Greenhouse Canada

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Green Space: Raising the Green Roof

March 26, 2008  By Michelle Brisebois

Green roof trend is looking up

Garden centres are no doubt used to working with landscape architects and designers and maybe even contractors but it appears as though there’s another strategic alliance wemerging – this time with roofers. Green roofs are shaping up to be a long-term trend and one that promises to be huge for the gardening industry. Crazes and fads are short-lived events. Think pet rocks and mood rings. Trends are longer-term shifts in consumer behaviour and you can pretty much identify a trend with staying power when it’s propelled by several different factors. Green roofs are being driven by three strong forces; primarily the environment, with the economy and buying local running a close second and third. All of these factors have intertwined to create the perfect situation for green roofs to gain momentum. They’re cost effective, good for the environment and good for us. This is one trend that is definitely over our heads.

Green roofs have been with us since Nebuchadnezzar II built the Hanging Gardens of Babylon around 600 BC. Legend has it he built them as a gift to his wife, who missed the trees and fragrant plants of her homeland. Green roofs are not the same thing as roof gardens. A few containers of marigolds on a roof might be called a garden with it primarily functioning as visual interest. Green roofs are densely planted areas of low-maintenance grasses, mosses or succulents. Green roofs are primarily used to insulate the building, slow water runoff and generate healthy air.

Top: A green roof on a home in Walkers Point in northern Ontario. The roof helps to limit the building’s ecological footprint and merges it with the local environment.
Bottom: NOW magazine in Toronto was outfitted with a green roof in only two nights.

Green roofs also last longer since the vegetation protects the roof from the elements.  They benefit the environment by absorbing most of the rain water, minimizing runoff into city sewers that carries dog waste, road oil, roof tar and lawn chemicals into lakes and rivers. Laura Barker, Sales Manager of Elevated Landscape Technologies (ELT), a manufacturer of modular living roof systems, confirms that diminishing runoff is a huge benefit. “Living roofs will absorb about 50 per cent of the rainfall. That saves a lot from going down the drain.” They also release beneficial oxygen into the atmosphere and filter harmful carbon dioxide from industrial and auto emissions diminishing the “heat-island effect.” It’s estimated that this effect causes an eight-degree difference between the temperature of a city and that of the surrounding countryside. This heat island effect also promotes smog. Green roofs keep the building cooler, reducing the demand for air conditioning. 

These roofs are beautiful, attract wildlife and tend to have a lifespan about two to three times as long as a conventional roof. Europe and particularly Germany have embraced the idea of a green roof since the 1980s. In Germany, vegetated roofs cover 13.5 million square metres, which equates to 14 per cent of all flat roofs. Government policies dating back 20 years paved the way for green roofs to take root. In North America, the concept is becoming more popular as municipalities look for ways to help home and business owners save energy and leave a smaller carbon footprint. The City of Toronto estimates that if 50 million square metres of available roof space were landscaped, the savings would equate to $313.1 million for storm-water management, heating and cooling of buildings, along with $37.1 million in annual cost savings.

Further study results can be found at .

Toronto city council is also recommending the installation of green roofs on existing and new city-owned buildings. There was an incentive program in 2007 that provided a grant of $50 per square metre for home and building owners. Green roofs typically cost between $75 and $90 per square metre to install above and beyond the cost of a traditional roof (per the City of Toronto research study) and it’s estimated there are just over 100 green roofs in the city of Toronto. “The B.C. and Ontario provincial governments have led the way in encouraging and supporting green roof development,” confirms Barker. York University has created a 30,000-square-foot green on top of their Computer Sciences Building. The green roof was built in 2003 and has been monitored by the Toronto Region and Conservation Authority to gauge how much storm water is created and retained and to look at the quality of that water. 

There are three main types of green roofs. Complete systems that encompass different pieces of the roof including roof membrane are an integral part of the whole system. Modular systems float above the existing roof. There are also pre-cultivated vegetation blankets that consist of growing medium and plants rolled onto the existing roofing system with drainage mats and root barriers as required. ELT provides pre-grown and planted systems which are “turn-key” modules. These modules are ultra-lightweight and easy to retrofit into existing roofs. “Our modules survive about an inch above the roof membrane” says Laura Barker. ELT also provides training to the public on installing their green roof systems. “We have all kinds of people attend our training program,” confirms Barker. “Traditional roofers are becoming certified installers as well as individual homeowners and some horticulturalists. We work with a network of growers to offer the complete package to people – including the plants best suited to this type of application.” 

Many people are hesitant to consider a green roof because they’re not sure how to care for it. After all, if a busy family can barely find the time to water their potted fern inside of the house, how does it monitor 2,000 square feet of vegetation? “Our roofs come with a drip irrigation system that keeps the plants lush,” says Laura Barker. Drought resistant plants are also being bred and improved to withstand less direct intervention. Local plants are often well suited to this purpose. Barker has heard the questions first hand. “I have a green roof on my own home and the most common question I get from people is ‘how does it stay alive?’ It’s quite the attention-getter.” To that last point, green roofs may serve one other purpose that we’ve not considered – they’re great advertising vehicles. A garden centre roof is the perfect place to display your products up high where people driving by can see them. It’s probably the most environmentally friendly billboard you’ll ever create. 

Find out if there are any green roof installers in your area and make sure you support yourself and your key team members with some education on green roof systems. There are workshops and installation courses available all across Canada.

It’s a trend that’s not only important for our industry – it’s important for our planet. We need to take steps while we still have time to do so. As John F. Kennedy said, “The time to repair the roof is when the sun is still shining.”

There are several websites that serve as great green roof resources. For more information visit: (great resource for training programs in many North American cities) (Elevated Landscape Technologies for modular green roofs and training) (City of Toronto website with detailed research study results on the benefits of green roofs)  (Centre for the Advancement of Green Roof Technology, B.C., offering courses on green roof installation)

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