In an exquisitely private enclave of downtown Toronto, where the streets are really lanes and where lush foliage frames perfectly restored Victorian façades, sits an odd, new kind of secret garden.
It's a big square patch of mixed perennials sitting on the roof of a laneway garage, and it can only be seen from the second floor of its owner's home and from the neighbours' second floors.
It's the latest example of a green-roof trend in Toronto that has seen affluent and environmentally minded homeowners start experimenting with an idea that's been around for two decades in Europe and has caught hold in several western U.S. cities in the past few years.
And it's an ironic symbol of the ambivalence of Canadians toward environmental matters, since this particular green roof is perched atop a colossal garage that holds three vehicles.
Nevertheless, the 500-square-foot rooftop garden of luscious-leafed bergenia, spiky blue blazing star, sunny coneflowers, fluffy white lambs' ears and sweet-smelling lavender marks a step forward for the movement to green the rooftops of Toronto.
Until now, that movement has been confined to demonstration projects on a few large government, commercial and condominium buildings, but it is gaining wider acceptance as city and federal environment departments and a private coalition called Green Roofs for Healthy Cities spread the word about the benefits.
Monica Kuhn, the architect who included the garage green roof in her rebuild of a downtown Victorian home, says an increasing number of her clients are asking for green roofs.
The benefits are numerous.
Green roofs absorb storm water, slowing the runoff into city sewers that carries dog waste, road oil, roof tar and lawn chemicals into lakes and rivers.
They insulate buildings, moderating hot and cold temperatures and reducing energy use.
They release oxygen into the atmosphere, countering excess carbon dioxide levels from industrial and auto emissions and helping to reduce the "heat-island effect." That effect is the roughly eight-degree difference between the temperature of a city and that of the surrounding countryside, and it promotes smog.
They also extend the life-span of a roof to 30 years from 15, Ms. Kuhn says.
Green roofs are not the same thing as roof gardens. A few plant pots and some artfully arranged pieces of driftwood can be called a garden, and its main function is to provide a visually pleasing sanctuary.
Green roofs are densely planted expanses of low-maintenance grasses, mosses or succulents whose main purposes are to insulate the building, slow water runoff and generate healthy air.
At a recent conference Ms. Kuhn attended in Portland, Ore., a new concept of the roof as a home's "fifth façade" was bandied about by architects from Canada and the United States.
"You could say there are four walls and then the roof," Ms. Kuhn says. "It's about greening another layer. It's not just somebody making a pretty gesture on the roof -- though it is that as well -- this is infrastructure that helps the city."
Ms. Kuhn says that at the Portland conference, she was struck by how green-roof gardeners are still limiting themselves to grasses and sedums, when the landscaper she chose -- Terry McGlade of Gardens in the Sky in Toronto -- is experimenting with many new species.
"Typically, the easiest thing is to plant the whole thing with sedums [commonly known as stonecrop]," Ms. Kuhn says. "Terry says 'boring' and he's trying all kinds of perennials. In my opinion, he's really pushing the envelope."
Mr. McGlade says the fact that Ms. Kuhn's project involved a newly built garage with a roof that could carry a lot of weight gave him the freedom to plant many different perennials that need six to eight inches of soil.
Most residential roofs cannot handle that much weight -- wet soil weighs about 100 pounds a cubic foot -- which limits gardeners to plants that will grow in about three inches of soil.
For Ms. Kuhn's project, Mr. McGlade even planted daffodils, which survived well this spring.
The landscaper doesn't have much time for fancy architectural talk about "fifth façades," he says.
"I'm the guy they need to actually realize this. In most cases, it's guys like me who are actually designing the garden, even though it's architects supplying the roofs. If it was all dead up there, what would you say?"
Ms. Kuhn is currently building another garage green roof, this one in Forest Hill. But she is most excited about a major project she hopes to build next spring -- a 12,000-square-foot green roof on top of the Hugh Garner housing co-op on Ontario Street.
The roof will feature a storm-water reservoir that will be used both for sprinkling the garden and cooling the building.
It is to be financed partly by the co-op's own maintenance fund and partly through donations from private groups. There are no municipal grants available yet for residential green-roof installation, but that could change soon.
The City of Toronto recently struck a task force to look at ways of encouraging more green roofs in the city.
Construction
A green roof is constructed with several layers.
A waterproof membrane is first, followed by a water-retention layer that resembles a giant egg carton whose shallow cups hold water. A drainage layer comes next, followed by the desired depth of soil. If the roof is a sloping one, baffles can be used to prevent the soil from sliding off.
A large factor governing the cost of such a project is how accessible the roof is. If a crane is needed to lift the soil, building materials and plants, the expense is much higher than if ladders or ramps can be used. Cranes cost $500 an hour to rent and there is usually an eight-hour minimum.
Another factor is size. Larger roofs provide economies of scale. A 10,000-square-foot roof can be done for as little as $12 a square foot, says Candy Venning of Gardens in the Sky, while a 1,000-square-foot roof would cost $15 to $20 a square foot.
Price also varies with the soil depth required. Only three inches is needed for grasses, sedums and other ground-cover plants, but six to eight inches is needed for perennials. Planting can be done with seeds or seedlings, and that changes the cost, too.
In the priciest scenario -- using a crane and eight inches of soil -- the cost would be about $24 a square foot, Ms.Venning says.
Benefits
Environment Canada has calculated that greening 6 per cent of Toronto's rooftops -- about 650 hectares, or 1 per cent of the city's land area -- would yield huge environmental and economic benefits for the city. The price tag is estimated at $45.5-million over 10 years. The gains would include:
An annual, direct reduction in air pollutants of 30 tonnes.
A 5- to 10-per-cent decrease in smog-alert days each year.
A drop in greenhouse-gas emissions of 2.18 million tonnes a year.
Annual energy-cost savings of $1-million.
A reduction of the urban heat-island effect of 1 to 2 degrees.
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