PLANT A GREEN ROOF

By creating a green roof layered with soil and plants atop your house, you not only add natural beauty to a landscape increasingly dominated by concrete and pavement. You also help reduce the urban "heat island" effect, by which cities tend to be several degrees hotter than surrounding areas, and you provide a roof-garden habitat for insects, songbirds and other wildlife.

Unlike the natural green areas that once covered the earth, most cities and suburbs are made primarily in shades of gray and black. Functional as they may be, the asphalt roads and tar roofs responsible for those drab colors also cause a host of problems:

• These manmade materials soak up the sun's radiation and reflect it back as heat, making cities at least 7 degrees hotter than surrounding areas. On Chicago's City Hall, by contrast, which features a green roof, temperatures on a hot day are typically 25 to 80 degrees cooler than they are on traditionally roofed buildings nearby. If all the roofs in a major city were "greened," urban temperatures could be reduced by as much as 12 degrees.
• The impermeable quality of traditional building materials makes storm water a problem, since there is nothing to prevent rainwater from rushing off rooftops, collecting pollution and heavy metal contamination along the way, and then overburdening urban sewage systems. Green roof strategies have been found to hold the pollutants in their soil while retaining up to 75 percent of the water and subsequently allowing it to return to the atmosphere through evaporation.
• Concrete landscapes also offer nothing to support the insects, birds and other wildlife that depend on vegetation to survive. Much like planting native gardens and backyard habitats, roof gardens can complement wild areas by providing "stepping stones" for songbirds and other wildlife facing shortages of natural habitat. Even in high-rise urban settings as tall as 19 stories high, it has been found that green roofs can attract beneficial insects, birds, bees and butterflies.

Sometimes known as "living roofs" or "eco-roofs," green roofs have also been found to extend roof life and to reduce heating and cooling costs dramatically.

Create a Green Roof on Your House

Green roofs are typically installed on flat roofs, but can be adapted for sloped roofs as well. They can be either "intensive," with about 12 inches of soil and a wide variety of plants, or "extensive," with about 3 inches of soil and a more limited selection of suitable plants. Extensive green roofs are less expensive, lighter, and easier to maintain. You should speak to a structural engineer or architect to assess an existing roof before making plans to convert it into a green roof.

How-to information, products, services and do-it-yourself kits are available from:

• Greenroofs.com
• ELT Easy Green GreenRoof Systems
• Green Roof Plants
• Roofscapes
• Green Roof Solutions
• Green Roof Tops
• BBC Gardening
• Green Roofs for Healthy Cities

A directory of green-roof experts and professionals is available at Greenroofs.com, and other suggestions and green roof links are available at Earth Pledge and Emery Knoll Farms.

Green Your Community

There are many examples of community efforts to create green roofs on shared buildings, including some notable projects in Portland.  A searchable database of green-roof projects throughout the world is available from GreenRoofs.com and volunteer opportunities abound.

To initiate a green roof project yourself, begin by asking building owners in your community to investigate the possibility of greening their rooftops. Sample letters are available from Greening Gotham.