By Linda Erskine

	Green roof gardens like this one at Toronto's City Hall help to alleviate some of the heat island effect prevalent in many urban areas.

Fact: Studies have shown that 150 square metres of "plant surface area" produces enough oxygen for one person for a day.

Fact: Rooftop gardens help to insulate buildings, decreasing rooftop temperatures from 60�C to about 25�C. A reduction in air conditioning use translates into savings in electricity.

Fact: Rooftop gardens help to reduce the amount of water lost to evaporation and run-off, with plants absorbing much of the rainfall, thereby alleviating the pressure on the city's network of sewers.

Fact: Gardens, whether they be rooftop gardens or a traditional planting bed help to evoke a sense of community, and contribute to reducing external and internal stresses.

You would think that with all of these obvious benefits, that cities would be proliferated with rooftop gardens on every high rise. Although this would be a definite exaggeration, there is a concentrated move to make this a reality. A search on the Internet five or six years ago might turn up a few examples of rooftop gardens. Today, a random search turns up a plethora of information on rooftop gardening in Canada, the United States and as far away as Russia. The reason? There are many, the most important being the environmental impact these gardens could have in reducing the heat island effect prevalent in many cities, where trees and landscapes have steadily been replaced with asphalt and buildings. Often dark in appearance, these barren rooftops tend to store and intensify the sun's rays, heating up the buildings and the surrounding area by as much as 4�C to 7�C. Air pollution is also a major problem, especially for people with cardiac and respiratory problems; with high temperatures comes a proliferation of smog, which in addition to affecting the aforementioned residents, has also been linked to low birth weight, premature births, stillbirths and infant deaths. The City of Toronto just last year recorded an all-time high of 20 smog alerts.

Eva Legiti, executive director of the Clean Air Partnership, an initiative of the Toronto Atmospheric Fund and former Environmental Commissioner of Ontario, sees this overheating of our cities' core as a problem that will not go away, despite recent efforts to reduce our use of fossil fuel. But, as she wrote in a recent article in the Globe and Mail (April 22, 2002), we can work on alleviating the heat island effect through long- and short-term efforts, such as the creation of rooftop gardens to bring more green, shade and oxygen into the atmosphere, and even providing lighter-coloured roofing materials and painted rooftops to reflect some of the sun's rays away from these buildings. The City of Toronto is one leader in this initiative, conducting ongoing urban heat research, which they intend to share with leading Canadian and U.S. scientists at the Urban Heat Island Summit, May 1 to 4. And, part of this research comes from another project undertaken by the City, their own rooftop demonstration garden at Toronto's City Hall.

Because of their drought tolerance, native plant material has the best survival rate of the plant material used in the City Hall demonstration plots. Rooftop gardens are just one idea for bringing a little green and heat relief to cities � another strategy is the use of light and reflective colors on roofs.

Unveiled in November 2000, the City Hall Green Roof Demonstration Garden, with its eight extensive and intensive garden plots, has survived two full winter seasons, albeit not too severe, with satisfactory results to date. While not all the data is in on its overall success in reducing the heat island effect common in major cities, the demonstration gardens have had some impact, if only in providing city residents and visitors a chance to experience a rooftop garden. Kaaren Pearce of Elevated Landscape Technologies and designer of the City Hall demonstration plots, is happy with the plants' survivability thus far. Their success is even more relevant given the fact that there was no irrigation system to give the plants regular waterings, depending on only four hand waterings in the year and whatever natural precipitation had occurred. As expected, the native plants fared the best with the lack of irrigation as they are more drought tolerant than other plants. But, says Pearce, not having an irrigation system to rely on was an even better indicator of how these plants would survive if the garden plots were planted and then abandoned, as would be the case with some rooftop gardens. The extensive gardens worked extremely well, says Pearce, "because of the plants' low root depth and spreading habit. The intensive plots did not work as well, probably because we had to cut the roots in half to fit them into the soil depth," she says, indicating that while the semi-intensive and urban agriculture plots performed extremely well, these were unfortunately victims of vandals. The alpine phlox did not survive, as well as the bearberry and the irises. The reason for their demise, says Pearce, may be the cultivars selected or planting too late in the season. The irises, she believes, did not survive not because of the plant material itself or its hardiness but because of poor planting. While the big bluestem, taken from the High Park gene pool and planted in the Black Oak Savannah plot, did not grow as large as expected, Pearce indicates that this may have been a blessing in disguise. Usually reaching six feet in height, this big bluestem grew only four, because, says Pearce, instead of growing vertically in the soil, the roots moved laterally. "I think it would have been too heavy and too large a root system for the roofing membrane to handle," she says. Pearce reports that weeds did not pose to be too much of a problem, although goldenrod seemed to jump from bed to bed. More data will be available on the gardens' overall success in the long-term future, confirms Steven Peck, executive director of the Green Roofs Coalition, but first there are a number of tests to be conducted. In the meantime, however, in an effort to raise awareness of green roofs to the public, starting June 5, the Green Roofs Coalition will host tours of the City Hall demonstration plots every Wednesday from 12:30 p.m. to one p.m. The next phase in the Green Roofs Coalition master plan will continue this May with the opening of the second green roof at Eastview Collegiate. The demonstration plots should be implemented as soon as May 2002, with the greening to be completed this June. "I am really looking forward to working on the Eastview demonstration plots," says Pearce, noting that only two to three inches of soil will be used. Similar studies will be conducted at this site, with research conducted on the reduction in temperature, stormwater run-off, etc. Toronto is not the only city that deserves attention in its initiatives to promote green roofs and more importantly, to squelch a potentially life-threatening problem. As Ligeti notes in her guest editorial in the Globe, the City of Chicago announced a new by-law that would see the inclusion of a green roof system on all new multi-use/story buildings in the city's core. Terry McGlade, principal of Perennial Gardens Corporation and the creator of the new rooftop garden at the Merchandise Lofts Building in Toronto sees this move as a good step to environmental stewardship on the part of the politicians. "There's a political message here," he says. "The same movement that created the demand for natural plantings and the reduction in pesticides by municipalities is starting to come to the fore of the consciousness of our politicians. It's just natural (with all the environmental ramifications and benefits in air quality, lowered atmospheric temperatures and increase in oxygen) that the next step would be to go up on the roofs." McGlade knows of what he speaks. He's been designing and constructing similar rooftop gardens for commercial and residential clients through his Perennial Gardens business, and has done so very successfully. The Merchandise Lofts Building is one of the latest in his landscape design portfolio, and it's different than previous "container" style rooftop gardens in that it uses the green roof infrastructure, with structural roofing support, thermal insulation, roofing membrane, filter cloth and growing medium with limited soil depth. The Merchandise Lofts Building, formerly the five-storey steel and concrete warehouse owned by Robert Simpson Co. Ltd., now houses a multitude of residential loft units, above-grade car and bicycle parking spaces, loading bays, food and retail stores, as well as office space, a major grocery store chain, a restaurant and indoor pool, party room and outside dipping pool. It also features two extensive green roof plots, showcasing a prairie meadow. The two plots measure approximately 10,000 sq. ft., surrounded by another 15,000 sq. ft. of hard surface concrete pavers. In addition to the immediate environmental impact, these rooftop gardens have many other less obvious advantages � including food production. The City of Toronto took this step with the inclusion of its "urban agricultural" plot on the podium roof, donating crops to the Toronto Food Bank. In St. Petersburg, Russia, the main goal of its rooftop gardening initiative in 1993 was to examine rooftop gardening techniques, as well as producing greens and vegetables for urban people who have no access to land outside of the city. The techniques, developed by Dr. Martin Price of Education Concerns for Hunger Organization (ECHO) in the U.S., saw the possibility of producing 2,000 tons of vegetables. According to a web site produced by City Farmer, Canada's Office of Urban Agriculture, St. Petersburg has approximately 15 rooftop gardens, as well as two gardens in the largest prison in the city. These gardens, one at rooftop and one at ground level at the "Kresty" prison, help to feed 10,000 prisoners. Then there is the emotional benefit. With less and less space in people's homes and an increasing need to get back to the basics, urban gardeners (and some suburban ones) find they need to go further or be more creative in their gardening endeavours. The answer to some: rooftops, balconies and containerized gardening. For Vancouver, British Columbia's Waterfront Building, which combines a ground floor office, retail or service use with a mixture of commercial and "live/work" space, a green roof system was the perfect opportunity to create an aesthetically pleasing community recreational space. Open to the public, the Waterfront Building Green Roof was completed in Fall 2001 and features both intensive and extensive garden plots. The extensive plots rely on Poa alpina and blue grass, while the intensive plots use more diverse plantings such as Rosa meidiland 'White'. For more information on either green roofs at Toronto's Merchandise Lofts Building or Vancouver's Waterfront Building, please visit the Canadian Mortgage and Housing Corporation web site at www.cmhc-schl.gc.ca. Also look to future issues of Landscape Trades for more in-depth articles on these two green roof systems.