Window Condensation Explained: Causes, Fixes, and Prevention

Condensation on windows is a common concern, especially during colder months or after installing new energy efficient windows. It is important to note that windows do not cause condensation.

They simply provide a surface where moisture in the air becomes visible. Understanding why condensation happens and how to control it can help protect your comfort, indoor air quality, and the performance of your home.

Condensation is the point in which moist air turns into a liquid when surface temperatures fall below the “dew point” of the room. When warm air comes into contact with a cool surface, such as a window, condensation occurs.

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What Causes Condensation?

Above average levels of humidity in a home will result in condensation. Window glass traditionally has a low surface temperature thus producing the first signs of condensation.

Both new and older homes that do not comply with current building codes can also experience condensation in attics, inside exterior walls and within floors and ceilings.

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Why Am I Experiencing Condensation With My New Windows?

A properly installed, new window will make your home more energy efficient, as it provides an air-tight seal. Original drafty windows commonly allow excess humidity and heat to escape, whereas your new windows provide a warmer surface for condensation to occur. Causes of condensation can include humidity levels that are too high, uneven heat distribution throughout the home and poor circulation around your new windows and doors.

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How Do I Minimise Humidity and Condensation?

Increase ventilation and control the source of excess moisture. You can mitigate humidity causing factors by performing regular maintenance, acquiring the services of a qualified inspector, installing a humidistat or by purchasing an inexpensive hygrometer that will measure the relative humidity in your home.

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Causes of Surface Condensation

Windows

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Doors

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Walls

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How to Reduce Surface Condensation

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Windows & Doors

a. Replace or adjust weather stripping  

b. Replace exterior doors with new energy efficient models  

c. Replace your windows with CSA approved & Energy Star rated products  

d. Add fresh air duct to your heating system

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Bathrooms

a. Open windows after showering

b. Install a ceiling vent exhausting outside  

c. Close the bathroom door when using the shower or bathtub  

d. Properly insulate walls and ceilings  

e. Use moisture proof paint or wallpaper

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Kitchen

a. Open windows to release stale, humid air and allow fresh dry air to enter  

b. Operate vented exhaust over oven range when cooking

c. Install a ceiling fan  

d. Trim cupboard doors so air can circulate

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Living Areas

a. Seal light fixtures and insulate attic hatch  

b. Exhaust all vents to the exterior  

c. Install and seal a chimney fire stop

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Exterior Walls  

a. Add insulation to wall cavity  

b. Run furnace fan continuously  

c. Install or repair flashing to direct rain away from the wall  

d. Caulk exterior siding corners, window brickmoulds, etc.  

e. Seal and insulate basement walls

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Recommended Humidity Levels