Short answer: Interior waterproofing catches water inside the basement with a drain tile and sump pump. Exterior waterproofing digs down outside and seals the wall so water never reaches it. Interior systems usually cost less and are less disruptive; exterior work can make sense for new construction or when the outside is already being excavated.
How interior waterproofing works
A contractor removes a strip of concrete floor along the inside of the foundation walls, lays a perforated drain tile in gravel next to the footing, and pours new concrete over it. Water that comes in at the wall-floor joint or through the wall is collected and carried to a sump pit, where a pump sends it outside.
Many systems add a plastic vapor barrier on the walls that directs seepage down into the drain. Interior drain tile typically runs $60 to $120 per linear foot, according to Angi and This Old House.
How exterior waterproofing works
The soil is dug away from the outside of the foundation down to the footing. The wall is cleaned, cracks are repaired, a waterproof membrane or coating is applied, and a new footing drain is installed before the hole is backfilled.
This Old House puts exterior waterproofing at $7,000 to $15,000, plus excavation. Costs climb with depth, decks, porches, driveways and landscaping that have to be removed and replaced.
Side-by-side comparison
| Interior drain system | Exterior waterproofing | |
|---|---|---|
| What it does | Collects water that reaches the basement and pumps it out | Seals the wall so water doesn't reach it |
| Disruption | Inside the basement; walls must be cleared | Excavation around the house; landscaping removed |
| Typical cost | $60 to $120 per linear foot | $7,000 to $15,000 plus excavation |
| Weather | Can be done year-round | Easier in dry months |
| Needs a sump pump | Yes | Usually, for the footing drain |
Which one is right for your home?
- Choose interior drainage when water enters at the wall-floor joint or through the floor, and you want the least disruption and cost.
- Consider exterior work when the outside is already being dug up, the wall itself needs repair from the outside, or you want to stop water from soaking the wall at all.
- In very wet soil, some contractors recommend both, but most existing homes in Ohio are fixed from the inside.
Frequently asked questions
Does interior waterproofing actually stop water?
It doesn't stop water from reaching the wall. It controls it, so the water drains away instead of spreading across the floor. For most homes, that keeps the basement dry.
Is waterproofing the same as damp proofing?
No. Damp proofing is a thin coating meant to slow moisture through the wall. Waterproofing is designed to handle water under pressure. Many older homes only had damp proofing, if anything.