In the Garden:
Sedums and other succulents are excellent greenroof plants for flat roofs. (Photo by Ed Snodgrass)
To Green the Roof or Not to Green the Roof
With all the buzz about growing sedums, native plants, and grasses on rooftops, I'm curious about how a green roof works. And how to build one, of course. It's not as easy as replacing shingles with plants. The first green roof could have been a 5,000-year-old Irish passage grave or a Norwegian hut covered with grass, explained Ed Snodgrass, owner of Green Roof Plants and Emory Knoll Farms Inc., in Maryland. Snodgrass spoke at Bowman's Hill Wildflower Preserve's 7th Annual Land Ethics Symposium in February. Green Roofs as Living Machines was one of several topics in keeping with the theme of Creative Approaches for Ecological Landscaping.
While the Norwegian hut with grass seed tossed on the roof was a natural ecosystem in that maritime climate, today's successful green roofs are carefully engineered -- for weight, planting media, plants, and irrigation. Europe, especially Germany, is in the forefront, with cities like Stuttgart, homes, and businesses converting to or building with green roofs to control storm water runoff and conserve energy.
"Green roofs work best combined with other technologies," said Snodgrass. "They're natural machines that manage storm water, reduce a city's heat island effect, use space well, reduce air pollution, and get better as they grow. "A mere 6 inches of mineral media on a flat parking garage roof is not a lot of loading ... with a lot of possibilities." Mineral media is coarse material such as lava rock, gravel, pumice, extruded shale. Snodgrass' plants of choice are sedums -- more colorful cultivars and varieties than imaginable -- that he grows specifically for planting on green roofs.
The United States is slowly finding its way, mostly by designing and engineering new industrial, municipal, and academic buildings for a green roof rather than expensively retrofitting existing buildings with sloped roofs. The Ford Motor Company Rouge facility in Dearborn, Michigan, has the largest extensive green roof (10.4 acres). Chicago supports, and in some cases requires, green roofs for developments, and the city offers $5,000 grants to property owners and small businesses for green roof installation.
How about installing a green roof on your home? Not if it's steeply sloped. Even if it's nearly flat, think twice and do your homework. Residential application isn't up to par, said Melissa Muroff of Roofscapes Inc. in Philadelphia. "Ten years into it, green roofs (for residences) are starting to fail. The plants are dying." With no government standards or regulations, the homeowner depends solely on the contractor, who may or may not have expertise. She suggested buyers educate themselves well before greening any roof.
Snodgrass encourages experimenting, though, with your doghouse, shed, or birdhouse. I couldn't find building directions for these on the Web, though I recall a delightful green roof shed dripping with succulents at Bed and Borders Nursery on Long Island. Perhaps there's information in Snodgrass' book, Green Roof Plants: A Resource & Planting Guide. For a good overview and detailed information about green roof research at Michigan State University, visit: http://www.hrt.msu.edu/greenroof/.
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