How to get rid of dampness in my basement wall

To get rid of dampness in a basement wall for good, you stop the water from the inside with full-perimeter interior drainage routed to a sump pump, plus a 12-mil wall vapor barrier and a dehumidifier. That is our Forever Dry System, and it runs $3,000 to $30,000. Patching paint or sealing the inside of the wall hides the damp for a while. It does not stop it.

Here is why a foundation wall sweats and weeps in the first place.

When your house was built, a trench got dug around the foundation and then filled back in. That backfill soil is looser than the ground it replaced. It drains slow and holds water. So every rain and every snowmelt, water collects right against your wall and presses in. NH frost heave makes it worse. Freezing soil swells and pushes the wall inward over the winter. The dampness you feel is that water working through the concrete or block, then evaporating into your basement air.

Now the fix. You have two ways to deal with wall water, and only one of them lasts.

The first is exterior excavation. Dig the foundation back out, coat the outside, backfill again. We do not do that. In our field experience that fix tends to fail in about two to three years once the soil settles and shifts again. You pay a lot to dig your yard up twice.

The second is interior drainage, and that is the durable fix. We install a drain channel along the inside base of the wall, right at the floor wall joint where most water shows up. Water that comes through gets caught and carried to the sump pump instead of sitting on your slab. The pump throws it out of the house. A 12-mil vapor barrier goes on the wall so moisture coming through the block never reaches your finished space. A dehumidifier dries the air that is left. That whole system carries the 603 guarantee, 100% guaranteed to be dry for life!

The main pump runs on house power, sized 1/2 hp per 120 feet of drain. The backup is a battery unit, not a second power line. A charged backup battery can pump about a residential pool’s worth of water during an outage, roughly 15,000 to 20,000 gallons by typical pool-volume figures. That keeps you dry when the power drops in a storm, which around here is exactly when you need it.

What drives the cost is how much wall you are protecting, how the slab is laid out, and whether you need one sump or two. A short stretch of damp on one wall costs less than wrapping a full perimeter. We give you the number after a free inspection, and the quote comes within 24 hours.

You might not need the full system yet. If you only see a little surface condensation in July and the wall is dry the rest of the year, that can be a humidity problem, not a groundwater problem. A dehumidifier alone may handle it. We will tell you that on the inspection rather than sell you drainage you do not need. The EPA notes that moist basement air can carry radon up from the soil too, so if you are opening up the basement anyway it is worth a radon test (EPA action level is 4.0 pCi/L). See EPA radon and NH DHHS radon [verify].

If the dampness is in a dirt or low crawl space under the house rather than a full basement, the answer is different. That is crawl space encapsulation, not Forever Dry, and it runs $3,000 to $25,000. The Department of Energy notes that up to about a third of a home’s heat loss can come from an uninsulated foundation or crawl, so sealing it helps your heating bill, not just the damp. See DOE Building America.

Want it gone? Call us at 603-610-1770 or book your free inspection and we will tell you exactly what your wall needs.

Read more on our basement waterproofing page, our crawl space services, and the 603 guarantee.

Related questions

Why is my basement wall wet only after it rains? Rain saturates the loose backfill soil packed against your foundation, and that water presses through the wall. It dries between storms, so it looks like it comes and goes. Interior drainage catches it every time instead. See basement waterproofing.

Will sealing paint stop the dampness? No. Sealer slows the look of it for a season, but the water pressure behind the wall is still there and will push the paint off or find another spot. You have to give the water a path out, which is what the drain and sump do. See the 603 guarantee.

Does a dehumidifier alone fix a damp basement? Sometimes. If it is summer humidity and the wall is dry the rest of the year, a dehumidifier may be all you need. If water is coming through the wall or the floor wall joint, the dehumidifier only treats the air, not the source. We will tell you which one you have for free.

Is interior drainage really better than digging the outside? For lasting dry, yes. Outside excavation tends to fail in two to three years once the soil shifts, and it costs more. Interior drainage to a sump is the fix we stand behind for life. See basement waterproofing.