Green roofs, essentially rooftops covered with a layer of lightweight growing material and planted with drought tolerant plantings that sit on top of waterproof barriers of existing roofs, have been embraced throughout Europe for the past 30 years. The market for green roofs continues to grow throughout the world. In Germany, for example, more than 145 million square feet of green roofing has been installed in just the past 10 years. In comparison, New Jersey has millions of square feet of black roof surfaces available for "greening."

Green roofs have become so popular in Europe in part because of government legislation and financial support. Yet the many benefits of this emerging technology are reason enough to consider the investment.

At its most basic, a green roof system is simply an extension of a building's existing roof. The green roof system includes a high-quality waterproofing layer; root barrier; drainage system; a filter fabric; and a lightweight, engineered growing medium designed for green roofs. Depending on the size of the roof, the types of plants selected and whether or not the system is accessible to building tenants, the project can range in cost from $10 to $24 per square foot.