By Gil Strachan

Revisions and additions: 07 Feb 97, are in bold.

Condensation will occur on any surface that is below the dew point of the air in contact with it (temperature at which condensation will occur at the existing humidity level). In most houses in winter, the inner surfaces of the windows are the coolest surfaces and condensation will usually occur there before it appears on other surfaces. 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 where the insulation is reduced, or in confined spaces where the circulation of warm room air is restricted. In some cases this can lead to mildew and the growth of mould.

When condensation becomes excessive the moisture load must be decreased or the ventilation rate increased. To reduce the moisture load, humidfiers should be shut off, automatic dryers vented outdoors, clothes drying indoors avoided, and the structure checked for other possible moisture sources (ventilation, insulation and moisture barriers in the attic, basement or crawlspaces; open cisterns; seepage in the basement etc.)

HANDY HINT

Thoroughly dry a damp spot on an exposed foundation
wall or floor with a hair dryer. Tape a 12 inch square of
heavy plastic over the spot, and check it in one or two
days. Seepage will cause the underside of the plastic to
be wet, but condensation will form on the top side!

If only a moderate or minimal amount of condensation is experienced, switching the fan on a forced-air furnace to the "continuous" or "summer" setting can help reduce humidity in moist areas, by circulating and blending the air throughout the house.

Attic ventilation is normally provided by vent openings totalling approximately one square foot for every 200 to 300 square feet of ceiling area (not more than 50% through the roof, and no less than 50% through the gables or soffits).

Activities Moisture Produced (pounds) (litres)