Ask an Expert is an occasional feature where we pose a question submitted by readers to our Healthy Building Scientist Joe Medosch.

Reader Question: I Know That Moisture And Mold Go Together. What Can I Do When It Is So Wet Outdoors?

Rainy and snowy days now often mean moldy days later. Some molds can take up to 30 days to develop, so minimizing risk means doing more than just quickly fixing leaks and drying damp spots while it is wet outside.

There are many myths about mold, but one thing is for sure, mold thrives in damp environments. Here are two common scenarios for moisture and mold growth:

Moisture And Mold In Warm Climates

In warm/humid climates like Florida, Georgia, and Alabama or marine climates like Oregon or the California coast, extended periods of wet weather are followed by warm day and moisture accumulates. But it doesn’t get warm enough for long enough to really dry out the house, especially within exterior walls. The result: damp spaces where mold can bloom in the following days and weeks.

Moisture And Mold In Cold Climates

In cold/dry climates like Minnesota, Michigan, and New York and moisture issues tend to come from inside the house. Sealed up tight against the cold, moisture from everyday activities like showering, cooking, and laundry tend to accumulate in the house. With long periods of cold temperatures and low ventilation, dampness can linger and mold can follow. Cold climates can also see large amounts of snow pile up against the house and then melt leaving behind wet exterior walls and damp interior wall cavities where mold can grow.

What Can You Do?

Mold removal methods must be effective at removing the mold, safe for the occupants of the house, and not cause unintended consequences later. Chemical sprays and other mold treatments do not meet these criteria. Here’s what you can do:

• • Air out your house. Use dry weather days to open doors and windows to circulate air, which will help to dry everything out. At a minimum, open 2 windows (1/2”) on opposite sides of the house or one on each floor and keep them. open. f
  • Run fans. Bathroom fans, range hood fans, and basic tabletop or box fans can all help to extract or dissipate excess moisture. In extreme cases, you may opt to run a dehumidifier.
  • Keep snow and water away from the sides of the house. Make sure you have proper drainage and don’t shovel / plow snow up against the house, leave a few feet of space.
  • Test for moisture. You read that right, it’s better to test for moisture instead of mold. If you can see what looks like mold growth then you just need to remove it by carefully wiping the surface clean with a damp cloth and a mild, non-fragranced cleaning agent. If you smell a musty odor, but don’t see visible mold you need to find the source and either clean or remove it.

For more information on how you can deal with moisture and mold at home after wet weather, read our blog here on four actions to stop unknowingly growing mold in your home. To learn more about toxic mold, read our blog on the truths (and myths) of black toxic mold. You can also visit the EPA’s guide to Moisture and Mold in Your Home.

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