Ask three contractors what a basement costs and you will get three very different answers. Published prices in Ontario run from $35 to $130 a square foot, which on a 700 square foot St. Catharines basement is anywhere from $24,500 to $91,000. That gap is not us being vague. It is the market genuinely not agreeing with itself.
St. Catharines runs old to new across its six wards. Port Dalhousie is a protected heritage district down by the lake, and the housing there and through the older parts of Merritton reflects it, with lower ceilings and materials from long before 1990. Grantham and the newer edges of the city are a straightforward job by comparison. The dividing line that matters most here is not the neighbourhood though, it is the year the house was built, because the city’s flood help stops at 2012.
These are the prices other companies publish, not ours. We show you where each one comes from so you can judge it yourself.
| Scope | Published range | What that range rests on |
|---|---|---|
| Basic finish, no bathroom, about 700 sq ft | $24,500 to $91,000 | Contractor estimates spanning $35 to $130 per sq ft |
| Adding a three piece bathroom | Add $15,000 to $35,000 | Contractor estimates, a spread of nearly six times |
| Legal second unit, permits included | $50,000 to $180,000 | Contractor claims. Building permit records for basement suites declare a median nearer $25,000 |
| Lowering the floor or underpinning | $30,000 to $100,000 | 17 permit records for underpinning with finishing, median $60,000 |
Pulled from published Ontario contractor prices and municipal permit records on 1 August 2026. We show you the full spread instead of picking an average, because the sources really do disagree by up to four times, and two of the bigger ones turned out to be publishing the same numbers as each other. Your price comes from a free visit, fixed, with HST already in it.
St. Catharines reimburses nine tenths of what it costs to put in a backwater valve, a sump pump and backup, or to disconnect your weeping tile, up to five thousand dollars. Two conditions catch people: the house has to be detached or semi detached and built before 2012, and you cannot start any of the work until they have approved your application.
This is worth repeating on its own because it is where people lose the money. If the work is already done, the grant is gone. If your basement has ever taken water, get the application in before you book anyone, including us.
The city covers 70 percent of eligible costs to a maximum of forty thousand dollars for an added unit inside the house, and more for a detached one. The main house has to be at least five years old, in the improvement area, with no tax arrears, and you apply within ninety days of getting your building permit. It is a real amount of money and the timing rules are strict.
In a house built before 1990 the law puts this on you as the owner rather than on your contractor, and you have to hand the report to anyone quoting. Around the older parts of the city that is most houses.
For a rental unit in a house that is already built, the rule is 6 feet 5 inches across the space, not the 7 feet people quote at you. Plenty of basements written off as too low actually pass. It takes two minutes with a tape measure to find out.
If the main drain drops down into the floor, a basement bathroom is straightforward. If it leaves the house above the slab you need a pump, and that changes the price. Nobody can tell which you have from a photo, which is one of the reasons we come and look.
Give us the address and a time that works for you. No sales pitch and no waiting on a callback.
Ceiling height, damp, wiring, where the drain sits, and what the rules allow for what you actually want. About 45 minutes.
Written down, HST included. If there is anything we cannot price without opening a wall, we say so next to the number instead of hiding it.
One free visit, one fixed price, HST included. No sales pitch and no callback loop.
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