Case Study - Chicago Green Roof
Chicago is a pioneer in several urban heat island reduction measures
One example of green roof mitigation is the city of Chicago, Illinois. As mentioned before, Chicago has a long history of fatal heat waves. To mitigate the effect of UHI, Chicago was selected to participate in a program piloted by the EPA called the Urban Heat Island Pilot Project (UHIPP). Chicago was one of five cities that participated. The objectives of the project included (Huang, et al., 1990):
- Assist cities in efforts to adopt and evaluate heat island reduction strategies and programs;
- Encourage research, education, and communication;
- Demonstrate and document successful heat island reduction projects that may be adopted in other communities; and
- Build community support and understanding of heat island reduction strategies.
Chicago is a pioneer in several urban heat island reduction measures. The most successful mitigation methods included, landscape ordinance, energy code, rooftop gardens, open space impact fee ordinance, asphalt alley reconstruction, parking lot resurfacing and greening (USEPA, 2011b).
The famous rooftop garden in Chicago is located atop City Hall. The rooftop garden began construction in 2000, after 1.5 years of planning. The garden includes 20,000 herbaceous plants consisting of 156 varieties, 112 shrubs, and 37 vines were planted in a special blend of compost, mulch, and lightweight absorbent materials occupying 20,000 ft² of the 38,800 ft² roof (Huang, et al., 1990). Before the garden was constructed, the roof’s albedo was approximately 0.27. The roof’s albedo total albedo now is 0.45 (Huang, et al., 1990). Aside from the increased albedo and aesthetic value, the rooftop garden also has significant energy saving benefits. Due to reduced solar absorbance and increased evapotranspiration, the projected total direct electricity savings were 9,272 kilowatt-hours per year, and the corresponding savings in natural gas for heating were 7.372 therms per year (Huang, et al., 1990).
(By Kiersten Lee/Gregory Möller)