Extensive green roofs are lightweight adaptations of sod roofs, like those found in Scandinavia during the Viking and Middle Ages. In fact, reconstructions of Norse sod houses dating from 1000 A.D. are protected as a UNESCO World Heritage Site in L’Anse aux Meadows, Newfoundland, and commemorate the earliest known European settlement in North America. Green roofs are an old idea!
During the oil crisis of the 1970s, West Germany explored lightweight adaptations of sod roofs for the purpose of energy conservation. Since that time, extensive green roofs have been lauded for their many benefits as cost-effective solutions for urban environmental problems. By 2005, an estimated 13 million m2 roof area in Germany was covered with plants.
As cities in other parts of the world learn about the benefits of extensive green roofs, adoption of this lightweight technology has been growing worldwide. In North America, the industry association Green Roofs for Healthy Cities was founded in 1999, and has organized annual green roof conferences every year since 2003. Cities that have adopted programs and/ or policies which promote extensive green roofs include Chicago, New York, Toronto, Portland, and Washington D.C.