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Pacific Northwest | April 25, 2004Pacific Northwest MagazineApril 25, home
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Living Roofs
Imagine helping create a corridor of nurturing green above us
In the public space at Pickering Barn in Issaquah, several pavilions like this one are topped with green roofs to serve as both ornamental gateways and shelter for visitors.
THE VIEW OF the green and growing roof on Jon Alexander's Ballard garage, sprouting strawberries, chard, lettuce and tomatoes, influenced his new neighbors to buy their house.

While still an unusual sight here, in cities like Stuttgart and Mannheim, commercial buildings are required to have "green" roofs. "The Germans are light years ahead of us," says Patrick Carey, an architect who heads up the Northwest Eco-Building Guild's Green Roof Project. He's learned from the bottom up, starting out building eco-roofed chicken coops, and moving up to cutting-edge research and advising on public incentives. The city of Seattle is taking an active role in encouraging public and residential green roofs, and in Portland developers can build taller if they top out with a living roof.

Carey has been involved in designing and building 16 residential green roofs in the past eight months as part of the guild's project. Why would a self-employed architect spend years volunteering for a nonprofit? "This is the greenest thing you can do in building, rather than not build at all," enthuses Carey. He says the idea of capping homes with alpine meadows "struck my radical core — this is seriously sustainable, and a building element that actually gives back to the environment."
Illustration Now In Bloom
Euphorbia characias subsp. wulfenii 'Tasmanian Tiger' is a new addition to this showy species of spurge. Boldly striped in creamy white and topped with pale-yellow flower bracts in springtime, 'Tasmanian Tiger' grows 3 feet high in sun or part shade.
A green roof is simply a shallow expanse of garden atop a roof — a layered cake of deck, waterproof membrane and soil-filter fabric, topped off with several inches of light-weight, pumice-rich soil mix. All you see is the top layer of drought-tolerant hardy plants, sometimes enlivened with vegetables, annuals and perennials.

Think of all that extra gardening space up in the sky, a microclimate of unobstructed sunlight, watered by rainfall and beyond the reach of slugs.

But are green roofs a practical idea for our typical homes, especially those with sloped roofs? What happens when November rains set in and soak all that dirt and turf?

Some slant is preferred for drainage; in Switzerland, green roofs have even been used on chalets with a 60 percent slope. But even a fully saturated green roof weighs no more than one made of tile — about 15 pounds per square foot. Surprisingly, the soil need only be 3 to 4 inches deep to gain all the ecological benefits, although deeper soil built up where supports are strongest allows for a greater variety of plants. Carey maintains an experimental list of 200 possible rooftop species. He's convinced that any house can be retrofitted with a green roof. And the cost? A residential-quality living roof can be built for $8 to $12 a square foot — about the same price as tile or slate, or roughly twice as much as metal.

A green roof needs to be irrigated and weeded regularly for the first year, but when planted with drought-tolerant fescues, mosses and sedums, it can get by after that on rainfall and a twice-yearly weeding. The dirt and plantings provide a cushion, protect from sunlight and mitigate the extremes of temperature that cause a roof to wear out, so a living roof lasts two to three times longer than a composition one.

And the ecological benefits? A green roof acts like a storm window to reduce energy use, insulating the house from summer heat and winter chill, produces more oxygen than a family uses in a year, and both absorbs and deflects noise. It acts as a wetland to collect pollution from the air as well as capturing, filtering and slowing water run-off, a great benefit for salmon streams and overburdened storm sewers. I love the idea of green roofs forming a wildlife corridor in the sky, offering safe haven, food and shelter for birds and insects far above the human fray.

Learn more
Interest in green roofs seems to be exploding this spring, with multiple events planned in the next month. A first-ever tour of 15 Seattle-area living roofs is scheduled for May 8 as a benefit for the Northwest Eco-Building Guild. To register, e-mail Patrick Carey at, or call the Guild at 206-575-2222. Carey is teaching a green-roof workshop at Seattle Tilth on May 22 (206-633-0451,, and Portland is hosting the second annual international green-roof conference June 2-4, "Greening Rooftops for Sustainable Communities." See for information.

Valerie Easton is a Seattle free-lance writer and contributing editor for Horticulture magazine. Her e-mail address is

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