Here we will address four principles that will help us better understand how our homes perform. Moisture movement 2. Dewpoint temperatures 3. Heat flow 1. Moisture wants to move from areas of high vapor pressure to areas of low vapor pressure.
Vapor pressure is the pressure exerted by water molecules in a mixture of air.
RH is a percentage that indicates the amount of moisture in the air relative to the maximum amount the air can hold at that temperature. Warm air can hold more moisture than cool air, so the RH of a sample of air will change as the temperature changes, even though the actual amount of moisture in the sample does not. This is a function of both temperatures and the amount of moisture in the air. If we have a dewpoint of 40 degrees, any surface in the home that reaches this temperature will have liquid water on it. To prevent this condensation, we can either raise the surface temperature or lower the relative humidity.