The Nature Conservancy (TNC) in New York recently developed a robust characterization of green roofs in New York City. This Summer of Maps project sought to support efforts to plan for future green roofs by analyzing site availability and need for green roofs across the city. First, Anna developed a prioritization model to identify New York City Neighborhood Tabulation Areas that stand to benefit most from new green roof installations, incorporating social vulnerability, heat vulnerability, existing green space, and need for stormwater management to mitigate combined sewer overflows. The second phase of the project was a site availability assessment to identify buildings potentially suitable for green roof installation. Based on a report from Columbia’s Urban Design Lab, conversations with Brooklyn Grange, and the funding requirements from the NYC Department of Environmental Protection’s Green Infrastructure Grant Program, “suitable” buildings were defined as those constructed between 1900 and 1970, with at least 3,500 contiguous square feet of flat rooftop area, and no existing green roofs. Flat roofs were defined as areas with a slope of 9.5 degrees or less. The prioritization model and suitability assessment were combined to assign NYC’s Neighborhood Tabulation Areas scores representing need and potential for green roof installations.
In total, the analysis identified 20,975 buildings across the city as suitable for green roofs, almost 2% of all buildings. This represented nearly 200 million total square feet of potentially appropriate rooftop area. Sixty million of which are located in areas in the 75th percentile or higher for need. These high-potential, high-priority areas include large portions of the Bronx and Queens.
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