Presenters: Jennifer Cass and Sandeep Mehrotra, Hazen and Sawyer
Session 24: Keep It Out of the Sewer

The Osborne Association’s 100-year-old Osborne Green Career Center in South Bronx, N.Y., will soon be outfitted with a blue and green roof. The new roof will become part of the center’s green jobs training program for the formerly incarcerated. Trainees will learn how to maintain the roof and monitor its effectiveness. The roof will be paid for in part by the Osborne Association and the New York City Department of Environmental Protection’s Green Infrastructure Grant Program (see the winners). Each year, the roof should manage more than 908,000 L (240,000 gal) of stormwater with the goal of reducing combined sewer overflows to the East River.

Blue roofs are a fairly new technology. They are non-vegetated but detain stormwater for gradual release. The Osborne Green Career Center’s blue roof will be composed of aluminum trays, geotextile, and crushed stone. According to presenters, blue roofs typically cost less than green roofs. In addition, blue roofs generally require less maintenance and have a reduced deadload of approximately 73 kg/m2 (15 lb/ft2), compared to vegetated roof systems under dry conditions. However, green roofs provide additional benefits, such as carbon storage, reduced heat-island effects, and more.