Building constructed: 1911
Roof type: Semi-intensive, test/research
Size: 20,300 square feet
Year installed: 2001
The green roof on the Chicago City Hall building was installed as part of a Environmental Protection Agency study and initiative to reduce the urban heat island effect in the city and improve air quality. The one-block wide, twelve-story building had a substantial roof area that was ideal for planting and data collection. The green roof only covers the City Hall half of the City Hall-County Building, allowing for comparative testing of the green roof and traditional roof.
As a semi-intensive green roof, a combination of 20,000 herbaceous plants, 112 shrubs, and 2 trees were planted. The growing medium varied from a depth of 3 inches for the extensive plantings to 24 inches for the intensive plantings, and the semi-intensive areas averaged 8 inches in depth.
Source: U.S. Department of the Interior, National Park Service