The city bylaw requires green roofs to be 80 per cent 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 the state’s prolonged drought, 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 metres of green roofs built in Toronto in 2014
232,000: Square metres of green roofs already in existence
185,000: Additional square metres approved.
4,984 hectares: Land area identified as the total available area for green roofs in the City of Toronto, about 8% of the total.
20 %: Minimum area that must be covered by green roof on new buildings.
2 tonnes: Amount of produce produced by a 929-square-metre farm on the roof of Ryerson University’s George Vari Engineering and Computing Centre last summer.
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