Late last year, a couple called me about some leaking windows on the back of their 5-year-old stucco house. My company hadn't built the home; it was part of a tract development in Southeastern Pennsylvania thrown up during the recent housing boom. Other houses in the neighborhood had similar problems, and the owners were frustrated that, despite several attempts, the original builder hadn't been able to stop the leaks. They called me because I had fixed the same problem for neighbors across the street.

More often than not, the culprit behind a leaky stucco wall is a poorly detailed drainage plane, and that was certainly the case here. The first thing I noticed was that there was no casing bead around the windows. Casing bead creates a separation between the stucco and the window or door casings, so that the framing and sheathing can expand and...

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