Blue, white and green roofing innovations promise to make buildings more, well, green
By Melanie Collison
Photos by R.Thornton (Alberta Ecoroof Initiative roof)
In 1875, Fort Calgary was the city's first public building with a living roof. The prairie sod soaked up rainwater, kept the fort cooler in the summer, and trapped in heat in the winter.
While it's been around for 150 years, green—or living—roofing is a trend that's been slow to develop. Alberta also hasn't seen a rush towards white (reflective) or blue (stormwater collecting) roofing, either, despite the industry's push to become more environmentally sustainable.
Compared to traditional flat commercial or industrial roofs, all three roofing systems have pluses and minuses.
A white roof adds points towards a building's LEED score and reduces the need for air conditioning, which works well in the southern U.S., where the cooling-to-heating ratio is 80:20; however, the heating costs under a white roof clearly rise in Canada, where the ratio is more like 20:80.
And there's another concern: "White [roofing] is often single ply and very vulnerable to hail damage," explains Kerry Ross with IBI Group Architects.
A blue roof has real appeal where stormwater management is a concern, as it is in most of Alberta.
As the first Canadian municipality to adopt a sustainable building policy, Calgary has been requiring stormwater management on city buildings for a decade. "The vast majority of projects are done by private industry and private consultants, so we encourage efficient management of stormwater," says Justin Pockar, energy and environment coordinator with the City of Calgary.
The city has been working with SAIT to develop a rainwater-harvesting handbook that spells out how and why to design and install a rainwater collection system. Blue roofing is certainly a step up from a simple cistern collection system, but there are still concerns.
"Blue roofs will address stormwater well if they're designed well, but they don't offer thermal protection, amenity space or preserve roof membranes," Pockar explains. "It's an economical solution if you're just building a better standard roof. They're cheaper than green, but slightly more expensive than a regular roof because you have to beef up the structure."
Green roofing seems to be the best choice as far as energy and environment go; however, they might be the most complicated to develop and maintain.
The City of Calgary sees the benefits of green roofing and has conducted research on best practices and technical requirements, has streamlined the permitting system and is allowing developers higher density if they install environmentally sustainable roofs.
"We've done several things to make green roofs in particular go more easily through our process," Pockar says. The city has started with a checklist of things to include when applying for permit because a green roof is a fairly technical addition to a building.
"The easier we can make things, the more acceptable it becomes to industry," says Marco Civitarese, chief building official in the inspections and permit services branch of building regulations. "We've set up a green building website...and created a matrix that outlines for 97 per cent of the cases what permits you need and when you'll require professional engineers."
Green roofs range from intensive rooftop gardens to extensive low-maintenance and low-cost systems, according to Ross, who has been involved in the installation and maintenance of over 40 of them.
Ross's green roofing foray began 15 years ago, when she needed to get a development permit for one in Banff, and she has since become IBI's green roof specialist.
Rooftops comprise about 30 per cent of a city's impermeable surfaces and may cover as much as 70 per cent of the downtown core. A huge benefit to cities, Ross points out, is that it's easier to modify a roof to manage stormwater than a road.
Additionally, a green roof will improve air quality through both the plants' CO2-oxygen exchange and the replacement of asphalt materials that produce off-gas. And, the plants and greenery on the roof can double or triple the lifespan of the membranes beneath it by absorbing the UV rays and heat that normally ages roofing materials quickly.
"There's great acoustical value from having the added mass near airports, under flight paths," Ross adds. Because of this, they can be used on buildings where the occupants might be sensitive to sound, such as kindergartens.
There is also the visual appeal. "Look from the Calgary tower down at the ugly roofs. You could bring a visual natural experience to many of these downtown offices."
And in the inner city, where the high cost of real estate means open space can't compete with built facilities, green roofing can provide amenities or outdoor living spaces.
"If you're using the roof for people, you might want to invest more in both up-front installation and maintenance, so be clear about your objectives," Ross advises. "There's a beauty in a naturalized landscape, as opposed to something that has to be mowed and weeded."
While providing a great source of insulation, living roofing also creates habitat for birds and pollinators.
When Ross planted her first demonstration project in Calgary a decade ago—the Alberta Ecoroof Initiative on the Alastair Ross Technology Centre in the University of Calgary's Research Park—she used predominantly native plants. Since then the plant community on the roof has evolved as seeds arrive on the wind.
She's been experimenting methodically with different depths and plants to determine the lowest-cost, lowest-maintenance design for extensive roof coverings.
"How little growing medium can you use in our climate and still have a viable plant community? We have not just wide but quick temperature variations. The snow cover in Edmonton keeps roots insulated, but high winds [in Calgary] threaten them. We are finding a palette of viable and consistent plants."
Intensive roof gardens need continuing maintenance, but her extensive naturalized plantings pretty much take care of themselves after the first couple of years, like a meadow.
Still, green roofs are a tough sell because there isn't enough documentation to prove the underlying membranes last longer, says Stephen Teal, manager at the Flynn Group of Companies. Flynn supplies roofing systems, and metal and glass components of buildings.
"We do most of the green roofing in Canada on bigger projects," Teal says, but, "sustainable roofing, generally speaking, is a non-starter with most people. Half the green roofs...don't go ahead because the first thing the [owners or builders] axe [in the budget] is the green roof."
"It's all about getting the initial cost down," he says.
The City of Calgary is tackling the lack of documentation head-on with its project to re-roof the municipal building.
"We put in a standard inverted roof membrane as a control, as well as a green roof," Pockar says. "We're looking at stormwater quantity and the quality of the runoff, biodiversity and more, and taking the data to academics to prove it."
There's a strong belief that green roofs are better, but nobody knows how much better, he says. "We want to be able to furnish real numbers and real installation advice and costs."