An engineering study done from July 2005 to Jan. 2007, shows that a green roof has the potential to lower stormwater runoff from 65% to 94%, as well as allow building owners to reduce the size of stormwater detention tanks needed for peak rainfall. These benefits can offset the cost of a green roof by 30% to 60%, according to Magnusson Klemencic Associates. Click here for the full story.