What Causes Window Condensation

The homes today are being built more airtight than ever before. But in addition to sealing in the heat and air conditioning, these energy efficient homes can also hold in too much moisture-laden air.

If your home contains excessive moisture and its cold outside, one of the first places condensation will show is on your windows. The first thought may be a problem with your windows, but in fact window condensation is usually an indicator of poor home ventilation.

Window condensation is typical in a new home, where the moisture of the building materials are drying out and trying to escape. It may also occur on new energy efficient replacement windows in an older home where the old drafty windows allowed the moist air to escape the new windows are now stopping it.

Occasional window condensation on the glass is usually not a problem. It is likely a bathroom mirror and window will steam up during a hot shower. Or a kitchen window may get foggy when boiling water on the stove. But in most cases this moisture clears up in minutes.

If however your windows are sweating at other times, or stay that way for extended periods of time you may have bigger problems.

The glass on the window itself may not be affected by condensation but the excess moisture can damage other parts of your home. If you have wood windows the sash and frame can eventually rot or warp if exposed to excess moisture. Paint can peel and other finishes can become stained. Insulation and other porous materials can become breeding grounds for mold and mildew. This is why it is important to manage and reduce excess moisture in your home.

The moisture can come from a variety of sources like cooking in the kitchen, running the sink and using the dishwasher. It can come from hot showers, hot tubs and spas. Washing machines and indoor-vented dryers can also contribute to the moisture level in your home. Basements and crawl spaces can allow moisture to channel into your home if not properly sealed with a vapor barrier. A leaking roof, or siding can also allow moisture into your home. These are all areas to scrutinize if you suspect excess moisture in your home. You may also be contributing as well. A family of four can easily generate up to 18 gallons of water a week in the form of humidity.

To get rid of excessive moisture the homes humidity level needs to be lowered and ventilation should be increased. Proper ventilation and the use of dehumidifiers in the high humidity areas such as baths, kitchens and laundry areas should be implemented, ideally venting the moist air to the outside. Take shorter showers and install water-restricting faucets that will lower humidity levels as well as energy costs. The use of a good dehumidifier and using power vents for a longer period of time can also help reduce moisture levels. Check drainage around your home and make sure downspouts are routing water away from the foundation.

Many people will use a humidifier during the winter months to make it feel warmer and to offset the dry static filled air. In older homes excess window condensation is not usually a problem because the home breathes through unsealed cracks in the construction, creating an exchange of indoor and outdoor air. Today’s modern construction techniques with an emphasis on energy efficiency keep the home from breathing and need additional help to reduce humidity and moisture levels.

So how much humidity is enough to keep the environment comfortable but not damage the structure and create a breeding ground for mold? That depends on the outside temperature. Below are suggestions from the University of Minnesota Engineering Experiment Station based on an inside temperature of 70 degrees Fahrenheit.

Below -20Ã?° F —— humidity level 15%

-20Ã?° F to -10Ã?° F — humidity level 20%

0Ã?° F to 10Ã?° F —— humidity level 25%

10Ã?° F to 20Ã?° F —– humidity level 35%

20 F to 40 F —– humidity level 40%

The basic principal of reducing window condensation is simple. When there is excess condensation on your windows it usually means the humidity level in your home is too high for the current outside temperature. As most building professionals will point out windows should not be blamed for condensation. They are simply an indicator of excess moisture in the home.

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