As temperatures soared and New York City broke records for electricity use at the end of July, landscapers were installing a "green" roof at Silvercup Studios in Long Island City, Queens, where the television series "The Sopranos" is filmed.

Sitting above Tony Soprano's head will be New York City's largest green roof, a thin layer of plants covering 35,000 square feet, or 3,300 square meters, designed to reduce air pollution, control heating and cooling costs, and absorb storm runoff. Getting this particular roof in place has taken more than two years, but its proponents are hoping to use data collected from the installation to persuade New York City's commercial property owners and developers that not only are green roofs good for the urban environment, but they also can benefit the bottom line.

While studies in Chicago and in cities in Canada and Europe have demonstrated the environmental benefits of green roofs, green roof proponents know they need hard numbers to convince New York's development community of the economic benefits. The highly visible location in New York, near the large Silvercup Studios' sign and visible from the Queensboro Bridge linking Queens to Manhattan, will be the green roof's best advertisement.

A matrix of 1,500 planters will have 20 species of plants intended to display red, yellow and green when they are in full bloom. Not to be confused with a roof garden, however, a green roof is less an aesthetic amenity than a workhorse. The carefully selected plants and soil engineered to weigh a fifth as much as typical dirt help clean the air and absorb rain that would otherwise become runoff. When many of them are clustered together, green roofs can reduce the urban heat effect. Densely populated cities tend to be hotter than surrounding areas because of the heat-trapping properties of tall buildings, asphalt and concrete.