Top 10 Green Roofing Options

Modified Bitumen (Tar)

You probably wouldn't associate a cauldron of hot tar with a cool roof, but this is not your highway department's tar. The key lies in the modification. "It's modified with a plastic, and it's layered with reinforcing material," Clark says. "What really makes it cool is that it's a cap sheet."

The technology can be used to top off an insulated roof, or it can be used as the primary roofing system. Some cap-sheet technologies require torching or hot-mopping the surface to seal it, and some modified bitumen products come with attached adhesive, like a big contact sheet. By eliminating the hot-mopping, the material can be installed without generating fumes.

Some products are fire- and wind-resistant, and with the right surfacing, this material can be a bona fide cool roof, as well.