It’s the concept of greenroofing, and it’s explained in great detail at Greenroofs.com. [1]
Basically, greenroofs are vegetated roof covers, with growing media and plants taking the place of bare membrane, gravel ballast, shingles or tiles. The number of layers and the layer placement vary from system to system and greenroof type, but at the very least all greenroofs include a single to multi-ply waterproofing layer, drainage, growing media and the plants, covering the entire roof deck surface.
What are the advantages of greenroofing? [2] There are ecological, economic [3], aesthetic & psychological advantages.
Here are some of the economic advantages: [4]
Overall building energy costs can be reduced due to the greenroofs’ natural thermal insulation properties – structures are cooler in summer and warmer in winter. The urban “heat island” effect can also be greatly reduced since vegetative roofs reduce ambient air temperatures. Therefore, less electricity costs are expected from lower a/c and heat usage.
According to an article from the Environmental News Network, “a 3- to 7-degree temperature drop translates to a 10% reduction in air conditioning requirements. For a one-story structure with a green rooftop, cooling costs can be cut by 20 to 30%.” The Weston Design Consultants recently conducted an energy study for the city of Chicago which estimated that it would be possible to save $100,000,000 in saved energy annually with the greening of all of the city’s rooftops. The bottom line is that “Peak demand would be cut by 720 megawatts – the equivalent energy consumption of several coal-fired generating stations or one small nuclear power plant.”
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