Chicago’s Center for Green Technology was the first municipal building in the country to be awarded the prestigious LEED Platinum rating and in 2007 the city was ranked the #1 Green City based on amount of LEED certified buildings (27 in total) by Business Facilities magazine.
Over the years, Mayor Daley's plan to turn his hometown into the "greenest city in America" has turned into a revitalization program mimicked in cities throughout the country. This progressive approach on urban planning has provided an effective response to the rapidly changing expectations that business executives and residents have for cities.
The Daley administration has planted 500,000 trees, built the most energy-efficient and environmentally sensitive municipal buildings in the country, has agreed to provide developers with a more efficient permit process if they construct green buildings, instituted a $600-million-a-year program to repair neighborhoods and city parks, promised to obtain 20 percent of the electricity used by the city from clean and renewable sources and converted hundreds of abandoned and contaminated properties into new businesses.
In fact, Chicago’s City Hall building features a rooftop garden. City Hall (an 11-story office building in Chicago's Loop) along with the adjacent Cook County building appear to most people as one building spanning a city block bounded by LaSalle, Randolph, Clark and Washington streets. First planted in 2000, the City Hall rooftop garden was conceived as a demonstration project - part of the City's Urban Heat Island Initiative - to test the benefits of green roofs and how they affect temperature and air quality. The garden consists of 20,000 plants of more than 100 species, including shrubs, vines and two trees. The plants were selected for their ability to thrive in the conditions on the roof, which is exposed to the sun and can be windy and arid. Most are prairie plants native to the Chicago region.
Like all green roofs, the City Hall rooftop garden improves air quality, conserves energy, reduces storm water runoff and helps lessen the urban heat island effect. The garden's plants reflect heat, provide shade and help cool the surrounding air. The water draws heat as it evaporates, cooling the air in the process. Plants also filter the air, which improves air quality by using excess carbon dioxide to produce oxygen. The rooftop garden mitigates the urban heat island effect by replacing what was a black tar roof with green plants. The garden absorbs less heat from the sun than the tar roof, keeping City Hall cooler in summer and requiring less energy for air conditioning. The garden also absorbs and uses rain water. It can retain 75% of a one inch rainfall before storm water runs into sewers.