When Port Coquitlam became the first municipality in Canada to mandate green roofs on large commercial buildings in 2006, developers expressed skepticism. The zoning bylaw required green roofs on all new buildings of more than 5,000 square metres (53,281 square feet).
At the time, developers claimed the higher price for green roofs, which are planted with a growing medium such as grass, made them uneconomical.
When the Beedie Group decided to build one of the few industrial buildings large enough to be covered by the policy, it was allowed a variance because much of the warehouse space had neither air conditioning nor heating. The city, therefore, allowed the building to proceed with a green roof covering only a small office portion.
Now, however, the 650,000-square-foot Freemont Village in Port Coquitlam by the Onni Group is seeing both a large Walmart and a new Canadian Tire store outfitted with green roofs – and they won’t be the last in the development.
Onni development manager Mike Mackay said that the $1 million Walmart green roof, covering 151,300 square feet, cost three times more than a conventional roof.
But McKay said the extra cost should pay off in both public relations and long-term energy savings for clients. The Walmart roof is planted with a variety of local and foreign plants, including California poppy and Arctic bluegrass.
McKay said that, aside from Walmart and Canadian Tire, three more buildings in the big-box Freemont Village could have green roofs installed.
According to Port Coquitlam city officials, the main purpose of the green roof policy is to obtain environmental benefits, including reducing storm water run-off, improving building thermal performance and energy consumption, and reducing the urban heat island effect.
The city estimates that the higher cost of green roofs are recovered within the first two years of building operation, while the energy savings and storm water reductions continue for the life of the building.
Laura Lee Richard, director of development services for the City of Port Coquitlam, said there is a variance policy that allows developers to not include a green roof if other energy-saving and environmental issues are addressed. But she said the green roofs should not be a deterrent to large buildings.
Green roofs are not required on smaller commercial and industrial buildings, she added.
The arguments in favour of green roofs transcend the environment, according to Green Roofs for Healthy Cities (GRHC), a Toronto-based advocate for green roofs.
According to its studies, green roofs and other sustainable efforts in commercial buildings lead to higher lease rates, enhance property values and have been shown to reduce tenant turnover in office buildings.
For retailers like Walmart and Canadian Tire it could also reduce employee turnover because the buildings will be more attractive and comfortable. Or so the thinking goes.
However, resistance remains. The Langley-based Roofing Contractors Association of BC, which offers a Roof Star warranty on all roofing done by its members, has expressed concerns about the reliability and safety of green roofs.
In the dormant winter months, the roofs are actually covered in dry grass and plants, pointed out RCABC executive vice-president Ivan van Spronsen, “which may constitute a fire hazard.” He added, “From a pure roofer perspective [soil and plants] are potentially damaging to a roof.”
Dean DeHamel, president of Olympic Roofing Ltd. of Port Coquitlam, noted that green roof repairs are also a concern.
“If the roof begins leaking, you would have to dig through soil and plants to fix it,” he said.
Other RCABC members, while welcoming any green roof contracts, note that green roof technology is not yet perfected though municipalities are mandating its use. Others doubt that reducing the urban heat island effect should be of much concern in a suburban business park.
Van Spronsen said a roof can represent 12% to 15% of the total cost of large commercial building, so tripling that cost to add a layer of green roofing is a substantial decision.
There is also ongoing maintenance that has to factor into the cost. For example, the near six-acre (2.4 hectare) green roof atop the Vancouver Trade and Convention Centre requires annual grass mowing and weekly monitoring for weeding and drainage checks.
However, some costs can be lowered by using slow-growing plants that do not require mowing, such as those chosen for the Walmart roof in Port Coquitlam.
“Green roofs are barely practical, but we can understand why some people want to do it,” said van Spronsen. “There are ways of putting [green roof] systems together that appear to be functional.”
Some building experts, however, say the whole green roof movement is more about aesthetics than sustainability. Writing in the journal of the American Society of Heating, Refrigeration and Air-Conditioning Engineers recently, Toronto-based engineer Joseph Lstiburek said, “This green roof stuff is getting out of hand.”
According to Lstiburek, better energy savings could be found by adding insulation to a roof and installing a reflective membrane than by “adding dirt and grass.” •
