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The green roof at the Robertson Building in downtown Toronto was designed and installed by Gardens in the Sky in June 2004. It covers 4,000 square feet or half of the historic building's roof with more than 11 hardy perennials commonly found in Ontario. (Showwei Chu)

In Depth

Environment

Green roofs

Rooftop gardens can help the planet - and save money

Last Updated Sept. 7, 2007

Janna Levitt and her husband had no idea that more than 2,000 people would walk through their door when they listed their environmentally friendly house in this year's Doors Open Toronto, a popular free tour of landmark buildings and cultural spaces.

But that's how many came to see and hear first-hand the benefits of owning a green roof, a traditional flat roof that incorporates vegetation.

"The green roof is essential," Levitt told a group of garden enthusiasts on a recent tour sponsored by the Toronto Botanical Garden and Gardens in the Sky. "When it's really hot out, there's no wall of heat you walk into. You don't feel that here. It's not cool, but it's not boiling hot."

The flagship Mountain Equipment Co-op store in Toronto was one of the first places to employ a green roof in the city. In 1998, it installed a 10,000-square-foot system covering 50 per cent of the roof. The company says it has been a success in reducing stormwater runoff and the urban heat island - the effect when roofs, buildings and other hard surfaces absorb heat from the sun and cause a metropolis to be hotter than the surrounding countryside. (Showwei Chu)

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A cooler building interior when it's hot outside is one of the more noticeable benefits of a green roof. It also absorbs rainwater, reducing storm-water runoff and stream erosion, according to studies by the National Research Council and the British Columbia Institute of Technology's Centre for the Advancement of Green Roof Technology. And it helps improve air quality, conserves energy and mitigates the urban heat island, the effect when roofs, buildings and other hard surfaces absorb heat from the sun and cause a metropolis to be hotter than the surrounding countryside.

The concept isn't new. In Germany, vegetated roofs cover 13.5-million square metres — 14 per cent of all flat roofs — because of progressive government policies dating back to the mid-'80s. In North America, the concept is gaining momentum, and more green roofs are being installed on schools, municipal buildings and warehouses as cities adopt policies to encourage their use and industry players create more public awareness through education, demonstration centres and conferences.

Canadian cities adopt green roof policies

In Toronto, a 2005 study commissioned by city council to analyze the environmental costs and benefits of green roofs concluded that their widespread use in the city would provide huge economic benefits. If 5,000 hectares or 50 million square metres of available roof space were landscaped, the city estimated it could save $313.1 million in new infrastructure costs for storm-water management, heating and cooling of buildings, along with $37.1 million in annual cost savings.

To promote green roofs, Toronto city council approved 27 recommendations, including the installation of green roofs on existing and new city-owned buildings and an incentive program now in its second year that provides a grant of $50 per square metre for home and building owners. To date, there are 102 green roofs in the city (a total area figure was unavailable).

Other Canadian cities that have embraced green roof policies include Port Coquitlam, B.C., which amended a bylaw in 2006 to require vegetated roofs for buildings over 5,000 square metres. The city also fast-tracks applications from developers that provide green building technology and social housing.

Durham Region in Ontario and other cities require builders to meet the Leadership in Energy and Environmental Design or LEED green building rating system for new construction. Significant credits could be collected through the use of green roofs, they said.

Early adopters include schools and firms

Municipalities are not the only groups to embrace green roofs. Individual businesses, schools and warehouses are also employing them.

The Fairmont Royal York hotel in the heart of Toronto's financial district has been operating a rooftop herb garden as part of its chef apprenticeship training program for 10 years. This year, the hotel began offering tours of its rooftop herb garden with its afternoon tea service. On a recent visit, executive chef David Garcelon spoke of the Niagara region grapes he's trying to grow that he hopes to make wine from in a year or two.

"This is the world's smallest vineyard," said Garcelon, of the garden, which grows mainly herbs, tomatoes and edible flowers in raised wooden beds. "So we're hopeful � We'll see if they'll be back here next year."

The George and Kathy Dembroski Centre for Horticulture at the Toronto Botanical Garden has a sloped green roof so that it can be seen from the ground. The green roof was designed and installed in October 2005 by Gardens in the Sky using various drought-resistant sedums, such as Sedum album and Sedum spurium, and it's estimated that it cuts the centre's energy consumption by about 30 per cent. (Showwei Chu)

In 1998, Mountain Equipment Co-op paid $120,000 to landscape 10,000 square feet or three-quarters of the roof on its store in Toronto with indigenous plants. The green roof, which consists of various sedum, grasses and wildflowers, has also been an inspiration for other businesses, universities and schools, said Dave Robinson, the store's sustainability co-ordinator, who added that up to 3,000 people tour it each year.

"It's been very successful. All the benefits have been happening," Robinson said, adding that the store doesn't run its air-conditioning as much in the summers since the green roof was built, and that on hot days the roof temperature hovers around 30 C, unlike the typical 50 to 60 C reached on conventional roofs. "We haven't had any problems with the green roof."

Green roofs pose some concerns

Green roofs are not problem-free, however. They're expensive and require maintenance.

An extensive green roof, which requires less soil, could cost $10 to $15 per square foot depending on roof access and project scale, said Karen Liu, acting program head of BCIT's green roof centre. Industry association Green Roofs for Healthy Cities estimates the installation cost at $10 to $25 per square foot.

Each year, MEC and Fairmont Royal York pay $5,000 and $3,000, respectively, to maintain their green roofs.

"It's important to advise owners of maintenance," Liu said. "People have to understand it's a living thing."

There are also concerns that green roofs are more prone to leaks. In recent months, that perception led some B.C. insurance providers, still reeling from a local debacle over leaky condos, to indicate they were unwilling to insure condo projects with green roofs. The move threatened the green roof slated for the city's Southeast False Creek Olympic Village. But that project is now underway after the developer's insurance provider eventually agreed to coverage.

Studies from the National Research Council have shown that green roofs can help roof membranes last longer, because they reduce the temperature and temperature fluctuations. A typical green roof, which sits on top of an existing roof, consists of a waterproof and root-repellent layer, a drainage layer, a filter membrane, a growing medium and plants.

"It's not the green roof part that makes it leak. It's the [roof] membrane," said Liu, who authored some of those studies when she worked at the National Research Council. She cautioned that it's important for installers to ensure that the conventional roof is watertight and that no punctures occur, because tiny holes are difficult to find and repair after the green roof is installed.

Now that companies and individuals are starting to understand the benefits and costs of green roofs, Steven Peck, president and founder of Toronto-based Green Roofs for Healthy Cities, pictures a bigger role for them over the next decade in North America.

"Our vision is to have green roofs supported as a form of infrastructure like bridges and roads," he said. "From that perspective, we're still at the early stages."

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