Very often, the owners of a building complain of a serious problem of condensation and ice accumulation on the inside of windows, during the winter period, despite the fact that they maintain a moisture content ranging between 30% and 50%. This means that the windows have no resistance to condensation as prescribed in the NAFS standard.

In Canada, window performance is governed by a new harmonized standard, the NAFS (North American Fenestration Standard), which replaces the A-440 standard. The 2010 National Building Code imposes this new standard, which was developed by the Canadian Standards Association (CSA International). Thus, the NAFS standard states the minimum performance levels of windows evaluated under standardized conditions.

The characteristics defined in the NAFS standard relate to the following:

  • Air tightness;
  • Water tightness;
  • Resistance to wind loads;
  • Ease of maneuvering;
  • Resistance to forced entry;
  • Resistance to condensation;
  • The resistance of mosquito nets.

Windows are now categorized by performance category (CP). The higher the CP value, the higher the level of performance of the window.

Causes of condensation on the windows

Condensation on windows in the winter is an undesirable problem in a building. The causes of condensation on windows are many, here are some examples:

  • Occupant activities can affect this phenomenon, as certain activities or habits generate a high amount of water in the air. This causes a high relative humidity (RH) inside the building;
  • Closed curtains prevent the free flow of air on the surface of the window;
  • The positioning of the windows in the outer envelope also plays its role, because the larger the windows are installed to the outside, the more chances are that condensation will form;
  • The absence of an electric baseboard under the window;
  • The presence of objects placed in front of the windows also prevents air circulation on the surface of the windows;
  • The presence of a defect in the windows;
  • An air leak around the window;
  • Windows that are not approved for the climatic zone of the location of the building.

Climatic zones

Canada is divided into three (3) climate zones that are based on an average annual temperature indicator called " degree-days of heating (DJC) ".

The doors and windows to be installed must be approved according to the climatic zone of the building. In general, the poor quality of windows and their location in the building wall are the causes of ice formation on the windows.

Location of windows

According to the standard, "to improve resistance to surface condensation, we should study the possibility of setting up the window [...] taking into account the inner plane of the wall. The position of the window [...] in relation to the line of the thermal insulation of the wall can influence the surface temperature of the glass and the frame. Deep support prevents the heat of the room from heating the glass. Placing the window inward allows the heat of the room to increase the temperature of the inner surface of the glass and protects the outside of the product from the wind to the outside, allowing increase its thermal efficiency in general ".

Relative humidity and condensation

Relative humidity is the ratio of the amount of water in the air to the amount of water the air can hold. If the air in your house contains only half the water vapor it can contain, it is said to have a relative humidity of 50%.

In fact, humidity is water in the gaseous state, that is to say water vapor carried by the air. “Air can only contain a certain amount of water at a certain temperature, after which there is saturation. Humidity is always relative to this saturation rate, because the air's capacity to hold water varies with its temperature, the hotter the air, the more agitated it is and the more vapor it can hold. of water, if the air cools, the water condenses in precipitation, or in droplets on a colder surface ”(

At a given temperature, the air may contain a certain amount of water vapor. The temperature at the saturation point is called the dew point. When the air is cooled to the point where it can no longer hold more water vapor, "it is said to be saturated and its relative humidity is 100%. If the temperature drops further, a certain amount of water vapor will condense. This condensation will take the form of droplets of water or frost depending on whether the temperature is above or below the freezing point "(Energy Guide).

Recommended humidity level

The recommended indoor relative humidity is the one that minimizes condensation on windows during the heating season. If the humidity level in your home exceeds the recommended maximum rate, then your windows will be covered with mist or frost. Note that it is necessary to lower the indoor humidity level as the outside temperature drops.

If the humidity in your home is much lower than the suggested rates, you will have problems with static electricity, dust, and dryness of the mouth and skin. In terms of comfort and health, it is desirable to maintain, in winter, a relative humidity, indoors, between 30% and 35% during the heating season. Unfortunately, with this humidity rate, some condensation will form on most windows in cold periods.

Reduction of condensation on windows

There are simple ways to reduce the phenomenon of condensation on windows. If ever the application of these tips proves to be inefficient, then more complex solutions with higher costs should be considered (Smart Guide).

Here are some ways to reduce condensation on windows:

Reduction of the amount of moisture produced

  • Set down or turn off the humidifier, whether it is incorporated in the heater or not;
  • Cover the pots to reduce the steam;
  • Do not put laundry to dry inside;
  • Vent outside the dryer;
  • Shorten the duration of showers and baths;
  • Reduce the number of houseplants;
  • Do not store inside the firewood;
  • Cover the exposed floor of the basement and crawl space with a waterproof membrane. For this purpose, use 0,15 mm polyethylene (6mils) sheets, overlapping approximately 600 mm (24 in) at joints and grounded with old planks, bricks or 50 mm sand (2 in).

Improvement of air circulation

  • Open the curtains and blinds that cover the windows;
  • Move furniture and objects that obstruct hot and cold air vents;
  • Let the fan of the heater run slowly at low speed.

Increased ventilation

  • Use the kitchen extractor fan when cooking, and the bathroom extractor after the shower. These exhaust fans should vent to the outside;
  • Open external doors and windows for a short time to reduce condensation at a given point.

Improvements for windows

  • You can significantly reduce the condensation which forms on single- or double-glazed windows by installing storm windows. You can also adopt a more expensive solution that involves replacing existing windows with new energy-efficient windows;
  • Condensation between a window and storm window is due to an air leak that can be reduced by good caulking and laying weatherstrips. An interior storm window must be more watertight than the main window it covers and vice versa to prevent the warm, moist air from the house from being trapped between the two windows and causing condensation to accumulate;
  • Condensation inside a factory-sealed double glazing indicates that the seal is defective. The only solution, in this case, is to replace the sealed window. Most sealed windows are guaranteed, for a period of at least five years, against defective seals; contact the manufacturer for a replacement policy.

Resistance to condensation

"Whenever the surface temperature of any part of the window is low enough, the humidity in the air in the room will condense on the cold surface. If the condensation occurs long enough, it can create a significant amount of water that can damage the interior coatings, promote the growth of mold and, if the water seeps inside the wall under the window, it may damage the wall "(source: CMHC).

Condensation on windows in winter

Condensation on windows in winter