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Excess Moisture in the Home

Written by University of Minnesota Extension faculty

Do you have symptoms of excess moisture in your home? Symptoms include:

• condensation on windows during the winter
• mildew growing in the bathroom
• mold growing in the corner of a closet, kitchen or bathroom
• peeling, cracking or blistering paint

Indoor activities such as bathing, cooking, dishwashing, and just breathing all produce moisture. Other moisture sources in the home include plants, large pets, humidifiers, stored firewood, leaky plumbing and gas appliances, outside air during humid weather, and the damp soil under many basements and crawlspaces.

Relative humidity describes the amount of moisture in air at a given temperature. In colder weather, keeping relative humidity lower helps to reduce moisture problems in homes. When the relative humidity is more than 50%, moisture problems may occur. This could cause damage to the structure of the house and encourage mold growth which causes some people to develop allergies and respiratory problems. Keeping the relative humidity at 30 to 45% is healthy and comfortable for occupants and better for the house.

To control a moisture problem, you must identify the source. You can reduce or eliminate high moisture levels in your home by:

• reducing sources of water evaporation (bathing, cooking, humidifiers, etc.)
• installing a fresh air supply on the return side of the furnace (this can bring fresh, dry air into the home to replace stale, moist air that is exhausted)
• installing or inspecting and repairing exhaust fans in your bathrooms
• inspecting exhaust ventilation systems to make sure they are working properly
• installing an exhaust fan in the kitchen to remove moisture caused by cooking
• opening windows just a little allows warm moist air to leave the home and also allows cold, dry air to come in
• sealing openings that might allow warm, moist air to enter walls, ceilings, and the attic where it may become a cause of structural damage to the home