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Do you have too much moisture in your home?

Rain on window.

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

  • Condensation on windows during the winter.
  • Excessive mildew in the bathroom.
  • Mold growing on interior surfaces (corner of a closet, kitchen or bathroom).
  • Peeling, cracking or blistering paint on exterior or interior finishes.
  • Excessive dust mite populations (a cause of dust allergies).

Indoor activities such as bathing, cooking, dishwashing and just breathing all produce moisture. Other moisture sources in the home include:

  • Plants.
  • Humidifiers.
  • Stored firewood.
  • Plumbing leaks.
  • Unvested gas appliances.
  • Outside air during humid weather.
  • Damp soil under many basements and crawlspaces.

Relative humidity

Relative humidity describes the amount of moisture in air at a given temperature. Keeping relative humidity lower helps to reduce moisture problems in homes. When the relative humidity is more than 50%, several moisture problems may occur under certain exterior and interior conditions. Generally, in cold winter conditions the relative humidity levels must be much lower to prevent condensation and potential damage to the structure of the house or to encourage mold growth which causes some people to develop allergies and respiratory problems.

Keeping the relative humidity at 25% (winter) to 50% (summer) is generally considered healthy and comfortable for occupants and better for the house.

Identify the source of moisture problems

Pot of boiling water on the stove.

To control a moisture problem, you must first identify and remove the source. If that isn't possible, then moisture removal with ventilation or dehumidification should be used. Reduce or eliminate high moisture levels in your home by:

  • Reduce sources of water evaporation (bathing, cooking, humidifiers, etc.).
  • Install or inspect (and repair) exhaust fans in your bathrooms.
  • Install an exhaust fan in the kitchen to remove moisture caused by cooking.
  • Bring dry outdoor air into the home to replace stale, moist air that is being exhausted.
  • Check that exhaust ventilation systems are working properly.
  • Consider adding a whole house ventilation system.
  • In winter, temporarily open windows just a little to allow warm moist air to leave the home and also allow cold, dry air to come in.
  • In summer, use a properly sized air-conditioner or stand-alone dehumidification system to reduce the indoor humidity.
  • Seal 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.

Diane H. Corrin; Richard Stone, Extension educator; and Patrick Huelman, Extension professor

Reviewed in 2018

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