How to rid your home of musty odors coming from the basement.

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If your basement smells musty, here’s what to do about it.

First understand that musty odors mean fungal growth. Fungi like to grow where it’s dark, damp and undisturbed. Given the right conditions, mildew will proliferate quickly. The odor you detect is a byproduct of thriving mildew colonies, and a tipoff that mold is growing, but be aware that not all mold gives off an odor.

Besides being unpleasant, mold and mildew can cause health problems, especially for people allergic to the spores. In addition, anything stored in the area can mildew and be irreversibly damaged. That includes clothing and textiles, upholstered and wood furniture, books, art, photographs and luggage.

When it gets cold, below 50 degrees, most molds and mildew go dormant, and the same is true if their environment dries up. That’s why the basement seems musty in the spring and summer, but not in the winter.

You will never end the threat of mold growth. Mold spores are ubiquitous, found thousands of miles in the sky and even frozen in Arctic ice. Indeed, they’re floating invisibly in the air in your home right now.

Mold growing in the basement produces spores (think seeds), and they don’t stay down there. Mold and mildew colonies pump millions of spores into your household air. Your goal is to keep them dormant. That means making your home as inhospitable as possible to keep the tough little characters nonproductive. That means cleaning up any current mold, and keeping everything dry so it won’t return.


Clean. Wash surfaces with a detergent water solution.

If you see signs of mold or mildew, treat with a solution of 1 cup chlorine bleach to a gallon of water. A spray bottle works well for corners and small areas. Bigger areas require a bucket and sponge or brush.

Apply the solution, wait about a minute and wipe off. Rinse and wipe dry and move on to the next area. Start from the top and work down. Always be sure to test the solution in an inconspicuous area first to make sure it’s safe and won’t lift colors or harm surfaces. Wear eye and hand protection when using bleach. Keep the bleach solution or mist from contacting any textile or carpet. It will take the color out.

Mitigate. Sunlight kills mold and mildew. Pull whatever you can out into the sun as temperatures allow. This is especially effective on breezy days with low humidity. Vacuum upholstered furniture thoroughly outdoors and dispose of the vacuum bag immediately to keep from scattering spores the next time you vacuum. (Realize that some mildew stains may not be removable. Depending on what’s affected, contact professionals at dry cleaners, photography stores, bookstores and luggage stores for information on how to remove mildew stains from objects.)

Prevent. Once mildew is removed to the best of your ability, change conditions in your basement:

• Keep outdoor moisture out. That’s snow melt, rain, etc. Be sure gutters and down spouts are in good condition and deposit water at least 10 feet from the house’s foundation. Ensure that the soil (not just the landscape rock or mulch) slopes away from the house. Even if the basement doesn’t leak, concrete easily transports moisture in the form of vapor from soggy soil to the basement air, increasing humidity and mold growth opportunities.

• Consider using drying agents, sometimes called desiccants, available at most home-improvement stores. (Seattle’s Dri-Z-Air lists retailers for its drying products at

• Don’t let wet clothing or towels lie around in piles or in the washing machine.

• Operate a dehumidifier. If you can add the ventilation and dehumidification of an air conditioner, that will help too.

• Consider installing a mechanical ventilation system. Such appliances do an excellent job of controlling humidity and eliminating mildew in the home. Contact a heating or air-conditioning specialist.

• Generally, keep basement windows closed. When warm, moist outdoor air comes in contact with the cool basement air, it will condense on the walls, pipes and floor. However, when air is at low dew points (in the 50-degree range), you may want to open the windows for a short time to help ventilate the basement.

Seattle Times staff contributed to this feature