Interior vs Exterior Basement Waterproofing in Toronto: Cost and Scope
Last updated: By Below-Grade Records Desk
Interior is the cheaper route by a wide margin: $50 to $180 per linear foot against $150 to $475 for exterior excavation and membrane, per Project Landscaping, Nusite Group and OCM Excavation. The two are not substitutes. Exterior keeps water off the wall and replaces the weeping tile in the same trench. Interior leaves the wall wet and manages what gets through.
Once you have picked, WaterproofingIndex's own dataset holds 225 basement waterproofing contractors across the Greater Toronto Area at an average Google rating of 4.84★ over 19,019 reviews (August 2026), so you can move straight from this verdict to a ranked shortlist of pros who do the work.
WaterproofingIndex reconciles conflicting contractor quotes by widening the range rather than picking a favourite, and reviews every figure before publishing.
Comparison
Interior waterproofing or Exterior waterproofing: what actually differs?
Every price in this table names the Canadian source that published it, in the cell itself. Rows that carry no price are statements about how the two methods work, not claims about cost.
| Criterion | Interior waterproofing | Exterior waterproofing |
|---|---|---|
| Cost per linear foot | $50–$80 basic, $70–$120 with a drainage membrane, $100–$180 with a backup pump (Project Landscaping) | $150–$300 GTA market rate (Nusite Group); $250–$400 at a 7 ft basement and $300–$475 at 8 ft (OCM Excavation) |
| Whole basement perimeter | $3,500–$15,000+ on a typical GTA home (DryShield) | $15,000–$35,000 (Nusite Group), or $25,000–$55,000 for a four-wall wrap on an average detached home (OCM Excavation) |
| One 30 ft wall | $2,100–$3,600 at the $70–$120 membrane-system rate (Project Landscaping) | $8,500–$13,500 all in on a Toronto semi, including parging, membrane, drainage board, new weeping tile and backfill (OCM Excavation) |
| Where water is stopped | At the inside face. Water that reaches the wall is collected below the slab and sent to a sump. | At the outside face. Membrane and drainage board keep water off the concrete. |
| Weeping tile | New drainage tile is laid inside the footing, under the slab. | The exterior weeping tile is exposed and replaced in the open trench, $90–$140 per linear ft as a line item (OCM Excavation) |
| What gets torn up | The slab is cut and broken out around the inside perimeter. The yard is untouched. | The ground is opened to the footing. Decks, AC units and gas meters on the dig line come out and go back at $500–$2,500 (OCM Excavation) |
| Access | Work is from inside, so a tight side yard does not change the price. | $50–$100 per linear ft surcharge where a mini excavator will not fit, around 4 ft side yards (OCM Excavation) |
| Season | Runs year round; nothing depends on the weather. | Excavation needs unfrozen ground, so it is typically an April to November job. |
| Sump work usually priced with it | $2,200–$3,000 for pump, basin and discharge (Rock Basements) | $2,500–$4,500 where the weeping tile has to be severed off the sanitary sewer (OCM Excavation) |
Contact
Which basements call for interior waterproofing?
Interior is the right call when the goal is a dry floor and the budget has to stay inside five figures. On the same 30 ft wall it comes out at roughly a quarter of the exterior price, and none of it depends on the weather or on getting a machine down the side of the house.
- Your side yard is too tight to dig, or a deck, patio or AC unit sits on the wall you need done.
- You want the work in February. Interior runs year round; the dig does not.
- The wall itself is sound and the problem is water arriving at the floor joint rather than a failing wall face.
- You already need a sump pit, at $2,200 to $3,000 with pump and discharge (Rock Basements), so the collection side is going in anyway.
Contact
Which basements call for exterior waterproofing instead?
Exterior is the right call when the wall face itself has to be dealt with, or when the weeping tile is due. It is the only version of this job that puts a membrane on the outside of the concrete and replaces the drain line, and the $8,500 to $13,500 single-wall figure from OCM Excavation already includes both.
- The weeping tile is suspect. Replacing it in an open trench is $90 to $140 per linear foot (OCM Excavation) against a much larger standalone dig later.
- The wall needs parging or exterior crack work that cannot be reached from inside.
- You are already rebuilding or regrading that side of the house, so the trench cost is partly spent.
- You want the water kept off the concrete rather than collected after it arrives.
Prices
What does each cost on a real project?
Take one 30 foot foundation wall on a Toronto semi, the most common single-wall scope in the GTA. Both routes are priced straight off the rows above:
- Interior membrane system, 30 ft at $70–$120 per linear ft
- $2,100–$3,600 (Project Landscaping)
- Sump pit and pump, where none exists yet
- $2,200–$3,000 (Rock Basements)
- Interior route, all in
- $4,300–$6,600
- Exterior dig on the same wall, all in
- $8,500–$13,500 (OCM Excavation)
- Included in that exterior figure
- Parging, membrane, drainage board, new weeping tile, backfill
The exterior wall costs roughly double the interior route on the same 30 feet, and the gap is not markup. The OCM figure buys a new drain line and a membrane on the outside face; the interior figure buys a collection system and a pump. Price them as different products, because that is what they are.
Frequently asked questions
Is interior or exterior basement waterproofing better?
- They fix different things, so the honest answer depends on where the water is failing. Exterior excavation and membrane keeps water off the outside face of the wall and replaces the weeping tile while the trench is open. Interior drainage lets the wall get wet and collects the water below the slab. If the drain line is the problem, interior does not address it.
How much cheaper is interior waterproofing in Toronto?
- Project Landscaping prices interior drainage at $50 to $180 per linear foot across three tiers, while Nusite Group publishes $150 to $300 per linear foot for exterior and OCM Excavation publishes $250 to $400 at a 7 foot basement and $300 to $475 at 8 feet. On a whole basement that is $3,500 to $15,000 and up interior (DryShield) against $15,000 to $55,000 exterior. Add 13% HST to any of it.
Why do exterior quotes vary so much per linear foot?
- Depth is the multiplier, not floor area. OCM Excavation prices the same wall at $250 to $400 per linear foot at 7 feet and $300 to $475 at 8 feet, before anyone changes the membrane spec. Access is the other variable: a side yard around 4 feet wide that cannot take a mini excavator adds $50 to $100 per linear foot in hand digging.
Does interior waterproofing repair a cracked foundation wall?
- No. Interior drainage manages water; it does not restore the wall. A leaking crack is priced separately, at $300 to $800 per crack for a professional injection according to Nusite Group. Ask any quote to state plainly which line item repairs the concrete and which one moves the water, because they are different scopes at different prices.
Questions to ask your contractor
- Are you quoting interior drainage, exterior excavation, or both, and what rules out the other one? Interior versus exterior, side by side
- If you are digging outside, how far down do you go, and does it reach the footing? Sourced per linear foot pricing
- Which membrane and which dimple board go on the wall, by product name?
- Is the weeping tile being replaced, or flushed and left in place?
- What exactly does the warranty cover, how long does it run, and does it transfer to the next owner?