Choosing a waterproofing contractor is difficult because the most important parts of the work are buried before you ever see them.
To choose a waterproofing contractor in Toronto, get three answers in writing: what is excluded from the price, whether the drainage stone is wrapped in filter fabric, and whether a dimple board goes over any exterior membrane. Then confirm they hold a valid City of Toronto business licence, which is required for any work claimed under the $6,650 flood protection subsidy.
Before the quote
1. What is the actual cause, and how did you determine it?
A wet basement has six common causes and four of them are cheaper than a waterproofing system. Anyone who quotes a full perimeter without walking the exterior — downspouts, grading, window wells, visible cracks — is not diagnosing.
2. What are the cheaper options, and why do they not apply here?
There is almost always a cheaper option. A contractor who cannot name it and explain why it is insufficient for your house has not considered it.
3. Interior or exterior, and why that one?
The honest answer depends on access, foundation type and what sits above the wall. A company that recommends the same method to every customer is describing their business model rather than your house.
About the price
4. What is excluded?
The most valuable question on this page. Ask it in exactly those words, and get the answer in writing.
Common exclusions: reinstating interlock, decks and planting; removing and replacing finished basement walls; the sump pump itself; permits; disposal.
5. What is the total to a finished state?
Not the per-foot rate. The number you will actually pay by the time the basement is back to usable. That is the only figure worth comparing between quotes.
6. For underpinning: what unit, and what quantity?
Underpinning is quoted against linear feet of wall, square feet of finished floor, or square feet of excavated face, and nobody states which. The same job can be presented as $35,000 or $180,000 depending on the denominator.
Ask for the unit and the quantity. The full explanation is onunderpinning cost per linear foot.
About the work itself
7. Is the drainage stone wrapped in filter fabric?
The highest-value technical question a homeowner can ask, because it is the most common corner cut and it is invisible once backfilled.
Without fabric, Toronto clay fines silt the stone bed solid within a few years and the new drainage stops working.
8. For exterior work: is a dimple board going over the membrane?
Membrane alone is damaged by backfill and holds water against itself. The dimple board protects it and creates the drainage gap. Both layers, or it is not a complete exterior system.
9. Who actually does the work?
Employees or subcontractors, and if subcontracted, who carries the warranty. This is not a trick question and there is no wrong answer, but you should know before there is a problem.
About the company
10. What licences and insurance do you carry?
There is no single provincial waterproofing licence, which is precisely why this matters. Backwater valve work requires a licensed plumbing contractor. Drain work requires the appropriate City of Toronto drain contractor licence. And any work you intend to claim under the subsidy requires a valid municipal business licence.
Ask for liability insurance and WSIB clearance too. An uninsured contractor injured on your property is your problem.
11. What is the warranty, and what voids it?
"Lifetime warranty" is close to meaningless without the second half. Whose lifetime, transferable to a buyer or not, covering labour as well as materials, and what voids it.
Get the exclusions. A warranty void if any future owner finishes the basement is a very different product from one that is not.
Three answers that should concern you
"We can start tomorrow." On underpinning this is close to disqualifying — the work needs stamped engineering and a permit, which take four to ten weeks.
"Save up to $6,650 with the City rebate" presented beside a waterproofing price. The subsidy covers devices, not waterproofing. Seethe subsidy page.
A price that expires today. Deadline pressure on a five-figure structural decision is a sales technique, not a scheduling reality.
What a fair quote looks like
Verified Toronto ranges for 2026: interior waterproofing$80 to $150 per linear foot, exterior $150 to $300 per linear foot, underpinning $350 to $800 per linear foot. Full tables are onour cost pages.
A quote well below those ranges is usually missing scope rather than offering value. The specific things that go wrong when it is are onwhat can go wrong.
And when you have the answers, the last check is what other customers say —our reviews.