Green Roofs are Great! … But Not Cheap Green roofs are rightly in the technical news. A plant-covered layer of soil on a roof can provide insulation and cooling in summer (http://en.wikipedia.org/wiki/Green_roof). Green roofs can provide insulation in winter (http:www.sciencedaily.com/releases/2005/11/0051126141309.htm). The plants in a green roof can help decompose pollution. Green roofs even have their own web page at http://www.greenroofs.com/ . Green roofs are defined as plant-covered roofs (not just a roof painted green). They function in two ways. First, the layer of soil and plant material is a significant addition to the typical roof insulation. Second, plants transpire moisture to the atmosphere and prevent heating of the roofing surface. (This is analogous to the way people sweat to prevent overheating.) As additional benefits, green roofs can produce crops, they can be exotic small parks for office buildings or condominiums.