Why do I have fog / condensation at the base of the insulated glass?


[All Tips]

Why do I have fog / condensation at the base of the insulated glass?


[All Tips]

What is the cause?

Condensation on the interior surface of the insulated glass a room is due to the ambient humidity, which must be controlled based on the outdoor temperature.

In early fall, when the heating system is not consistently on, the humidity level in the home may be too high, leading to condensation problems on the interior surface of the glass.

Of course, humidity is essential for your health and comfort, but it is important to know how to control it in order to prevent problems, such as high heating costs, discomfort or even mould. And controlling ambiant humidity can be a challenge for any house types.

Renovated Homes New constructions
Over time, your home’s doors and windows will deteriorate, which may result in air leaks … these are good for releasing humidity, but can harm your quality of life and wallet.

Moreover, by renovating your home or buying new window products, you are indeed controlling the air leaks, but then you have to watch for the ambient humidity level using a hygrometer.

There are some lifestyle habits that affect humidity levels; you can improve this situation by reading our tips below.
Did you have your home built?
You should know that it is normal for condensation to appear in the first year, and it has nothing to do with your window products.

During the first winter in a home, several materials, such as gypsum, concrete/cement, wood, etc. gradually dry, and, as a result, produce condensation.

Therefore, we recommend that you read the tips below to maintain the value and airtightness of your home.

During winter, the ideal humidity level for those living in the home is between 15% and 40%. Lower than 15% irritates the respiratory tract, according to medical authorities.

For example, when the outdoor temperature is below -10°C, the recommended humidity level is 30%.

The following chart provides the recommended relative humidity levels:

Temperature (°C)
Relative Humidity with an Indoor
Temperature of 20°C (68°F)
-30° or under No higher than 15%
-30° to -24° No higher than 20%
-24° à -18° No more than 25%
-18° à -12° No more than 30%
-12° à -6° No more than 35%
-6° à 0° No more than 40%
Source: CMHC Canadian Mortgage and Housing Corporation. www.cmhc-schl

Follow our advice

Here are a few tips to reduce humidity levels and keep your home comfortable:

  • Remove and store screens from casement / awning windows for the winter.
  • Leave the curtains open to air the surface of the glass.
  • If your home has a crawl space, seal it with an impermeable membrane.

Below are some good habits that allow to control indoor humidity:
  • To eliminate cooking fumes, run the oven fan.
  • Turn on the bathroom fan or open the window, leaving the door closed, when showering or bathing.
  • Make sure the clothes dryer evacuates air outside the home.
  • Avoiding hanging wet clothes inside the house.
  • Turn off all humidifiers until you obtain the recommended humidity levels.
  • If you do not have an air exchanger, open the windows on the main floor or upper floors to refresh the air.

By following these few tips, and using a hygrometer, you will be able to control the ambiant humidity and achieve an optimal humidity level.

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