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Raising the (green) roof

Green roofs are the new black tar



Anyone building a new home or business--or renovating an older structure--could slash their heating and cooling bills by 25 percent, double the life of their roof, reduce stormwater runoff, help clean the air, create urban wildlife habitat, and make their building look fabulous by changing just one thing. When it comes time to replace ugly asphalt shingles or a tar and gravel roof, do it with what's called a "green roof." It's a shallow expanse of garden that can be installed on any structure--house, office, school, factory, shopping mall.

The green roof on Chicago's City Hall was designed by a team that included Conservation Design Forum, a pioneer in the application of green roof technology in the United States - PHOTO COURTESY OF CONSERVATION DESIGN FORUM
  • Photo courtesy of Conservation Design Forum
  • The green roof on Chicago's City Hall was designed by a team that included Conservation Design Forum, a pioneer in the application of green roof technology in the United States

Green roofs vary in construction, but what they all share are tough-as-nails plants growing in a lightweight soil mix. The soil covers a waterproof liner so all you see are colorful plants. This ecosystem is enclosed by an edging that allows water to drain from flat roofs, and the edging safely contains the plants and soil on pitched roofs.

The plants used on green roofs can survive extreme temperatures, drought and lean soil. Soil as shallow as 4 inches nurtures low-growing succulents such as sedums, hens-and-chicks and ice plants. Wildflowers, bulbs and herbs such as columbine, hyacinth and lavender thrive in only 6-8 inches of soil. Soil more than 8 inches deep allows shrubs and small trees to grow. Philadelphia-based design and installation firm Roofscapes names their various options "Flower Carpet," "Aromatic Garden," "Meadow," "Woodlands," etc.

In other words, green roofs are a modern version of the medieval sod roof, a perfect example of low-tech meets high-concept.

So how does a lean, green roof do all these great things?

  • The soil and plant carpet insulates the building while providing thermal mass and evaporative cooling, helping keep out both summer heat and winter cold.

  • The plants and soil absorb water, reducing stormwater runoff and improving water quality for our slippery friends.

  • The leafy shade mitigates the "urban heat island" effect caused by our urban ovens of masonry. (Atlanta, for instance, is 13 degrees hotter in summer than the farmland beyond its suburbs.)

  • The roof itself is shielded from the sun's UV rays that break down conventional roofing. The longer-lived green roof saves landfill space (not to mention cuts down on the use of petroleum-based shingles, tar roofs and cash).

  • The plants absorb air pollutants and create animal habitat--in fact, a duck nested and hatched ducklings on the green roof of Mountain Equipment Co-op in Toronto.

    Anita Bahe is an environmental consultant for Lynx Group International LLC who's working with Durham's West Village on a proposed green roof that will be accessible to tenants of the refurbished Chesterfield building, between downtown and Brightleaf Square. She says the return on investment makes the inclusion of a green roof in a project "in most cases, a no-brainer."

    Although the green roof industry is very young in the United States, it has grown up in Europe--mainly in Germany--over the last 35 years. In 2001, more than 3,000 acres of buildings in Germany were shaded by vegetated roofs.

    In Canada, the Toronto City Council recently committed to putting green roofs over 50 to 75 percent of the footprint of new public buildings. After the savings in utilities pays for the roofs' higher sticker price, millions of dollars will be available for other public needs. A hotel in Vancouver saves $40,000 a year by growing all the herbs its restaurant needs on its green roof, which local garden club members maintain in exchange for free use of the hotel's gym.

    The idea is finally taking hold in the United States, even at an initial cost of twice that of a conventional roof. In fact, after Mayor Richard Daley visited Europe in 1998, he committed to making Chicago the greenest city in America. He can now boast of more than 120 public and private buildings topped with living roofs, including a McDonald's and an Apple computer store.

    The fourth-floor green roof on Atlanta's City Hall serves as a plaza for visitors to the fifth-floor cafeteria, and a green roof on a business center in Baltimore covers three-quarters of an acre and reduces runoff into the Chesapeake Bay by 50 to 75 percent. Green roofs adorn a Mormon conference center in Salt Lake City and cover a below-ground parking deck in Houston.

    Low-growing succulents can survive brutal rooftop conditions - PHOTO COURTESY OF BROWN AND JONES ARCHITECTS, INC.
    • Photo courtesy of Brown and Jones Architects, inc.
    • Low-growing succulents can survive brutal rooftop conditions

    Right here at home, there's a green roof on the downtown Raleigh offices of Brown & Jones Architects, Inc. They held an old-fashioned roof-raising in February 2003, inviting colleagues to help install their 1,400 sq. foot green roof. A desire to reduce stormwater runoff is a driving force behind a green roof on a UNC-Asheville building that Brown & Jones designed.

    Charles Brown knows of only one green roof being considered for a single-family house locally. And at present, only one has been installed residentially on the East Coast--in Philadelphia. But there are dozens in the Pacific Northwest and many more in Canada. Given all the financial, aesthetic and environmental virtues of green roofs, it's reasonable to wonder why they aren't more common in the United States. In Planting Green Roofs and Living Walls (Timber Press, 2004), Nigel Dunnett says that it's due to more to a lack of awareness of the benefits than to technical hurdles. With examples on display in more and more cities, green roofs are poised to be one of the most affordable and successful design solutions that an individual or community could commit to.

    Will the Triangle take a step that enhances the health of our built environment and ultimately saves tax money, too? Or will new public construction--such as Wake County's proposed $1 billion school bond--give us the same old, expensive, planet-ruining crap? The answer to that question will depend on whether you, reader, apply pressure to our local officials.

    One green roof at a time, and we'll have it made in the shade.

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