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Waterproofing prices
HomeAdvisor lists an average of $4,400 for waterproofing a basement with a leaky foundation and $575 for a sump pump installation. NerdWallet gives about $4,500 on average, or $5–$10 per square foot.
| Area | At $5–$10 per sq ft | With sump pump |
|---|---|---|
| 500 sq ft | $2,500–$5,000 | $3,075–$5,575 |
| 800 sq ft | $4,000–$8,000 | $4,575–$8,575 |
| 1,000 sq ft | $5,000–$10,000 | $5,575–$10,575 |
| 1,200 sq ft | $6,000–$12,000 | $6,575–$12,575 |
| 1,500 sq ft | $7,500–$15,000 | $8,075–$15,575 |
| 2,000 sq ft | $10,000–$20,000 | $10,575–$20,575 |
Fix water before you finish
Drywall, carpet and wood framing hold water and grow mold. Most finishing contractors will not start until the basement stays dry through a wet season. Start with gutters, downspout extensions and grading, then interior drains and a sump pump, then exterior membranes for the worst cases.
Moisture comes first
Finishing materials hide water problems until they become mold problems. Before framing, tape a 2 × 2 ft sheet of plastic to the slab and to a wall for two days: water under it means moisture is coming through the concrete; water on top means humid air is condensing. The first calls for drainage or sealing, the second for dehumidification. Keep a hygrometer in the finished space afterward and aim for the EPA's 30%–50% range.
- Extend downspouts several feet from the foundation.
- Slope soil away from the house.
- Use materials that tolerate moisture below grade: foam board, treated bottom plates, vinyl plank.
- Leave access to the sump pit, the radon fan and the main water shutoff.
Where basement moisture comes from
| Source | Sign | Usual fix |
|---|---|---|
| Rain and snowmelt | Wet floor edges after storms | Gutters, downspout extensions, grading |
| Groundwater | Water through cracks or under walls | Interior drain and sump pump |
| Humid outdoor air | Musty smell, sweating pipes in summer | Dehumidifier, keep windows shut on humid days |
| Vapor through concrete | Damp under a plastic test sheet | Vapor barrier, foam board, sealer |
| Plumbing and appliances | Local stains | Repair leaks, vent the dryer outside |
Common waterproofing methods
| Method | What it does | Best for |
|---|---|---|
| Gutters and grading | Keeps roof water away from the walls | Every basement, first |
| Interior perimeter drain | Collects water at the footing and sends it to a sump | Water entering at the floor-wall joint |
| Sump pump | Pumps collected water outside | High water tables, drain systems |
| Exterior membrane | Seals the outside of the foundation wall | Persistent wall leaks; excavation needed |
| Crack injection | Seals individual wall cracks | Isolated leaks |
| Sealer or coating | Slows vapor and dampness through concrete | Damp but not leaking walls |
Common questions
How much does basement waterproofing cost?
HomeAdvisor's average is $4,400; NerdWallet gives $5–$10 per square foot.
Related calculators
Sources
- https://www.homeadvisor.com/cost/basements/
- https://www.nerdwallet.com/article/mortgages/cost-finish-basement