A 'Green Roof' Movement to Counter Pollution

Rain runoff from roofs of buildings across the United States adds to the pollution of lakes and streams and can overburden sewage systems and storm drains. But more of those roofs are turning "green." There's a push under way to grow plants on the tops of buildings to capture rainwater and air pollutants.

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ALEX CHADWICK, host:

This is DAY TO DAY.

Flying into many cities you see a green blanket of treetops giving way to miles of black roofs. When it rains those hard roof surfaces spills huge volumes of storm water runoff and that leads to flooding and that overwhelms drainage systems and the result, raw sewage flows into lakes, streams, bays, yuck.

But now some of those roofs are going green.

NPR's Chris Arnold reports.

CHRIS ARNOLD reporting:

A green roof is a roof that has grasses or plants all over it and the idea is not new. People have used turf roofs on their dwellings for more than a thousand years, back in ancient Mesopotamia it's believed that King Nebuchadnezzar built the elaborate hanging gardens of Babylon on the rooftops of his castle.

Most roofs these days, though, are what green roof advocates call tar deserts, forgotten wastelands above our heads. But there's a growing push to change that.

Mr. BRIAN GLASSCOCK (Director Environmental Services, Boston): Every bit of green space helps the city. Every bit of hardscape we can convert back to some sort of, you know, living, breathing plant helps offset the environmental footprint of development in the city.

ARNOLD: Bryan Glasscock is the head of environmental services for the city of Boston. Glasscock's standing on the roof of a one-story parking garage for hotel on the Boston waterfront. It's not exactly the hanging gardens of Babylon, but he's surrounded by little shrubs and mulch and some garden footpaths.

Mr. GLASSCOCK: We're actually standing on the roof and it's sort of the illusion of being on the ground plain because its landscaped area, I mean there's, you know, semi-mature trees up here and its green space where none existed before.

ARNOLD: When it rains, the plants and soil here soak up a lot of water and keep it out of the sewer and storm water system. Green roofs also insulate the buildings that they cover saving money on heating and air-conditioning.

Green roofs like this have been getting more popular in Europe for years and more are starting to be built in the U.S.

Mr. STEVEN PECK (Founder and President, Green Roofs for Healthy Cities): I wouldn't be surprised if we had a growth rate next year of 125, 140 percent.

ARNOLD: Steven Peck is the founder of the non-profit Green Roofs for Healthy Cities and he says the square footage of green roofs across the U.S. nearly doubled between 2004 and 2005.

Still they're pretty rare in this country. In Europe they've become more common with some cities even mandating them for new development, but short of that to green any significant number of American rooftops…

Ms. KATRIN SCHOLZ-BARTH: You'd have to bring the price down and if you can't bring it down to less than a dollar a square foot, we may as well just go home.

ARNOLD: Katrin Scholz-Barth is standing on a crowded convention floor at a green roof conference in Boston. Scores of companies are selling membranes, soils and irrigation systems, but Scholz-Barth who teaches a class on green roofs at Harvard's Graduate School of Design says these complex green roof systems are expensive from $8.00 to $20.00 a square foot, so she and her students are trying a new approach, just scattering a tough kind of succulent plant over flat, gravel covered roofs.

They want to see if you can cheaply seed the rooftops of all kinds of buildings, malls, apartment buildings, warehouses.

Ms. SCHOLZ-BARTH: If you're in any urban area you see those gravel roofs everywhere, miles and square miles of it. It could be green. Most of our cities that are suitable for it, for the application.

ARNOLD: Scholz-Barth says her cheap green roofs might cost about a dollar a square foot, at that price, she says converting roofs to green roofs might save big companies money on energy, storm water management costs, and even maintenance since they could make the roofs last longer.

Chris Arnold, NPR News, Boston.

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