Why have an ordinary roof of no value, when instead you can build a living roof and benefit the environment and your city? People in cities around the world are choosing to turn the negative space of a traditional roof into a garden on both residential and commercial buildings. There are millions of acres of rooftops around the globe that could be converted to green space.
A typical green roof consists of many layers. Vegetation lives in a growth medium; an engineered soil composite is used to reduce the weight. Several membrane layers lie underneath the soil. A drainage layer allows excess water to flow freely and a root barrier layer prevents the roots from penetrating the roof. There are two types of green roofs: intensive and extensive. Intensive green roofs require a fair amount of regular maintenance but can sustain a wide range of plant species. Extensive roofs are more common because they require less work. Extensive roof soil is typically only 2 to 4 inches deep compared to 1 or 2 feet of soil in an intensive roof. A shallower depth inhibits weeds from establishing themselves on the roof.
There are many benefits to these living roofs. They help to reduce storm water run off by absorbing rainwater. The water that does drain off flows slower and is cleaner because the vegetation and soil mixture act as a filter. Green roofs can help reduce the amount of storm water that has to be treated by municipal water treatment plants and therefore lessens the threat of sewer overflows.
Although the installation cost of a green roof is typically two to three times more than a traditional roof, energy savings can make up for this initial expense. The vegetation and soil of green roofs act as effective insulation, reducing heating and cooling costs by as much as 20 percent. This additional insulation also acts as a sound barrier, which is pleasing for homeowners close to busy highways or noisy streets. The reduction of the urban heat-island effect is a large advantage provided by green roofs since they stay cooler than conventional roofs.
The sun breaks down the material of traditional roofs over time and forces homeowners to replace the roof. The shelter that the vegetation and soil provides can greatly increase the roof life span. Green roofs can also create a habitat for wildlife. Birds and insects can easily find homes in the living environment of a green roof. It is even possible to graze goats!
In Portland, Oregon, fee reductions and other incentives encourage builders and homeowners to consider green roofs. In Germany, approximately 14 percent of the country’s total roofs are green partly because some cities levy a tax on conventional asphalt rooftops. Living roofs are required by law on roofs of suitable pitch in some cities in Germany, Switzerland, and Austria. Although the number of green roofs is increasing in America, extra incentives could help to speed up the trend.
So why not swap your shingles for vegetation? Utilize the wasted space to help reduce storm-water runoff, increase energy efficiency, and enhance your neighborhood surroundings.
Klinkenborg, Verlyn. “Up on the Roof.” National Geographic May 2009: 84-103.
Colwell, Dara. “Green Roofs: Building for the Future.” Alternet (2007): 31 Jan 2010.