Waterproofing from the inside
An inside system manages water that has already arrived. That is useful, and it is also a different promise than keeping the wall dry.
Waterproofing a basement from the inside means collecting water at the footing and routing it to a sump pump, not blocking it at the wall. The wall may still get wet. The floor and the room are what the system protects.
This page prints no prices. It explains the system so you can judge a proposal.
What an interior system is made of
- A channel or pipe along the inside edge of the floor, at the footing.
- Gravel and a drain path under or beside the slab.
- A sump pit and pump that lift the water out.
- A discharge line that carries it away from the house.
The drain tile page shows how the parts fit together.
Why the pump matters as much as the pipe
The drain only works if the water has somewhere to go. A pump that fails in a storm leaves the system full. Think about power loss and backup before you think about the drain. The sump pumps section covers that side.
What it does not do
It does not stop the soil outside from staying saturated. It does not repair a cracked or moving wall. And it does not make the wall look new. Anyone who promises a perfectly dry wall from the inside is selling more than the system can deliver.
When it is a good fit
An inside system makes sense when digging outside is impractical: a deck, a driveway, a property line, mature planting. It also suits houses where the water rises at the floor edge. If you are weighing the two, the interior vs exterior page lays out the trade-offs.
Do the free work first
Take a position: no inside system should be signed until the outside is sorted. Downspouts, gutters and soil slope cost nothing to check. Plenty of wet basements improve with just that. The budget waterproofing page gives the order that gets the most from the least.
Questions to ask before you sign
Where does the discharge go, and is that allowed locally? What happens in a power cut? Is the water test written into the plan? Ask for all of it in writing and compare more than one proposal.
Local rules and structural limits
Sump discharge, permits and inspections are set by your state and town, so ask your building department. Bowing walls and wide horizontal cracks are structural. They belong to a licensed structural engineer, and an independent one has no repair to sell you.
Frequently asked questions
What does waterproofing from the inside mean?
It means collecting water at the footing inside the basement and pumping it out, instead of blocking it at the outside of the wall.
Will an interior system keep my walls dry?
Not necessarily. It protects the floor and room by routing water away. The wall itself may still get damp.
Why does an interior drain need a sump pump?
The drain collects water, but something has to lift it out. Without the pump, the system just fills.
Is interior waterproofing better than exterior?
Neither is better in every case. Inside suits houses where digging outside is impractical. Outside is more thorough but more disruptive.
What should I do before agreeing to an inside system?
Fix gutters, downspouts and soil slope first, then ask about discharge, backup power and local permits in writing.
Sources
What this page explains is based on these official sources. If you check one and it does not match what you read here, send it to us and the article gets corrected.