Dew Point and Mold

The Dew Point is the temperature to which the air must be cooled before it becomes saturated. When it is saturated, it is holding all the water vapor it is able to hold. The dew point cannot be higher than the temperature. It can be the same, but not higher

Warm air can hold more water than cold air or said another way, as air cools, it loses its ability to hold water. The dew point (the temperature at which moisture will condense out of the air) correlates with absolute humidity 100%.

The dew point is an indication of how much water vapor is in the air. The more water vapor, the closer the dew point is to the temperature. When the air becomes saturated, the dew point and the temperature are the same.

Understanding the dew point is one step in better understanding where mold might come from in your home. Certified Industrial Hygienist Barry Westbrook writes in the American Home Inspectors Directory,

"Dew point is the other scientific principle necessary to understand the mold phenomenon. For water vapor in the air to condense onto a surface, the temperature of that surface must be below the dew point. At that point, the air is 100% saturated and can no longer hold all the moisture. The air begins to drop some of the water onto the surface as condensation. The colder the surface, the more condensation will form. That is why there is usually more mold underneath bathrooms and kitchens. These floors are not insulated as well as carpeted floors, and become very cool in the summertime.