Interior drainage vs exterior waterproofing
Two solutions to what looks like one problem. One costs three times the other. Neither is a scam and neither is always right.
What each one actually does
Interior perimeter drain (drain tile + sump)
Break the slab inside, lay perforated pipe in gravel, run it to a sump. Does not stop water entering the wall — it collects it under the slab and pumps it out. Cheapest reliable fix, and the one most national franchises sell.
| Modelled range | $50–$100 per linear foot |
|---|---|
| Disruption | Inside: slab cut, dust, 2–4 days. Outside untouched. |
| Expected life | Pipe itself: decades. The pump is the wear item — 7–12 years. |
| What it does not do | Stop water entering the wall. The wall stays wet; the water is collected under the slab and pumped away. That is fine for a utility basement and a problem if you plan to finish it and put wood against that wall. |
| Depends on | A pump, and therefore on electricity, forever. |
Exterior excavation + membrane + footing drain
Dig to the footing, clean and seal the outside face of the wall, add a drainage board and a footing drain. Keeps water out of the wall instead of managing it after it is in. Two to four times the price.
| Modelled range | $100–$250 per linear foot |
|---|---|
| Disruption | Outside: excavator, landscaping and hardscape gone, 1–2 weeks. |
| Expected life | Membrane 20–30+ years if backfill is done right. |
| What it does not do | Help with water arriving under the slab from below. If the water table rises above floor level, the outside of the wall is the wrong place to be working. |
| Depends on | Access. Attached garages, additions, decks, mature trees and a neighbouring wall three feet away can make it impossible at any price. |
Which one the soil points to
| Water at the wall-floor joint or through the floor | Interior. The water is under the slab and exterior work does not reach it. |
|---|---|
| Water through the upper wall, or a specific crack | Neither, yet. That is surface water or a single crack. Fix the grade or inject the crack. |
| Poorly or very poorly drained soil, shallow water table | Interior drainage plus serious pump redundancy. Exterior helps but does not remove the need for a pump. |
| Well drained soil, deep water table, but a wet wall | Look for the construction cause before buying either. In this soil the ground is usually not the culprit. |
| You are finishing the basement as living space | Exterior becomes much more attractive, because a dry wall and a managed wall are different things once there is drywall against it. |
| Historic stone or rubble foundation | Get someone who works on those specifically. Both standard approaches can damage a rubble wall, and interior drainage that undermines a shallow footing is a real failure mode. |
Get both approaches quoted on the same scope
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