by Heather Livingston and Tracy Ostroff

In architecturally sedate Washington, D.C., it appears that the green roof phenomenon has at last taken root. At 1425 K Street, NW, in the heart of the business district, a public/private collaboration among Blake Real Estate, Casey Trees Endowment, and DC Greenworks has yielded the city’s first commercial green roof. At 3,500 square feet, the roof will provide a weather monitoring station for a local news affiliate, a rainwater control area, and, perhaps most importantly, a sliver of nature in the midst of the nation’s capital. Eager to see how a rooftop can provide an urban oasis, AIArchitect arranged a tour with Barbara Deutsch, senior director, programs and research for Casey Trees, and Kelliann Whitley, property manager for Blake Real Estate.

Whitley said that when they began the project about two years ago, few people connected with the real estate company even knew what a green roof was. Now, the company is fully behind the concept and plans to implement green roofs on its other buildings as their roof decks need to be replaced. And why not? Apart from the inherent public air and water quality benefits and the private financial benefits, Blake has received significant attention from companies pursuing LEED™ certification that have embraced the project as an exemplar of best management practice.

Not your father’s roof garden
Our guides explained that a green roof and a roof garden are very different. Whereas a roof garden, like the one atop Rockefeller Center in New York City, typically has about six inches of soil and may include non-indigenous flowering plants, grasses, and trees, a green roof consists of low-maintenance plants that require little soil and no watering. This particular green roof boasts 9,730 plants made up of 11 species of sedums—ground-covering succulents that can withstand dramatic temperature variations—native to Alpine conditions.

DC Greenworks, a design-build firm, raised $60,000 for the project and served as the general contractor. They also coordinated a team of young adults from Covenant House, a national nonprofit agency that serves at-risk youth, who hand-planted the sedums. The building’s concrete roof deck was covered with a waterproof membrane, an electronic leak detection system, polystyrene insulation, geotextile filter fabric, root barrier/drainage course, three inches of engineered soil, and, finally, the sedums. A biodegradable jute covering holds the plants in place until they are fully established—a period of one to two years. Casey Trees will provide volunteers to monitor the green roof, an important part of the research and demonstration project. The Chesapeake Bay Small Watershed Grand Program—administered by the National Fish and Wildlife Foundation and the Watershed Protection Division of the D.C. Department of Health—is providing additional financial support.

Going green to save some green
DC Greenworks Executive Director Dawn Gifford said many clients and architects are interested in incorporating green roofs into their buildings but shy away from the process once they are presented with cost estimates. But, she said, the estimates are often needlessly high because they result from an “overdesigned” program. The plans, she said, often stem from architects and engineers relying on specifications for “intensive green roofs” that are too much for the project and budget. That’s why it’s important not only to have the architectural and engineering component, she said, but to have a partner with horticultural expertise to parse out the specifications for soil and plant requirements.

Built in the late 1960s, 1425 K Street was re-roofed a couple of years ago and should not have needed a new roof for at least another 10–15 years, Whitley said. So what made Blake invest in a green roof? Initially, the push was made by tenant Casey Trees, a local nonprofit whose mission is to restore, enhance, and protect the tree canopy of Washington, D.C. Not surprisingly, Blake—a family-run company with 11 buildings—was skeptical. According to Whitley, this Class A building is the “jewel in Blake’s real estate crown.” So, like any good client, they asked a number of questions and exhaustively researched the project and process.

What Blake discovered surprised them: Green roofs last two to five times longer than traditional roofs, require less maintenance, save energy by regulating temperature variations, reduce sound pollution, lower storm-water utility fees, receive energy tax credits, and increase property values. And, in this case, it provides tenants access to private green space, a psychological benefit that’s sure to contribute to tenant satisfaction and an increase in occupancy rates. Echoing Gifford’s admonition to involve a green consultant at the project outset, Whitley advised, “Do your homework and keep it simple.”

Personal observations
But what impressed us most about the green roof is that people actually use it; they were coming and going throughout our one-hour rooftop tour. (Granted, many of them were smokers in search of refuge, but it has the potential to become a place of quiet solitude.) As the plants grow in, they will absorb not only air pollution but also noise pollution, lessening the din of the city below. And the vision of the potential collaborative is beautiful: a city filled with visually pleasing green roofs that collectively will lessen sewage pollution by reducing storm-water runoff as much as 56 percent, create healthier air in a region that suffers from poor air quality throughout the summer, and reduce heat islands. Green-roofed buildings have the potential of reducing rooftop ambient temperatures from 155 degrees to 86 degrees. Eighty-six degrees in Washington, D.C. in August—now that’s an oasis!

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