The "wet buildings" I see have waterpenetration problems for a number of reasons. Some buildings have poorly installed or punctured vapor barriers, others have inadequate ventilation. Sometimes, the building has a wet basement or crawlspace, or the owner may be at fault (four cords of wet firewood in the basement, for instance, or a clothes dryer vented indoors). But the most common problem I see is inadequate caulking and flashing. Faulty Flashing Let's review a few cases. Recently, I was called to look at a water problem at a hospital in the Midwest. The exterior wall was brick. Behind the brick there was a small air gap. Then came a layer of gypsum, 6 inches of insulation, and, finally, foil-backed drywall.