Housing...Inside and Out

May 7, 1999
Moisture Control

Water in your home can come from many sources. Water can enter your home by leaking or by seeping through basement floors. Showers or even cooking can add moisture to the air in your home. The amount of moisture that the air in your home can hold depends on the temperature of the air. As the temperature goes down, the air is able to hold less moisture. This is why, in cold weather, moisture condenses on cold surfaces (for example, drops of water form on the inside of a window). This moisture can encourage biological pollutants to grow.

There are many ways to control moisture in your home:

  • Fix leaks and seepage. If water is entering the house from the outside, your options range from simple landscaping to extensive excavation and waterproofing. (The ground should slope away from the house.) Water in the basement can result from the lack of gutters or a water flow toward the house. Water leaks in pipes or around tubs and sinks can provide a place for biological pollutants to grow.
  • Put a plastic cover over dirt in crawlspaces to prevent moisture from coming in from the ground. Be sure crawlspaces are well-ventilated.
  • Use exhaust fans in bathrooms and kitchens to remove moisture to the outside (not into the attic). Vent your clothes dryer to the outside.
  • Turn off certain appliances (such as humidifiers or kerosene heaters) if you notice moisture on windows and other surfaces.
  • Use dehumidifiers and air conditioners, especially in hot, humid climates, to reduce moisture in the air, but be sure that the appliances themselves don't become sources of biological pollutants.
  • Raise the temperature of cold surfaces where moisture condenses. Use insulation or storm windows. (A storm window installed on the inside works better than one installed on the outside.)
  • Open doors between rooms (especially doors to closets which may be colder than the rooms) to increase circulation. Circulation carries heat to the cold surfaces. Increase air circulation by using fans and by moving furniture from wall corners to promote air and heat circulation. Be sure that your house has a source of fresh air and can expel excessive moisture from the home.
  • Pay special attention to carpet on concrete floors. Carpet can absorb moisture and serve as a place for biological pollutants to grow. Use area rugs that can be taken up and washed often. In certain climates, if carpet is to be installed over a concrete floor, it may be necessary to use a vapor barrier (plastic sheeting) over the concrete and cover that with sub-flooring (insulation covered with plywood) to prevent a moisture problem.

Maintain And Clean All Appliances That Come In Contact With Water

  • Have major appliances, such as furnaces, heat pumps and central air conditioners, inspected and cleaned regularly by a professional, especially before seasonal use. Change filters on heating and cooling systems according to manufacturer's directions. (In general, change filters monthly during use.) When first turning on the heating or air conditioning at the start of the season, consider leaving your home until it airs out.
  • Have window or wall air-conditioning units cleaned and serviced regularly by a professional, especially before the cooling season. Air conditioners can help reduce the entry of allergy-causing pollen. But they may also become a source of biological pollutants if not properly maintained. Clean the coils and incline the drain pans according to manufacturer's instructions, so water cannot collect in pools.
  • Have furnace-attached humidifiers cleaned and serviced regularly by a professional, especially before the heating season.
  • Follow manufacturer's instructions when using any type of humidifier. Experts differ on the benefits of using humidifiers. If you do use a portable humidifier (approximately 1 to 2 gallon tanks), be sure to empty its tank every day and refill with distilled or demineralized water, or even fresh tap water if the other types of water are unavailable. For larger portable humidifiers, change the water as recommended by the manufacturer. Unplug the appliance before cleaning. Every third day, clean all surfaces coming in contact with water with a 3% solution hydrogen peroxide, using a brush to loosen deposits. Some manufacturers recommend using diluted household bleach for cleaning and maintenance, generally in a solution of one-half cup bleach to a gallon of water. When using any household chemical, rinse well to remove all traces of chemical before refilling humidifier.
  • Empty dehumidifiers daily and clean often. If possible, have the appliance drip directly into a drain. Follow manufacturer's instructions for cleaning and maintenance. Always disconnect the appliance before cleaning. 
  • Clean refrigerator drip pans regularly according to manufacturer's instructions. If refrigerator and freezer doors don't seal properly, moisture may build up and mold can grow. Remove any mold on door gaskets and replace faulty gaskets.

Clean Surfaces

  • Clean moldy surfaces, such as showers and kitchen counters. 
  • Remove mold from walls, ceilings, floors, and paneling. Do not simply cover mold with paint, stain, varnish, or a moisture-proof sealer, as it may resurface. 
  • Replace moldy shower curtains, or remove them and scrub well with a household cleaner and rinse before rehanging them.

SOURCE: Environmental Protection Agency


Written by Dr. Francis Graham (Retired)

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