- Exterior waterproofing stops water before it reaches the foundation: dig to the footing, membrane, drainage board and new weeping tile. It's the most complete fix, typically $150 to $300 per linear foot.
- Interior waterproofing catches water at the base of the wall and pumps it out through a sump. It's less disruptive and usually costs less, typically $80 to $180 per linear foot.
- Exterior usually wins when water comes through the walls and you can dig. Interior usually wins when access is blocked, the basement is finished, or water comes in at the floor-wall joint.
- In Burlington, Oakville and Milton, Halton covers 100% of disconnecting weeping tile and adding a sump pump, up to $6,500, which can cover part of an interior system.
Why basements leak in the first place
The soil around your foundation holds water. When it's saturated, during the spring thaw or after a big storm, that water builds pressure against the wall. Building scientists call it hydrostatic pressure, and the National Research Council has noted that water trapped in fine backfill can build enough of it to force water through joints and cracks in a foundation wall.
Weeping tile at the footing is supposed to relieve that pressure by carrying water away. When it clogs, collapses or never existed, water finds the easiest way in: a crack, a tie hole, a pipe penetration or the joint where the floor meets the wall. Every basement waterproofing solution deals with that water in one of two places: outside the wall, or inside before it reaches the floor.
Dampproofing vs waterproofing: what the code says
The Ontario Building Code draws a clear line between the two. Where the ground outside is higher than the floor inside, foundation walls below ground have to be dampproofed, which means coated to resist moisture. Where hydrostatic pressure occurs, the code requires waterproofing instead. Many older homes only have the tar-type coating on the outside of the wall, which wasn't built to hold back water under pressure and often flakes away with age.
The code also requires drainage at the bottom of foundation walls. Drain tile or pipe has to be at least 100 mm in diameter, laid with its top below the floor slab and covered by at least 150 mm of crushed stone, and it has to drain to a sewer, a drainage ditch or a dry well. Foundation drains can't be connected to the sanitary sewer.
How exterior waterproofing works
Exterior waterproofing is how you waterproof basement walls from the outside, and it's the standard approach in Canadian building research for controlling water around a foundation: protect the outside of the wall, give water a free path down to drain tile, connect that drain tile to a sump or storm sewer, and slope the ground away from the house.
- 01
Excavate to the footing
We dig along the wall down to the footing, protecting what we can above ground.
- 02
Clean, inspect and repair
The wall is cleaned so we can see it properly, and cracks are repaired from the outside.
- 03
Membrane and drainage board
A rubberized waterproofing membrane goes on, then a dimpled drainage board that lets water drop straight to the footing instead of sitting against the wall.
- 04
New weeping tile
New drain pipe is laid in clean stone at the footing and carried to a sump or a proper outlet.
- 05
Backfill and grade
Clean backfill is placed and compacted, and the grade is sloped away from the house so surface water runs off.
Because it keeps water off the wall entirely, exterior work is the most complete fix, and it's the right time to repair the outside of the wall while it's exposed. The trade-offs are cost, time and digging up whatever is beside the house. Our exterior waterproofing service page has the details.
How interior waterproofing works
- 01
Open the perimeter
We cut the slab along the walls and dig a channel below floor level.
- 02
Drain and membrane
Perforated drain goes in the channel in clean stone, and a dimpled membrane on the wall guides any water down into it.
- 03
Sump and discharge
The drain runs to a sump that pumps the water outside and away from the foundation.
- 04
Patch and finish
The floor is patched along the perimeter and the basement is ready to finish.
Interior waterproofing manages water rather than keeping it off the wall. Water still reaches the outside of the foundation, but it's captured and pumped out before it reaches your floor. For most basements, the result is a dry, usable space, delivered in days rather than weeks.
Interior vs exterior: side by side
| Exterior waterproofing | Interior waterproofing | |
|---|---|---|
| What it does | Keeps water off the wall entirely | Captures water at the base of the wall and pumps it out |
| Where the work happens | Outside, excavated to the footing | Inside, along the basement perimeter |
| Disruption | Digging beside the house; landscaping over the trench needs replacing | Dust and a cut slab along the walls; no digging outside |
| Timing | A few days per wall, weather depending | Usually faster, often done in days |
| Typical cost per linear foot | $150 to $300 | $80 to $180 |
| Typical detached house | $20,000 to $40,000 | $10,000 to $20,000 |
| Best for | Water through the walls, failed weeping tile, open access | Blocked access, finished basements, leaks at the floor-wall joint |
Typical Hamilton-area ranges before tax. Depth, decks, driveways and tight lots move the exterior price; wall length and the sump move the interior price.
When exterior waterproofing is the right choice
- Water is coming through more than one wall, or through the wall itself rather than one crack.
- The old weeping tile is clogged or collapsed and needs replacing.
- The foundation has only an old tar coating and needs a real membrane.
- You want water kept off the wall, not just managed inside it.
- There's room to dig: no addition, deck, driveway or neighbour's wall in the way.
If a wall is also cracking badly or bowing, exterior work gives you the chance to repair it while it's exposed.
When interior waterproofing is the right choice
- Outside access is blocked by an addition, a deck, a driveway or a neighbour's wall.
- The basement is already finished and you'd rather not dig up the yard.
- Water is coming in at the floor-wall joint along several walls.
- Your weeping tile drains to the sanitary sewer and needs to be disconnected anyway.
- You want the job done quickly and for less.
Just one leaking crack? You may not need either system. A crack in a poured wall can usually be injected from inside in one visit. See our guide to cracks in a basement wall.
Permits, new-home warranties and subsidies
Permit rules vary. Haldimand County lists adding drainage, dampproofing or waterproofing to a foundation as work that needs a building permit. Oakville and Mississauga list damp-proofing a basement as work that doesn't, and Toronto says waterproofing repairs don't need one. A new sump pump can need a permit too, especially if you're claiming a subsidy. We check the rules for your address before any work starts.
If your home is new, check your warranty first. Tarion's two-year warranty covers water getting in through the basement or foundation walls. It covers actual leakage rather than dampness, so report a leak to your builder in writing before you hire anyone.
Subsidies can help with the drainage side. In Burlington, Oakville and Milton, Halton covers 100% of disconnecting your weeping tile and installing a sump pump, up to $6,500. Read our guide to basement flooding subsidies for what each municipality pays.
Basement waterproofing questions
Is exterior waterproofing worth the extra cost?
Can you waterproof a finished basement without tearing it out?
Do sealers or waterproof paint work on the inside?
Will waterproofing fix a bowing wall?
How long does basement waterproofing take?
Waterproofing work we do
Related guides
AVH Foundations handles the structural side. Same family, one visit to assess both.
Basement Worx works across Hamilton, Burlington, Oakville, Milton, Ancaster, Dundas, Stoney Creek, Waterdown, Cambridge, Brantford, Caledonia and Grimsby.