Flat roofs are now made using polyvinyl chloride (PVC) or polyolefin. New welding and sealing methods involve hot air rather than open flames, and are much safer for roofers to work with, Groves says.

However, flat roofs are more difficult to dry-in, and work should be scheduled only when there isn’t any chance of precipitation. Don’t let winter weather stop you from re-roofing your home.