Moisture Condensation Problems

Rocket science part 2 - moisture condenses on cold surfaces, such as windows and outside walls, due to a combination of relative humidity and temperature. As air cools, caused by its contact with cool surfaces, the relative humidity of the air increases until it reaches saturation. When that saturated air is cooled, some of its water vapor turns to liquid water and clings to the cold surfaces that cooled the air. Condensation occurs most frequently and plentifully on the room's coldest surfaces. Condensation increases as relative humidity increases and as surface temperatures decrease.

Effective strategies for reducing moisture condensation include:
1) Reducing relative humidity by reducing moisture sources.
2) Equalizing pressure between indoors and outdoors.
3) Installing or improving air and vapor barriers to prevent air leakage and vapor diffusion from transporting moisture into building cavities.
4) Ventilating with drier outdoor air to dilute the more humid indoor air.
5) Removing moisture from indoor air by cooling the air to below its dew point, with refrigerated air conditioning systems and dehumidifiers.
6) Adding insulation to the walls, floor and ceiling of a home to keep the indoor surfaces warmer and therefore more resistant to condensation. During cold weather, well-insulated homes can tolerate higher humidity, without causing condensation, than poorly insulated homes.

Next Topic: Actions to Control Relative Humidity