Condensation Causes & Cures

A significant part of the maintenance of your new home is ensuring that you create a balance of moisture content within the environment. It’s also important to be informed on the effects of too much and too little condensation. Extremes can cause potential damage to hardwood floors, wooden furniture and even artwork.

Today’s homes can be so tightly sealed to prevent air leakage, decrease drafts and conserve energy that we experience reduced ventilation to the outdoors. During the winter when we heat our homes, these factors may also contribute to increased condensation, which could be hazardous to your health and home maintenance.

Experts recommend some change to your heating and ventilation system if there’s visible condensation on your windows that requires repeated wiping. In addition to damaged window frames and potentially hazardous mold, risks include damage to surrounding walls. Low air quality can also be harmful to those with respiratory problems, particularly small children.

In the construction of new homes, The Ontario Building Code requires builders to install a ventilation system to provide you with fresh outside air and to protect your home against moisture damage.

What causes window condensation?

Insufficient ventilation that results in increased humidity levels indoors. When warm, moist air within your home meets cooler surfaces such as windows during the winter, condensation forms. A good analogy for this is a glass with a cold beverage during the summer.

Stained ceilings, water streaming from windows, mould on walls and windowsills are often indications of excessive water vapour in the air. Condensation problems arise because air can only hold a limited amount of water vapour, an amount that varies with temperature. For example, cold air is able to hold less water vapour than warm air.

Air cooled by contact with cooler surfaces such as windows will therefore deposit water vapour on the glass or the sash because as the air is cooled it loses its ability to hold water vapour. This surface condensation can therefore be an indication of excessive water vapour in the air.

Condensation is at its maximum in newly constructed homes. As your home was being constructed, gallons of water went into the concrete of your building. This water slowly evaporates consequently raising the moisture content above normal. Many other construction materials, like wood, take 6 months to a year to dry out naturally.

Proper ventilation will promote the natural drying-out process which will allow everything in your home to adjust as steadily as possible. We urge you not to try to speed up the process by creating extremely high temperatures, as this will exaggerate the normal shrinkage that comes along with the natural process of drying out.

The need for ventilation is dependent on your lifestyle, i.e. the amount of cooking, washing you do. Cooking, showering, drying clothes (even breathing – believe it or not) all add to your home’s moisture content. In the past homes weren’t constructed to be so air–tight and moisture would escape to the outdoors through small cracks surrounding doors and windows.

Quite simply, we must increase the ventilation in our homes to supply the fresh air, which is necessary to vent off water vapor. Already, your condominium has a built-in source of fresh air. This is achieved through the gap around your suite’s front entry door. With the help of pressurized corridors, fresh air constantly enters your home. The gap also assists with the air circulation within your suite.

How to Increase the Ventilation in Your Home

  • Open windows periodically
    This may increase your heating bill slightly, however it’s the most cost effective way to solve your moisture problem
  • Use exhaust fans consistently
    Bathroom fans should be used during every bath and shower, and remain on for 15 minutes following Cooking fans should be used during meal preparation The fan on your clothes dryer is temperature sensitive and in most cases, launched automatically

Fortunately, the homeowner can control most condensation problems. The key to controlling excess condensation lies in understanding today’s building standards and how relative humidity impacts on airtight homes. Listed below is a chart* indicating recommended maximum relative humidity level for different outside temperatures.

Outside Air Temperature
Degrees Celsius

-30 and colder
-30 to -25
-24 to -19
-30 and colder
-12 to -7
* Please note that this chart is designed to be used as a guideline only.

Desirable Maximum Inside Relative Humidity (%) Indoor
Temperature of 21°C (70°F)
not over 15
not over 20
not over 25
not over 15
not over 35

The first step in solving condensation problems in your home is a willingness to reduce humidity levels. While some humidity is recognized as necessary for comfort and health, any increase in moisture levels must be monitored to alleviate excess condensation.

Windows have a limited heat loss resistance and are often the coolest component of the home’s enclosure. Because of this characteristic, windows are usually the area where condensation is most visible. As condensation occurs on the inside window surfaces, it may be a warning signal to reduce the humidity level in your home.

Do not worry about the small amount of heat you will lose by providing enough ventilation in cold weather to control the humidity. It will cost a great deal less than the damage condensation can do to your windows, walls and woodwork. Remember that it is the homeowner’s responsibility to maintain proper ventilation via the heating and air systems to protect the home from stale air and moisture damage.

Lifestyle and Tips to Control Your Homes Ventilation & Humidity

  • Make it a habit to use your bathroom fan when showering and your kitchen exhaust
    fan when cooking. This procedure will help remove the moist air from your home.
  • Refrain from the use of humidifiers unless the relative humidity levels are below
    the levels suggested in the chart on the previous page.
  • Refrain from over watering household plants.
  • Leave the fan running on the vertical fan coil unit during extremely cold weather to help the air circulation throughout the home.
  • Avoid hanging wet clothes inside the home. Ensure the clothes dryer is vented to the exterior and the exhaust fan is operating during the use of the dryer.
  • When smoking in the unit we ask that all residents ensure that their exhaust fans are running to avoid air filtration into the common area hallways.
  • Free circulation of air is important. Keep drapes open as much as possible so the air can circulate freely over the windows. If necessary you may open your windows to reduce localized condensation.
  • Be sure to clean the dryer lint screen and the supplementary lint trap after each use of the dryer machine.
  • Replace your fan coil filters as required.