Photo courtesy Elevated Landscape Technologies Inc., eltgreenroofs.com.

The Environmental Protection Agency in Denver has a green roof made of sedum plants. Visit epa.gov/region8 for more information. Photo by Tim Davis, courtesy U.S. Environmental Protection Agency/Region 8.

The green roof of prairie grass and irises on Steve Jordan’s Longmont home helps him save on energy bills. “Between the roof and some passive solar, my gas bills are $15 per month,” he says. Photo by Steve Jordan.

Denver Botanic Gardens is installing a green roof that will be a pilot project to test how different plants fare in Colorado’s climate without irrigation. The photo shows the roof in progress; the rendering (below) shows the completed project. Photo and Illustration courtesy Denver Botanic Gardens.

Besides their ecological benefits, green roofs just look nice ‘n’ natural.Photo courtesy Elevated Landscape Technologies Inc., eltgreenroofs.com

Up on the Roof

From rooftop lawns to balcony oases, green roofs make buildings environmentally friendly from the top down.

By Tyera Eulberg

To touch up his roof for winter, Steve Jordan doesn’t need shingles or nails, just a nice iris or two. His Longmont home boasts a “green roof” topped with flowers and grasses that blend into the Colorado prairie. In spring, the roof bursts with green-colored growth. But it’s most green—­environmentally—in winter. Living plants and earth insulate and protect Jordan’s house better than any artificial material.

Green-roof technology, simply using vegetation and soil on top of a waterproof membrane, dates back thousands of years. The Hanging Gardens of Babylon were the first recorded examples of green roofs, with lush flower beds and trees covering terraces that reached several stories high.

But beyond the grandly aesthetic, humans across the globe have also turned to plant roofs for everyday building, from Viking huts to American sod houses. Jordan’s house dates from the late 1970s, marking a rediscovery of green roofs within the early environmental movement. But today in the 21st century, this roofing technique is really taking root.

For the environmentally conscious, a plant roof offers a number of benefits, including the prevention of water pollution. A conventional roof sheds rain immediately, and a neighborhood of houses sends a deluge of dirt, debris and chemicals into streams and rivers. A green roof’s natural soil and vegetation collects storm water and releases it slowly into the atmosphere, cleansing the water in the process.

The plants also filter carbon dioxide and pollutants from the air, and reduce the amount of heat absorbed by the roof. In addition, plants insulate better than typical roof membranes, keeping the house warm in winter and cool in summer (and marvelously silent inside).

Jordan relishes his roof every time he pays his energy bill. “Between the roof and some passive solar, my gas bills are $15 per month,” he says. And of course there’s the maintenance. Sure, he loses some dirt during each windstorm, but plants are used to snow, sun and wind, and a living ecosystem survives Colorado’s mercurial weather better than tiles and shingles. In fact, experts estimate that green roofs last more than twice as long as conventional ones.

Green Around Town
As energy consumption and water and air pollution become more urgent concerns, green roofs have sprouted in cities across the United States. Chicago and Portland have led the way, topping dozens of buildings with grass and gardens. But Colorado roofs are getting green, too. In downtown Denver, the U.S. Environmental Protection Agency/Region 8 headquarters sports 20,000 square feet of sedums on top. This type of green roof, called “extensive,” supports a few species (six) in a broad swath of earth just 4 inches deep.

Denver’s new Museum of Contemporary Art will boast a more “intensive” green oasis. With a soil depth deeper than a foot, the MCA green roof is slated for a wide variety of plants, including prairie and desert alpine species. The designer, Louisville-based landscape architect Karla Dakin, is also constructing a shade bed that “you can walk under like the sod houses of yore,” she says. Working on a roof still presents limitations, though. “I only have 1 to 2 feet of soil. When you think of your typical garden, that’s not much,” Dakin says. “That really restricted the grasses I could use.”

Another constraint is irrigation. Sprinklers and hoses would overwhelm the shallow beds, so Dakin is using xeric and native plants, like beaked yucca and desert willow, to minimize the need for water beyond normal rainfall. Since most new green roofs have grown up in moister climates like Portland, Dakin’s project is sailing uncharted waters. But, she says, “This is an art museum—it’s about pushing boundaries.”

Nearby, Denver Botanic Gardens hopes to eliminate the green-roof irrigation problem altogether. Senior horticulturist Mark Fusco, who consulted for Dakin’s project, spends his days on the roof above the gift shop installing DBG’s newest experiment—a no-water green roof. “In the past and the present, sedums have been the primary plants used,” Fusco notes. “But on an nonirrigated roof, they won’t live.”

Fusco’s roof beds host dozens of trial plants to see which ones will work best in our arid climate. Currently, he’s testing everything from ice plants and cacti to penstemons and evening primroses. “We’re not going to just use the typical root depths for roofs,” he says. “Sometimes plants that usually have really deep taproots will send out more lateral roots instead. So they might thrive up there.”

The DBG green roof is covered with green material—with just enough space for rooftop visitors—to maximize environmental gains as much as to experiment with plants. “We’re using this as a pilot project to investigate the effectiveness and feasibility of green roofs in this climate,” Fusco says. And more importantly, the roof will serve to educate locals about green roofs and teach them how to set up their own.

While Denver’s new examples are on large commercial buildings, green roofs are practical for the smallest home and the technique seems well suited to Boulder County’s urban and suburban neighborhoods. Fusco points to new planting mediums that are light enough for conventional houses to support. Sophisticated drainage and moisture-retention mats waterproof the house, but help retain enough water to nourish the vegetation.

And though green roofing is easier and cheaper on a flat roof, thatching techniques and ballast systems mean pitched roofs can go green as well. As for maintenance, that’s up to the homeowner. “There are rooftop gardens which require just as much care as any garden,” Fusco says. “But green roofs can be very, very simple.”

Steve Jordan tends his roof only rarely. Wild grasses blown in from the prairie thrive on their own, and the irises—originally an experiment—do well, too. “They get moisture from the winter to bloom,” he says.
With just a hint of color, Jordan’s snug living roof is as green as can be.

Tyera Eulberg is former assistant editor of Boulder County Home & Garden Magazine. She’s now pursuing a master’s degree in mass communications research at CU, but remains interested in the green grass of home.

© 2007 Brock Publishing Company
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