Published: Jan 2009
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TO UNDERSTAND MOISTURE PROBLEMS IN BUILDings, one must correctly determine the moisture sources. This chapter discusses the major sources of moisture in buildings, the rates associated with those sources, and frequencies of moisture dissipation. Several key equations are presented to estimate moisture sources for unique site-specific conditions. Excessive moisture within buildings can cause mold, mildew, and potentially damaging concealed condensation which, in time, distresses the building envelope's thermal and structural performance. Interior moisture sources are more important in colder climates, with more than 2,222 heat degree days (HDD) base 18.8°C (4,000 HDD base 65°F) and an average January temperature below 4.4°C (40°F) where the relative humidity within the building could be 45%. In the summer, moist outside air is the more important moisture source. Moist air from the outside is generally an important moisture source of concern in regions meeting the ASHRAE definition of a humid climate . A humid climate is defined as one in which one or both of the following conditions occur: 1. A 19.5°C (67°F) or higher wet-bulb temperature for 3,500 h or more during the warmest six consecutive months of the year. 2. A 23°C (73°F) or higher wet-bulb temperature for 1,750 h or more during the warmest six consecutive months of the year.
Christian, Jeffrey E.
Program manager, Oak Ridge National Laboratory, Oak Ridge, TN