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Tecta America Green Roof Limits Stormwater Runoff by 77 Percent at USPS Facility
SKOKIE, Ill. — A green roof installed by Tecta America Corporation on top of the U.S. Postal Service’s Morgan Processing and Distribution Center in New York has been found to limit storm water runoff by 77% according to a study by Columbia University.
“The findings of this study are important to building owners given the stronger emphasis more cities are placing on the management of stormwater runoff,” said Angie Durhman, Tecta Green Manager. “In addition to the environmental benefits, minimizing stormwater runoff can save building owners thousands of dollars in reduced fees and tax-based incentives.”
The study tracked rainfall throughout June 2011, and found that the vegetative roof of the Morgan facility prevented 77% of all rainfall on the facility from entering the New York City sewer system in the form of runoff. Limiting stormwater runoff can help prevent debris, chemicals and other pollutants gathered on pavement and building surfaces from entering a sewer system, and eventually lakes, streams and rivers.
“Not only is this the largest green roof I’ve ever studied, but the depth of the soil substrate and how effective it has proven to be in managing rain water truly set it apart,” said Dr. Wade McGillis, the Columbia University Lamont Research Professor overseeing the study. According to McGillis, the depth of soil on the Morgan facility roof measures between 4 and 8 inches, compared to the 1-inch depth standard on most green roofs in New York City.
“In addition to limiting total stormwater runoff, this roof is significantly reducing the flow during peak downpours by as much as 97%. These heaviest periods of rain can have the greatest impact on combined sewer overflow (CSO) during a storm, making the roof’s efficiency during these times even more significant.”
Other results of the study found that the green roof was able to neutralize the effects of acid rain, altering the pH level of initial rainfall from 4 to more than 8 once passed through the plants and soil atop the roof. Additionally, the study found that the temperature of the Morgan facility green roof was more consistent and cooler overall than other traditional roofs throughout the month. This is a benefit that Durhman claims can extend the life of the roof’s membrane to twice that of a standard roof.
This semi-intensive roof was installed in 2008 on the 7th floor of the Morgan Processing and Distribution Center and has an area of 109,000 square feet. This is currently the largest green roof in New York. The TectaGreen system consisting of plants and vegetation native to the region comprises approximately 59% of the roof, and nearly 90% of the original roof materials were recycled and reused on the roof. The new roof system consists of 80-mil PVC loose laid membrane installed over 1/4-inch DensDeck board and 3 inches of extruded polystyrene insulation. Tecta America Company J.P. Patti, based in Saddle Brook, N.J., completed the installation and provides ongoing maintenance of the roof.
McGillis resides in the Geochemistry Division of the Lamont Doherty Earth Observatory and in the Department of Earth and Environmental Engineering at Columbia University. He leads a team of graduate students in the ongoing research of the green roof along with Dr. Patricia Culligan, professor of Civil Engineering & Engineering Mechanics at Columbia University.
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