Sticky Business: Controlling Humidity

June 30, 2022 (Reston, Virginia)

Many people understand indoor climate control means heating and cooling your home. But humidity is an important factor that can affect comfort, health, and even a home’s structural integrity.

In the DC area, summer humidity is all too familiar. At warmer temperatures, humidity prevents sweat from evaporating, making the temperature feel even hotter, and increasing the risk of heatstroke, heat exhaustion, headaches, and dehydration.

Indoors, excessive humidity can cause wooden doors to swell and stick. Worse, it promotes the growth of mold that can rapidly feed on, stain and even destroy wood, carpeting, paper, fabrics, and other materials. Condensation forms when cooler air or surfaces meet warm, saturated air in areas like windows, bath fixtures, and uninsulated air conditioning ducts and pipes. The resulting wetness can rust metal, damage drywall and plaster, and encourage pests like roaches and dust mites.

Molds produce allergens and irritants that can trigger allergies and aggravate asthma. They can also release potentially toxic substances (mycotoxins), which is why professional remediation is so important for significant mold issues.

Indoor relative humidity levels between 30 and 50 percent are generally recommended, although in old homes staying below 50% helps keep moisture from infiltrating walls. You can use a digital or analog hygrometer to measure humidity in the surrounding air.

In warmer months, central air conditioning helps lower humidity throughout a home. A whole-house humidifier can be added to the system to maintain more consistent humidity. Older central and room air conditioners are less effective at removing moisture and may need replacement.

Kitchens and baths require adequate ventilation systems, and in many homes a room dehumidifier in the basement is useful to avoid moisture problems. Proper attic ventilations and effective vapor barriers for basements and crawl spaces are essential. Very tight, energy-efficient houses hold more moisture; you may need to run the bath and kitchen ventilation fans longer or open a window briefly.

In winter, very low indoor humidity can make noses stuffy, eyes burn, skin itch or flake, and cuticles crack. There’s some evidence that dry air can increase susceptibility to colds and other viruses.

Very dry air can also increase static electricity, damage leather, make wallpaper peel, and cause wood furniture to crack. As wood floors shrink in the dry environment, the joints between boards widen, and shrinkage of building materials may cause cracks to appear, requiring replacement of caulk or other fillers. Low humidity can be particularly hard on wooden musical instruments, which can fall out of tune or warp or crack over time. If you have valuable instruments, you may need to dedicate a space go keep relative humidity at 45-55 percent year-round or use a humidifier designed for the instrument.

If it’s very cold out, it’s best to maintain 30-40% relative humidity indoors, as higher humidity is more likely to cause condensation. You can increase interior humidity through portable humidifiers, particularly in bedrooms, nurseries, and living rooms. Adding houseplants helps release moisture to the air, and you can take advantage of moisture sources by opening the dishwasher after the final rinse to let the steam flow out, and letting bathwater cool before draining the tub.

For more info, see the EPAs information humidity and side effects:
https://www.epa.gov/mold/brief-guide-mold-moisture-and-your-home
https://www.epa.gov/mold/what-are-main-ways-control-moisture-your-home