Condensation

Condensation in homes usually occurs when warm moist air comes in contact with a colder surface. Warm air can hold more moisture than cold air, it has a higher "dew point" than colder air. For example, when the air in a home is heated it can hold more moisture than the colder air at the outside of the home. If the warm air absorbs a great deal of moisture and then comes in contact with a cold surface, e.g. the roof sheathing, then the moisture in the warm air changes from a vapor into a liquid. It condenses. This is turn can cause all sorts of damage including fungal wood rot.

See also: Topics: Gutters, Downspouts, and Drains