Moisture Control: A Home Humidity Must?

Controlling humidity in a house makes the home more comfortable, saves on heating and cooling costs by reducing energy consumption, and prevents mold and mildew growth. Indoor moisture build-up has many sources.

Moisture Control

Controlling humidity usually means addressing more than one source of moisture and mitigating them if possible. Eliminating leaks. Taking shorter cooler showers. Cooking with lids on pots. Filling the dishwasher. Using dehumidifiers and exhaust fans helps to reduce moisture and humidity in the house. Air circulation prevents moisture from accumulating.

Where Moisture Comes From?

Moisture moves in and out of houses in various ways. Some moisture is created just by living.

  • Air Movement. Most moisture in wall cavities occurs because of gaps, cracks, and holes in the building envelope. Air moves from high pressure areas to low pressure areas quickly.
  • Poor Insulation. Allows warm and cold air to come in contact–creating condensation.
  • Poor Ventilation. Lack of efficient ventilation allows moisture to accumulate inside the house.
  • In Home Moisture. Moisture is created inside the home by showers, laundry, cooking, exercising (sweat), and just breathing. Also water leaks in walls and plumbing and accumulated build-up in crawl spaces.

How to Control Moisture in a Home

Different climates present unique humidity challenges. Consulting a local HVAC expert is always a good idea but all of the following suggestions should be considered regardless of location.


Water leaking into the house is a constant source of humidity. Check the attic and roof. Seal any wall penetrations like pipes and vents with spray foam or caulking. Fix drafty windows and door frames. Install storm windows and/or insulate windows and doors with new weatherstrip. Repair damaged siding and cracked stucco to prevent leaks into the building envelope.

Make sure that the yard is sloped away from the house to prevent water build-up and that all gutters are clean and working. Extend downpipe runoffs to 10’ away from the house.

Crawl Spaces and Basements

Crawl spaces can accumulate water. Encapsulating the crawl space or insulating the crawl space keeps moisture from migrating into the home’s living space. At the very least, cover the floor with 6 mil poly and insulate the rim joists.

Concrete and concrete block basements can leak if they are not sealed. Foundation insulation and sealing are best done on the exterior–an expensive project. If the leakage is minor, it can often be stopped by sealing the interior of the walls with concrete repair products.

Exhaust Fans

Bathroom and kitchen exhaust fans must be vented out of the house–not into the attic–to get the moisture outside the building envelope. Make sure the exterior hoods and interior filters are clean. Let fans run for at least 15 minutes after showering and cooking. Vent clothes dryers outside and remove built-up lint regularly.


Humidifiers, some types of heaters, and appliances like water kettles add moisture to the air. Turn them off–if possible–when condensation appears on windows. Or keep usage to a minimum.


In hot humid climates air conditioners and dehumidifiers are very beneficial for removing moisture from indoor air. Clean them regularly to prevent mold and mildew growth in the filters, on the coils, and in collection containers. Mold spores can be distributed throughout the house when the machines are re-started.


Heating Ventilation and Air Conditioning (HVAC) systems circulate air throughout the interior of the building. Air movement helps keep condensation from windows and walls. They also bring in fresh air and remove moist air from the building.

Moisture will often accumulate on walls and in corners that have poor air movement. Move furniture away from walls. Condensation, and even ice, forms on windows in colder climates where heavy curtains reduce air movement. Keep drapes partially open or place a small battery-operated fan on window sills to move warm air over the glass.

Air circulation in the home can be enhanced with fans. Two or three in different parts of the house will keep the air moving. (Many new fans are almost silent.) Leave doors–especially closet doors–open.


Carpets not only hold dirt. They absorb and hold moisture–especially when laid on concrete. Install 6 mil poly on the concrete, then build a subfloor of 2 x 4s, batt insulation covered with plywood. Then install the carpet. Or use area rugs that can be washed and dried. Other types of flooring such as laminate, linoleum, or tiles are a better option.

Recommended Humidity Levels

A home’s humidity level does not have a one-size-fits-all solution. Exterior temperature and humidity should be used to determine the ideal house humidity. For instance: Freezing external temperatures and high interior humidity cause condensation on windows. Many people prefer higher humidity to reduce static electricity inside the house. It isn’t always a beneficial choice. A good dehumidifier can help reduce humidity to recommended levels.

Outdoor Temperatures and Recommended Indoor Relative Humidity

+20o F.35%
+10o F.30%
0o F.25%
-10o F.20%
-20o F.15%

Humidity and Health

Comfort is not the only reason to control humidity in the home. Too much humidity and moisture is an invitation to pests–like termites–and mold, and mildew. Mold spores are often toxic. Breathing hot humid air can be difficult for people with compromised lungs. Home moisture control is worthwhile for many reasons.