Wet basement: where the damp comes from and what to try first
Damp air, roof water and groundwater each leave different marks. Telling them apart costs nothing, and the simple fixes are worth trying before the expensive ones.
Three kinds of wet
Condensation. Warm, humid summer air meets a cool wall, floor or cold-water pipe and leaves water on it. It shows up in July, not April, and on surfaces all around the room. To check, tape a square of plastic tightly to the wall for two days. Moisture on the room side is condensation. Moisture underneath has come through the wall.
Runoff. Rain from the roof or the yard reaches the foundation and finds a way in. It follows storms closely, and it favours one side of the house: the side with the short downspout, the sunken flower bed or the window well.
Groundwater. The soil fills from below and water appears at the floor seam, often a day after the rain and for days afterwards. A sump pump that runs hard at the same time confirms it.
Try these first
Wisconsin's consumer protection bureau says it in its own fact sheet on basement waterproofing: expensive waterproofing is not always the answer.
Clear the gutters
An overflowing gutter drops a roof's worth of water in a line along the wall.
Lengthen the downspouts
Each one should empty well out into the yard, on ground that slopes away, not at the corner of the house.
Rebuild the slope
Add soil where it has settled beside the foundation so the surface falls away from the wall. Keep it below the siding.
Deal with the window wells
Scoop out the leaves, check the drain takes a bucket of water, and add covers.
Dry the air
Run a dehumidifier through the warm months and keep basement windows shut on humid days.
Check the sump outlet
If the pipe ends beside the wall, the pump is recycling the same water.
When to stop trying and call
- The outdoor fixes are done and water still comes up along the floor seam.
- More than one wall is involved.
- Boxes stored on the floor get wet every spring.
- You plan to finish the basement and need to know it will stay dry behind the walls.
At that point the question is how to give groundwater somewhere to go, and that needs someone to look at the house.
What to tell the company
Lead with the pattern, not the product you think you need. Say which of the three kinds of wet it resembles, which season it happens in, which walls, and what you have already tried. Mention the age of the house and whether there is a sump pump. A company that hears all that and still recommends its largest system without visiting has told you something useful.
Wet basement questions
Is a damp basement bad for the house?
Over time, yes. Constant damp rusts the furnace and water heater, lifts paint and flooring, and lets mold grow on anything made of paper, fabric or wood.
When should a dehumidifier run?
Humid outdoor air is the problem in warm weather, so that is when the machine earns its keep. In the heating season indoor air is usually dry enough without one.
Should the water be fixed before I finish the basement?
Yes. Framing and drywall hide the wall, so a small seep becomes mold that nobody sees. Watch the bare basement through at least one spring before building anything against it.
Talk it through with a local company
Call and describe what the water is doing. You will speak with an independent local waterproofing company about coming out to look at your house.
For homeowners: basements, crawl spaces, sump pumps and drainage.
Call (262) 257-3901Racine Basement Waterproofing Help is a referral service, not a contractor. Calls may be recorded. Referral disclosure.