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Vancouver Convention Centre, British Columbia. Design Architect: LMN Architects. Prime Architects: Musson Cattell Mackey Partnership and DA Architects & Planners. Photo courtesy LMN Architects. G reen roofs are becoming increasingly popular in Canada. According to igures gathered by Toronto-based Green Roofs for Healthy Cities, nearly one million square feet of green roofs were installed in 2010. That compares with 2008, when about half a million square feet were installed. The trend appears to be continuing. Preliminary igures for 2011 suggest that it will surpass 2010 in square footage installed, says Carole Dobson, green roof advisor for Western Canada at Soprema. Of the two main types of green roofs – extensive and intensive – extensive green roofs account for about 85 per cent of new green roo ing, says Dobson. It is not hard to see why. They weigh less, typically no more than 35 per pounds per square foot, fully saturated with water, have less than six inches depth of soil or other growing media, often have less plant diversity, are sometimes inaccessible – on top of big-box stores, for example – are simpler to install and usu- by Godfrey Budd ally cost less. Intensive green roofs, on the other hand, are almost always accessible and are sometimes used as parks, weigh more and have a deeper growing medium, have greater plant diversity, require more maintenance and cost more. Among Canadian cities, market penetration is highest in the Greater Toronto Area (GTA), partly as a result of the City of Toronto's green roof bylaw, passed a few years ago. Nonetheless, "Vancouver also has a good number of green roofs, even in the absence of green roof bylaws," says Dobson. Besides legislation, LEED points are another driver for green roofs, says Dobson, who notes some related advantages. "A green roof doubles the life of the membrane, but that's not the main reason for installing them. But it attracts tenants to a highrise, and improves the overall desirability of the building, probably one of the main reasons for having them. For hospitals, they improve the well-being of patients." Many irms, she says, face a learning curve and require information on optimal design approaches for green roofs. The good news, however, is that, "Expertise is spreading, with Montreal, Vancouver and Toronto the main areas of expertise, but also growing in Edmonton and Calgary," says Dobson. Both Alberta cities have a relatively robust construction sector right now, she notes, but it is not clear how many green roofs will be installed in the near future. But, even on the prairies, with their harsh winters, more green roofs are feasible. Dobson points out that Chicago, the U.S. mid-west windy city with cold winters, has the highest volume of green roo ing of any city in North America. Many green roof suppliers and installers are seeing a steady expansion of the sector. "We're seeing about 10 to 15 per cent growth each year. Demand is mostly for extensive with shallow growing media," says Denis Gingras, sales manager for Hydrotech Membrane Corporation. The market, he says, is growing broader. As well as prestige institutional, provincial and city buildings, "Green roofs are moving to seniors' residences, of ice towers, and big [roof] surface stores and condo towers. But each market has a different eco-system," Gingras says. Hydrotech uses a built-in-place system. "This means a single-source warranty for the whole assembly that also includes the roof itself," he says. The increased up-front costs of green roofs can be offset by lower life-cycle costs. Gingras points to several green roof factors that help improve the life-span of the membrane: reduced exposure to freeze-thaw cycles, no direct UV rays and less risk of membrane damage from people walking about. As Gingras and other green roof proponents note, some types of green roofs can Greening the View As cities battle increased stormwater run-off and the related costs, they are embracing green roofs to help meet infrastructure needs Green Roof Systems p.34-39Greenroofs.indd 35 dramatically reduce the extra load on a city's stormwater system when it rains. "The drainage system [of our green roofs] acts as a water reservoir with the use of a water retention mat. In the average rainfall situation, it can keep 90 to 95 per cent of the water on the roof and then drain it off slowly," says Chris Johnston, maintenance manager at Nedlaw Living Roofs Inc. In the system used at Nedlaw, a root barrier sits immediately above the roof membrane, then above that, is a drainage device or panel that releases excess water, while retaining enough for plant sustenance, and above that, a ilter cloth. "That helps hold soil and roots in place. Then the soil, and this is where you get the [increased] insulation factor," says Johnston. With six-inch-deep soil, fully saturated, the complete assembly weighs about 22 pounds per square foot, he says. Certainly, the Toronto bylaw has been good for the green roof sector in the GTA, but Johnston worries that the competitive in lux vying for business could include some less than fully experienced contractors. "This could hurt some clients," he says. Others share this concern. "The green roof market is a bit of a wild west right now. A lot of people have rushed in," says Rick Buist, a partner at Living Architectural Systems. He suggests the problem stems from a lack of performance standards written into the Toronto bylaw. The impetus behind the bylaw was to save the city money by reducing stormwater overlow, and achieve better energy conservation by cutting the heat island effect in summer. The absence of rigorous performance standards could make it hard to attain these goals. Buist says contractors should install systems that can retain water and use types of plants that can help cool roofs. "But that's not always happening," he says. On the other hand, providing a design that achieves the appropriate standards in moisture retention and roof cooling can mean winning some environmental kudos – and a contract. Buist's irm recently completed a green roof project for the Dr. David Suzuki Public School in Windsor. Built in 2010, the new school, as one might expect, incorporates a host of sustainability features. "They received lots of proposals and chose ours because of its performance on storm water retention and cooling and use of native plants," says Buist. As well as installations, the irm's services include performance audits, feasibility studies and assisting with green roof strategies that integrate renewables like solar PV. It has done a range of APRIL 2012 /35 3/26/12 2:22:45 PM