No one can argue the environmental by product of roof gardens.
They insulate a building from overheating in summer, reduce heat loss in winter, purify the air and soundproof the roof, and they absorb rainwater that would over-extend city sewers.
Installing a green roof also protects it from Canadian heat/freeze cycles, and negates the destructive elements of the sun's UV rays, both of which can result in leaking roofs.
While the initial cost of installation of a sustainable roof can be high, the economic benefits begin as soon as the first season's energy bill. In addition, according to the Green Roofs for Healthy Cities (GHRC), using sustainable roof materials may double a roof's life.
"The biggest deterrent to green roofs is that many building owners often do not consider the long-term benefits," says Stephen Teal, director and past president of the Canadian Roofing Contractor's Association, and manager at Flynn Canada Ltd., a building envelope contractor. "They only look at the upfront cost and not the potential lifecycle cost and benefits."
But with the combination of wealth of knowledge available, field of experts being trained in LEED certification and the support of GHRC in addition to the incentives of devoted municipal governments Canada has the potential to be a leader in sustainable roofing.
Green roofs in their modern configuration can be integrated into the design plans of a new flat or modestly sloped roof on a building, factory, institute or condominium, or can be added to an existing roof.
Primary to that equation is how much weight the roof can handle. So step one entails consulting an engineer who will ascertain what's possible.
Green roofs can weigh as much as 50 kg per square metre, including the weight of water retained. In some cases, like factory roofs, infrastructure is designed for the weight of the roof plus snow and that's it.
Secondary is whether the building owners want to create an environment for human appreciation, or just fulfill a minimum standard to gain the benefits of energy savings, water runoff reduction and longer roof life.
Both the GRHC and the CaGBC offer green roof courses in their education modules. The GHRC also offers courses that cover everything from 101 basics, maintenance and materials, to the dynamics of design.
As in Europe and the United States, Canadian cities like Toronto and Vancouver have weighed in by offering significant incentives to integrate green roofs into existing buildings. They've also legislated green roof standards for all new commercial, condominium and institute buildings, with industrial buildings following next year.
In support of this, the Eco-Roof Incentive Program will pay building owners $50 per square metre for a green roof, up to $100,000 maximum.
"It's all come from our Climate Change Action Plan," says Kristina Hausmanis, manager of the Eco-Roof Incentive Program for Toronto. "We're working to make sure that we're better adapted to climate change by creating standards and programs that promote sustainable development to make our building's more energy efficient and reduce our city's greenhouse gas emissions."
Stephen Teal, AGRP, understands. Flynn helped found GHRC a decade ago and has been designing, constructing and roof landscaping ever since.
"I usually say it will cost approximately double the price of a high quality roofing system, but even that is only a very rough approximation," says Teal, who recommends builders and building owners avoid the shell game of roofers who don't include all elements of the job.
"Being able to offer a complete package with a single source of responsibility and a single warranty gives us an edge when dealing with a knowledgeable customer," he says.
As an industry, green roof potential may well be skyscraper high.
In addition to the lifecycle cost and benefits, there are numerous factors to think about when contemplating and implementing a green roof.
Installation requires a high-quality roof/waterproofing assembly to seal the existing roof entirely; however, in some cases, replacing an existing membrane may provide a more suitable surface. Have a green roofing expert conduct non-destructive testing and a structural evaluation to determine the best course of action.
The green roof assembly should include both a root-proof layer to prevent plant roots from penetrating the membrane, and a drainage layer of natural or recycled materials, followed by a filter membrane that spreads the water across the roof and prevents erosion.
Next is the growing media (soil) itself, which has to be light and fire resistant. If it's not irrigated, peat-based media may dry out in a drought, creating a potential fire hazard. Mineral soils mixed with lava, expanded shale or crushed brick are generally favoured although this is dependent upon the vegetation requirements.
An erosion control layer consisting of a fiber material with nylon woven through it or a biodegradable mat may be installed to prevent water and wind erosion of the media until the plants are established.
Which plant species to incorporate depends on the homeowner's maintenance and aesthetic requirements. In Toronto, drought resistance might be important. In Vancouver, it's the opposite.
Other issues to evaluate before implementing a green roof include slope, building height, moisture retention, structural considerations, life safety issues for workers and the general public (if the roof is accessible), wind erosion and aesthetics. Costs can also vary widely, depending criteria such as the height of the building, access, type of vegetation, depth of growing media, irrigation, accessibility to the public and location.
Whatever the project, consult an expert with roofing and applicable roof landscaping experience, or better yet an accredited Green Roof Professional (GRP), for details.