Cooling down Chicago

Chicago's attempt to reduce its heat island results in interesting research findings

On June 6, 2001, the Chicago City Council approved an ordinance that substantially revised the Municipal Code of Chicago. Included in the ordinance was an upgrade of the code's existing insulation requirements to require compliance with ASHRAE Standard 90.1-99, "Energy standard for buildings except low-rise residential buildings," and add prescriptive provisions that required low-slope roof systems to have an initial solar reflectance of 0.65 and maintain a solar reflectance equal to or greater than 0.50 for three years after installation.

Given that Chicago historically has been a bitumen-based roofing market, with built-up and polymer-modified bitumen membrane roof systems making up a majority of the low-slope roofing inventory, this ordinance's minimum solar reflectance requirement, in effect, mandated a major change in roofing material and product usage in Chicago.

The ordinance initially was passed by the Chicago City Council with virtually no notice to or input from the roofing industry. Also, the city initially indicated the ordinance was intended to modernize the city's energy code with a focus on improving energy efficiency while providing for flexibility in building design. Subsequently, city officials also acknowledged a large motivation behind the ordinance was an attempt to reduce the urban heat island phenomenon in downtown Chicago.

What follows is an account of our participation in helping revise the city's energy code. We have adapted our research paper, "Study of roof system reflectivity and near-surface air temperatures in Chicago, Illinois," that we presented at the Cool Roofs Symposium in May in Atlanta for this article.