Green Roofs

If you're thinking that green roofs are some kind of tree-hugging, 21st-century eco-design trend, think again. The earliest settlers of the Great Plains lived in sod houses. So did 18th-century Germans and 12th-century Icelanders, who carved these sod-covered homes out of hillsides; they found that the pesky vegetation that grew naturally on their rooftops provided needed insulation.