The American Society of Landscape Architects
2002 Professional Merit Award
Visible from many of the surrounding buildings, this green roof is one of the most photographed and publicized green roofs ever. Initiated by Mayor Daley as part of Chicago City Hall Urban Heat Island Initiative project, Roofmeadow provided the engineering expertise to give this roof a good start in life and our licensee in the Chicago area installed this award-winning green roof. The highly recognizable mounds of the City Hall roofscape consist of layers of lightweight insulation topped with a thin, veneer layer of green roof media which sustains the native and non-native plant palette. The plant palette consists of a number of native species including prairie grasses. Sedum is used throughout the roof to stabilize the environment and create better growing conditions for the perennials and grasses.
Roofmeadow was retained to develop the construction documents and install the elegant landscape design prepared by Conservation Design Forum. The installation includes four distinct profiles, based on classic German green roof approaches. In particular, this project involved the first use of dual-media profiles and retention of irrigation water at the bottom of the green roof profile in the United States. The project is irrigated throughout and maintained regularly by crews supervised by horticultural experts from the Chicago Department of Transportation.
The logistics of the installation were particularly complex as the building is at the intersection of one of the city’s busiest intersections. The installing Roofmeadow Network contractor used a crane to load the materials up to the roof of this historic building.
Approximately 14,000 cubic feet of polystyrene was used to create the illusion of a rolling terrain. The landscape design followed a formal garden plan instead of the more common meadow-like environment. This project included a drip irrigation system, fed partially by water collected from the adjacent penthouse roof.
The project was intended to demonstrate the benefit of green roofs in moderating summer temperatures within ultra-urban environments. The roof is monitored to demonstrate these benefits. The City Hall green roof is currently, on average year-round, 7 degrees cooler than the surrounding roofs and as much as 30 degrees cooler in the summer.
The rooftop habitat is home to more than the usual pollinators that visit perennial gardens. The city has a beekeeper that tends to two beehives. In 2010 Roofmeadow celebrated the 10 year anniversary of the installation of the Chicago City Hall green roof.