Green Roofs Help to Curb Polluted Runoff, Especially If Space is Limited

Though more costly than other remedies, vegetation atop buildings can meet stormwater requirements in developed areas.

When Rick Seavey first told municipal officials in Lancaster, PA, that he planned to install a green roof, they thought he was talking about paint color.

That was a decade ago, before affixing water-absorbing membranes and plants to the tops of buildings became a popular solution for businesses looking to absorb stormwater runoff from new construction. And the 16,000-square-foot green roof Seavey planned to build as CEO of the National Novelty Brush Co. would be the first for the South Central Pennsylvania city and the surrounding county of the same name.

Like many cities and counties in the Chesapeake Bay watershed, Lancaster city had adopted stormwater management regulations that required developers to offset the stormwater runoff that new buildings would generate. Most developers met their requirements through less expensive features, such as stormwater retention ponds.

But Seavey wanted to keep his family’s business in downtown Lancaster, where there wasn’t room for a retention pond near the new building. He decided that a green roof, though more expensive to install, would be the best option to satisfy the requirements and benefit the Bay — even if no one nearby was doing it.

“The closest firm that knew how to build one was in Boston,” Seavey said. “Architects had to come in from Philadelphia and Boston to help me.”

A decade later, green roofs like Seavey’s are emerging as a timely tool for urban areas looking to absorb their stormwater runoff, which is still the fastest growing source of water pollution in the Bay watershed.

Green roofs were the focus of the 14th annual CitiesAlive conference that took place in November 2016 in Washington, DC, where the nation’s capital was highlighted as a leader in green roof implementation to an international audience of 500. The city has installed more square feet of green roofs than any other in North America for each of the last five years.

Since 2014, the District's stormwater regulations have required new developments to retain the first 1.2 inches of rain that falls in a storm. In a city already crowded with concrete — and prevented from growing skyward by building height restrictions — experts say green roofs are often the best option to absorb water with limited space.

“If you’re a downtown developer, you basically have to do a green roof on your lot to capture rainfall there,” said Jeffrey Seltzer, associate director of the District Department of Energy & Environment’s stormwater management division.

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