Homes with flat or low-slope roofs generally have a "built-up roof" more commonly called tar-and-gravel. A built-up roof consists of several layers of roofing felt, each coated with a layer of asphalt. The top layer is covered with crushed rock or gravel to protect the asphalt-felt layers from the Sun. You can expect this type of roof to last between 15 and 20 years.

Extensive exposure to intense sun and heat causes blistering. Fortunately, they are reasonably easy to repair. First, clear the area to be repaired of all gravel and debris. Then use a utility knife to cut into the asphalt and roofing felt until the pressure under the blister has been released. Cover the cut and surrounding area (about two to three inches to each side) with a generous amount of roofing cement. Cut a small patch from a piece of roll roofing and nail it down over the prepared area with galvanized roofing nails. Then cover the repair with more roofing cement and replace the gravel when the cement has started to dry.

Large repairs (one foot or more) should be made by a professional roofer. And remember, roof repair is not an alternative for a roof badly in need of replacement.