NEW GREEN-ROOF TAX INCENTIVES

Martin Meltzer thinks they can. Spurred by the prospect of the tax abatement, Meltzer, a retired physician and the president of the co-op at 395 Riverside Drive, and his seven-member board have given the go-ahead to a committee to obtain cost estimates for a green roof. It would sit atop their 116-unit Manhattan cooperative at 112th Street and cover roughly 6,500 square feet.

According to Dr. Paul S. Mankiewicz, the executive director of the Gaia Institute and a board member of the New York City Soil and Water Conservation District, that's enough to make an ecological impact. "Each 10,000 square-foot green roof can capture between 6,000 and 12,000 gallons of water in each storm event," he says. "This is rainfall that will never enter the combined sewer [system]. At the same time, the evaporation of this rainfall will produce enough heat removal to noticeably cool ten acres of the city."

What else can a green roof do? Advocates says it reduces smog; provides better building energy efficiency by reducing cooling and heating loads, thereby saving fuel and electricity; captures storm-water runoff that otherwise may overflow sewers and overwhelm wastewater treatment plants; improves air quality, by virtue of the increased plantings; and produces local food and habitat for birds, insects and plants.

No Irrigation Irritation

As environmentally savvy New Yorkers know, there are two types of green roof. The first, the "intensive green roof," or roof garden, generally features trees and other large plants and requires deep soils, intense labor and high maintenance. Its purpose is usually ornamental, but gardening is also possible. The second, the "extensive green roof," is characterized by drought-tolerant vegetation grown on a thin layer of growing medium, and it requires little maintenance and usually no irrigation.

Studies done in Germany in the 1980s showed that grasses will dominate a green roof when the soil is between 10 to 20 centimeters in depth. If the soil layer is less than 10 centimeters (2.5 inches), the genus Sedum and mosses are most successful. Sedum, a hardy succulent with water-storing leaves and five-petalled blossoms, is the extensive green roof plant of choice, and it's what you'll see in most urban installations. Also common are native grasses and another succulent, semper vivus, says Leslie Hoffman, executive director of the Manhattan-based environmental non-profit Earth Pledge.

Rob Crauderueff, policy director for Sustainable South Bronx, says a three-inch layer of gravelly soil topped by plants weighs 30 pounds or less per square foot when dry, information an engineer will have to consider when estimating how much a green roof will weigh. Sustainable South Bronx has a green roof installation team that provides estimates and consultations.

Hoffman reports "many calls" about green roofs from co-op and condo board members, asking for presentations and advice. "They're interested to know, can my building support a green roof and what will it cost?" she says. Hoffman advises them that "your first step is to get a structural engineer to tell you what your potential roof load is." She says most buildings will be able to take "at least a thin-profile green roof that weighs 15 to 20 pounds per square foot." And the tax abatement can be "enough to make the return on the building's investment make sense," she says. "If you start with a $20 per square foot price and you can get $4.50 a square foot back, that's a substantial benefit...."

Alexandra Woods, a psychoanalyst and co-op owner, chairs the committee investigating a green roof at 395 Riverside Drive. She went with Meltzer to an August 20 presentation about green roofs and stormwater management hosted by the Hafele Showroom in Manhattan and presented by Green Home NYC in association with nonprofit environmental groups. She left inspired and energetic about the project and ready to begin contacting engineering firms for a roof-load estimate come September.

"We're just getting started," she says. "More and more people have been talking about green roofs in the neighborhood." She notes that 395 Riverside has just installed a new roof to halt leaks, which makes the decision to consider the green roof "quite gutsy." Woods believes a green roof will ultimately raise the value of the property. She anticipates future buyers who are environmentally aware will factor it into their decision to buy.