says. “And the answer was: Nothing. There’s nothing that delivers everything that a green roof does.”
Still, Pollum says the city is unlikely to pass a law similar to that in Toronto. “I don’t think the City of Philadelphia would pass a by-law requiring green roofs since that would only limit the options for new construction projects to manage stormwater,” Pollum says. “PWD definitely recognizes that green roofs provide an enormous benefit, both environmentally and aesthetically to an urban landscape. But in our experience, they are also one of the more costly stormwater management practices around.”
Green Roofs for Healthy Cities’ Richie estimates the cost of installing a green roof ranges from $7 to $32 per square foot, compared to about $3 per square foot for a rain garden or up to $6 per square foot for permeable pavement.
But proponents argue that green roofs are worth the cost because of all the other benefits they provide to cities that other forms of stormwater management do not—like increasing health outcomes of residents, decreasing urban heat, encouraging biodiversity and animal life, and improving air quality. The annual “State of the Air Report” found that in 2014, the Philadelphia area is tied for 11th most polluted in the United States for year-round particle pollution and the 2015 report by the Robert Wood Johnson foundation studying the overall health of every county in Pennsylvania put Philadelphia at dead last. Plus, there all the intangibles it’s impossible to quantify: The pure pleasure of plants and flowers.
“When we were researching, we asked ourselves, what other alternatives are there in terms of meeting the requirements for urban heat, stormwater, and biodiversity?” Welsh says. “And the answer was: Nothing. There’s nothing that delivers everything that a green roof does.”
Header Photo: Flickr/Karen Stintz