In Search of the Greenest Roof

To paraphrase Tragically Hip’s Gord Downie, the Toronto Islands are sinking man, and I don’t wanna swim.

It’s odd to be barred from the city’s collective playground indefinitely. It’s also odd that, back on July 8, 2013, our screens were, well, flooded with images of 1,400 GO passengers stranded beside the Bayview Extension as water rushed through the lower floors of their nightly commuter train; rescued by dinghy, it would take six to seven hours to get them home that night.

While she’s not out to sound the alarm bells just yet, Liat Margolis, director of the University of Toronto’s GRIT Lab (Green Roof Innovation Testing Laboratory) at the John H. Daniels Faculty of Architecture, Landscape and Design, suggests that, while you may not have heard of her group, in coming years GRIT’s unique perspective may come in handy, as freak weather events become less freaky.

“In our defence,” she begins, “we’ve been so busy in building our credibility in terms of getting the data out – and it took us a while to get to this point – but now, we have a dozen publications that we can point to in high-ranking scientific journals [so] we can now give you some serious information.”

And one piece of serious information that she, her colleagues and her graduate students – who come with undergraduate degrees in civil engineering, mechanical engineering, biology, landscape architecture and architecture – can give us is that “all green roofs are not created equal.”

The corollary, of course, is that in order to prevent flooding from becoming worse, we are going to have to invest heavily in green roofs. Toronto, of course, has had a head start: In May, 2009, it became the first city in North America to adopt a bylaw requiring a percentage of green-roof space on new buildings with a gross floor area of 2,000 square metres or more. And, since then, as aerial photos of the city’s roofscape have slowly gone from grey to green, GRIT Lab, which formed in 2010 shortly after Prof. Margolis arrived from New York (where she headed an international materials-research firm), has been working hard to arrive at a “Green Roofs 2.0.

“Rather than have a ‘one recipe that fits all,’” she explains, “[we need] to begin to break down and figure out which material combinations are most significant for water management, thermal cooling, biodiversity, pollinator habitats and where in the city would we prioritize these decisions.”

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