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Controlling Moisture and Humidity in the Home

Excess moisture in your home can lead to damage and encourage harmful mold and mildew growth. Learn how to reduce moisture and prevent the problems it causes.

Living Room.

Indoor Moisture and Humidity

Moisture condenses into water droplets when warm, humid air contacts a cool surface. Activities such as cooking, bathing, clothes drying and dish washing add moisture to the air. Some heating appliances, such as unvented natural gas or kerosene models, also increase the moisture inside your home. During the winter, windows, walls and doors that lack proper insulation are common cool surfaces. Uninsulated cold-water pipes are examples of cool surfaces in the summer. Droplets can accumulate on these surfaces and run down into the walls, windows and structural components, causing rot and peeling paint, and providing a good environment for mold and mildew growth.

Controlling Indoor Moisture

Bathroom Exhaust Fan.

When you see moisture accumulating, dry it promptly and deal with the source of the problem. Two basic elements of controlling moisture buildup are minimizing cool surfaces and reducing humidity.

Storm doors and windows minimize cool surfaces in the winter by separating the interior from cold, outside air. Double- and triple-pane windows also insulate interior glass from the cold. In addition to reducing moisture, adding these improvements will make your home more energy-efficient year-round. Pay attention to window treatments as well. Opening drapes and blinds in the winter allows warmth to reach the interior glass. Some condensation may occur, but the improved circulation makes it less likely to accumulate. Insulating cold-water pipes eliminates a common cool surface in warm weather. Straight and angled sleeves let you fit insulation to your pipes — just slide on the sleeves and seal the slits and joints with duct tape.

Your heating and cooling systems can also help control moisture in the home. Gas and electric furnaces reduce humidity with dry heat. Air conditioning lowers the moisture level in the air as it cools. Keep registers open and unblocked to allow good air flow, and have the systems inspected and serviced regularly to make sure they are functioning properly.

Caulking and weatherstripping improve energy efficiency and prevent humid air from entering a home, but they also reduce the air exchange that allows moisture to move out of the house. Bathroom exhaust fans, dryer exhaust and ducted kitchen exhaust hoods that vent to the outside remove moisture that activities such as showering, bathing, clothes drying, dish washing and cooking create. Keep the devices free of dust, lint, grease or anything that could keep them from working efficiently.

Other simple ways to reduce air moisture include:

  • Covering pots while cooking, when possible
  • Leaving room doors open to allow good air circulation
  • Storing firewood outside
  • Covering aquariums

If high humidity is a problem you can't overcome by other methods, remove moisture from the air with a dehumidifier. They're effective in laundry rooms, basements, bathrooms and any room that isn't air-conditioned or has poor air circulation. Look for ENERGY STAR® qualified models, which consume less energy than conventional dehumidifiers.

Good to Know

Humid air leads to condensation problems, but air that's too dry can be uncomfortable or unhealthy and can lead to static shocks. Keep the relative humidity in your home between 30 and 50 percent. You can purchase a weather station that measures indoor humidity levels.

Other Moisture Considerations

Gable Power Vent.

Moisture in the home is not always as obvious as water beading on a window. Knowing other places it can accumulate can help you prevent problems.

Poor ventilation in an attic can result in condensation, promoting mold growth in the framing elements of the house. This can affect your home's structural integrity. Keep eave vents clear of insulation and make sure you have adequate air flow. See Ventilate Your Home for ideas to improve air circulation in your house.

A sealed, unused fireplace creates an opportunity for moisture problems. If air doesn't circulate in the fireplace, condensation can accumulate on the walls and soak into the masonry. Make sure some air can flow through the fireplace, but rain cannot enter it.

If you have a crawlspace, moisture from the soil can enter your home, increasing the level of humidity. A vapor barrier over the bare soil blocks the moisture, keeping it out of your living space.

Rain that seeps into your home's foundation can lead to moisture problems. Make sure your gutters work properly and direct water away from your home's foundation. Read Gutter Cleaning and Repair for instructions on maintaining your gutters.

Caution

Some moisture problems require more complex solutions, and sources of moisture may be hidden. Consult a professional if you have serious condensation or mold problems or if you suspect you may not have adequate ventilation.