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Green Roofs

By creating a green roof layered with soil and plants on top of 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 grey and black. Functional as they may be, the hard surfaces responsible for those drab colours also cause a host of problems:

• These manmade materials soak up the sun's radiation and reflect it back as heat, making cities 2 to 3 degrees centigrade hotter than surrounding areas. On a building which features a green roof, temperatures on a hot day are considerably cooler than they are on traditionally roofed buildings nearby.

• 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.

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.

We recommend a visit to www.livingroofs.org for more info.