Winter Home Moisture Problems (1221)

If you have persistent condensation on windows, mold on ceilings and walls, and musty odors, the following information may help you solve these annoying problems. These winter problems usually occur because the humidity in the house is too high for the cool wall, ceiling, and window temperatures. These symptoms used to be confined to the basement in warm weather. Now, homeowners who have tight homes face them throughout the house during the winter.

Maintaining the right humidity level in your home during the winter is a balancing act. You want to avoid the problems that accompany very low humidity. However, humidity levels must be low enough to avoid condensation problems. Housing specialists recommend a relative humidity between 35 and 50%. A quick rule of thumb says humidity levels are too high if condensation persists on tight, double glazed windows when outside temperatures are above zero or on single glazed windows when outside temperatures are about 40 degrees or above. This does not include condensation on windows behind shades or drapes or small amounts of condensation after showers or cooking.

There are several ways to reduce winter condensation problems. One way is to reduce humidity levels. Check for leaky roofs or plumbing that may be adding moisture to the house. If there are no signs of leaking water, look for ways to cut the moisture generated in your house. A few easy ways to do this are to avoid line-drying clothes indoors, vent clothes dryers outside, cover pots and pans while cooking and don’t store lots of firewood indoors.

If you have done all of these and you still have condensation problems during the winter, try ventilating your house. During the winter, ventilation reduces humidity levels quickly. Cold winter air holds little moisture. When it enters the house and warms up, it can hold much more moisture. Moisture from the existing air diffuses into this new dry air and gives you a lower relative humidity level. In addition, ventilation exhausts some of the old moisture-laden air.

Use existing kitchen and bathroom vented fans to provide ventilation for moderate moisture problems. Fans are more efficient if you crack open a window at the opposite corner of the house to provide replacement air for the exhausted air. You can also purchase ventilation systems designed for tight homes. These systems, referred to as heat recovery ventilators, are often a good investment for a new home, but may not be cost-effective in an older home. Dehumidifiers are not a good solution to excessive winter humidity problems. They consume a lot of energy, and residential models do not drop humidity levels much below 50%.

Sometimes, high relative humidity is not the reason for winter moisture problems. Moisture can condense on cold surfaces even when humidity levels are below 40%. A single-glazed window is a good example. The temperature on the inside of the window falls below the dew point when outside temperatures drop below 20 degrees even when your thermostat is set at 70 degrees. Moisture in the air next to the window then condenses on the glass. A second layer of glazing prevents condensation until temperatures drop below zero.

You may also see condensation on poorly insulated sections of walls and ceilings. The corner between the ceiling and outside walls, the corner between two outside walls, and the area under windows are often problem spots for this reason. Closets on outside walls also present problems. Add insulation to solve these condensation problems. You could also increase the air circulation to the area. For closets, leave the doors open. In other areas, fans may help force air against problem walls. Finally, you could turn up the thermostat. This increases the wall temperature and increases the air’s moisture holding capacity.

For more information on this subject, Please visit the College of Agricultural Sciences Publications Web site.

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