More about Air-Transported Moisture
Air-transported moisture is water in the form of vapor carried through the air allowing the water vapors to leak into, or out of, buildings. There are several factors to be considered when decreasing the effects of air transported moisture. Independent pressure sources (such as wind or stack effect) and controlled sources (fans and air handlers) can move substantial amounts of moist air past a building's envelope through holes. Leaky ductwork can cause moisture problems by increasing the level of infiltration, and by drawing air in from a humid crawlspace or basement area. As this moist air travels through a building, moisture will condense on any surface with a temperature that is below the dew point. The amount of condensation that forms depends on several factors: inside versus outside temperatures, the relative humidity, and the speed of the air moving across the condensing surface. Windows and poorly insulated walls are colder surfaces that condense moisture more easily. Air moving more slowly allows more time for condensation to form. There is more moisture available when the relative humidity is higher. Effective sealing against infiltration, sealing the ductwork, and pressure-balancing the HVAC system are the best defenses against outside air carrying moisture. Exhaust fans in all bathrooms and kitchens help to remove indoor air moving moisture at its source when used correctly. Remove potential sites for condensation by heating and cooling areas at temperatures above the dew point.