Green Roofs – Science Nation

MILES O'BRIEN: The rooftops of Manhattan are as varied as the city itself. Ventilation systems and water towers are pretty commonplace. But something else is taking root up here. STUART GAFFIN: It's a roof of living plants and its' a new form of urban vegetation. MILES O'BRIEN: Columbia University climate scientist, Stuart Gaffin, is a man of green gables. He's on a green roof, topped off with layers of material for drainage and a chemical substrate lighter than soil that supports plant growth. STUART GAFFIN: We are just really discovering them in the United States and their versatility. I dont' do any weeding. MALE: Oh. MILES O'BRIEN: With the help from the National Science Foundation, Gaffin and his teammates at Columbia are finding that green roofs have a beneficial effect on harsh urban environments. STUART GAFFIN: You can start with temperature. Plants are geniuses at staying cool in sunlight. The temperature differences on a black roof versus a green roof are astonishing.

I've seen them get up 180 degrees, whereas if you had a green roof, typically, the plants are about the same temperature as the air. MILES O'BRIEN: In summer, the concrete of a city absorbs and stores a lot of heat. Gaffin believes enough green roof space could counteract that with a cooling effect. Then, he says, there are the water benefits. STUART GAFFIN: When we get a typical rainfall, we get a wave of water from all of these buildings and streets hitting our municipal sewer system which can't handle it, and so, it actually triggers pollution events in our rivers. MILES O'BRIEN: But after a rainfall, some of the green roofs soak up all the water that hits them. STUART GAFFIN: Now, thats an astonishing thing because a standard roof has 100% run-off, and the list goes on and on. There's noise reduction and we've seen acid rain reduction. We've seen pollutants removed. So, these systems, as living systems, do wonderful things. MILES O'BRIEN: In the lab at Columbia University, civil engineer and project lead Patricia Culligan is working to make green roofs greener by growing vegetation in waste materials like this pulp from paper manufacturer. PATRICIA CULLIGAN: It's lightweight, so it offers a promising alternative to the current media that are used.

MILES O'BRIEN: If green roofs flourish, as these researchers hope, it may have planted the seeds of a revolution worth shouting about from the rooftops. For Science Nation, I'm Miles O'Brien..