Green roofs are nice, but rooftop farms are better.
They’re the future of living architecture, say International green roof advocates who gathered in Toronto last week.
Traditional green roofs reduce energy consumption by keeping buildings cooler in the summer and warmer in the winter, and they also absorb rainwater instead of sending it into storm sewers. For this alone, they have become official policy in Toronto.
But rooftop agriculture — or agritecture — does all this while also providing jobs, generating electricity, training youth and of course, growing food.
“Toronto is a leader in North America for green infrastructure — not only green roofs, but community gardens. This is about putting those two ideas together,” said Steven Peck, president of Green Roofs for Healthy Cities, which hosted the two-day Grey to Green conference.
“We have a handful of agricultural green roofs and all of them are community projects,” like Eastdale Collegiate, Ryerson’s Engineering building and the Carrot Common, said Peck. “But we don’t have any commercial-scale agriculture on roofs — that’s the next thing.”
Last month, Toronto was recognized as North America’s second best city for building green roofs, with only Washington D.C. building faster.
Thanks to the green roof bylaw passed in 2009, all new buildings over six stories tall and with more than 2,000 square meters of floor space must have at least 20 per cent green roof.
But because planners envisioned using perennial plants, certain regulations discourage seasonal crops, said Arlene Throness, who designed and operates the 929 square meter farm on the roof of Ryerson University’s George Vari Engineering and Computing Centre.
The city by-law requires green roofs to be 80 percent covered three years after planting. If you’re harvesting crops every season, the green roof is periodically naked while the new crops grow, and this breaks the law, Throness explained.
“I think the fear was that edible plants would take too much labour and water,” and the city wanted to give developers a low-maintenance solution for building green roofs, Throness said. “But we’ve been monitoring our water use and don’t require any more.”
After a pilot project in 2013, last summer the roof hosted a five-crop rotational farm that produced more than two tonnes of vegetables, she said. “We’ve found that we can grow everything here.”
The harvest is split between campus kitchens and the Gould St. farmer’s market on Wednesdays.
Ontario imports billions of dollars of produce from California each year and this supply is becoming threatened due to their prolonged draught, said Throness. Rooftop agriculture adds local food security to the existing environmental benefits of green roofs.
For Peck, while rooftop farms aren’t appropriate everywhere – older buildings often can’t handle the extra weight – they’re an essential part of the future of the city.
“There are still hundreds of millions of square feet of roofs in Toronto that could still be greened,” Peck said. “We invest billions and billions of dollars on grey infrastructure. It would pay great dividends to devote a small part of that to green infrastructure.”
By the numbers:
72,020 square meters of green roofs built in Toronto in 2014
232,000 square meters of green roofs already in existence
185,000 more square meters have been approved.
4,984 hectares or approximately 8% of the total land area identified as the total available area for green roofs in the City of Toronto.
20 % minimum area that must be covered by green roof on new buildings in the city
2 tonnes of produce produced by a 929 square meter farm on the roof of Ryerson University’s George Vari Engineering and Computing Centre last summer.
Source: Toronto Star Marco Chown Oved Staff Reporter, Published on Mon Jun 08 2015