By Roberta Rosa and Naelle Le Moal
Imagine going for a walk in the park — 22 floors up.
That’s the dream held by Steven Peck, who came to Ottawa last week to teach local architects, roofing constructors and engineers how to build parks in the sky.
“There isn’t a single technology that can deliver us as many benefits as a green roof technology in the cities in Canada,” says an enthusiastic Peck. “Nothing can come close to it.”
Green Roofs are an emerging trend for environmental buildings. Plants which grow across the rooftop improve air quality, reduce storm water run-off and lower energy costs.
Peck is promoting green roof technology as a way to reshape cities and make dense downtown cores more livable.
Green roofs can “make roof spaces more useable for people and other creatures like butterflies and birds,” he says. “We need to grow cities up and not out.”
Peck started developing green roof technology in 1997. He is the founder and president of Green Roofs for Healthy Cities, an industry association based out of Toronto. He travels throughout North America to convince cities to adopt green roof technology.
Elie Petraki, an architect who works for Foreign Affairs Canada, was a student in Peck’s one-day course last week.
He plans to use what he learned immediately, on the construction of a new Canadian Embassy in Morocco.
“The next embassy we are going to build, we are trying to use green roof principles,” he says.
Several buildings in Ottawa already have green roofs.
The largest is seen on the top of the new War Museum in LeBreton Flats. The modern-looking building is covered by a 11,000 square meter lawn that creates a sunny spot for visitors to walk.
A smaller garden sits on top of a one-storey research lab on National Research Council land, where patches of grass and juniper bush cover half of the roof. The other side is bare, providing a reference to measure the energy benefits of a green roof in the Ottawa climate.
The vegetation allows some of the rain water to evaporate rather than run straight off the roof, keeping the green surface cooler, says Karen Liu, a chemical engineer with the National Research Council.
During the winter, the vegetated roof acts as insulation, keeping more heat in the building.
The biggest savings occur during the summer, she says. “In the winter we only see about 10 per cent in terms of the energy thermal performance, but in the summer we’re looking at probably 80 to 90 per cent reduction in terms of the heat coming into the building.”
But Peck says green roof developers need to focus on more than just the energy benefits if they want people to invest in the technology.
“If you just look at one benefit, like energy, it would be very expensive,” he says.
“But if you look at all benefits together, it becomes much less expensive.”
Those arguments don’t convince Robert Vaillancourt, a building manager with the city of Ottawa.
He doesn’t see green roofs sprouting up in Ottawa on a large scale anytime soon.
“Green roofs are not a tremendous technical advantage in terms of cost for money. They’re quite expensive for the value that you gain,” he says.
Where urban concentration is denser, rooftop gardens are a good option because of the extra green space they provide. But that is not the case in Ottawa, which still has many parks and green spaces, Vaillancourt says.
Green roofs “do have advantages, but they are still one of the more costly ways to participate in energy and environmental management.”