You are here

The Interior Building in Washington, D.C. Gets a "Green Roof"

Green roof atop Chicago City Hall

This green roof is atop the Chicago City Hall; it covers 38,000 square feet. Photo courtesy of Roofscapes, Inc.

The National Park Service's parent agency, the U. S. Department of the Interior, recently completed a project with both literal and symbolic "green" benefits. Earlier this week, Secretary of the Interior Dirk Kempthorne announced completion of a "green roof" on the 3rd wing of the Main Interior Building in Washington, D.C.

Green roof technology has been growing rapidly, especially in other parts of the world. An estimated 10% of all flat roofs in Germany are now "green," and the technique is catching on in the U.S. In case you aren't familiar with this approach, it involves a lot more than the color of the roof.

There are different types of green roofs, but all involve these basic elements: a waterproof membrane, soil (or another growing medium) and a variety of living plants that grow in the soil on top of the roof.

"What more suitable place for a green roof than the headquarters of America's conservation department in Washington, D.C.?" Secretary Kempthorne asked. With more than half of Washington, D.C. covered with paved or constructed surfaces that do not allow water to infiltrate the ground, 75 percent of rainfall becomes runoff." The vegetation and soil on the green roof will absorb rainwater and curb runoff.

Washington, D.C. has a huge problem from storm runoff and sewer overflows. Each year in Washington, approximately 1–2 billion gallons of raw sewage are discharged into the Potomac River, Anacostia River and Rock Creek—all tributaries to the fragile Chesapeake Bay Watershed.

The green roof at the Main Interior Building will help alleviate this problem and provide other benefits as well:

• Improve water quality by neutralizing acid rain effects and filtering pollution from rainwater.
• Hold up to .7 inches of rain to reduce stormwater runoff entering the sewage system and reduce streambank erosion.
• Shield the roof from the sun's direct rays, which extends the roof's life span, insulates the building during the summer and saves energy as well as mitigates urban "heat island" effects.
• Improve air quality by filtering the air that moves across the plants and, through photosynthesis, convert carbon dioxide into oxygen.
• Provide habitat for songbirds and pollinators.
• Reduce noise transfer from the outdoors.
• Provide a visually attractive sight for employees and visitors.

Are these benefits just feel-good hype? Not according to several studies, including one by the American Society of Landscape Architects. That group put a green roof on their headquarters in the nation's capital in 2006, and decided to gather some hard data over a year's time. Among their findings: the roof retained nearly 75 percent of all precipitation that fell on it, lowered the air temperature by as much as 32 degrees and saved about 10 percent on energy costs.

The project at the Interior Building started more than seven years ago when Mike Cyr, National Business Center's Chief of the Division of Facilities Management Services, read an article on the benefits of green roofs in Europe. Although such roofs were not commonplace at the time, Cyr's group decided to explore possibilities for installing a green roof on the Main Interior Building.

Other agencies in the Washington, D.C. have also adopted the concept, including 68,000 square feet of planted roof at the Department of Transportation's new headquarters and a 104,000 square-foot green roof on the Census Bureau's headquarters complex in Suitland, Md.

Even the Bureau of Alcohol, Tobacco, Firearms and Explosives—not an agency that immediately leaps to mind if you're looking for environmentalists—has gotten on board at its headquarters.

Will some criticize this project as a fad and waste of tax dollars? You can count on it, but it's appropriate for Interior and other agencies charged with good environmental stewardship to set the example in energy conservation, clean water and similar issues. This project at Interior's headquarters in Washington confirms that there are dedicated employees in the agency who are willing to break out of the "business as usual" rut and try new approaches to solving long-standing problems.

This is a small step in the right direction.


Nice article Jim.

Rob Mutch
Executive Director,
Crater Lake Institute

Drip, drip, drip...roof will eventually leak costing taxpayers $$$$ for this nonsense.

Don't all roofs eventually leak?

Walks like a duck, quacks like a duck ... and most likely is a fad.

Eric "Griz" Grunwald offers the rejoinder:

Don't all roofs eventually leak?

Yes, true enough, but the impervious layer that needs fixed isn't covered by a layer of soil, preventing inspection & access.

Although it is easy enough to apply a layer of dirt to a roof using efficient heavy equipment, it is going to be very tricky (expensive) to remove it in order to fix a leak, without ripping the membrane beneath and causing a lot more leaks.

Have you never tried to figure out just where a compromised roof is actually leaking, Griz?

And when is it that we normally find out that a roof is leaking and needs attention? Why, normally at the beginning of the rainy season, of course, and the green roof is now saturated, and the weather will be bad for several months. Oh boy.

The #1 ecological drawback of this idea, is that the living roofs will have to be watered during dry weather, if they are not to die ... and then watered again and again and again ... much more frequently than the suburban lawns we criticize for gobbling up water.

Water is fast emerging as the leading environmental limitation being encounter by especially urban culture. Does Germany have an excess of water? How about California? Maybe they can take control of the Columbia River and canal it down to LA...

Did we forget that dirt is heavy, and the building will have to be built more strongly than with a lighter roof, heavier, more-massive, and use more resources, emit more CO[sup]2[/sup] in added concrete & steel to supply the strength to support the dirt on the roof?

Green? Good grief.

LOL. You expounded upon this nonsense much better than I did, Ted!
Another example of "green" idiocy!
When are many enviros gonna realize there is no free lunch?

Speaking of fads, I realize it's en vogue to ridicule any attempt to steer the status quo toward more environmentally friendly practices, but the unfortunate facts are that green roof technology is constantly improving, learning from its mistakes, and showing some real benefits.

Many green roofs these days are using easily removable trays that can be laid out in a grid, allowing easy access to the actual roof in case of a problem. One of the originators and suppliers of the trays is here in Michigan, actually.

The trays in particular, and many roofs in general, are using plants adapted to harsh and semi-arid conditions. Sedum has been the plant of choice in many areas and is proving to need very little if any watering, even in areas like Portland, Oregon with significant hot and dry periods.

Yes, it takes a strong structure to support the weight of a green roof, but even in Pittsburgh, where many of the buildings are from the age of "build 'em quick and cheap" they're finding many of them well-suited to green roofs. It doesn't require a radical change in structure or materials to allow a roof to grow some Sedum.

Back to Portland, again, they've had lepidopterists up on their roofs studying butterflies because the roofs are proving to be oases of insect diversity in easily accessible (to people) urban environments. Entomologists are doing field work up the steps from their office. This has the potential to reduce habitat fracturing and provide opportunities for study of island effect in insect populations.

Finally, while it hasn't been quantified, there's psychological benefit to humans. Folks that are cynical about every attempt to beautify and "green" the urban landscape probably wouldn't enjoy it, but to many folks, being able to take a lunchtime stroll among some greenery, flowers, birds, and butterflies is an antidote for urban malaise and stimulant to a buried or repressed biophilia (ala Ed Wilson).

Forgive me for not being sour on green roofs, but I've met the people studying and producing these things. They aren't enviro-wackos and are far from Pollyanas about the problems.

-Kirby.....Lansing, MI

Thanks, Kirby, for pointing out that the people designing, building, and maintaining green roofs are not idiots, and should not be expected to ignore the obvious. Criticism of green roofs is typically rooted in a very shallow appreciation for human ingenuity and ability to learn from experience. Green roofs are here to stay, and thank goodness for that. Energy savings notwithstanding, building green roofs can help alleviate urban heat island effects and improve the viewscape.

I just don't understand why some people can be so pessimistic about positive environmental actions. Of course, these projects may not be as perfect as they should be but it should always be considered as a first step towards our ultimate goal. This project may be flawed for some, but that doesn't mean the people behind it are not doing something to improve it.

Add comment


This question is for testing whether or not you are a human visitor and to prevent automated spam submissions.

National Parks Traveler's Essential Park Guide