When he first started designing his house, Robert Sweet envisioned a grassy rooftop over the first floor. "The purpose would have been to add insulation value and stormwater runoff," says Sweet, principal of Redondo Beach, Calif.-based ras-a inc.

But he soon came to this realization: Because the site is covered mostly in vegetation and gravel, runoff wouldn't likely be a problem. "The green roof would have just been bling," he explains. "It didn't make a lot of sense." So instead, he covered both roofs with a more affordable white elastomeric coating that deflects the sun's heat.

Whether or not a green roof is right for a project depends on three factors: site conditions, budget, and aesthetics. For more on the pros and cons of green roofs, read senior editor Nigel F. Maynard's Doctor Spec column from the March 2007 issue.