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Manage Indoor Humidity to Prevent Mold & Mildew

Tuesday, December 1, 2015 - It happens often here in the Northwest. When warm moist air inside homes settles on chilly surfaces such as glass windows or outer walls, you get condensation. Water runs down the window panes or moisture collects on other surfaces, and that can contribute to dry rot, mold and mildew problems.

Industry research shows that visible indoor mold and mildew may be present in as many as one-third of all Northwest homes. Most vulnerable are older houses with single-pane, metal-framed windows, those with blinds and drapes that are often closed, homes with high indoor relative humidity, and multifamily and manufactured housing. But mold and mildew can occur in both new and older structures.

Click to read tips for managing indoor humidity

  • Get rid of moisture in the air by making sure your exhaust fans are operating at top performance. Always use your kitchen fan when steaming vegetables or simmering other food.

  • Use bathroom fans to pull hot, moist air outside. Test your fan by holding a single square of toilet paper to the fan. If the fan is not holding the tissue to the outlet, it is not working like it should. You may want to install a high-volume bathroom fan rated to draw a minimum of 100 cubic feet of air per minute. Quality fans are also rated for noise.

  • There are trade-offs when conserving heat by closing mini-blinds and using heavy curtains. The blinds and curtains keep the heat in, but they also allow windows to become colder, which can result in more condensation on the glass. If your windows are vinyl, make sure the "weep holes" at the bottom of the frames are clean and functioning to allow moisture to drain.

  • House plants put a lot of moisture into the air around them. Consider reducing your indoor plant population or select plants that need little watering.

  • Make sure that clothes dryers are vented outdoors.

  • Repair leaky faucets as soon as possible.

  • Measure indoor relative humidity using a hygrometer, a device available in most hardware stores. Homes should have humidity levels less than 50 percent to avoid mold and mildew. For best health and comfort, humidity levels should be less than 30 to 40 percent, experts say.