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Green roofs sprouting in US Rocky Mountains

FLORENCE, Montana - On a small farm in Montana’s Bitterroot Valley, Nate Lengacher recently harvested thousands of sedums: low-maintenance plants with a key place in the small but growing world of green roofing.

Lengacher’s sedums are succulent plants that store water in their leaves and grow from a multilayered system of soil and root and water barriers.

On roofs, the plants moderate building-top temperatures and cut heating and cooling costs below. Pointing to the rows of mats topped by thin layers of soil and plants on his operation, Lengacher described an unusual harvest.

Despite the sluggish economy and the high cost, about $200 million worth of green roofs were installed in the United States and Canada in 2009, up about 16 percent from 2008.

That was about half the growth rate of 2008, but installations picked up to about 20 percent growth this year, industry group Green Roofs for Healthy Cities said.

Notable structures include Chicago’s City Hall and Ford Motor Co’s truck assembly plant in Dearborn, Michigan.

The industry has been relatively slow to take off in the United States, where less than 1 percent of buildings have green roofs. In Germany, for example, an estimated 12 percent of flat roofs are green and in Scandinavia sod roofs have been used for centuries.

Jeff Bruce, chairman of the Green Roofs industry group, said there were many incentives in North America, including rights to build oversize structures and letting green roof developers jump to the head of the line for building permits.

Portland, the biggest city in Oregon, in 2006 began offering discounts on stormwater fees for buildings with green roofs since they absorb and filter rainwater that otherwise would drain into overtaxed city sewers.

Earlier this year, Toronto became the first city in North America to pass a mandatory green roof measure, requiring new buildings with 21,500 square feet in space and larger to incorporate plants into roofs.

Roof Plants

The upfront costs for living roofs can be steep — as much as 30 percent higher than roofs covered with traditional materials. This is partly because planted roofs must be flat, which boosts building costs.

The initial high cost can be offset by the savings in energy bills and the fact that the vegetation helps extend the life of the roof, said Pat Supplee of Studio Modera, an architectural company in Missoula, Montana.

Supplee is a specialist in sustainable building, which she made her specialty in 2004. In the past three years, she has designed several houses with green roofs, starting with her own in 2007.

Her home is planted in a ponderosa pine forest between the rugged Bitterroot and Sapphire mountains of western Montana. It is a landscape sustained by periodic wildfires, an environmental cycle that Supplee took into account when she installed a roof of water-bearing succulents that resist flames.

Supplee said climbing energy costs lead some clients to favor such features as living roofs, but she would steer them in that direction regardless.

“We’re at a stage where people are sensitive to issues like global warming and the impact we’re having on the Earth,” she said.

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