Chicago’s City Hall has a famous garden on its roof.
In the year 2000, the ballasted, black tar roof was planted as a demonstration project to test how green roofs affect temperature and air quality. Since the building was intended to hold another floor, the structural integrity was already in place. The wells of ten existing unused skylights were reinforced and the parts in between contoured with polystyrene leaving 20,000 square feet of planting area whose depth ranges from 3.5 inches” to 1.5 feet. The remaining 38000 square feet is used for maintenance walkways and mechanicals.
The original design included numerous species of perennial sedums, some shrubs species and two trees. In the years since, the sedums have been replaced with over 230 of mostly native perennial plants and grasses. The result has been a huge draw for wildlife. Fifty five species of birds have been catalogued as well as seven species of dragonfly, six species of bees and numerous butterflies and other insects.
A slice of nature was created at eleven stories high.