Green Roofs

A growing trend, green roofs consist of a thin layer of plants covering roofs of buildings are "designed to reduce air pollution, control heating and cooling costs, and absorb storm runoff". Also from the International Herald Tribune:

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.

Results of studies in Chicago are positive, showing a reduction in July 2003 roof temperatures by 19 - 31%. The city continues to grow the initiative by offering benefits to buildings with green roofs as well as placing requirements on new construction. Chicago now estimates approximately 2 million square feet of green roofs. In New York, however, where the implementation is just getting underway, has only about 60,000 square feet of green roofs.

The biggest benefit of this trend results when there are many green roofs in one area, it changes the "micro climate of the area and reduces demand of energy".  The trend is also popular in Canada and Europe.

International Herald Tribune: "’Green’ roofs sprouting across US skylines"

Green Roofs for Healthy Cities

City of Chicago Green Roof Info