Growing plants on the roof can replace some of the environment displaced by buildings and bring a payoff in lower costs over the years.

“Green” roofs are a fairly recent trend in building development, but the Romans and the Vikings did it too, notes Steven Peck, executive director of Green Roofs for Healthy Cities, a coalition of public and private organizations supporting the green roof industry.

Modern work on the idea started in Germany in the 1960s, and today, 75 municipalities in that country now either require green roofs or provide incentives for developers to use them in new construction or retrofitting buildings.

Albertans can get a look at the state of the art next month at workshops being held in both Calgary and Edmonton by Green Roofs for Healthy Cities.

Photo courtesy of Mountain Equipment Co-op.
The 10,000-sq.-ft. green roof on Mountain Equipment Co-op’s Toronto store was the biggest in North America when it was built in 1998.

The Calgary workshop will be December 3 at the Rosza Centre at the University of Calgary, and the Edmonton workshop on December 4 at the Fine Arts Building at the University of Alberta.

The workshops hope to attract a variety of interested parties, including architects, engineers, planners, building owners and managers, environmental scientists and horticulturists.

Green roofs have private benefits for their owners and public benefits for everyone.

They aren’t the same as a rooftop container garden – they’re an actual extension of the roof using a special root-repelling membrane, a drainage system, a lightweight growing medium and appropriate plants.

Tang Lee, an architecture professor at the U of C, notes that every building constructed destroys the ecology on the ground.

“It’s the nature of the thing. We have to put the building somewhere but it alters the ecosystem,” he says, by shifting the habitats of water, plants, animals and micro-organisms.

Cities are also heat islands, warmer than rural areas due to building heat and exhaust, cars and industrial exhaust and heat. During summer, air conditioning dumps the heat from the inside to the outside, making cities warmer yet.

Green roofs reduce those effects because they don’t heat up as quickly as the tar-and-gravel roofs used on many buildings. The traditional roofs are replaced by an ecosystem.

“Simplistically, you can take a slab away and put it back on top of the building, regaining some of the functions of the ecosystem,” says Lee.

The rooftop ecosystem helps clean the air, absorbing carbon dioxide and other gases and giving off oxygen. One green roof isn’t much, but along with hundreds of others, the benefits can add up.

Allan Yee, an engineer with the City of Edmonton, says the city is building a research facility at its waste-management centre with a green roof.

The green roof costs about the same as a conventional roof, has the same roof performance, is low maintenance and yet will be sustainable. The city compost plant will provide some of the growing medium.

A mix of plants will be seeded on to the roof, and the soil mix will be lighter than regular topsoil, he says. The result should be a self-sustaining garden that will out-compete the weeds.

Peck, of Green Roofs for Healthy Cities, says that a heavy rain on a big city can overwhelm its stormwater system. Green roofs manage stormwater, trap air particles and absorb carbon dioxide.

“What would happen if Edmonton had 15-per-cent green roofs?” he asks. “Is there a business case for Edmonton to offer incentives as has been done in Portland?”

Portland, Ore., uses density bonuses, adding two storeys to building heights for green roofs and reducing stormwater fees.

Peck says green roofs can be more expensive than conventional roofs, but a price comparison is like comparing a tricycle to a Ferrari. “That’s why we need public incentives,” he said. The higher cost is a disincentive to developers, because savings are only realized after several years.

Green roofs also give more business to horticulturists, soil-mix manufacturers and companies that make the confining membrane material that protects the roof from roots and water.

ONE OLD HOUSE

It might take a two- or three-way deal to save the old Rouleau house in Calgary’s Beltline.

Either that, or a benevolent landowner, says Neil Richardson of Heritage Properties Corp., who says he has spoken with the owner of the building at 114 18th Ave. S.W.

Richardson says buying the old house, moving it to a site that would cost money to purchase and prepare, and then renovating it could total upward of $500,000.

“You end up with a building that you have paid way, way more for than you could ever make on it.”

He adds that as a piece of heritage, it has a few things going for it – it’s a 19th-century structure, it’s one of the few houses that old left in the city and it was once the home of Dr. Edouard Rouleau, an early leader of the Calgary francophone community and one of the founders of the Holy Cross Hospital.

Richardson’s company earlier preserved the Lorraine Building in the Beltline and the old Northwest Travellers Building downtown. It’s now working on the Lougheed Building.

PERMITS JUMP

Calgary issued $207 million in building permits in October, a 10-per-cent jump from the same time last year, city hall reports. Residential permits were up eight per cent to $154.2 million.

Non-residential permits were up 17 per cent to $52.8 million, compared to $45.3 million in October 2002. So far this year, the city has issued permits worth $2.11 billion, an increase of seven per cent from $1.96 billion in the first 10 months of last year. The city notes that building permits represent intentions in the construction industry, not actual starts.

Web Watch:
www.greenroofs.ca