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20 For 20 Retrospective

Chicago City Hall Green Roof

green roof project urban heat island Chicago

 

OVERVIEW

Chicago’s iconic City Hall Green Roof demonstration project is credited with accelerating the green roof/green wall movement in Chicago and across North America. As part of former Mayor Richard M. Daley’s commitment to making Chicago “the greenest city in America”, the City Hall green roof was conceived as a demonstration of the innovative practices initially developed in Europe.

 

As a pioneering application of green roof technology on the City’s main administrative building, the rooftop landscape has become one of the more prominent examples of the emerging practice of living architecture, and has helped usher in a new era of a greener, more resilient Chicago.

 

The Mayor’s office selected a project team with CDF as the design lead to convert the City Hall rooftop into a green roof pilot project. Structural loading, historic building status, deteriorated parapet walls, skylights long-since covered, and the logistics of an 11-story construction project with minimal access by stairs through a mechanical penthouse room all influenced the solution that was ultimately implemented.

 

The result has become a highly recognized, beautiful, diverse urban garden space that continues to be enjoyed, studied and written about after more than a decade. It remains a leading-edge example of an ecological system wholly integrated with building architecture.

 

The project was largely funded by a grant from the U.S. EPA Urban Heat Island Pilot Project Initiative, with a focus on urban cooling, reduction in stormwater runoff, water conservation, air quality, and urban ecology. Data collected over the years shows that rooftop temperatures in the summer are on average 30 degrees cooler than the standard roof, and saves the city as much as $10,000 per month in energy costs. The plants utilize much of the rainwater that falls on the roof, reducing the load on the city’s over-burdened storm sewer system by as much as 75%.

 

The landscape is largely self-irrigating with available rainfall, including rain that is harvested from the upper-story mechanical room roof and stored in two 500-gallon cisterns. Some supplemental water is provided through a drip irrigation system. The rooftop landscape is maintained through the City’s Greencorp jobs training program, and as a living system, becomes healthier and more diverse with each season of stewardship. As it has evolved, species diversity has approximately doubled, with new native species added throughout the year.

 

Home to a multitude of indigenous plants and flowers, the roof has beehives that produce approximately 200 pounds of honey each year. In addition to nurturing songbirds and insects, thousands of residents and office workers in the 30 skyscrapers surrounding City Hall also enjoy the garden’s beauty year-round.

 

PROJECT FACTS

Size: 21,000 s.f. green roof portion; 38,000 s.f. total roof area

Program: Raise awareness of UHI while providing building department staff, elected officials, developers and real estate investors the opportunity to see and understand the potential for living systems to provide a wide range of benefits for both individual sites and the city overall. 
Completion: 2001
Construction Budget: $2.5 million (including building repairs/improvements)

Recognition: ASLA Merit Award for Design 2002; IL-ASLA Honor Award for Design 2002; World Wildlife Fund (WWF) National Earth Hour City Challenge 2014

Project Team: Conservation Design Forum – Lead Designer, Landscape Architect, Ecological Design
Weston Solutions – Project Lead, Project Management
McDonough + Partners – Architect
Atelier Dreiseitl – Green Roof Engineering
Bennett and Brosseau – Roofing Contractor
RoofMeadow (formerly Roofscapes) – Green Roof System
Intrinsic Landscape – Planting Installation
Greencorps Chicago– Long-term Landscape Maintenance

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