Research News

National Science Foundation Grant Supports Research on Columbia University Green Roofs

2009-08-14

For the first time in history, more people reside in urban centers than rural areas, making sustainable and interdisciplinary urban design more important than ever. One strategy that addresses a number of key urban afflictions—from urban heat to stormwater runoff pollution— is the use of green roofs, which can transform the otherwise harsh environments of urban rooftops into cooler, greener spaces.  Columbia University and the Earth Institute are receiving considerable attention for their work in this area.

The National Science Foundation is awarding Columbia University $476,000 to continue its work on comparing and evaluating the effectiveness of different green roof technologies.  Project goals include improving scientific understanding of green roof performance, optimizing the technologies’ functionality, and realizing countless potential benefits to human health, economic efficiency and pollution reduction.

The project, referred to as the Columbia Green Roof Consortium, is led by Earth Institute scientists Patricia Culligan, a professor of civil engineering and engineering mechanics, Stuart Gaffin, an associate research scientist at the Center for Climate Systems Research (CCSR) and NASA Goddard Institute for Space Studies (GISS), and Wade McGillis, Doherty Research Scientist and a professor of earth and environmental engineering. The Office of Environmental Stewardship, under the direction of its senior executive vice president, Robert Kasdin, has also contributed substantial support to the project. In addition, researchers and faculty from the Earth Institute’s Urban Design Lab as well as Barnard College are collaborating closely on the project.

“Since arriving at Columbia University in 2004, it has become overwhelmingly apparent [to me] that the University has the research and facilities to be international leaders in sustainable environmental technologies – particularly green roofs,” says McGillis.

Kasdin is enthusiastic about the project. In a recent issue of his environmental stewardship newsletter, he wrote, “We congratulate this outstanding interdisciplinary team of faculty, administrators and students who are helping us become, as the New York Times recently put it, ‘green-minded Columbia.’”

New York City is one of many municipal governments around the world that provide incentives to adopt green roofs in recognition of their environmental and public health benefits. Green roofs counteract the ill effects of abundant impermeable roofs, roads and sidewalks in developed areas by acting as permeable surfaces that collect excess rainwater, averting floods and helping to prevent the overflow of untreated sewage into watersheds. They can potentially reduce combined sewer overflows (CSOs) in cities like New York by as much as 40 percent. The Columbia Green Roof Consortium hopes to better quantify how and to what extent different designs can effectively minimize CSOs.

In addition, it is widely acknowledged that green roofs efficiently cool urban environments by counteracting the urban heat island effect, a phenomenon wherein temperature increases of up to 10 degrees at street level (and up to 40 degrees on roof surfaces) are generated by traditional rooftops that act as heat reservoirs, trapping and conducting excess heat into buildings and the environment below. Plants on a green roof cool the air around them through a process known as evapotranspiration. Green roofs also provide natural building insulation in colder months, retaining heat and significantly lowering utility costs for tenants. They can become habitats for insects and birds, and they tend to have greater longevity than traditional roofs.

Green roofs also address one of the most pressing concerns of New York City residents and officials: air quality. Plants in urban settings act as important air purifiers, trapping airborne particulates and filtering and sequestering pollutants and greenhouse gases.

The structure of a green roof consists of several layers. The base layer is a waterproof surface membrane, and additional component layers provide growing media, drainage and root protection, allowing for the growth of hearty, drought-resistant vegetation.

So far Columbia has seven green roofs, two of which are also research stations where investigators gather quantitative data about the environmental functions and economic advantages of green roof adoption in New York City.  One of these research stations was recently featured in the July 2009 LI-COR Biosciences Newsline. This article goes into more detail about the experiments that McGillis is conducting to collect data on mass flux of water and carbon dioxide. You can find it at http://www.licor.com/env/newsline/july09/green_roof.jsp.

Columbia green roofs have recently received tremendous media coverage by the Associated Press, including this video: http://video.ap.org/?g=0719dv_carbon_landscape&f=CAFRE

The Columbia University Green Roof Consortium is not only an important collaborative effort between LDEO, SEAS, CCSR, Barnard and the Urban Design Lab, but will also help Columbia realize its pledge to the city of New York to reduce its 2005 carbon footprint by 30 percent by 2017.

McGillis hopes that other urban institutions, architecture firms and private building owners will use the knowledge gathered by the Consortium to realize the social, environmental and economic benefits of converting all feasible buildings to green roof buildings.