MOISTURE AS CONDENSATION IN THE WINTER TIME (1 of 2)

Excessive condensation of moisture on windows is a source of increasing concern in homes in winter. It not only creates a nuisance by limiting visibility and by wetting adjacent walls and floor surfaces, but in more severe cases it can cause rotting of wood and deterioration of paint and plaster. To the builder the problem takes on a special significance because the homeowner frequently assumes that window condensation is a fault of construction. He does not readily appreciate that his own living habits are of prime importance, nor that a well built house is often more vulnerable to excess moisture problems than one that is loosely constructed.

Fortunately most cases of window condensation can be controlled by the occupant once he understands the basic causes of the problem. It is our purpose to discuss these causes and to provide suggestions for controlling excessive moisture in houses.

Some things are pretty basic. If you have too much moisture in the home, then look for some of these occurrences:

• Constantly dripping faucets.
• Any containers in the home that have water standing often or all the time such as sinks and pet bowls and open fish tanks.
• Indoor air-drying of clothing.
• Use of gas cooking. Moisture is a by-product of gas combustion.
• Keeping lids open on commodes thus allowing more evaporation.
• Not running the exhaust fan during baths and showers to remove the moisture.
• This is most important during the summer months and normally is not needed during the winter time. It may even be desirable in some homes to add moisture in the winter.
• Excessive use of things like steamers, plant misters or tea pots.
• Some building slabs may not have a vapor barrier. You may see sweating of slab where visible.
• Overuse of humidifiers.
• Faulty plumbing such as leaks in walls or under cabinets, etc.
• Moisture under frame homes or in basements.
• Leaking indoor clothes driers. This is one of the most major sources.
• Leaking hot water heaters or water piping.
• Excessive plant containers indoors that require watering.
• Saunas and hot tubs.
• Outdoor drainage that holds water against slab or bricks. You may need to inspect your sprinkler system, too.
• Faulty shower piping or faucets and seals leaking into walls, etc.
• Faulty refrigerators or ice machines that leak or drain excess water or moisture.
• Poor ventilation in closets and bathrooms, etc. Add air conditioning supply grills and/or make sure the doors are not so tight as to not allow circulation of air from the room.
• Extensive soaking of clothing, etc. in open water containers. You may wish to move these to the garage or utility areas.
• Wet clothing, wash rags or towels repeatedly left laying out.
• Leaving floors very wet after mopping.
• Rainwater leakage into attic and/or walls.
• Use of open space gas heaters especially at high room temperatures. Common in bathrooms, too.
• Poor refrigeration or faulty conditions of the cooling system that doesn't remove enough moisture from the air during the summer. Have it checked by a technician. Choose a good hot summer day for this inspection.

WHAT IS CONDENSATION?:

Condensation problems arise because air can hold only a limited amount of water vapor, an amount that varies with temperature. When air at a certain temperature contains all the water vapor it can hold it is said to have a relative humidity of 100 percent. If, at the same temperature, it contains only one-half the water vapor it is capable of holding, then the relative humidity is 50 percent.

If the temperature changes but no water vapor is added or taken away, then the relative humidity will also change and will increase as the temperature falls. The relative humidity will continue to rise with falling temperature until the dew-point is reached - that is, the temperature at which the relative humidity becomes 100 percent. Any further decrease in temperature will force some of the vapor to condense as water (when the temperature is above freezing) or as frost (when the temperature is below freezing).

Air cooled by contact with the cold surfaces of windows will therefore deposit some of its water vapor on the glass or the metal sash whenever it has more water vapor than it can hold at its new temperature that it achieved as it brushed against the cooler glass or sash.

Condensation may occur on either the inside surface of the inner window or the inner surface of the outer window. The first case indicated that there is too much water vapor in the air for the weather conditions prevailing at the time. The second cause indicates air leakage outward around the inner window, and will occur even when the amount of water vapor in the air is quite low. This latter form of condensation is more prevalent on upstairs storm windows and the down-wind side of the house.

Condensation usually occurs first on windows because they have the lowest temperature of any of the interior surfaces in the house. It seldom appears on walls because they are normally warmer, although occasionally condensation may occur on cold spots such as nail heads and in the corners of outside walls and closets where the insulation value is reduced and circulation of warm room air is restricted. In extreme cases this has led to mildew and the growth of mold.

HUMIDITY LEVELS IN HOUSES IN WINTER:

Humidity levels should be controlled so that little or no condensation appears on the inside surface of the glass. With double glazing this still permits quite high relative humidity except during the most severe weather as indicated in the following which shows the maximum humidity levels that can be tolerated if condensation is to be avoided in the cold weather.

  Outside Air          Desirable Maximum
Temperature, F           Humidity, %
    -20                      20
    -10                      25
      0                      30
     10                      35
     20                      40

If only single glazing is used, much lower humidity will produce condensation (less than 12% at 0° F); storm windows can be installed, however, to provide the thermal equivalent of double glazing and thus permit these higher humidity levels to be maintained.

In practice, condensation will occur first over the lower part of the window because the glass surface temperatures are not uniform, being lower at the bottom than at the top. Condensation at the base of the window and also at the sides tends to be more severe with metal sash and with some special units such as factory sealed double glazing where the method of assembly results in increased heat transfer at the edges. Drapes or other window coverings can contribute to the problem by restricting the flow of warm room air over the glass surface.

The homeowner need not measure the humidity directly, he can simply use the windows as a guide to the proper humidity level within the house. As soon as the objectionable condensation occurs on the inside surface of the window, steps should be taken to reduce the relative humidity by controlling the moisture sources or by increasing ventilation.

It is common belief that for health reasons there should be a lot of moisture in the air during the winter months. There is, however, no conclusive evidence that either the health or the comfort of most people will be adversely affected if humidity is kept at a level that will prevent excessive condensation on the interior surfaces of double windows. Comfort and nasal dryness will, however, be noticeably affected if the percent of relative humidity drops excessively low.