The City of Chicago's City Hall Rooftop Garden project was conceived as a pilot project - part of the city's Urban Heat Island Initiative - to test the benefits of green roofs and their potential to mitigate the urban heat island effect. The garden consists of 20,000 plants of more than 100 species, including shrubs, vines and two trees. The results are quite promising. In terms of direct cooling savings from the green roof, it is estimated that the project avoided energy costs of US$3600 /year, amounting to a savings of 9272 kWh/year.

Construction of the rooftop garden began in 2000 and the first flowering species were observed in the garden in early April 2001. City Hall's 38,800 square foot roof was outfitted with a 20,300 square foot garden consisting of 20,000 plants and more than 150 varities. The species chosen for the rooftop garden were specifically selected for their hardiness and suitability in light of the arid, windy and harsh conditions that consistently afflict the area. Like all green roofs, the City Hall rooftop garden improves air quality, conserves energy, reduces stormwater runoff and helps lessen the effects of the urban heat island.

The municipal population will benefit both directly and indirectly from the rooftop garden atop City Hall. The 2.8 million inhabitants of the city have access to visit and learn about the garden as well benefit from the environmental improvements the garden offers (improved air quality, reduced smog, decrease in sewer overflows). Additionally, individual residents and small business owners can take advantage of the city's Green Roof Grants project, thus benefitting financially from the city's green roof incentives program.

Individuals: Since the development of the pilot project, the City has launched the Green Roof Grants Program. The mission of the initiative is to utilize, develop and expand upon 'green' technologies that will mitigate the urban heat island effect, beautify Chicago and educate the public. The goal of the program is to provide an opportunity for Chicagoans to reduce urban air temperatures, lower electricity usage, reduce air pollution, and increase green space. Specifically, the initiative will include projects such as installing green roofs, painting or installing light coloured roofs and breaking up asphalt parking lots through the use of plants and alternative planting. In 2006, forty residential and small commercial green roof project were selected to receive grants. Grants up to $5,000 per project were awarded and details of the selected projects will be available to the public once the projects are completed. Society:The City of Chicago is quick to point out to citizens that Green Roofs reduce the effect of cities overheating in the summer thus reducing Chicago's pollution levels and decreasing energy consumption. Another key benefit is that green roofs add beauty to the urban landscape and help improve air quality. The notiriety of the City Hall green roof in Chicago has made the city a draw for individuals looking to implement green roofs; this has increased the fame and presitge of the City.Economy:The results from the City Hall Rooftop Garden Pilot Project are promising. In terms of direct cooling savings from the gree roof, City hall is already reaping the economic benefits of its green roof; it saves the City almost $10,000 annually in energy costs, amounting to a savings of 9,272 kWh/year. During summer and winter months, the roof exhibits superior insulation properites, requiring as much as 30% less from City Hall's heating and air conditioning systems over the last four years. This is apparent from a temperature reading when there was a 50 degreeF difference in temprature between the green roof on City hall the adjacent black roof on the County building.Environment:In addition to the savings of 9,272 kWh/year saved, the green roof also absorbs as much as 75% of the rainwater that falls on it, reducing the load on the city?s sewer system. And, in addition, there are indirect energy savings available from an increase in the cover of green roofs throughout the city as well as an improvement in air quality. Due to their cumulative effects, green roofs have the potential to reduce the ambient air temperature and thus the need for energy.

Indirect Energy Savings from a Green RoofIndirect savings are due to the cumulative effect of additional green roofs throughout the city and their effects on ambient outdoor temperature and humidity at City Hall. If rooftop gardens eventually cover a significant portion of the urban landscape, reduced air temperatures would be expected in the area immediately above and downstream of the green roof.Air Quality BenefitsThrough a citywide program of green roofs and "greening" of other areas throughout the city, there will be expecte measurable improvements in Chicago's air quality by the reduction of ozone and smog.Additionally, the direct benefits of green roofs both for an individual building owner and the City of Chicago community are being used to mainstream further greeing. The primary benefits include reducing storm water runoff. Green roofs hold rain like a sponge - moisture is then dissipated naturally thereby relieving pressure on an already taxed storm sewer system. A reduction in the urban heat island effect is another reason the City is encouraging both the public and private sector to get involved.

Individuals:Through the Green Roof Grants Program, the City of Chicago is utilizing the experience it gained in creating, maintaining and evaluating its green roof to educate citizens and encourage them to make this practice a mainstream way of conserving energy. They are using vast awareness and education campaigns to show that green roofs have a number of benefits, both for individual building owners and the surrounding Chicago community. They are mainstreaming the idea that green roofs not only reduce environmental impact (reduce storm water runoff and the 'urban heat island' effect) but also result in energy savings (from more efficient heating and cooling systems), and create conditions for a longer-lasting roof system. The City now offers a Guide to Rooftop Gardening which provides step-by-step instructions for planning a rooftop garden.Society:The greening and beautification of much of Chicago?s public realm is in itself leading to the mainstreaming of this form of energy efficiency. The City of Chicago has issued green roof guidelines, which shows that the technology is becoming more popular and mainstream. Chicago, and from their example, many other cities are realizing that not only can they save money while reducing their impact on the environment, but also they instead of investing in expensive sewer infrastructure underground, can require new developments to have green roofs, whose beneficial water retention systems help reduce storm runoff, cutting down on sewer overflow into rivers and streams. Economy:By investing US$1.5 million in building the City Hall green roof and subsequently investing $300,000 in grants to mainstream the building of green roofs, the City of Chicago is providing economic incentives to mainstream energy efficiency. The grants are helping residential and/or small commercial (less than 10,000 square feet) building owners with a green roof project. Environment:The City of Chicago has been working to mainstream the environmental benefits of green roofs through City Hall's green roof but also through several other key initiatives including:the Chicago Energy Conservation Code - passed in 2001, the City Council passed the Chicago Energy Conservation Code, an amendment to the Chicago Building Code that consolidated disparate code requirements to formulate a modern energy-efficiency standard; andthe Chicago Energy Plan - an energy strategy first created in 2001, to ensure clean, affordable and reliable energy for the city?s future.

Following the success of this project, the City of Chicago has instituted various programs to increase the presence of green roofs in the city and provide incentives for their construction. As a result, the City of Chicago now boasts more than 80 municipal and private green roofs in the city and has a significant number more planned.

Because city hall's green roof has proven so successful, Chicago is leading by example and is leveraging similar roofs in many other cities around the world, including: Portland, Minneapolis, New York, Seattle, Toronto, Boston and, Vancouver.  By so succesfully implementing their City Hall green roof, Chicago is not only ensuring that green roofs continue to be built within its city boundaries but also in cities around the world