Green has hit the condominium roof. Although the greening of roofs is relatively new in Canada, Toronto is the country's leader in green roofs.
In fact, the city claimed the Canadian top spot in 2007 for the most green roof space added in a year (more than 7, 700 square-metres).
Environment Canada's 2002 Green Roof report estimated that greening six per cent of Toronto's rooftops - about 6.5 million square metres or 1 per cent of the city's land area - would reduce the city's summer air temperatures by one to two degrees Celsius.
Shortly after this report, the City of Toronto adopted green roofs as part of its strategy to fight pollution, reduce summer temperatures and minimize storm water runoff.
Not all green roofs are created equal. They differ in soil depth, plant species and cost.
The intensive system, with deep growing medium, is the most expensive but also the most attractive because it supports trees, shrubs and perennials.
The extensive system, with shallow growing medium, usually supports only sedums and mosses. However, what extensive systems lack in plant diversity, they make up for in lightness, low maintenance and lower cost.
Semi-intensive systems are somewhere in the middle in soil depth and plant species.
In the last couple years, more developers have started to contemplate "green roofs" for their new residential highrises. When Concert Properties started building their condo-style, 28-storey Jazz rental residences on 167 Church St., they contacted Xero Flor Canada.
Xero Flor's chief operating officer, Sasha Aguilera, vividly remembers installing the two 150-square-metre extensive green roofs on the eighth floor on Nov. 29, 2005.
"It was a very cold day, it was even snowing some," she recalls.
Xero Flor's extensive system includes a waterproof membrane, followed by a root barrier, a drainage layer, water retention fabric and then finally the layer that contains the high mineral content media with eight to 12 different sedum species.
The sedum species and the thin layer of media are grown for a year and half on a farm in Princeton, Ont., between Paris and Woodstock.
"We put our vegetation carrier on this protective film and we fill that with two centimetres of soil and the seeds go in there as well," says Aguilera. "When it's ready, we just basically start to roll it up since it's not attached to the ground."
The rolled-up sedums with media are whisked away to the building site on pallets.
Over the last five years Xero Flor has installed 16 green roofs on residential highrises. Although relatively new to Canada, their system has been used on rooftops in Germany for more than 30 years.
It's unlikely the condo board would allow an individual to set up a green roof on their balcony or terrace.
So, what information can a sole condo gardener glean from green roofs for their own growing space? Plants. If you have a windy, hot site, green roof plants would probably grow by leaps and bounds. Sedums flourish; useful species include S. acre, S. album, S. floriferum and S. spurium. Indigenous plants suggested by the city include junipers, spireas, sand cherry, a variety of sedges, asters, penstemons and bergamot.
For an extensive list of green roof plants, pick up Green Roof Plants: A Resource and a Planting Guide by Edmund C. Snodgrass and Lucie L. Snodgrass (Timber Press, 2006 $22.40).
Cristina da Silva will be conducting a condo gardening seminar on Saturday, Oct. 4, at 3: 30 p.m. at the Toronto Condo Show. More information at torontocondoshow.com.