Cities encourage green roofs.

• Position: News & Numbers - Brief article

Green roofs may seem like a new development, but they've been in use for nearly 100 years.

They vary greatly in size and composition. Extensive green roof systems are relativey low-maintenance, using low-lying plants to create a light roof load, while intensive green roofs might include trees and other large plants. As far as scale, the new Facebook office building in Menlo Park, California, has a nine-acre green roof with a walking path and more than 500 trees.

Green roofs are seeing a resurgence in popularity because of their many benefits --they last 200 to 400 percent longer than a standard roof create energy and stormwater control savings that pay for the cost of the roof in as little as five to six years, and can generate energy cost savings of 25 percent to 50 percent, according to ConstructionDive. But the best reason...