Abstract: When discussing moisture-related problems in high-humidity buildings, natatoriums and museums typically come to mind as the most challenging building types. However, specific design requirements for temperature, relative humidity (RH), and air pressure differentials in hospitals and healthcare facilities can create moisture conditions that are equally problematic. The impact of the interior environment on the building enclosure is often overlooked in favor of other design criteria in what are often considered "mission critical" facilities. This can result in both visible and concealed moisture problems that are difficult and expensive to repair. The American Society of Heating, Refrigeration, and Air Conditioning Engineers (ASHRAE) provides guidelines and recommendations for healthcare and outpatient facilities in its 2007 HVAC Applications handbook. Conditions for most spaces are generally in the range of 68-75°F and 30-60% RH annually with relatively high ventilation rates (up to 20 air changes per hour). However, some special-use spaces have more extreme temperature and RH requirements?including radiology (78-80°F and 40% winter RH) and post-operative suites (75°F and 45-55% winter RH). The exterior enclosure for these two spaces must be designed to accommodate interior dew points of up to 54°F and 58°F, respectively. Other areas, such as specialized equipment rooms for medical imaging, may similarly require humidification to control electrostatic discharge (ESD), which could cause damage to the sensitive equipment. Although 30% RH is relatively low when compared to the 50-60% levels encountered in museums or indoor swimming pools, it is sufficient to cause condensation, especially during the winter months. In ventilated, non-humidified buildings, interior moisture levels are largely dependent on the exterior conditions. During the winter, when low exterior temperatures create the greatest risk of interior condensation, the ambient moisture levels are also low.