Condensation in your home

315807334_f57641773eABOUT CONDENSATION

During cold winters, there is a great temperature difference between the inside of a house and the weather outside.  When the temperature drops outdoors, the glass on you windows and doors tends to have lower temperatures than other surfaces in your house, and is the first place that you’ll notice condensation in your home.  This is not due to any defect in your window or door; it’s simply a sign of thea high humidity in your home.  Warmer air is capable of holding much more moisture than cooler air.  When the temperature reaches its dew point, the moisture condenses, attaching to the nearest cool surface.  The first surfaces where you’ll notice this happening is the glass on windows and doors.  Condensation is an unsightly problem.  The last thing you want on your windows is a fog blocking the view.  But the problem goes deeper than that—if condensation is a chronic occurrence in your home; chances are it is accumulating on other harder to see surfaces such as wall and roof cavities.  If left uncontrolled, excess moisture can have serious consequences, including:

  • Mold or mildew
  • Wood rot and warping
  • Roof ice build-up
  • Damp, ineffective insulation
  • Discolored, blistered or bubbling pain
  • Damaging moisture inside walls and attic

Excessive humidity is more likely to occur in newer or recently remodeled homes with tight energy efficient construction, causing a build up of moisture to the interior.  There are ways you can reduce humidity in your home.  Please consult the next two articles on this topic.


You can determine how much moisture is in your home with an inexpensive Hygrometer that can be purchased from your local hardware store.  Place the Hygrometer in your home for a few days and record the readings each day.  Compare your data to the chart below.  As outside temperatures drop, the indoor relative humidity level of your home should decrease.  For homes with windows equipped with insulating glass, the University of Minnesota Agriculture Extension Service reports that the follow humidity levels can be maintained in the home without causing window condensation.  If your home’s relative humidity is higher than this chart, please consult Excess Moisture: Causes and Cures for tips on identifying and eliminating sources of excess moisture in your home.  Outside air temperature with ideal inside relative humidity for 70 dgr. Fharenheit indoor air temperature:

  • -20 dgr F outside should be 15% to 20% humidity inside
  • -10 dgr F outside should be 20% to 25% humidity inside
  • 0 dgr F outside should be 25% to 30% humidity inside
  • +10dgr F outside should be 30% to 35% humidity inside
  • +20dgrF outside should be 35% to 40% humidity inside


  • Cause:  Inefficient windows with extremely cold glass surfaces.
  • Cure:  Install energy-efficient windows and doors.  High-performance windows, such as those made with Low E II coatings with argon gas, make the most of the sun’s heating rays during cold months and maintain a remarkable temperature difference between the indoor and outdoor panes of glass.
  • Cause:  Inadequate ventilation of windows.
  • Cure: Keep window coverings open during the day to allow air circulation and make sure patio doors have heat vents beneath them.
  • Cause:  Moist air trapped in attic.
  • Cure:  Seal around indoor light fixtures to prevent warm, moist air from rising to the attic.  Install soffit vents to prevent attic rot, making sure to keep vents clear of dirt and garden debris.
  • Cause:  Radiator or kerosene heat.
  • Cure:  Use dryer sources of heat such as gas or electric furnaces.
  • Cause:  Cooking and dish washing.
  • Cure:  Vent stove range hoods and dishwashers to the outside. Cover pots while cooking.
  • Cause:  Stale, damp air.
  • Cure:  Install an air-to-air heat exchanger to vent moist air outside. Some air quality systems recover up to 97% of the existing warmth and energy to heat incoming air.
  • Cause:  Showers and baths.
  • Cure:  Make sure bathroom exhaust fans are vented to the outside and use fans regularly.