Energy adviser: Now’s the time to fight mold, mildew



Cold, damp weather in the Pacific Northwest means bathrooms and showers, as well as window sills and even walls, can become susceptible to mold and mildew.

In the worst cases, the moisture can wick into adjoining wall timbers and generate dry rot and other structural damage, as well as health problems for some people.

“A lot of homeowners and renters face this problem with our cold-but-humid winters,” said DuWayne Dunham, an energy counselor at Clark Public Utilities.

Builders have long battled to keep moisture and cold air outside, and dry air and heat inside. Homeowners face the challenge now more than ever because a modern home is built to be energy-efficient, or “tighter.” Tighter homes actually hold in more moisture.

During Western Washington’s heating season, when humidity levels often exceed 40 percent, moisture that hangs in the air can condense, turning into water and possibly adding to a moldy indoor environment. Even house plants and firewood stacked inside can add to an indoor humidity problem.

George Tsongas, a consulting engineer and professor emeritus at Portland State University, said that visible indoor mold and mildew problems are present in as many as a third of Northwest homes.

Most vulnerable are older homes with single-pane, metal-framed windows; those that keep blinds and drapes often closed; those with high indoor relative humidity; and multifamily and manufactured housing. Mold and mildew can occur in both new and older homes, Tsongas said.

Mold and mildew can be a health hazard, he said.

“The microorganisms can cause allergic reactions such as hay fever-type symptoms and pathogenic reactions such as respiratory infections,” he said.

Whether mold or mildew have toxic effect is unproven, he said.

How much mold is out there? According to research, there are 100,000 varieties of mold.

Battle strategies

A low-cost way to fight mold and mildew is to use indoor heat and air movement, Dunham said.

“If the area is exposed to heat and air movement, it is harder for mold to take hold,” he said. “If it does take hold, there are a lot of websites with advice on how to battle the problem.”

If moisture problems are severe, Dunham said, the homeowner might need to call a professional for mold remediation. This can sometimes require demolishing and rebuilding walls, floors or ceilings. And that can be expensive.

Tsongas’ recommendations for moisture control in homes include a heavy reliance on high-volume ventilation exhaust fans in kitchens and bathrooms. These fans should exhaust outdoors, should be located directly over showers and tubs, and could possibly be attached to automatic timers. Installing dehumidifiers also might help.

Ideally, Tsongas said, homes should have humidity levels of less than 50 percent to avoid mold and mildew; for best health and comfort, humidity levels should be less than 30 percent.

Homeowners who want to test their indoor humidity levels can use a hygrometer, which can be purchased at most home-improvement stores.

In addition to drier indoor air, homeowners should keep surfaces clean, because greasy film from cooking oils and soap scum both offer mold a good growing environment.

Homeowners also make sure that clothes dryers are vented outdoors. They should cut back on the number of indoor plants, which give off moisture and are a source of mold spores, and fix leaky faucets as soon as possible to reduce excess moisture in the home.

Homeowners should not use unvented combustion heaters indoors and should consider removing firewood stored indoors.

“The key to mold control is moisture control,” Tsongas said in his report, “Moisture & Mold: Prevent and Solve” (visit A workable strategy for keeping mold and mildew at bay is a mix of ventilation and dehumidification, he said. Spot ventilation with fans are key.

]Energy Adviser is written by Clark Public Utilities. Send questions to or to Energy Adviser, c/o Clark Public Utilities, P.O. Box 8900, Vancouver, WA 98668.