Tar Beach Meets the Great Lawn:

The Green Roof Movement Hits New York

By Meera Subramanian

© 2005

Butterflies are rarely used as the basis for an architectural design plan. Unless you are New York landscape architect Kathleen Bakewell, who was inspired by the monarch butterfly’s eastern seaboard migration route when developing a green living roof as part of the LEED certified St. George Ferry Terminal renovation on Staten Island. She imagined a rooftop garden planted with butterfly weed and grass-leaved goldenrod, smooth asters and showy stonecrop and envisioned people coming each September to observe the butterflies passing through, as many do in Central Park, and take in a view of the Manhattan skyline. Bakewell, who has been designing green roofs in New York since 2000, always asks herself, “What’s special about this place?”

Working with the St. Louis-based HOK (Hellmuth, Obata, + Kassabaum) design firm at the time, Bakewell believes that “a green roof should work with the local ecology.” Far from being an isolated project, New York City is actively joining other North American cities such as Chicago, Portland, Oregon, and Vancouver B.C. in the movement to green its rooftops.

Greening Gotham

Chicago pioneered the North American green roof trend, in part in an attempt to alleviate scorching mid-summer temperatures that in a 1995 heat wave killed hundreds of Chicago residents. As a step towards addressing this urban climate change, Mayor Richard M. Daly turned to city hall. Actually the roof of city hall, which is now covered with a garden, transforming a steaming asphalt-covered, polluted-water-runoff-causing, energy-wasting rooftop into living breathing greenery. Chicago now boasts of having two million square feet of green roofs throughout the city, including on police stations, libraries and public transportation buildings.

But New Yorkers will quickly assure you that they were never far behind Chicago. “We’ve been at this for four years now,” says Leslie Hoffman, executive director of Earth Pledge, an organization promoting innovative technologies as a means to restoring balance between human and natural systems. “We’ve educated thousands of designers and architects and horticulturists and engineers and others about green roofs,” she explains, sitting in the Manhattan townhouse that serves as the Earth Pledge office, complete with green roof. She sees education as the first step in the move toward a foliage-capped city. The web page for Greening Gotham, a project of the Earth Pledge Green Roofs Initiative, features an expansive view of Manhattan from the air, a geometric landscape of grey, until you guide an enchanting circle across the screen that transforms each dirty, empty rooftop into a plant-covered oasis.

The friendly New York-Chicago rivalry peppered the speeches at the Green Roofs, Cool City Conference in New York in March. In a maneuver reminiscent of another race to the sky between the two cities, New York City announced plans last year for the world’s largest green roof. Still in the design process, and another HOK commission, the renovation of the Jacob K. Javits Convention Center on Manhattan’s West Side currently features a 22-acre green roof, including five acres of usable lawn space, a design inspired by the geography of the Hudson Valley and the model of Central Park’s Great Lawn.

The Role of Green Roofs

Last year, the great urban theorist Jane Jacobs, author of "The Death and Life of Great American Cities," expressed her endorsement of the green roof trend in a New York Times article entitled “The Greening of the City.” Back in 1926, Le Corbusier included roof gardens as one of his Five Points of a New Architecture. But green roofs go even farther back than that, mainly to Europe, where they have been a common architectural element for hundreds of years.

Today, green roofs, sometimes called living roofs, come in two main types of designs. “Extensive” roofs have two to four inches of soil and a simple living groundcover such as sedum or grass, while “intensive” roofs incorporate enough planting medium to support a complete garden with shrubs and sometimes even trees. In both cases, soil and plants are installed over a matrix that includes a waterproof membrane, a water-retention layer and a drainage layer.

A variety of companies now offer complete rooftop systems, such as American Hydrotech, which uses layers of materials, and GreenTech, which created modular units that can be moved with a forklift. These exemplify the surge of new products emerging from the burgeoning trend to go green.

Tar Beach No More

While many New Yorkers deal with sweltering summer heat by fleeing the city in search of ocean or country, most residents remain in the city and sweat their way through what scientists call the “urban heat island effect.” Colin Cheney, director of Earth Pledge Green Roof Initiative, explains: “New York is a tar beach during the day. At night, out in the country or in the suburbs where there is more vegetation, the area is able to cool down. But in the city all that heat is radiated back so that there is a heat pocket over the city.”

The heat generated by the tar beaches that top city structures adds to the heat island effect. While an asphalt roof can reach 175 degrees during peak summertime temperatures, green living roofs stay a relatively comfortable 95 degrees.

Cities like New York also face sewage systems unable to handle the sudden influx of water during rainstorms, causing a problem called combined sewage overflow (CSO), which dumps sewage and storm water untreated into surrounding bodies of water. Green roofs help control this rain runoff as well as pollution, the plants and soil absorbing water and filtering it slowly, improving overall water quality.

Simultaneously, the vegetation purifies the air, taking in excessive carbon monoxide and returning oxygen to the atmosphere. While an individual roof mostly provides sweet air for those in its immediate vicinity, if enough are built in an area, the hope is that the cumulative effect will begin to take place.

Green Spaces Where They’re Needed Most

In the 1970’s, New York City was in ruins. While much of the city has witnessed a resurrection of parks and other public spaces, areas such as the South Bronx still reel from neglect and a dearth of vegetation. The result is poor air quality and a soaring asthma rate that is one of the highest in the nation. The South Bronx New Roof Demonstration Project (NDP) is a collaboration between HM White (where landscape architect Kathleen Bakewell now works), Columbia Ph.D. student Joyce Rosenthal and Majora Carter, the executive director for Sustainable South Bronx. Construction of the 3,000 square foot roof on the Banknote Building in Hunts Point began this spring.

The South Bronx NDP design combines the living plants of a green roof as well as reflective material used in “cool roofs.” Cheaper and easier, but with fewer environmental benefits, Bakewell says that while she prefers to see living roofs, she finds cool roofs “quite compelling. You just put it up and you’re done.”

The Bronx Initiative for Energy and the Environment (BIEE) also offers hope for a greener northern borough. The BIEE program, funded by the borough president’s office, is offering over $2.1 million dollars to be used for sustainable projects including tree-planting, solar panels and green roofs. Nine of the fourteen groups who received funding are incorporating green roofs into their design.

Getting Back to Basics

Joe Seaman, LEED architect for HOK in New York City, sees sustainable design as getting back to basics. Currently overseeing the St. George Ferry Terminal renovation, which will be unveiled on May 20, Seaman sees green roofs as just another element in what he refers to as smart design. “To start to be able to integrate systems,” he explains, “to tie the systems in the building and the ideas together, makes a stronger concept of design.” The 25,000 square foot green living roof, covering 20% of the total roof area of the ferry terminal, sits atop the maintenance building for the facility and incorporates a rainwater cachement system to water the plants using an efficient drip irrigation system.

HOK, which is responsible for the creation of energy-efficient buildings around the world, were “doing LEED before LEED existed,” says Seaman. HOK as a firm was guided by the influential work of Sandy Mendler, AIA in HOK’s San Francisco office, who co-wrote The HOK Guidebook to Sustainable Design with William Odell. “HOK is extremely supportive of sustainability and sustainable design,” says Seaman as he stands on the terrace that overlooks the St. George green roof, in the exact spot where visitors will be able to watch the monarch butterflies. Just like the butterfly weed that will act as a lure to the delicate creatures that will use the rooftop garden as a stepping stone to the south, HOK’s commitment has attracted clients both public and private who want sustainable elements incorporated into their buildings. “Clients request it and HOK suggests it. They attract us and we attract them.”

A Sensible Urban Planning Strategy

Laurie Kerr and John Krieble, architects for New York City’s Department of Design and Construction (DDC), are a little more tempered in their enthusiasm for green roofs as an environmental benefit for the city. Starkly aware of the limited funding they have available for projects, they need to “get the biggest bang for the buck,” says Krieble. This means they are more inclined towards cool roofs than green roofs, and other more practical means of creating a high-performance building, such as daylighting design, efficient HVAC systems and low-e windows. “Our computer models show a 400 to 600 year payback on investment,” says Kerr about green roofs. “You don’t exactly say we should jump all over this,” follows Krieble.

But both Kerr and Krieble, part of the DDC’s Office of Sustainable Design, agree that green roofs have their paybacks in non-monetary ways. They prefer to approach green roofs as an urban planning strategy rather than an environmental one. “Green roofs are a terrific amenity,” explains Krieble. “There are a lot of benefits aesthetically for people that crave access to plant material in dense urban areas.” In this way, he advocates intensive green roofs in places where city residents can actively use and enjoy them. Otherwise, you’re better off using the simpler, cheaper cool roof materials.

Getting the Numbers

While there has been extensive anecdotal evidence about the benefits of green roofs and some limited studies, more serious research is needed to get the numbers that will back up the claims of the green roof movement. The New York Ecological Infrastructure Study (NYEIS) is one comprehensive partnership that is investigating “the form and function of an ecological infrastructure,” including green roofs. Researchers from Hunter College/CUNY and NASA Goddard Institute for Space Studies, as well as partnerships with Columbia and Pace Universities, The Gaia Institute, and Parsons School of Design, will analyze climate, hydrology, design, policy and cost-benefits of the burgeoning field of green architecture.

Earth Pledge also just launched two research projects in Long Island City to do in situ monitoring of storm water on both the building and drainage basis scale. “Doing local research is very important,” say Leslie Hoffman of Earth Pledge. Often, studies are limited to computer modeling, but on the ground, or in this case, on the roof, testing is crucial to backing up the data, she explains. The two sites, one 10,000 square feet and the other 30,000 square feet, will be testing for quantity and quality of water runoff, as well as temperature and heat flux. “What are the quantified values that green roofs can deliver both in terms of public and private benefit?” asks Hoffman. This is what they intend to find out.

A Greener New York to Come

This combination of large-scale public projects and smaller demonstrations like the one in the South Bronx, along with the movement towards more LEED-certified buildings throughout New York City, give hope that even in one of the densest urban areas in the country, smart design can be sustainable design. Jane Jacobs wrote last year about the trend of installing green roofs from Vancouver, B.C. to Long Island City as a “quiet revolution wrought by today's landscape architects and ecologists.” Looks like the revolution has arrived in Gotham, floating in on butterfly wings.