Prevent Water Vapor Damage in Your Basement With These 4 Tips

Candace Nelson
Written by Candace Nelson
Updated January 18, 2022
Renovated basement with new furniture and laminate flooring
Photo: Anatoli Igolkin / iStock / Getty Images Plus

If you have to ask if it smells like mildew in the basement—it does

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We all know that musty smell—mold and mildew in your basement are never welcome. Unfortunately, water vapor that condenses down there can lead to costly water damage. But there are ways to encourage water vapor to go somewhere other than your lower-level living space.

Preparing to Waterproof Your Basement

If you have a water condensation or leaking issue in your home, don’t delay addressing it. You can reduce the chance of mold if you dry the area within 48 hours, according to the Environmental Protection Agency. You’ll also want to waterproof your basement or find a local waterproofing contractor so the problem doesn’t happen again.

1. Install a Vapor Barrier

A home’s foundation is often a concrete slab. While it provides a nice, even surface for your house to sit on, concrete is porous. That means moisture can get in, so you need a vapor barrier to waterproof your basement.

A vapor barrier, usually in the form of polyurethane sheeting, is your first line of defense against water seeping in and potentially ruining the important boxes of family heirlooms under the stairs or your expensive theater room furniture.

If there isn’t already one there, install a vapor barrier between the concrete and your flooring. Lay the barrier over the floor, overlapping edges by at least 12 inches. Be sure to seal all joints or cracks in the wall with a waterproofing caulk.

The walls of the basement should also have a vapor barrier. Builders usually staple the sheeting to the frame before installing drywall and finishing the walls.

2. Prevent Water From Coming In

Couple removing autumn leaves from gutters
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Some outdoor maintenance can also keep water draining properly and away from your basement. 

  • Clean and repair roof gutters regularly.

  • Avoid damage from clogged gutters by regularly clearing them, and point gutter downspouts away from your house. You can also attach an extra length of downspout at the elbow of your gutter to extend it out further from the house.

  • Make sure the ground slopes away from the foundation. The ground should slope one-half inch to an inch per foot, so that water does not enter or collect around the foundation.

  • Landscape to prevent basement floods with rain gardens and native plants

3. Monitor Indoor Humidity Levels

Condensation can build up inside the house, leading to mold and mildew issues. To minimize problems, you can try the following methods.

  • Keep indoor relative humidity between 30 and 50 percent. You can pick up a humidity meter for about $10–$50 at many hardware stores.

  • Keep air conditioning drip pans clean and the drain lines unobstructed and flowing properly.

  • Reduce condensation in the home.

  • Act quickly when you see condensation, a sign of high humidity, collecting on windows, walls or pipes. Dry the wet surface and run a dehumidifier.

  • Use bathroom and kitchen vents.

  • Use charcoal briquettes. They absorb moisture, so in a pinch. Set a few in a bowl and let them dehumidify your basement. 

If mold and mildew have already taken over your basement, you should call a mold remediation company near you.

4. Inspect Your Basement

Sump pump installed in a home basement
Photo: IcemanJ / iStock / Getty Images Plus

Basements hold the house up, and walls can crack as the house settles. Additionally, much of the plumbing is housed in the basement. All this to say that things can go wrong down there. If it feels damp or has that fresh mildew smell, start looking around for ways to keep your basement dry.

  • Check for cracks: Even small cracks in the foundation, walls, or windows can allow moisture to get into the basement. Replace windows or add caulking to seal them up as needed.

  • Check your pipes: Since all pipes lead to the basement, any cracks or leaks could cause moisture issues down there.

  • Check the sump pump (or get one): You need a sump pump to drain water from the basement. If it’s no longer keeping up, it might be clogged with debris.

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