Chicago is known for its large number of green roofs downtown. The city claims that it has more green roofs than any other city in the United States. Millennium Park is said to be the world’s largest green roof as it sits on the top floor of an expansive parking structure. Green roofs are an important aspect to sustainability as they offset the urban heat island effect, a phenomenon caused by a higher density of impermeable surfaces, such as in a highly developed area. It is characterized by unusually higher temperatures than the surrounding area. According to the National Geographic Society, these Urban Heat Islands are subsequently plagued with lower air and water qualities. The City of Chicago has passed policy to curb urban development to encourage green roofs; such as tax incentives, the Chicago Green Homes Certifications, and the Chicago Green Program with the city’s “green permits.”
Also, to lead by example, the city has also installed a green roof on city hall so that the city can lead by example. It is also one of the larger green roofs in a major American city’s central business district. Green roofs help level the ratio of green space to cement and concrete which helps absorb heat instead of insulating or reflecting it. If green roofs are utilized far more than asphalt roofs, then a true remediation and possibly even solution to the urban heat island effect might be possible. According to Birch et al. in the Penn Institute for Urban Research, “developing or refining supportive public policy and programs give cities and regions clear guidance and tools relating to national sustainable development priorities.” Since the passing of the ordinance and the city’s Climate Action Plan, green roofs in the city have gone up, making Chicago number one in green roofs.