Eco Wise

Raise the Roof by Making It Green

Covering a roof in vegetation creates an energy-saving insulation layer, says Nancy Somerville of the American Society of Landscape Architects.
Covering a roof in vegetation creates an energy-saving insulation layer, says Nancy Somerville of the American Society of Landscape Architects. (By Jay Paul For The Washington Post)
Sunday, July 6, 2008

At Sixth and I streets NW, amid the Chinatown bustle, Nancy Somerville is standing in front of a rolling meadow sprinkled with black-eyed Susans. It's no urban mirage: This colorful mosaic of plants lives four stories high atop the American Society of Landscape Architects' building. Somerville, the society's chief executive, is one of her industry's biggest advocates of green roofs -- layers of soil and hardy plants that replace conventional black-tar or shingled roofs.

The virtues of vegetation-covered roofs are many, says Somerville, 51, and she's eager to give people the dirt on why they should green the space over their heads. For one, green roofs provide a "wonderful insulation layer" that can save energy in both sloped-roofed homes and larger commercial buildings. And once these aboveground gardens get established, "they're good to go," Somerville says. "In return, you get back a whole wealth of really neat environmental benefits."

For instance, green roofs can reduce storm-water runoff, a major source of pollution in the Anacostia River. Before Washington was developed, soil and plants would soak up most of the storm water. But with acres of pavement and concrete now blanketing the city, most of that water is rushing back into the river and picking up pollutants along the way. Green roofs are "a way to put back in a natural vegetative system," Somerville says.

Green roofs became popular in Germany and Austria about 50 years ago, but in the United States, the idea has gained traction only in the past five years in such cities as Chicago and Portland, Ore. Somerville first read about green roofs in the 1990s and became more interested in them after joining the landscape society in 2000. "I was really taken by the way green roofs can transform the wasted real estate and hostile environment of a conventional roof," she says.

The native Washingtonian says much of her passion for the environment comes from her mother, Marjorie Smigel, who in the 1980s led a successful grass-roots effort to pass right-to-know legislation about pesticide use in Montgomery County neighborhoods. "She was a great role model for me when I was growing up -- and, really, still is," Somerville says. "Many of the practices she instituted when I was growing up -- not using pesticides, buying organic, conserving energy -- are pretty commonplace now, but they certainly weren't back then."

To get your own green roof project blossoming, Somerville advises having a structural engineering study done on your roof, which will ensure that it can hold the vegetation's weight. Some wood-frame constructions won't support a green roof, but Somerville has seen local homes with green roofs atop porches, garages or additions. Hardy plants such as sedums grow well in the thin soils ideal for green roofs, she says. Other successful roof plants include nodding onion, thread-leaved tickseed, butterfly milkweed, flame-leaf sumac, smooth sumac, trumpet vine and pasture rose.

Apartment dwellers need not be left out: They should encourage their building owners to green their roofs as an amenity, Somerville says. "It's a nice little outdoor space that you wouldn't really have," she says. Although the cost of installation might make some, well, hit the roof (green roofs can run about $4 to $6 more per square foot than their conventional counterparts) homeowners make up for it in energy savings and longer-lasting structures, Somerville says.

"When you layer the aesthetic improvements on top of significant environmental benefits and long-term energy and cost savings, green roofs should be a no-brainer."

-- Christine Dell'Amore

To tour the American Society of Landscape Architects' green roof (636 I St. NW), call 202-898-2444 or visit

© 2008 The Washington Post Company