Two contractors can walk into the same basement and quote you very different numbers, and both can be quoting honest work. They are simply proposing opposite strategies.
Understanding the difference is the single most useful thing a homeowner can do before getting quotes.
They solve the problem in opposite directions
Exterior waterproofing stops water from reaching the wall. The foundation is excavated to the footing, the wall is cleaned and repaired, a waterproof membrane goes on, drainage board goes over it, and new weeping tile is laid at the footing in clean stone.
Interior waterproofing manages water after it reaches the wall. The concrete floor is cut along the perimeter, new drain tile is laid inside the footing, and everything is routed to a sump pit and pumped out.
That distinction explains everything else. Exterior keeps the foundation dry. Interior lets the foundation get wet and drains it.
Side by side
- Cost: exterior $300 to $400 per linear foot. Interior drainage and sump $120 to $250 per linear foot. Interior is typically the cheaper of the two.
- Disruption: exterior tears up your yard, landscaping, walkways and decks. Interior tears up your finished basement.
- Weather: exterior needs open ground, so in Edmonton the window closes once the frost sets in. Interior can be done in January.
- Protects the wall itself: exterior yes, interior no.
- Ongoing dependency: exterior is passive. Interior depends on a sump pump, which means power, maintenance and eventual replacement.
When exterior is the right call
Choose exterior when the wall itself is the problem. That means visible bowing or inward movement, deteriorating block or mortar, multiple failing cracks across one wall, or a foundation that has to stay dry because the space beyond it is finished and valuable.
It is also the right call when the yard is already coming up for other reasons, and when you want the fix to outlive you rather than depend on a pump.
When interior is the right call
Choose interior when water arrives at the wall-floor joint rather than through the wall, when the original weeping tile has failed but the foundation is structurally sound, or when exterior access is genuinely blocked by a neighbouring structure, a zero lot line, mature trees or a concrete patio you are not willing to lose.
It is also the practical answer in November, when nobody is excavating anything.
When neither is the answer
This is the part contractors skip. Plenty of wet basements are fixed by:
- Grading. If soil slopes toward the house, water is being delivered to your foundation on purpose.
- Downspouts. Six feet minimum from the wall. This is the cheapest waterproofing that exists.
- Window well drains. A well that holds water is a bucket sitting against your foundation.
- Single crack injection. One defined crack in an otherwise dry basement is $1,200 to $2,000, not a system.
Anyone who quotes a full system before they have ruled out grading, downspouts and a single crack is not diagnosing your house.
How to tell which one you need
Look at where the water shows up:
Through a crack, mid-wall: start with crack injection.
Along the joint where the wall meets the floor, across a run: the weeping tile has failed. Interior or exterior, depending on access and budget.
Through the wall surface generally, with efflorescence and damp block: the wall is saturated. This is an exterior problem.
Up through the floor drain or the toilet: that is sewer backup, not foundation seepage. A backwater valve is the fix.
In through window wells or at the top of the foundation: surface water. Grading and drainage.
What to do next
Text us a photo of where the water shows up and we will tell you which category you are in before anyone comes out. If you want it looked at, the inspection and the written quote are free.
Related reading: Edmonton waterproofing prices.
Find out which one your house needs.
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