'Green' Roofs Sprout Up All Over

Growing Plants on Buildings Said to Offer Environmental Benefits

Roof of Portland's Multnomah County Building

Portland's Multnomah County Building features an eco-roof completed in the summer of 2003. Ketzel Levine, NPR hide caption

itoggle caption Ketzel Levine, NPR
A green roof in Portland, Ore.

This eco-roof -- with views of downtown Portland, Ore. -- sits atop a high-rise affordable housing project. Ketzel Levine, NPR hide caption

itoggle caption Ketzel Levine, NPR

It all started in ancient Mesopotamia. That's how old the idea of a "green" roofs is. From the Ziggurat of Nanna to the fabled hanging gardens of Babylon, humans have been growing plants on roofs. Turf and sod have topped an array of human dwellings — but the emergence of a bona fide green roof industry is fairly recent.

Here in the United States, that industry is just a few years old. But green roofs are being touted as the answer to a number of environmental problems — and they're showing up all over the country. NPR's Ketzel Levine reports.

Commercial green roofs are not roof gardens; many of them can't take foot traffic. Instead, they're like green skins, layers of vegetative matter that grow directly on rooftops. They are far less romantic than they sound.

Green roofs are tools for dealing with stormwater runoff and reducing urban heat islands. Other industry claims include their ability to reduce energy use by insulating buildings from extreme temperatures. The scientific data to support these and other benefits are still being collected, but based on how they've performed — for decades — in Germany and the Netherlands, green-roof specialists are confident in their curative powers.

A growing number of architects, engineers, urban ecologists and city planners agree. Increasingly high-profile green roof projects have been built in the United States in the last five years. Among the best-known green roofs are the ones atop Chicago's City Hall and a Ford Motor Co. facility in Dearborn, Mich. Some of the newer roofs making the news include a residential high-rise in New York City, a prairie-covered library in Evansville, Ind., and the top of the Multnomah County Building in Portland, Ore.

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