Condensation: It's Causes And Cures

What causes condensation with windows and doors?

Whats causes condensationCondensation is a naturally occurring phenomenon that is not caused by nor cured by windows. Condensation occurs when excessive relative humidity is present inside the house. This can be caused by cooking, boiling liquids, washing and drying clothes, taking showers, watering indoor household plants, aquariums, and dishwashing. When this warm, moist air inside the house comes into contact with a cold surface such as a window pane and is cooled suddenly, condensation will form.

Excessive relative humidity inside the home can be reduced to help control condensation. Newer homes are especially prone to condensation as they are weather-stripped tighter, have better insulation and vapor barriers than older homes, thus trapping more moisture inside the home.

How can I stop condensation with my windows and doors?

Excessive relative humidity can be reduced by the following methods:

  • Running exhaust fans in bathrooms when showering and in the laundry room when doing laundry.
  • Check clothes dryer vent for leaks.
  • Run kitchen range vent when cooking or boiling liquids
  • Make sure attic and crawl spaces are properly vented
  • Properly vent all gas heaters to the outside
  • Open windows temporarily in bathrooms, kitchens, and laundry rooms to vent out excessive moisture.
  • Consider a dehumidifier if condensation problems persist.

During the heating season, the indoor relative humidity levels should be around 30-40%. When indoor humidity levels exceed 40% in cold weather, moisture problems usually begin to surface. Controlling this excess relative humidity using the methods described above will greatly reduce the likelihood of condensation formation.


The following resources were used in obtaining the above information:

Window & Door Manufacturers Association (WDMA)
1400 East Touhy Ave., Ste 470
Des Plaines, IL 60018


ASHRAE Handbook of Fundamentals 1999
[American Society of Heating, Refrigerating and Air-Conditioning Engineers, Inc.]
1791 Tullie Circle, NE
Atlanta, GA 30329


EWC [Efficient Windows Collaborative]
Alliance to Save Energy
1850 M Street NW, Suite 600
Washington, DC 20036

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