As an architect who has worked with the roofing industry since 1977, I often inspect leaking roofs. I have found that poor flashing details - at penetrations, at roof edges, or where a roof changes planes - are much more likely to be the cause of a leak than the roofing itself. Similarly, many leaks are caused by the use of insufficient or inadequate fasteners for sheathing, flashing, or roofing, and by the attempt to substitute caulk or roofing cement for flashing. The cost of installing the roof on a new building usually amounts to less than 5% of the total construction cost. Yet some lawyers estimate that 60% to 80% of construction lawsuits involve roof failures. Often, it's a small leak that quickly grows into a big, expensive problem. The following problems are among the most common I encounter. In every case, the leak could have been avoided had the installer used and paid more attention to detail.
Problem: No support at sheathing edges. The plywood sheathing on this flat roof was installed without blocking under the edges. If someone walks on the roof, the roofing may crack when the sheathing flexes at the plywood joints.
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