By Barry Stone
Dear Barry,
A home inspector has faulted my garage roof for lack of drainage. This is a flat roof, and the joists have sagged, allowing rainwater to pond at the center, rather than draining toward the roof edges. Fortunately, a new layer of hot mopped roofing was installed less than one year ago, and no leakage occurred during the last rains. Still, the home inspector regards the lack of drainage as a substandard condition. Is it possible that this home, which was built in 1979, predates the current requirement for roof drainage? Leonard
Dear Leonard,
Lack of adequate drainage is a common problem, affecting nearly half of all so-called "flat" roofs. Insufficient roof slope promotes standing pools of rainwater, a condition known as ponding, and this increases the likelihood of eventual leakage as a roof becomes older.
A home constructed in 1979 would be subject to the 1976 Uniform Building Code. According to that code, "Unless roofs are sloped to drain over roof edges or are designed to support accumulated water, roof drains shall be installed at each low point of the roof." Since the roof joists on your home have sagged, it would seem that they were not designed to support accumulated water. Therefore, the addition of drains at the low points of the roof would appear to be in order.
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