Cover and backer plates require more installation time but effectively shield lap joints where water leaks often occur. High-performance, elastomeric caulk also helps keep out water. Metal flashings must be large enough to do the job but small enough to prevent unnecessary movement. Most roof problems are due to water leaking in and around the perimeter and at corners or junctions in the roof plane. To avoid these problems, architects must think through the details three-dimensionally.
Perspective drawings help architects think through the detailing at corners and transitions.
Another cause of roof leaks is poor maintenance. Roofs should be inspected after major storms, heavy winds, and during and after construction. Understanding what lies beneath the flashing determines the quality of the job. The roof deck and the flashing systems may be adequate, but the deck may have poor nail-retention properties. As a result, the flashing will pull out under high winds, temperature extremes, or other stresses.