The Environmental Benefits of Roof Gardens

Imagine peering down from the window of an airplane that's flying over a major city and seeing a veritable forest of green below. Sound like the Utopian vision of a science fiction novel? This scenario is actually becoming a reality, albeit gradually, as more and more urban buildings are using their only available space - their rooftops - to cultivate gardens that can work wonders on the surrounding environment.

America has been a little slow in comprehending and capitalizing on green roof technologies, and its markets remain immature in comparison to many countries across the Atlantic. Roof gardens, which feature layers of soil deliberately placed over roofs to support vegetation, were first developed in Germany in the 1960's. From there they spread to other European countries. It's estimated that 10 percent of German rooftops have become "greened". In America, the practice is becoming more common in cities like Chicago, Atlanta, and Portland, where legislation encourages it.

Chicago's City Hall roof garden, one of the most prominent and well-known in the U.S., is significantly cooler during hot summer months than the surrounding area. The "heat island effect" occurs in cities when traditional building materials reflect the sun's radiation back as heat, making these urban environments at least 7 degrees hotter than other areas where the overall temperature would otherwise be the same. Gardens offset this problem by absorbing the heat into their soil and organic matter.

Rooftop gardens offer a slew of other advantages as well. They can produce food, as well as plants that are useful for other purposes (like botanical medicine). They store water, which can reduce flooding (and wastewater contamination) from stormwater runoff. Buildings with roof gardens benefit from increased thermal as well as noise insullation. There is simply no other way to bring nature's bounty into tightly-enclosed city environments than by taking advantage of unused roof space.

The gardens grown on these otherwise vacant spaces work to combat pollution, as well. Rooftop plants filter Carbon Dioxide and other pollutants out of the air. Their roots drink up the rainwater, removing pollutants and heavy metals out of it in the process. Rooftop gardens also encourage "green" practices in their tenants, like organic waste recycling through composting. All in all, they are increasingly becoming a focus for reducing the negative environmental impact of cities.

Last but not least, they can serve as feeding stations. A variation known as "brown roofs" - which consist of a thin layer of crushed ribble and gravel - are intended to be colonized by spiders and insects, which then provide food for birds.