A client calls to describe a problem. The building is a 12-storey south Florida hotel, with stucco on building paper on 6" steel stud (filled with batt) wall system finished on the inside with drywall and thick fancy vinyl wall paper. The building has a continuously-operated exhaust-only fan operating to remove stale air from the expensive guest rooms and is very well air-conditioned for comfort. The client explains that the guests are complaining of a musty smell in some of the rooms, especially near the top of the building. Explain your hypothesis about the cause of the musty smell. Describe the mechanisms at work. What do you expect to see when you fly to Florida and open up the walls to inspect them. Answer in the LEARN-provided box