You head downstairs and catch a musty smell, or spot a damp patch on the carpet, or a chalky white film on the concrete wall. Maybe it only happens after a big storm. Maybe it creeps in every summer. Either way, the sooner you deal with it, the cheaper it is.
So how do you keep your basement dry all year? Send water away from your foundation, keep the air inside from getting too humid, and have a backup plan for the days water gets in anyway. Most damp basements come down to just a few causes, and you can fix plenty of them yourself.
Where is the moisture really coming from?
“Damp” can mean two very different things, and the fix depends on which one you’ve got.
- Liquid water seeps through cracks, joints or the floor after rain or snowmelt. You might see puddles, dark stains or water trickling down a wall.
- Humidity and condensation feel clammy. Think fogged windows, beads of water on cold pipes or a musty smell, usually in summer when warm air meets cool concrete.
Here’s a quick way to tell them apart. Tape a square of aluminum foil, about a foot across, tightly to a bare wall or floor and leave it for a day or two. Moisture on the outside of the foil means humidity is the problem. Moisture underneath means water is coming through the wall or slab. Plenty of basements have a bit of both.
Keep your basement dry by fixing the outside first
Most basement water starts as rain that lands on your roof and ends up right beside your foundation. The fixes are cheap, and they solve a surprising number of problems.
- Clean your gutters at least twice a year, and more often if big trees hang nearby. Clogged gutters overflow right against the wall.
- Extend your downspouts so they empty several feet from the house. Many people aim for six feet or more.
- Check the slope of the soil. The ground should fall away from the house. A common rule of thumb is about an inch per foot for the first several feet, so add compacted soil where it’s settled.
- Rein in the mulch and plants. Heavy mulch beds and shrubs pressed against the foundation can hold water right where you don’t want it.
- Seal the obvious gaps around utility pipes and visible cracks, and keep window wells clear of debris so they drain.
How do you control humidity in a basement?
Even a basement with zero leaks can feel damp. Indoor humidity above roughly 60 percent encourages mold and dust mites, so many people aim for somewhere between 30 and 50 percent. A cheap hygrometer will tell you where you stand.
A dehumidifier is the usual fix. Size it to the space and how damp the room gets, and look for a model with a continuous drain option so you’re not dumping a bucket every day. If the unit sits far from a floor drain, a built-in pump can move the water for you. When you’re ready to shop, take a look at our picks for basement dehumidifiers with a pump.
A few habits help too. Run bathroom and dryer vents outdoors, never into the basement. Keep boxes off the floor and away from walls so air can move around them. And close the windows on muggy days, because warm outdoor air cooling down inside is exactly what creates condensation.
Is your sump pump ready for the next storm?
If your home has a sump pit, that pump is your last line of defense in heavy rain. It’s also easy to forget about until the day it fails.
- Pour a bucket of water into the pit every few months, and make sure the pump turns on, empties the pit and shuts off.
- Check that the discharge pipe is clear and sends water well away from the house.
- Clear any debris out of the pit.
- Remember that storms often knock out power, which is exactly when a plain electric pump stops working.
That last point is why many homeowners add a battery backup pump or a high-water alarm. If you’d like to compare options, here’s our roundup of battery backup sump pumps that come with an alarm. Keep in mind that pumps wear out, and a typical lifespan is often put at around ten years, though it varies with use.
Catching small leaks before they get big
Not every wet floor comes from outside. Water heaters, washing machine hoses, utility sinks and pipes can all leak, and the basement is the place nobody’s looking. A small water sensor near the water heater, the sump pit and the washer will let you know early. We’ve rounded up water alarms made for basements and crawlspaces if you want somewhere to start.
Want something that can also stop the flow? Some leak detectors come with an automatic shutoff valve. And if you’re curious about the rest of the house, our article on preventing water damage from leaks covers the plumbing risks upstairs.
When should you call a professional?
DIY has its limits. Call a qualified contractor or foundation specialist if you see any of these:
- Horizontal cracks, cracks wider than about a quarter inch, or walls that bow inward
- Water coming in through the floor again and again, even after you’ve fixed the gutters and grading
- Widespread mold, or a musty smell that comes back after everything dries out
- Standing water you can’t explain
One more thing, and it’s serious. Water and electricity do not mix. If there’s standing water near outlets, appliances or the electrical panel, stay out and have a professional shut off the power before anyone goes in.
Frequently asked questions
Why does my basement smell musty even when it looks dry?
A musty smell usually points to high humidity or hidden moisture, not just visible water. Check the humidity with a hygrometer, run a dehumidifier and look behind stored boxes for mold.
How often should I test my sump pump?
Every few months is a good rhythm, and right before heavy rain season is even better. Pour water into the pit and watch the pump switch on, drain the pit and shut off.
Can a dehumidifier fix a wet basement?
Not if water is actually seeping in. A dehumidifier handles humid air, but leaks need drainage fixes outside or repairs from a pro.
The bottom line
To keep your basement dry, start outside with gutters and grading, manage humidity inside, test your sump pump and keep an eye out for small leaks. Once the basics are covered, the roundups linked above can help you pick the right dehumidifier, backup pump or leak alarm.