Gardens - Specialty Gardens

Planning a garden on your rooftop

Roof gardens not only add a new dimension of beauty to your home, they offer many benefits for the planet, too

Saving energy

Although Lundholm sees energy savings as a potent marketing message in selling the green roof idea to homeowners, he’s clearly animated by their broader ecological potential as habitat. “Last summer we had a student researching insect biodiversity on our green roof test plots who found more than 200 species of insect—including one for which this was only the second record of occurrence in the province,” explains Lundholm. There were also plenty of dragonflies and butterflies. An added benefit is the showy flower displays insect-pollinated native plants tend to have: “We had a good spread of colour across the growing season,” he notes.

Lundholm’s comment points to the aesthetics of green roofs—an issue of prime interest to gardeners, yet something that can often get relegated to the back burner due to the technical nature of the green roof industry. Says Natvik: “I think we need to separate the roofing aspect from the garden aspect of green roofs. If you were to commission someone to do a garden, you wouldn’t ask a roofer.” Natvik stresses that he means no disrespect to roofing companies—it’s just that “roofing is roofing, but green roofs are primarily gardens, and it takes a competent, knowledgeable gardener to create one that will meet its full potential.”

Natvik, whose family roots are Norwegian, points to that country’s encouragement of small-scale residential green roofs through the development of national standards and the inclusion of green roof specifications in building codes. “In Norway, you can go to a regular hardware or building store and buy everything you need—growing medium, drainage board, et cetera.” Natvik sees the lack of comparable national standards in Canada as the biggest barrier to widespread implementation, saying that without them, “it will take a while for green roofs to become more affordable.”

“My green roof cost more than a regular one,” affirms Sharma, who didn’t receive a grant. A large part of the $5,000 for her project, however, was because she had to have a supporting beam put in the home addition to bear the added weight. “The engineering side of it was a bit tricky, but doable,” she adds.

Monica Kuhn, an architect who specializes in sustainable residential design and has been involved in green roofs since the early 1990s, stresses that for homeowners, the first step is to find out if their roof will actually support the load. Even the most lightweight green roof systems require from 15 to 20 pounds per square foot of carrying capacity, notes Kuhn, adding it’s imperative to have a structural engineer involved right from the project’s beginning.

Although there are many different green roof systems on the market, they all share certain characteristics. First, there is the waterproofing membrane that protects the roof and prevents water from pooling on the surface. Then there is a root barrier, a drainage layer and finally some kind of growing medium—usually engineered for its lightweight properties. The depth of this medium determines the types of plants that can be grown—the deeper it is, the greater the variety to choose from.

In the end, though, it’s important to remember that green roofs are first and foremost living gardens and, as with all gardens, there will always be changes, surprises and possibly even heartbreak. Having worked on some 20 green roof projects over the years, Kuhn encourages people to experiment. “After all,” she says, philosophically, “if a plant dies, it’s not the end of the world.” And just as some plants might disappoint, others might do better than expected.

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