Sunview Windows tip on Humidity & Condensation
A Saskatchewan Winter brings some challenges!
The moisture that suddenly appears in very cold weather on the interior or exterior of window and patio door glass can block the view, drip on the floor or freeze on the glass. It can be an annoying problem.
While it may seem natural to blame the windows or doors, interior condensation is really an indication of excess humidity in the home. Exterior condensation, on the other hand, is a form of dew — the glass simply provides a surface on which the moisture can condense. The important thing to realize is that if excessive humidity is causing window condensation, it may also be causing problems elsewhere in your home.
I have installed new windows and doors. Will this increase the level of humidity in my home?
Modern windows and doors generally have a lower air-infiltration rate than the older products. Also, when new framing is installed, with insulation and full caulking around the perimeter, the house is tighter than in the past has a lower rate of air-change. Consequently, condensation problems that were not apparent before may surface and some of the steps in the section ‘Controlling the Level of Humidity’ will need to be considered.
Do identical houses have the same condensation problems?
Generally not. Just as heating and hydro bills vary between identical houses, with the same number of occupants, so will the level of humidity. Much of this will depend on the life-style and activities of the household and although appearing identical one house may have a slightly lower air infiltration rate, or other factors, that could influence the humidity level.
Recommended Humidity Levels
Humidity is water vapor, or moisture, in the air. Usually it’s invisible. In the form of steam or ground fog, enough has condensed to be seen. All air contains a certain amount of moisture, visible or not.
Medical authorities indicate that the level of humidity indoors should not be below 15%. It is generally acknowledged that the level of humidity in houses with a good vapour barrier should not exceed 40%, or, in older homes without a vapour barrier, 35%. Table 1, below, shows suggested levels of relative humidity for inside the home for varying outside temperatures.
| Table 1 | Relative Humidity with inside Temperature of 20 C (68 F) |
| Outside air Temperature C | |
| -30 or below | not over 15% |
| -30 to -24 | not over 20% |
| -24 to -18 | not over 25% |
| -18 to -12 | not over 30% |
| -12 to – 6 | not over 35% |
| -6 to 0 | not over 40% |
Controlling the Level of Humidity
Control of the level of humidity is aided if humidistats are used to control humidifiers. If the level of humidity becomes excessive the humidifiers should be switched off until the level of humidity is reduced to the correct level.
For normal day-to-day control of the level of relative humidity in the home the following steps should be considered:
- Water vapour is one of the products of combustion with natural gas stoves. Water vapour is also a by-product of cooking. The kitchen fan should be large enough to remove such vapour, or the kitchen door closed and a window opened for ventilation.
- Showers, especially, are a source of water vapour. The bathroom door should be kept closed and the room ventilated, using an exhaust fan, or by opening a window.
- Drying clothes on a line indoors and unvented dryers are sources of water vapour. The washing cycle is another source. When doing the laundry consider opening a window in the laundry room.
- Crawl spaces can be a source of water vapour if they have earthen floors which are not covered by plastic sheeting, or other waterproof membrane.
- Keep all rooms, even if unoccupied, heated to a minimum of 10°C (50°F) as condensation will occur in unheated rooms.
- As a general rule, long periods of background heating, plus topping-up during periods of occupancy, are more likely to prevent condensation than the same amount of heat introduced over a relatively short period.
- Open a window, or windows, for a brief period to ventilate the house each day.
- Leaving the damper open in a fireplace, or lighting a fire, will increase ventilation and assist the rate of air change.
- If you have a hot air furnace, install a direct fresh air intake.
Room-side glass temperatures – the room-side glass temperature plays an important role in occupant comfort in the home. With high room-side glass temperatures there is less likelihood of condensation forming, down-drafts are reduced making sitting nearer the patio door or window more comfortable, and maximum use can be made of floor space.
The thickness of the glass has little or no influence on room-side glass temperature. With double and triple-glazing units the width of the air space is an influence as is, in the case of Low-E, the layer of invisible “insulation” that has been added to the glass.
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