Handyman

Fixing moisture issues with the crawlspace

Your air conditioner is a dehumidifier, and that’s why most moisture problems do not appear in the summer months.
Your air conditioner is a dehumidifier, and that’s why most moisture problems do not appear in the summer months. KRT

Q: I have lived in a 75-year-old house for over 20 years. This year is the first time I have noticed condensation on the living room windows. This room has a crawl space while the rest of the house has an unfinished basement with heat and air to it. It seems the basement is much damper than usual this year as well, and I found some surface mildew on items down there.

The living room windows have storms that have been there for more than 10 years. The furnace is checked every year, and I’m told all is OK with it. There are small vents in the crawl space/foundation. Should they be open or blocked for the winter? What other suggestions do you have? I am a retired lady and need a budget-friendly solution.

A: Depending on your geographical location, crawlspace vents should be treated differently. I live in the Midwest in a mixed-humid climate. In this type of climate, I suggest opening the vents in the winter and closing them in the summer. The idea is to control the humidity inside the crawlspace.

If there is only a minimal amount of humidity preset, i.e. a very dry crawlspace, the vents can be left closed year-round. If the crawlspace floods, regardless of the season, the vents should be opened to help dry out the crawlspace. When the humidity levels in the crawlspace are higher than the humidity levels outside the crawlspace, the vents should be open. Close the vents when the humidity outside is higher.

The sudden moisture change at the windows can be caused by various conditions inside the home. The fact that you believe your basement is much damper than normal leads me to believe you may have drainage issues on the exterior of the home. It is extremely important to drain water away from the home for several reasons.

Ensure gutters and downspouts are not clogged and are draining at least six feet away from the foundation. If the grading of the yard looks like it is not sloped to carry surface water away from the house, it will need to be regraded. Have someone check the roof and exterior walls for any obvious signs of water entry and repair if needed. As for the crawlspace, make sure you have a good vapor barrier (plastic sheeting) covering all of the exposed ground inside the crawlspace. The vapor barrier prevents moisture from the ground getting into the crawlspace and home.

Many times I have seen your foundation configuration of a combined basement and crawlspace with different moisture environments because one area is heated/cooled and the other has vents to the outside such as you have described. I suggest permanently closing the exterior crawlspace vents and providing a screen-covered opening between the crawlspace and basement. This allows for better moisture and temperature control of both the basement and crawlspace.

Your air conditioner is a dehumidifier and that’s why most moisture problems do not appear in the summer months. Adding a dehumidifier to the basement will help to control the indoor humidity problems.

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