If you were to cut a cross section of a green roof, it would look like a parfait or a terrine: layers of waterproofing, root barriers, insulation, drainage, soil and the plants themselves.
As part of its sustainability project, the City of Raleigh lists 13 spots that have vegetative green roofs, ranging from private homes to city offices to N.C. State buildings.
The benefits: They insulate structures from the heat, which decreases energy costs; reduce the amount of storm water runoff by absorbing it into the soil; provide birds and bees additional habitat; and mitigate the urban heat island effect—you've felt this if you've ever baked your brains while walking across a parking lot in the summer.
The challenges: You have to select plants that can survive the Southern heat; the roofs have to be reinforced because of the weight of what is essentially a garden on top of the building; you have to maintain the roof. (If you consider mowing your lawn burdensome, a green roof could prove too taxing.) Looking to install one? Try the directory at greenroofs.com.