In search of the greenest roof
At the U of T rooftop lab, researchers are looking to fine-tune a growing technology
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."
While this may come off as a little scholarly, anyone with even a slightly green thumb will understand that different plants thrive under different conditions – that shady spot in one's garden calls for one species, as does the sun-drenched patch – and things such as a tree-protected microclimate or a depression in the land will contribute to one's choices also. The same applies to green roofs: What works on a fifth-storey podium will not work on the 50th floor, and proximity to other buildings, or to large natural formations, such as the city's ravines, will have their impact on performance as well. Add to that the technical requirements in building a green roof, which, if done cheaply, can underperform or, worse, leak, and things become even more complicated.
In the downtown core, for instance, a green roof should hold and process water to keep it out of overloaded storm sewers; Prof. Margolis explains that, properly designed, a green roof can retain 85 per cent to 90 per cent of rainfall during the peak of a storm. In a future Toronto with, say 50-per-cent coverage, this would deliver "a significant contribution in flood reduction." If a green roof is closer to protected Greenbelt areas (these do dip into Scarborough), it's better to allow more of that water to find its way back into the soil, so, in that case, give the bees wildflowers instead. And Toronto's many towers-in-the-park areas (which Prof. Margolis quips are really "towers in the parking lot" since many were designed in the sixties and seventies and provided 2 1/2 parking spots a unit) might want to rethink how they use their land altogether.
Key to all of this is getting the message out. To that end, GRIT Lab works with industry partners, such as Tremco, Bioroof Systems, and Sky Solar, as well as the City of Toronto, and green-thinking firms. It also provides seminars to private industry. But, poised to open their new green roof at 1 Spadina Cres., they're considering symposiums and other types of public outreach.
Public tours might be a good idea. On a windy and unseasonably cool mid-May afternoon, this author inspected the rows of beds atop the old faculty building at 230 College St., and was fascinated by the rain gauges, infrared cameras and temperature sensors that resemble patio lanterns. "It's probably the most instrumented lab in the world for green roofs," Prof. Margolis says.
Your humble Architourist was also baffled by an array of solar panels shading the plant material in one area. These, the good professor says, are an experiment: "The two industries really compete against one another for the same roof space," she explains, "so what we're saying is 'why either-or, why not both?' so, what are the best heights, is the shade going to affect [the plants], and now you're going to have sheeting of rain right here, is that going to make a difference?"
Those results haven't been calculated yet, but with GRIT Lab on the job, the Toronto Islands, as well as the rest of the city, may avoid a future as a swimming pool.