Photograph Courtesy: ReNatur© 98 Brochure
The origins of green roofs began thousands of years ago. The most famous green roofs were the Hanging Gardens of Babylon. They were considered as one of the Seven Wonders of the Ancient World, were constructed around 500 B.C. They were built over arched stone beams and waterproofed with layers of reeds and thick tar. Plants and trees were then planted. In more recent times, people used sod to cover their roof tops for the purpose of insulation, it kept their homes cool in summer and warm in winter. Modern green roofs may have had their "roots" in ancient times but technological advances have made them far more efficient and expensive than their ancient counterparts.
Modern green roofs are made of a system of layers placed over the roof to support soil medium and vegetation. This is a relatively new phenomenon and was developed in Germany in the 1960s, and has spread to many countries, since then. Green roofs are also becoming increasingly popular in the United States, although they are not as common as in Europe.
There are two general categories of green roofs- intensive and extensive. The factors that differentiate these two types include soil depths, loading capacities and their functions. Extensive green roofs have thin soil depths and less numbers of soil layers, hence they are less in weight, less expensive and need less maintenance. In contrast intensive green roofs have deep soil layers, wide variety of plants are grown which add to the weight and also they require high maintenance.
More details on the various features, including history, types, advantages of greenroofs:
ASCE Student Chapter Presentation, by Preethi Kaluvakolanu, December 2006