The sedum roofs of today symbolize performance-oriented green roof design. Like fine-tuned engines, they run on leaner artificial substrates with almost no organic matter; volcanic rock or expanded shale, baked at 2000 degrees Fahrenheit (1093 degrees Celsius), make the substrates lighter and soil depths as thin as possible. They seem to be race cars in the fleet of green roofs — maximum performance paired with minimum weight. The simple soil mixtures and roof sections of the early days of green roofs developed into multilayered complex systems supporting the homogenous surface of succulents. The unkempt and rough gave way to the groomed and cultivated, reminiscent of the unrelenting beauty of agricultural fields.
