Bird’s eye view of New York’s green roofs and roof gardens. (Photo courtesy of www.gardenvisit.com)
Environmentally friendly roofs are sprouting up all over New York City. Susan Hassler of Spectrum magazine reports from a sky-high rooftop.
GELLERMAN: From the wetlands of Cape Cod, we now go to buildings in New York City where many roofs are starting to sprout green. These environmentally friendly green roofs are popping up on luxury buildings in midtown Manhattan, low-income housing projects in the Bronx, and private brownstones in Brooklyn. IEEE Spectrum’s Susan Hassler visited one of these sky-high gardens and has our report.
[CAR PULLING IN TO A PARKING LOT]
HASSLER: Leslie Hoffman, director of the group Earth Pledge, pulls into the parking lot of Silvercup Studios in Long Island City, Queens. She parks her car near a row marked “Sopranos cast only.”
[CAR DOOR SLAM AND ELEVATOR]
HASSLER: She walks past a catering truck, enters the warehouse-like studio building, and rides up a freight elevator. The doors open onto the real star of the show, at least for Hoffman: New York City’s largest green roof.
[DOOR OPENING AND CITY SOUNDS]
HOFFMAN: This is one section, and you see that whole section over there. And then there’s another roof across the “on” ramp to the Queensborough Bridge on the other side. This roof is a total of 35,000 square feet of greened area, all done in GreenTek modular boxes.
HASSLER: Hoffman peers over the railing of a landing at two large, flat sections of roof. They’re covered in pale plants, propped up in plastic crates. The roof doesn’t look particularly green; in fact, it looks brown. But for Hoffman, the term “green roof” has broader meaning than just a reference to color. It refers to a special kind of roof, built for its ecological benefits, on which heat-absorbing plants take the place of black tar.
[ROOF AND CITY SOUNDS]
HASSLER: On the side of the landing, more planting boxes sit on a bed of wires. The wires feed into a box attached to a pole that serves as a small weather station. The instruments collect data about how much heat the plants ward off and how much water they absorb.
HOFFMAN: What we’re really doing here is working to quantify the value of the benefits of green roofs, at least on the thermal and the storm water side in this particular research station, so that policy makers have a good basis from which to understand what the return on investment will be for them.
HASSLER: Widespread green roofs could help New York City deal with some persistent problems, such as heat and storm water runoff. But given that green roofs initially cost up to three times as much as standard roofs, is it worth it for the big apple to go green? Cynthia Rosenzweig is a climate scientist at the NASA Goddard Institute for Space Studies, and the Earth Institute at Columbia University. She leads an ongoing, city-wide study of green roofs, and says they have many benefits.
ROSENZWEIG: If you have about ten percent of available roofs in NY greened, vegetated, that would help, our studies have shown that would help with the urban heat island that we have right now.
HASSLER: This “urban heat island effect” keeps New York City four to ten degrees hotter than surrounding rural areas. Tall buildings trap hot air in the narrow spaces between them. And cities have dark roof surfaces, concrete sidewalks, and asphalt streets, which absorb heat as well.
Unlike dark roofs, plants reflect sunlight. They also cool air through a process called evapotranspiration, which is like a plant version of sweating. So a green roof keeps the building below it at more stable temperatures. In Chicago, green roofs have been shown to keep roofs up to 50 degrees cooler. Widespread green roofs could even change the climate of the city as a whole. And there’s more, Rosenzweig says.
ROSENZWEIG: Another public benefit that’s very, very important is reduction of combined sewage overflows. In our aging sewer system, because we combine our regular sewage pipes with our storm drains, and when there’s a big storm, the regulators have to divert some of that sewage to the open water.
HASSLER: When rain falls onto a standard roof, most of it slides off or washes down sewage drains. In heavy storms, city sewage drains often overflow, sending polluted water through streets and into rivers and oceans. Green roofs, however, act like giant sponges for stormwater. Thirsty plants and four to six inches of subsoil absorb up to 80 percent of rainfall during storms, while standard roofs absorb only 25 percent.
What’s more, the plants on green roofs filter the pollutants nitrogen and phosphorous from the soil, so any water that flows over the side is cleaner and less likely to taint rivers or lakes.
The greenest roofs in the U.S. may be in Chicago. In the windy city, most public building projects must have a green roof over at least half of free roof space, and Chicago now has over a million square feet of green roofs. All new roofs must be either green or cool. A cool roof is painted in a light-colored reflective surface and bounces sunlight off the roof, keeping a building at about the same temperature as green roofs.
[BATTERY PARK CITY SOUNDS]
HASSLER: In Manhattan, the area near the financial district has some of the city’s newest green roofs. Battery Park City is part of smoggy, gritty New York, but it has the strictest environmental building regulations in the country. Among its requirements are that every new building, residential or commercial, must have an extensive green roof covering 75 percent of its open roof space. Outside of Battery Park City, there are no regulations to force city developers to plant green roofs.
But some incentives are coming to New York, says Cynthia Rosenzweig.
ROSENZWEIG: Mayor Bloomberg signed into law a bill that requires capital construction for city buildings to follow the LEED that’s Leadership for Energy Efficient Design standards. And green roofs are one way that building owners can receive credits and points, they receive points towards their LEED certification with green roofs.
HASSLER: Right now, though, the costs of green roofs are higher than the actual benefits in terms of heating cost reductions. The Office of Sustainable Design at New York’s Department of Design and Construction recommends cheaper cool roofs instead.
Expensive green roofs aren’t the best route to earth-saving benefits, it says. Big storm water detention tanks are a far more cost-effective way to reduce storm water runoff. And trees on sidewalks provide more economical and more accessible greenery. In fact, the Office of Sustainable Design recommends green roofs only when they have some value as an amenity—when a neighborhood is severely lacking in green space.
[TRAFFIC SOUNDS FROM ROOFTOP]
HASSLER: But amenity value may be enough for style-conscious New York. Leslie Hoffman surveys the scene at Silvercup Studios, where lanterns hang over an open-air TV set and actors pass on the sidewalk below.
HOFFMAN: Green roofs have the wow factor that make people want them, which is actually wonderful.
For Living on Earth, I’m Susan Hassler in New York City.
GELLERMAN: Susan Hassler is the editor of IEEE Spectrum Magazine.
[MUSIC: Final Fantasy “Song Song Song” from ‘He Poos Clouds’ (Tomlab – 2006)]
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