Green roofs

Last summer I downloaded Google Earth so I could locate my daughter’s new apartment in New York City. Google Earth, if you aren’t familiar with it, is a free program that will take you anywhere in the world – plug in an address and you have a aerial photograph of that place in a couple of seconds. Zoom in or out for a smaller or larger view. So I did, finding my daughter’s neighborhood and her new apartment building right away, nestled in a fairly solid block of other 4-story buildings south of Houston Street.

The interesting thing about an aerial photograph of New York City is the sea of flat grey and black roofs. A few trees struggle up between the buildings providing a spot of green here and there, but mostly you see concrete, stone, and asphalt. Mile after mile.

So I was delighted when the September 2006 issue of Metropolis appeared in my mailbox. Its lead article features green roof technologies, highlighting several pioneering projects in Chicago, Long Island City, Washington, Boston, and Liuzhou, China. This is a technology that deserves a lot more attention. Picture New York City as a sea of green rooftops and you begin to see the potential.

One of the projects Metropolis zeros in on is Silvercup Studios in Long Island City, just across the East River from Manhattan. Silvercup has installed the largest green roof in New York, using a system of membranes and planting modules manufactured by GreenTech.

Long Island City was once heavily industrial, but its buildings are now being transformed into other uses. Apparently the city has lots of flat roofs, more than 26 million square feet of flatness that could be outfitted with green-roof technology – over 55% of the neighborhood. Move the idea across the East River and out to other cities and towns and you would have incredible benefits.

Ponder these facts, taken from the article:

  • Percent of 2005 population living in cities: 49
    In 2030: 60
  • Rise in average global temperature between 1900 and 2000: 1 to 1.5 degrees F
    Between 2000 and 2100: 3-5 degrees F
  • Fraction of U.S. energy that goes toward cooling buildings: 1/6
  • Temperature of a conventional roof membrane on a 95 degree day: 158 degrees
    Of a green-roof membrane on the same day: 77 degrees
  • Heat loss of green roof compared to conventional roof: 18 percent less
  • Reduction in summer cooling needed for a one-story building with a four-inch grass roof compared to one with a conventional roof: 25%
  • Stormwater retention rate of green roof compared to conventional roofing material: up to 6 times greater

Green roofs provide great insulation for buildings leading to lower energy consumption and they reduce stormwater runoff, but they also decrease the temperature of surrounding urban areas, clean the air, look beautiful, and create rooftop living spaces for people and wildlife.

Unfortunately, green-roof technology is just getting going. Metropolis Executive Editor Martin Pederson sums it up:

‘The Green Roofing of America’ certainly has a nice ring to it, but the idea remains more wishful thinking than reality. True, there are more green roofs in operation than ever before, but the bulk of new construction is built without any environmental considerations at all. Still, in this era of dwindling resources and rising temperatures, it’s worth noting that even the most banal green roof (think grass) offers real and lasting benefits. Like hybrid cars, green roofs look to us like an ecological no-brainer: an obvious solution to intractable problems.

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