Green roofs are springing up in the concrete jungle of New York City – plants growing on waterproof membranes on top of buildings – in all five boroughs. Considering the potential to reduce greenhouse gases, increase energy efficiency and capture storm-water runoff, this movement is understandable. “Most of this work is small in scale so far, but it should get us all thinking,” said David Smiley, assistant professor of architecture and urban studies at Barnard College. Green roofs are perceived as especially useful in New York because they absorb up to 70 percent of the rainwater that would otherwise drain away. The city – built on islands and bounded by two rivers — has long struggled with excessive runoff after heavy rainstorms that overwhelm the drainage system that overflow with raw sewage. Con Edison, the city’s energy supplier, pioneered urban greenery in 2008 by planting thousands of sedum on the roof of its building in Long Island City, across the East River from Manhattan.
“We’re slammed,” said Marni Majorelle, who founded Brooklyn-based Alive Structures to teach New Yorkers how to convert their rooftops into gardens. “There’s a growing demand for green roofs from homeowners and developers. I see it as part of people’s plans – so many architects now include it. It’s a new chapter for New York.” According to a 2008 New York Times report on green roofs, New York City has 944 million SF of rooftop surfaces, but records of how much is used as rooftop gardens are limited. It lags behind Germany and other American cities such as Chicago and Seattle, where – as Dwaine Lee, a green infrastructure professional, said – green roofs were have been planted for years.
New York is starting to catch up. “It will keep growing, because the cost is coming down and the manufacturers of roofs are getting into the game,” said John Coogan, of OCV Architects, which creates roof spaces, predominantly next to non-profit-making organizations in affordable housing units. It designed its first green roof in 2004 and has completed a dozen more spaces since. Some believe that green roofs are just the tip of the iceberg. Architect Vanessa Keith envisions an array of innovative ways to retrofit buildings – from roof ponds for cooling to electricity-generating water walls. “Perhaps the current dilemma, rather than being seen as a death sentence or a depressing indictment of wasteful society, can provide an opportunity to rethink and retool our existing way of life,” she said.
Several New York urban farmers are innovating with their rooftop gardens For example, there is the nearly one-acre Brooklyn Grange, Eagle Street Rooftop Farm, Gotham Greens, and the aeroponic growing system. An affordable rental building in the Bronx plans to open with a new rooftop commercial greenhouse, and the Brooklyn Grange will open a new farm on the Brooklyn waterfront to grow food and capture storm water, thanks to a grant from the city’s Department of Environmental Protection.
To encourage building owners to convert rooftops to food production, the New York City Department of City Planning (DCP) released a proposed zoning text amendment that would exclude rooftop greenhouses on top of commercial buildings from the lot’s floor area ratio (FAR) and height limits.
The city has proposed that 1,200 acres of commercial rooftops be made available for urban farmers to build greenhouses. “City law imposes restrictions on how tall buildings are allowed to be in different areas, which is one reasons why rooftops stay empty — developers often build to the maximum height possible,” said Sarah Laskow of Grist. “The planning department’s proposal would allow buildings to add rooftop greenhouses above regular height restrictions. And according to a study from the Urban Design Lab, that would mean 1,200 acres of empty, flat rooftops would be eligible for green penthouses.”
Urban farms – especially those on rooftops – have many green features. They insulate buildings; they absorb various gases that doesn’t belong in the atmosphere; and they help prevent rainwater runoff and pollution. These rooftop farms would be “required to incorporate rainwater collection and reuse systems, which will help the city mitigate the pressure that big rainstorms puts on the sewer system.”