Article reprinted from Western Roofing magazine July/August 2007.

Green Roofs

Urban Center Follows its Own Advice

by Robert Kravitz, AlturaSolutions Communications

According to the Center for Urban Ecology (CUE), 52% of Washington, D.C., is covered with impervious surfaces such as roads, buildings, parking lots, and sidewalks. This amount of imperviousness can cause serious problems for watersheds, the land area that drains water into a river system or other bodies of water.

In order to protect these watersheds from the pressures of increased development, CUE recommends to city planners the installation of Green roofs. After meetings with experts from the U.S. Environmental Protection Agency and the National Park Service, CUE took its own advice and installed a 7,000-square-foot green roof atop its headquarters in Washington. And the green roof system they selected? The modular system developed and manufactured by GreenGrid® Green roofs.

With the GreenGrid system, modules composed of 60% postindustrial, recycled plastic are preplanted with growth and plant media. The modules come in three sizes: 2 1/2” depth, 4” depth, and 8” depth.

But, the weight of the green roof was a big concern. CUE was unsure if the existing roof could support the added weight of a green roof. But this turned out to be one reason they liked the GreenGrid modular system.

A built-in-place system, the alternative to the modular GreenGrid system, can weigh as much as 45 pounds per square foot at an 8” depth. Compare this to the 8” module, which weighs only 28 pounds per square foot fully saturated.

“A green roof is easier realized than commonly believed… and structural upgrades [due to the weight] are not always necessary,” writes a CUE spokesperson. “The design simplicity [of this green roof system] and their benefits offer great potential for many rooftops in U.S. cities.” •••