Before you price anything, try the cheap fix
A meaningful share of wet basements are solved for $100 – $600: downspouts extended to discharge 6 feet from the house, gutters cleared, and soil regraded to fall about 6 inches over the first 10 feet.
Do that, then watch through one wet season. If the basement stays dry you have saved several thousand dollars, and the calculator will still be here if it does not. A waterproofing company has little reason to suggest this sequence; we have no reason not to.
How this calculator works
Interior and exterior systems are priced per linear foot of wall, so the estimate multiplies the unit price by the wall length you selected, scales it by severity, and applies a regional multiplier. Single-crack and equipment fixes are flat project costs instead.
Add-ons are itemized separately on purpose. A sump pump, a battery backup and a dehumidifier are the three items most often folded silently into — or quietly left out of — a waterproofing bid. Seeing them as their own lines makes a contractor's number checkable.
The unit prices behind the estimate
| Method | Typical range | Unit | What drives it |
|---|---|---|---|
| Regrading + downspout extensions | $100 – $600 | per project | The cheapest real fix. Worth ruling out before anything else. |
| Polyurethane crack injection | $350 – $900 | per crack | Seals a single leaking crack in a few hours. |
| Basement dehumidifier (installed) | $1,300 – $2,800 | per unit | For condensation rather than water entry. |
| Interior drain tile + sump pump | $65 – $130 | per lin. ft | Manages water that reaches the wall. Solves most chronic seepage. |
| Exterior excavation + waterproof membrane | $95 – $210 | per lin. ft | Stops water at the wall. For structural damage or finished space. |
| Exterior spot excavation + patch | $1,500 – $4,500 | per crack | Digging to one crack from outside. |
Source: Compiled from published 2025–2026 contractor cost datasets and waterproofing supplier pricing, normalized to installed cost including labor. Linear-foot prices assume a standard 8 ft basement wall. · Last reviewed July 30, 2026 · Reference data · How we compile these figures
Interior or exterior — the honest comparison
Interior drainage accepts that water reaches the wall and manages it: collect at the footing, route to a pit, pump it out. It solves most chronic seepage at roughly a third of the exterior price, installs year-round, and leaves your landscaping alone.
Exterior membrane stops water before it touches the wall. It is the right call when hydrostatic pressure is damaging the structure, when the wall itself is deteriorating, or when a finished basement cannot tolerate any water entry at all.
Most contractors sell what they install, which is worth remembering when a quote arrives with only one option on it. On a five-figure decision, an independent inspection ($300 – $600) tells you which system your specific water source calls for.
Make sure it is actually seepage
Tape a square of plastic sheeting tightly over a dry patch of wall and leave it 24–48 hours. Moisture on the room side means condensation — humid air meeting a cold wall, fixed with a $1,300 – $2,800 dehumidifier. Moisture behind the plastic means water coming through the wall, which is what drainage work is for.
This five-minute test is the difference between a dehumidifier and a $9,000 drainage system, and it is worth doing before either.
Where to go next
- Basement waterproofing cost — the full itemized guide.
- Wet basement repair cost — priced by water source.
- Foundation leak repair cost — when one crack is the problem.
- Sump pump installation cost — new install, replacement, backup.
- Foundation repair cost calculator — for structural work.