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N: On the roof of the Calhoun School, Beth Krieger walks among patches of grass, tulip leaves and dark brown earth showing through the sparkly white snow.
TAPE: Sound of snow (Up and fade).
N: This roof is not made of tar or shingles. Instead, it's alive, and growing: 3,000 square feet of space, about the size of a large back yard. It's one of several green roofs throughout New York City. School official Krieger says it's a place everyone can use.
TAPE: Krieger: We use it for light recreation sometimes. Kids can come up here between classes in the spring. Poetry classes come up here sometimes just to have a nice place to sit and talk.
N: High school students here have planted bean plants for biology experiments, while grade schoolers use the roof for geometry projects. They even grow herbs and vegetables for the school lunch. Green roofs are made of several layers of light rocky material and groundcover called sedum, a tough little plant like you might see growing out of a crack in the sidewalk. The layers help insulate the roof. Leslie Hoffman is the director of Earth Pledge, an organization that promotes these ecological roofs in New York.
TAPE: Hoffman: Green roofs are a fairly good insulator, and roofs that are well insulated tend to hold their snow longer than roofs that are losing their heat and melting from underneath.
N: Green roofs are more expensive than conventional roofs. The Calhoun roof cost around $60 a square foot. Hoffman says the cheapest kind would cost around $12 a square foot, but she says the benefits outweigh the costs. They help cool buildings in the summer, and studies show they could reduce overall temperatures in New York by up to 3.6 degrees Fahrenheit. University of Toronto Professor Brad Bass, has studied heat retention of green roofs in winter.
TAPE: Bass: The summer performance is better. With a very, even a lightweight green roof, you can reduce the amount of heat going through the roof to zero. In the winter you always have heat loss through the roof.
N: Bass designed a green roof especially for the wintertime, with a foot of soil and evergreen shrubs to create a canopy, and it decreased the energy used for eating by between 10 and 15%. Other potential benefits of green roofs include improving air quality, increasing property value, and reducing water runoff by absorbing at least half the rainwater that falls on them. A big problem in New York City is that heavy rains overflow the sewer system, polluting our rivers. Gavin Gong is assistant professor of Earth and Environmental Engineering at Columbia University.
TAPE: Gong: If you install a green roof everywhere, what percentage of the landscape are you really capturing and can you really capture enough to make a difference in terms of what percentage of the water gets into the system, the sewer system. You'd have to have an awful lot of green roofs I think!
N: Green roofs exist all over the world, from Japan to Germany. Recently Chicago passed a law to require that all new roofs be either solar, reflective or green by 2008. I'm Zaidee Stavely, Columbia Radio News.