Juniper shrubs on Ottawa test house roof – Photo: National Research Council Canada. Click to enlarge
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The simulation results at the test house in Ottawa were dramatic: heat flow from the building was reduced by more than 10 per cent. Even the energy-efficient house in Toronto, which was expected to see less of an improvement due to its cold-resistant design, saw a reduction of approximately 8.5 per cent.
On the Ottawa test house, the membrane of the green roof also saw a dramatic reduction in temperature fluctuations compared to that of a normal roof; a factor that should greatly extend its lifespan.
A Developing Market in North America
When people think of green roof designs, they mostly think of Europe. For instance, in Germany, where the trend began as early as in the 1960s, 14 per cent of total roof area is green thanks to federal legislation, local government incentives, and a number of universities that are conducting advanced research on the topic. Although North America falls behind in the business of green buildings, cities like Toronto and Chicago are now emerging as North American leaders in green roof science.
Toronto is the home of Green Roofs for Healthy Cities, a public-private partnership and research network which emerged from the first North American green roof review that was co-authored by Steven Peck, the organization's current director, Toronto architect and green roof advocate Monica Kuhn and Brad Bass. At the time, green roofs were merely seen as a niche-market technology, but the City of Toronto has now passed a green roof policy, based in part on a cost-benefit analysis that predated the winter green roof experiment. The winter green roof research provides an even stronger case for this technology and shows how it can be further adapted to our Canadian climate and how relevant it is to have it incorporated to our buildings.
The cities of Vancouver and Toronto both count over 600 green roofs now, and the concept is slowly spreading elsewhere in Canada. For example, Greenstone the LEED (Leadership in Energy and Environmental Design)-certified government building, which opened last October in Yellowknife, has a green roof to insulate the building all year round and gather rainwater for purposes not requiring potable water (in toilets, for example), allowing for a significant reduction of water and energy consumption. Greenstone is one of the rare buildings in the North equipped with a green roof, but further developments in the winter green roof technology could change that.
This recent research opens up a new avenue for designers, who may start to consider winter green roofs as part of a year-round strategy for energy efficiency.
After all, winter green roofs make sense when you consider the century's old practice of using turf and other plants as building materials for insulating homes while surrounding homes with trees to add shade in the warm months and protect them from wind in the cold months.
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