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blue roofs create temporary ponding and gradual release of stormwater

Rooftop Detention

DEP projects with stormwater management involve the various types of rooftop detention systems, including green roofs, blue roofs, and control roofs.

Blue roofs

Blue roofs are designed without vegetation for the primary purpose of detaining stormwater. Through weirs at the roof drain inlets, blue roofs create temporary ponding and gradual release of stormwater. To encourage widespread implementation on existing development, DEP is testing technologies that would allow for rooftop detention on sloped roofs; these technologies include trays, check dams, and silt socks.  A DEP repair yard in the Newtown Creek watershed is the planned site for a blue roof pilot to compare these technologies.

Green roofs

Green roofs are made up of a top vegetative layer that grows in an engineered soil, which sits on top of a drainage layer. Green roofs are more costly than conventional roofs but they are capable of absorbing large amounts of stormwater. In other cities, green roofs on just 10% of buildings resulted in a runoff reduction of 2.7% for the region and 54% for individual buildings. In addition, green roofs provide other social benefits: absorbing air and noise pollution, rooftop cooling by reducing UV radiation absorption, creating living environments for birds, and increasing the quality-of-life for residents.

Green Infrastructure Pilot Project

Through a partnership with the New York City Department of Education and School Construction Authority, DEP will design, construct, and evaluate the two rooftop detention strategies on an existing school building, P.S. 118 in Queens. Data from the study will be collected to compare the stormwater management performance of green, blue, and control roofs during a three-year monitoring period. Because all three surfaces will be on the same building, this pilot will compare costs and benefits under similar environmental conditions.

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