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Q.A customer has a building with a nearly flat roof surrounded by a parapet. The roof drains to a single scupper, which conducts the water to a downspout. Ice builds up regularly in the downspout, and the water backs up and spills down the wall. What’s the best way to keep the downspout free of ice?

A.Architect and roofing consultant Harrison McCampbell responds: No roof should depend on a single scupper or drain. In fact, this may be a code violation. Solving this problem probably requires installing an additional scupper or drain, and may involve adjusting the slope of the roof. In addition, the size of the existing drain opening and downspout may need to be increased.

If a roof depends on a single drain, and that drain gets clogged, the result can be catastrophic. Remember, water weighs over 5 pounds per square foot per inch of depth. Even 4 inches of standing water exceeds the live load capacity of most roofs.