Dealing with Moisture & Mildew within the Home

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Friday, January 5, 2001

Cooking, washing dishes, washing and drying clothes indoors, bathing, and even evaporation from house plants, aquariums, open toilet bowls, pets, and humans are principal causes of high moisture content in the indoor air. Moisture trapped within the home can lead to condensation on ceilings, walls, in attics and in closets when it is cold outside, and in extreme conditions can lead to mildew and mold growth. Since airtight windows have been installed moisture is more readily trapped, and steps must be taken to monitor the home and rid the home of moisture. Below are solutions that have proven successful.

Passive Solutions

  1. Use a hygrometer to monitor indoor relative humidity. In the winter the humidity in your home should be no more than 40%. Cook with lids on pans; open kitchen window to let any steam escape. Remember, too, that overly humid air contains more pollutants and is generally unhealthy.
  2. Reduce showering time, and open bathroom window to let steam from the shower escape; keep cover on toilet closed.
  3. Vent clothes dryer outside.
  4. Once a week, open all windows wide for 15 minutes. In between this airing, keep windows in the upstairs rooms open so that the weather-stripping barely shows. Alternately, open windows halfway for 10 minutes twice each day.
  5. During the night, open the bedroom windows.
  6. Make sure attic vents are kept clear of insulation and clutter.
  7. Keep closet doors open so air will circulate. It is especially important during heating season to allow warm air to reach your cold closet walls. Closets on exterior walls are particularly subject to severe condensation and resultant growth of mold and/or mildew.

Active Solutions

  1. Install and run a properly vented kitchen and/or bathroom ventilating fan. Recirculating range hoods do not reduce moisture.
  2. Use a dehumidifier to dry the air in your home. Place it as close to the problem area as possible.
  3. Install and use an air-to-air heat exchanger.
  4. Louvered closet doors will sometimes reduce build up of moisture in a closet by allowing heat and air to circulate against the exterior wall. However, tightly packed clothing tends to prevent proper air circulation.
  5. Turn your heat up or use portable heaters to warm the temperature of your wall surfaces. Moisture will not condense on the wall if the surface temperature is warm enough. The actual temperature needed to prevent condensation relates to the amount of moisture in the air in your home, so experiment with gradual increases.
  6. For block homes, adding siding with 1" board insulation will increase the inside temperature of the walls, thereby preventing condensation. Remember that warming the wall surface does not reduce the amount of moisture in the air, it only reduces condensation and thereby can reduce the mildew problem.

If you find mildew showing in your home, spray the area with X-14 which can be purchased at most area grocery and hardware stores. Upon request, GHI will make inspections and work with members towards resolutions of moisture problems within their units.