By Margarida Correia
The garden on the roof of St. Simon Stock Elementary School in the Bronx isn’t much to look at on a recent spring day. The dried remains of brown-eyed susans and orange columbines, flowers native to the area, and yellowed batches of Indian grass and switch grass, barely move in the breeze. But evidence of the garden’s vitality is everywhere. The four-foot stalks of butterfly weed, a favorite for bees and butterflies, are beginning to bud. Sparrows and turtle doves flutter about. The roof, which is almost completely covered with soil, is home to 20 native plant species, many of which grow to five to six feet.
The green oasis on top of the four-story brick school building provides an ideal setting for kids to learn about birds, bees and butterflies, while also helping the environment. The garden cools the roof in the summer and soaks up tens of thousands of gallons of rainwater throughout the year. That’s water that otherwise would have flowed into city sewers, so strained they often spill over into New York waterways during heavy downpours.
With growing fears of global warming, demand for green roofs like the one on St. Simon is heating up in New York and other cities across the country. In April, Mayor Bloomberg announced an incentive program for the installation of green roofs as part of his much publicized environmental plan to make the city greener, cleaner and more energy efficient by 2030. If the program receives state approval, building owners will be eligible for a property tax abatement to help offset the installation costs of green roofs.
Evidence is mounting that the eco-friendly roofs benefit the environment in several ways: in addition to retaining rainwater, they filter the air and insulate buildings, lowering the demand for air conditioning and heating fuel. The roofs also help curb what’s called the “urban heat island effect,” the trapping of heat in cities due to too much paving, a phenomenon that makes New York City five to seven degrees warmer than surrounding suburban and rural areas.
If Bloomberg’s plan succeeds, more of New York’s blacktop roofs may go green. While the exact number of green roofs in New York is unclear, Leslie Hoffman, executive director of Earth Pledge, a non-profit environmental group, said there could be as many as 100. The roofs crown high-rise luxury towers and affordable housing complexes and are beginning to appear on manufacturing facilities, municipal buildings and even public spaces like the Staten Island Ferry terminal, which has an 18,000-square-foot green roof designed to attract monarch butterflies. The biggest green roof in New York City—at 35,000 square feet—sits on top of Silvercup Studios, a movie and TV production studio in Long Island City.
Not all the roofs have the aesthetic appeal of St. Simon’s. An 11,000-square-foot eco-roof on top of Gratz Industries, a light metal fabricator next to Silvercup Studios, resembles a large industrial carpet made up of five-by-five-foot squares. Scattered patches of green and red sedum—hardy, succulent plants that spread easily—peer through the mixture of shale and dirt that covers the roof.
“It takes two years before it starts to fill in,” said William Riley, construction manager at Pratt Center for Community and Planning, as he pointed to the lonely “plugs” that survived last year’s initial planting. The roof was installed in August 2006 to measure the water retention, cooling capabilities and other environmental benefits of green roofs.
Green roofs have been cropping up on city rooftops across the nation for several years. According to Green Roofs for Healthy Cities, an industry association that promotes green roof technology, almost 2.2 million square feet of green roofing was planted in the United States in 2005, up 81 percent from almost 1.2 million square feet in 2004. In New York, green roofs more than doubled, jumping from 51,000 square feet planted in 2004 to almost 120,000 square feet in 2005. Despite the increase, New York still trails cities like Seattle, Portland and Chicago, where green roofs are used more widely and promoted more aggressively. Chicago, the country’s green roof champion, for instance, has about 300 green roofs totaling more than one million square feet.
Studies have shown that green roofs dramatically lower roof surface temperatures. For instance, one study by Columbia University revealed that surface temperatures on green roofs are more than 72 degrees F cooler than conventional roofs during the summer at midday. On average, they’re 34 degrees F lower during the day. The cooler surface temperature, green roof advocates contend, reduces the demand for air conditioning, thus reducing carbon emissions released into the atmosphere.
But skeptics argue that the benefits are over-hyped, saying that the best way to save energy and help the environment is to follow energy-efficient practices at home. They note that green roofs are expensive to install and maintain, costing builders and homeowners twice as much as conventional roofs as a general rule of thumb. According to Earth Pledge, a green roof in New York goes for $12 to $30 or more per square foot, depending on the sophistication and weight of the roof. A traditional blacktop roof goes for $10 to $12.
“A green roof is an expensive addition to a building,” said Andrew Padian, a building scientist at Steven Winter & Associates, noting that it doesn’t have any cost-saving performance if you have well-insulated walls, high-performance windows and high-efficiency heating and cooling systems.
Many engineers and architects contend that reflective roofs—roofs painted in silver paint—are just as effective as green roofs in cooling rooftops because they reflect the heat of the sun. They argue that they’re considerably cheaper, and when grouped together, can make just as big a difference on the urban heat island effect as green roofs can.
“Green roofs are beautiful, a great amenity and a nice place for birds to land, but I don’t see them as energy savers on any roof,” said Chris Benedict, owner of an architecture firm—Architecture and Energy Limited—that specializes in making buildings energy efficient. “They’re an extraordinary distraction when there are so many other things to save energy in buildings.”
Still, green roofs trump reflective and conventional roofs on several counts. They’re nicer to look at, can provide communal space for building residents and last twice and even three times as long, according to green roof advocates. Green roofs protect roofing membranes from extreme temperature fluctuations and the negative impact of ultraviolet radiation, which cause traditional roofs to crack. According to Earth Pledge, green roofs can last 50 years or more, while conventional roofs need to be replaced every 10 to 15 years.
But the biggest trump card is that green roofs retain storm water and reduce runoff, a huge environmental and public benefit. Like many other cities, New York’s sewer system combines sewage and rainwater runoff. When it rains, sewer pipes and treatment facilities become overwhelmed, causing raw sewage and storm water to flow into New York’s water bodies. According to Sustainable South Bronx, an environmental group in the South Bronx, an estimated 27 billion gallons of raw sewage and polluted storm water are released into the city’s waterways a year.
Green roofs help mitigate the sewage overflows. When it rains, green roofs act as giant sponges, absorbing 80 percent of the rainwater that falls on them, according to a Columbia University study. A conventional roof, in contrast, retains 24 percent of the rain. By conducting a storm water retention simulation, the authors of the study also estimated that if 50 percent of the buildings in one of the city’s 14 sewage-sheds had green roofs, runoff would fall by 10 percent.
Quantifying the other eco-benefits of green roofs—like energy savings, for instance—is much more contentious. While many studies show that green roofs are significantly cooler than black asphalt roofs, the extent to which it translates into actual energy cost savings is open to debate. Green roof advocates contend that green roofs reduce energy use by 10 to 30 percent. Skeptics counter that the savings are so miniscule that they’re not worth having.
The cost savings hinge on the characteristics of the building. Green roofs work best for buildings that have a large roof relative to the building’s size. A green roof on top of high-rise building, for instance, will have little impact on energy cost savings given the building’s higher air conditioning and heating demands. Green roofs will make more of a difference on low-rise buildings. According to the Columbia study, the energy cost savings for a single-story office building in Queens could be more than 20 percent, whereas for a Manhattan skyscraper the savings may be less than one percent.
“These roofs work and New York needs them,” said Mike Gubbins of Albanese Development Corp., a green builder that incorporates green roofs on almost all of its buildings, including its residential rental towers at the Solaire and the Verdesian in Battery Park City and at the Vanguard Chelsea. The 4,000-square-foot green roof at the Vanguard has been so popular that the developer will be expanding it.
For developers, the marketing and publicity value of green roofs make them worthwhile regardless of any real or perceived energy savings. Green roofs make buildings more marketable, providing residents with an amenity that has greater appeal than recycled carpeting, let’s say, or non-toxic paint.
“It’s one of many green features in a building, which, in aggregate, make an apartment attractive,” said Jordan Barowitz, a spokesman for The Durst Organization, a leading developer of green buildings in New York City. “People would prefer to look down on something green instead of blacktop.”
Green builders might also be motivated by the points that a green roof can add to a national environmental rating system known as LEED, Leadership in Energy and Environmental Design. A green roof can contribute seven to 23 points toward a LEED rating in categories such as storm water runoff and energy efficiency. The higher the LEED rating, the easier it is to apply for grants and loans from state and local environmental agencies and to comply with increasing green building requirements.
Unsurprisingly, organizations are emerging to spur the development of New York’s embryonic green roof industry. Greenproofing, the business arm of City College’s Environmental Engineering and Entrepreneurship Program, for instance, launched an initiative to install green roofs on New York City public schools and engage middle and high school students in the design, implementation and maintenance of green roofs. The group has met with dozens of schools and is slowly gaining traction.
Financial incentives such as the property tax abatement Mayor Bloomberg proposes should help the industry grow, said Hoffman of Earth Pledge. If approved, the property tax abatement will allow building owners to offset 35 percent of the installation cost of extensive green roofs on new or existing buildings. It is the most aggressive incentive for green roofs of any city in the country, said Ariella Rosenberg Maron of the Mayor’s Office of Long-Term Planning and Sustainability.
Currently, developers and building owners have very limited city support for green roofs. Green roof advocates, however, contend that the public benefits of green roofs make them worthwhile, particularly when it comes to reducing storm water runoff. Rather than spend millions of dollars on new sewage tanks, the city could instead fund green roofs and achieve similar reductions in sewage overflow, they argue. They estimate that 100 acres of green roofs could collect between 3 and 9 million gallons of water a year.
For some people, the benefits of green roofs are intuitive, requiring a leap of faith rather than scientific evidence.
“It’s probably kept it cooler for the school,” said St. Simon pastor Father Nelson Belizario, of the green roof on top of St. Simon. But by how much, he didn’t know. “One little patch of green roof” amid canopies of black asphalt rooftops, he admitted, didn’t stop the area from feeling like an oven, but he felt certain that it had made a difference.
“It’s one little oasis,” he said, “but at least it indicates there are a lot of possibilities.”