As I have mentioned in previous posts, the benefits of green roofs include reduced utility costs, reduced heat island effect, reduced air pollution, and reduced storm water runoff. In cities close to major bodies of water where storm water runoff is a major concern, green roofs can be used to help mitigate that concern.
In an article in Environmental Health Perspectives, Washington DC was sued to reduce storm water runoff in 2002. As part of the settlement, "...the DC Water and Sewer Authority provided $300,000 for green roof development....Those funds, managed by the nonprofit Chesapeake Bay Foundation, seeded a program of incentive grants that encouraged eight builders to choose green roofs over other traditional devices as their primary stormwater control device (stormwater control plans are required for any new construction or redevelopment of more than 5,000 square feet in the District)."
Clearly, the District takes this issue very seriously. Green roofs are becoming more popular in Washington, DC. Hopefully, more federal buildings will look like Chicago's City Hall.