Wet basement repair cost

Fixing a wet basement costs $2,000 to $15,000, typically around $6,000. The cheapest fixes are outside and cost a few hundred dollars. The expensive ones are inside and involve breaking the floor.

Doing them in the wrong order is the most common and most expensive mistake in this whole subject. Almost every wet basement is a surface water problem before it is a groundwater problem.

What it costs

Do these first, in this order

1. The downspouts. A roof sheds thousands of gallons a year, and a downspout discharging at the foundation puts all of it exactly where you least want it. An extension carrying it six to ten feet away costs ten dollars. This is the single most effective thing on this page and it is skipped constantly.

2. The gutters. Overflowing or blocked gutters do the same thing along the whole wall.

3. The grade. Soil should fall away from the house at about six inches over the first ten feet. Over decades, mulch and settlement reverse it. Regrading is $500 to $3,000 and it fixes more wet basements than any interior system.

4. Window wells. A well with no drain and no cover fills and pours in through the window.

5. Anything discharging near the house: an air conditioning condensate line, a sump discharge that has been cut short, irrigation running against the wall.

Those five cost $500 to $4,000 in total and they resolve a large share of wet basements. A contractor who quotes a $10,000 interior system without asking about them is selling a system rather than solving a problem.

Interior or exterior

If the water persists after the outside is right, the choice is between two approaches.

Interior perimeter drain. A channel cut around the inside of the basement floor, with drain pipe in gravel, feeding a sump. $50 to $120 a linear foot, so $4,000 to $12,000 for a typical basement. It manages the water that arrives rather than stopping it, which is a legitimate strategy and is what most companies sell.

Exterior waterproofing. Excavating to the footing, cleaning the wall, applying a membrane, installing or replacing the footing drain, and backfilling with gravel. $100 to $220 a linear foot, so $15,000 to $40,000 for a whole house. It stops the water reaching the wall, which is a more complete answer, and it destroys the landscaping and sometimes a patio.

Interior is cheaper, less disruptive, and leaves the wall wet. Exterior is more expensive, more disruptive, and is the actual fix. Most people do interior, and for most houses that is a reasonable decision.

What the symptoms mean

Water on the floor after heavy rain, near the walls. Surface water. Start outside.

Damp at the wall-floor joint continuously. Hydrostatic pressure, and that is where an interior drain earns its money.

Efflorescence, the white crystalline deposit on block or concrete. Water is moving through the wall and depositing salts. It indicates ongoing moisture rather than a leak event.

A musty smell with no visible water. Humidity rather than liquid. Often solved by a dehumidifier and by not storing cardboard against a wall.

Water at one specific point. A crack, a tie rod hole, a pipe penetration, or a window well. Cheap and specific to fix.

Damp only in summer. Condensation on cool walls, not a leak. A dehumidifier is the answer, and sealing the wall makes it worse.

Frequently asked questions

Does waterproof paint work?

On minor dampness and efflorescence, it improves appearances. Against hydrostatic pressure it fails, because pressure pushes it off the wall from behind. It is a finish, not a waterproofing system, and it is frequently sold as one.

Will an interior drain system fix a foundation problem?

No. It manages water. If the water has already caused settlement or a bowing wall, that is a structural repair and a separate cost.

Do these companies have lifetime warranties?

Many offer transferable lifetime warranties, and they are worth reading closely: what they cover is usually water on the floor from the treated area, not dampness, not mold, and not any wall they did not work on. Check whether the company is likely to exist in twenty years.

How much can a dehumidifier do?

For humidity, a great deal: a 50 to 70 pint unit draining to the sump keeps a basement in a healthy range for $200 to $500 plus $10 to $30 a month. For liquid water it does nothing.

Should I finish the basement afterwards?

Only after a full wet season with no water. Framing over a wall that still gets wet traps moisture in the cavity and grows mold where nobody can see it.