Not as dumb as it sounds:
Overall building energy costs can be reduced due to the greenroofs’ natural thermal insulation properties – structures are cooler in summer and warmer in winter.
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."
And for the flattops:
Acoustic insulation properties also exist with greenroofs, and many have been placed near airports yielding great results in noise reduction. Due to the soft plant level of extensive greenroofs, sound insulation can be reduced up to 8 dB
www.zinco.de/evorteile.htm. According to Erisco Bauder Ltd. of England, “Noise protection can be as much as 25% for the extensive roofs and more for the intensive alternative.” The exact amount of noise reduction is hard to quantify and depends mostly on the thickness of the soil substrate and additional factors, i.e., leakage from skylights, but overall, up to a 50 decibel noise reduction can be realized (McMarlin, May/June, 1996).
