NEW YORK — An architectural organization unveiled a new "green" roof for its own building Wednesday to showcase a trend toward environmentally-friendly technology.

The leafy rooftop of the American Society of Landscape Architects building in downtown Washington is a model of the techniques used increasingly to cool temperatures, filter air, and lessen the burden on sewers by absorbing rainwater.

Visitors are surrounded on three sides by a variety of plants, and the aluminum grating that serves as a walkway is suspended over more vegetation.

Green roofs, first championed in Germany, have grown in popularity around the world, and experts predict more growth as the practice sprouts as far away as China. In North America, green roof space grew 70 percent last year.

"What you're going to see is a meteoric rise in this industry because it takes serious issues like storm water and offers multiple solutions," said Steven Peck, president of Green Roofs for Healthy Cities, a non-profit industry association.

Germany, which helped launch the trend beginning in the 1950s, now has 50 square miles (32,000 square acres) of green roof space and adds an additional five square miles (13 square kilometers) per year, estimates Christian Werthmann, an assistant professor of landscape architecture at Harvard's Graduate School of Design.

Green roofs began to spread when some German cities encouraged building owners to substitute ballast and tar rooftops with vegetation. Werthmann estimates 40 German municipalities require green roofs in at least some cases.

The United States has only a fraction of the green roof space found in Germany -- but a study this month found U.S. green roof space grew 80 percent last year. North America has a total of 2,150,000 square feet (200,000 square meters), according to the study by Green Roofs for Healthy Cities.

Chicago was the U.S. leader, planting nearly 300,000 square feet (27,900 square meters) of green roof space last year.

Chicago Mayor Richard M. Daley has described green roofs as part of an effort to make his city "the most environmentally friendly" American city. Chicago, which installed a green roof on its City Hall in 2000, has offered developers more regulatory incentives than any other North American city, Peck said.

Steven Holl, a leading U.S. architect based in New York, has designed a number of green roof projects, but says the demand is greatest at his Beijing office.

The Beijing Linked Hybrid project, a self-contained city of linked vertical buildings designed by Holl, includes hundreds of apartments as well as stores and schools, and every roof is green. Storm water collected in rooftops will help feed a self-sustaining water system to protect the buildings against water shortages in Beijing, Holl explained.

"They want it and they're willing to pay for it," Holl said of his Chinese clients.

China launched a nationwide drive last month to make energy-saving buildings that help ease fuel shortages and reduce greenhouse gases. The country has also signed an agreement with the United Nations to promote environmentally friendly practices in staging the 2008 Beijing Olympics.

While some advocates say they would like to see more North American cities implement requirements for green roofs, Werthmann warns that forcing developers could result in half-hearted efforts that do little to help the environment.

"In the states it's all voluntary, so it's a totally different push," Werthmann said.

The ASLA roof cost $946,000 (euro761,400), but the organization says two-thirds of the budget was to make the showcase roof accessible.

"The ASLA roof is only 3,000 square feet and to have people and plants together in that amount of space is unique," Werthmann said, adding that typically only maintenance staff make it onto most green roofs.

Experts say green roof installation can be as cheap as $9 per square foot, and increased property value, energy cost savings and longer life for the roof can offset the investment.

Over the last six months, Peck said he has seen green roof associations spring up in Mexico, New Zealand and Australia. Next month, he is planning to announce a world green infrastructure association that will work with eastern European and developing nations to adopt green roofs.

"Green roofs should be treated as necessary infrastructure for a city," Perk said. "Like sewers and streets."

Source: Associated Press