Construction of a large luxury resort located in a warm, humid climate was coming to a close during the summer. Because the vinyl wall covering on the interior side of the exterior walls had an impermeable finish, it functioned as a vapor retarder (also referred to as a vapor barrier).

The HVAC system consisted of a continuous toilet exhaust and packaged terminal air-conditioner (PTAC) units. The outside air exchange rate in each guest room averaged six times an hour, all from infiltration.

In this case, problems developed both inside the building and inside the wall.

The combined effect of excessive outside air infiltration and an improperly located vapor retarder caused $5.5 million in moisture and mold damage, even before the facility was opened (Figure 1). If these same design combinations had occurred in a more temperate climate, the problems would have been limited to increased energy consumption and possible complaints about guest comfort.

This is one example of how hot, humid climates present unique challenges that are often overlooked by the design and construction community. However, challenges also occur for buildings located in other climates. Meeting these challenges depends on understanding a building’s local climate conditions and how they contribute to IAQ and mold problems.