Once the stuff of "home of the future" exhibits, green roofs are now becoming a reality on top of city buildings as well as regular homes in neighborhoods around the world. Technically speaking, a green roof is a vegetative layer grown on a rooftop [source: Environmental Protection Agency], but installing a rooftop garden isn't the only way to improve the "green" quotient for that unused space on top of your house.
The rooftop garden atop Chicago's City Hall is perhaps the best known example of a green roof in the United States. Completed in 2001, it occupies 20,300 square feet (1,866 square meters) of the 38,800 square-foot (3,605 square-meter) rooftop and saves the city approximately $5,000 each year in utility bills [source: Green Roof Projects]. With nearly 500 green roofs installed or under construction as of April 2010, Chicago leads U.S. cities in green rooftop square footage, but those 500 buildings account for just one-tenth of one percent of the 500,000 total buildings in the city [source: Kamin]. Compare this with Germany, where rooftop gardens can be found on 15 to 20 percent of all flat-roofed buildings, and it seems the United States has a long way to go in adopting green roof practices [source: Kamin].
With all their potential to reduce energy costs, alleviate the urban heat island effect, and even provide viable land for urban farming [source: Shulman], why have rooftop gardens been so slow to catch on in the United States? One probable factor is cost. A "green roof" in the true sense of the term can be yours for anywhere from $10 per square foot for a simple "extensive" green roof consisting of shallow soil and a hardy ground covering, to upwards of $25 per square foot for a more complex "intensive" green roof, complete with larger plants, shrubs and even small trees [source: Environmental Protection Agency].
Rooftop gardens clean the air, beautify urban landscapes, and contribute to cooler indoor and outdoor air temperatures, but if they are outside your budget, there are plenty of other options available to help you green your roof for less. Which one is best for you? Read on to find out!