Will green roofs be the next hot trend?
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Before establishing a green roof, consumers need to have some sense of what they want from it beyond the vague notion that they're good for the environment.

"Everything from roof materials to plant varieties has to be picked for the issue you want to address -- storm-water retention, more green space or thermal control," says Retzlaff. "Every green roof provides some of each of these things, but to decide you want a green roof because it's a good thing is not enough."

Benefits of lofty gardens
For example, Retzlaff cites a green roof in St. Louis on the seventh floor of a children's hospital that has a pond and large walkways.

"It costs $200,000 a year to maintain," he says. "But the benefit is that when those children go through those double-glass doors leading to the green roof, they can forget everything inside."

Retzlaff says Ford Motor Co. has a 10-acre extensive green roof in Dearborn, Mich., that remains the largest in the U.S. "It has a 2-inch depth, so they have to irrigate it. They catch storm water in retention ponds and irrigate with that."

In Chicago, the mayor is interested in lowering the urban center's heat-island effects that drive up temperatures. "He has been told by various research facilities that if about 65 percent of downtown buildings had green roofs, that would lower the heat by about 10 degrees," says Retzlaff. "So the city issues grants to offset the costs of installation and will fast-track building permits if a green roof is included."

Retzlaff expects G.R.E.E.N. to become a resource for would-be green-roofers around the country. "Eventually people will be able to contact us to find out exactly what growing medium and plants are best for their climate and purpose."

BuildingGreen's Roberts says he sees more incentives -- and so more green roofs -- for commercial buildings than homes right now, but there are several benefits that could make them appealing to homeowners. They include increased insulation and the fact that the additional garden materials make a roof more durable.

"For homeowners, a green roof on a low slope or flat roof can extend the life of that roof many years by shielding it from rain water and ultraviolet sun rays, which degrade roofing materials," says Roberts.

Green roofs also filter out some air pollutants, he adds.

Green roof solutions
In addition to collecting storm water, reducing urban heat and acting as insulation to cool down a building or home's occupants, green roofs are seen by advocates as opportunities to increase food production, beautify cities and provide sound insulation by absorbing, reflecting or deflecting noise by machinery, planes and traffic.

For the average homeowner concerned with rising energy costs, it's likely the insulation qualities of green roofs would prove most appealing.

Dennis Yanez, national marketing manager for Chicago's American Hydrotech, says his company offers waterproofing and all the components for garden-roof assembly, including Styrofoam, soil and plants. American Hydrotech also offers a single-source warranty, which Yanez says is unique in the industry. Clients are primarily architects and developers.

"We have not done a lot in the consumer market," Yanez says. "We do have some homes that have our systems in them, but they're all higher-end, in the 7,000- to 10,000-square-foot range."

That's because a homeowner who wants a green roof, Yanez says, would have to start by hiring an engineer or architect to design it. He estimates the price of building a green roof from "the high teens to the low $20s" per square foot.

Greenroofs.com estimates costs at $9 to $25 per square foot for extensive green roofs and $25 to $40 or more for the intensive variety.

"We've seen they have a growing appeal," Yanez says. "In general, sustainability and green building has taken off in the past five or six years. Putting together buildings that disrupt the environment as little as possible is becoming a real concern."