$1-$4 per sq ft Joist spacing measured Rot and soft spots found first Toronto and the GTA

Subfloor repair in Toronto

The deck under your floor has to hold a fastener before anything is worth nailing to it, so Toronto Flooring Co measures joist spacing and deck thickness and tells you which number your job has to meet.

Joist spacing measured and checked against Code and industry minimums

Deck thickness recorded, including whether it is plywood or OSB

Soft spots and rot traced back to a water source before patching

Levelling priced separately from structural repair

Get the deck looked at

The age of the house, what is on the floor now, and whether anything feels soft underfoot.

What can we help with?

Service

So the right crew reviews your project.

Any workmanship warranty is set out in your written quote, job by job.

Spacing decides thickness

Check joist spacing before you price a subfloor

The Ontario Building Code sets minimum subfloor thickness against how far apart the joists are, in Article 9.23.14.5 and Table 9.23.14.5.A. The principle is simple and it is the part worth carrying away: the wider the bay, the thicker the deck has to be, because the panel has more distance to span before it finds support. A 610 mm bay needs more material than a 406 mm bay. The table also treats materials differently, so plywood, oriented strand board, particleboard and lumber each have their own row. We are deliberately not reproducing the millimetres here, because the table that circulates online is from the 2012 and 2017 editions and the 2024 edition has been the legally effective code since January 2025. We measure your spacing, measure your deck, and check the figures against the edition in force rather than against a number somebody copied from a blog.

What subfloor work covers

Spacing and thickness recorded

We measure the distance between joists and the thickness of what sits on them, and we note whether it is plywood, oriented strand board, particleboard or solid lumber. Those four are not interchangeable at the same thickness and the quote says which one you have.

The water source traced

Rot and soft spots are downstream of something. A toilet flange, a shower pan, a supply line, a failed caulk joint or damp from below. We find it and say so, because replacing wet decking without closing the source books the same job again.

Structure separated from flatness

A weak deck and an uneven deck are different problems with different fixes and different prices. Structural repair runs $1 to $4 per square foot. Levelling runs $2 to $4. We quote them apart so you can see what you are buying.

Subfloor repair pricing in Toronto

Toronto and GTA ranges collected September 2026. Subfloor work is usually quoted alongside a floor, so ask any competing quote whether prep is included or excluded before comparing the totals.

Repair and prep

$1-$4 / sq ft

Loose boards refastened to the joists
Soft or rotten sections cut out and replaced
Overlay added where the deck is thinner than the fastener needs
Old floor removal and disposal $1-$3 per sq ft where required

Price deck repair

Levelling

$2-$4 / sq ft

Self-levelling compound over a sound deck
Roughly $1,000 to $1,500 flat for a whole floor
Over a concrete slab in a condo or basement $3-$6 per sq ft
Priced after flatness is measured over six and ten feet

Price levelling

Century home work

+$800-$2,000

What subfloor work typically adds on an older Toronto house
Board decks that have shrunk, split or worked loose
Knob-and-tube checks before anything is closed in
Quoted once the floor is open and the deck is visible

Ask about an older house

Our Process

How subfloor work is sequenced

1

Open and measure

Finish floor lifted where needed, then joist spacing, deck thickness and material recorded. Flatness measured over six and ten feet, because the tolerance differs for glue-down and nail-down.

2

Find the water

Moisture readings across the deck and a search for the source behind any soft area. Nothing is replaced until we know what wet it, because new material in the same spot fails the same way.

3

Cut out and rebuild

Damaged sections cut back to the joists, blocking added where a seam lands between supports, and new decking fastened down in the right material and thickness for the spacing we measured.

4

Flatten and hand over

Levelling compound where the flatness tolerance is not met, then a final set of readings and a written record of what the deck now is, so the floor going on top can be specified against it.

What we will find and what we will say

Subfloor work is the part of a flooring job nobody plans for, so we would rather set out in advance how we handle what turns up.

The industry minimum is stricter than the Code in one case

National Wood Flooring Association guidance for wood flooring sets plywood at a minimum of 5/8 inch and oriented strand board at 23/32 inch where joists are at 16 inches on centre, rising to 3/4 inch for both between 16 and 19.2 inches, and 7/8 inch plywood or 1 inch OSB beyond that. At the 16 inch spacing that is tighter than the Code minimum, and most manufacturer warranties follow the industry figure.

Flat enough for nails is not flat enough for glue

Industry flatness tolerance for mechanically fastened floors using fasteners of an inch and a half or longer is 1/4 inch in 10 feet or 3/16 inch in 6 feet. For glue-down it tightens to 3/16 inch in 10 feet or 1/8 inch in 6 feet. We measure before choosing a method, because a glue-down specified over a nail-down tolerance is a failure waiting for warm weather.

We stop for knob-and-tube

Knob-and-tube wiring was used in homes from the early 1900s to the 1940s, is no longer permitted for new installations, and many insurers refuse coverage where it remains. The Electrical Safety Authority recommends assessment by a licensed electrical contractor. If we open a bay and find it live, we stop and call one rather than closing a floor over it.

Bad news arrives early or not at all

Every soft spot we find gets photographed and priced before it is touched, and a change in scope is written down and signed before the work goes ahead. That is how the province requires mid-project changes to be handled, and it is also how you avoid a subfloor invoice you never agreed to.

Ask which subfloor number your warranty uses

Two different numbers govern your subfloor and they do not always agree.

The first is the Ontario Building Code, which sets minimum subfloor thickness against joist spacing in Article 9.23.14.5 and Table 9.23.14.5.A. The structure of that table is what matters: thickness steps up as the bays get wider, and each material gets its own requirement, so plywood, oriented strand board, particleboard and solid lumber are not read off the same row. There is also a reduction allowed in specific cases, for example where the finished flooring is matched wood strip of a certain thickness laid at right angles to the joists.

We are not printing the millimetres here. The version of that table circulating on contractor websites is from the 2012 and 2017 editions, and the 2024 edition, O. Reg. 163/24, has been the legally effective code since 1 January 2025. Quoting stale figures with a Code article number beside them is worse than quoting nothing, because it looks authoritative.

The second number is the industry one. National Wood Flooring Association guidance for wood flooring calls for plywood at a minimum of 5/8 inch and oriented strand board at 23/32 inch where joists sit at 16 inches on centre, 3/4 inch for both between 16 and 19.2 inches, and 7/8 inch plywood or 1 inch OSB beyond that. At the 16 inch spacing that is stricter than the Code minimum.

That gap is the practical problem. A deck can satisfy the Code and still fall short of what the flooring manufacturer requires, and it is the manufacturer’s number that decides whether a warranty claim is paid. We measure your spacing, identify your deck material and thickness, and tell you which of the two numbers your job has to clear.

Do not swap plywood for OSB in a subfloor

They look similar on a delivery truck and they behave differently under a nail.

Plywood is cross-laminated veneers. Oriented strand board is compressed flakes with adhesive. For equal fastener holding power, OSB has to be thicker, which is why every guidance table lists it separately with a higher number. A nail-down hardwood floor depends entirely on the deck gripping the fastener, so this is not an academic distinction: it is the difference between a floor that stays put and a floor that works loose and squeaks in its second year.

The other difference shows up around water. OSB that has been wetted swells at the edges and does not recover when it dries, so a deck that took a slow leak can end up with raised seams telegraphing through a vinyl or laminate floor even after the moisture is gone. Plywood tolerates a wetting event better. Neither tolerates an ongoing one.

In Toronto this maps roughly onto the age of the house. Later subdivisions are where panel decking turns up, and that is where checking the panel thickness against the joist spacing matters before anybody chooses nail-down.

Start with the bathroom subfloor

The worst subfloor in most houses is in the smallest room, and the reasons are all plumbing.

A bathroom deck takes water from a toilet flange, a shower pan, a tub surround, a vanity supply and condensation, and a tiled surface hides every one of those until the damage is advanced. What we find under a failed bathroom floor is usually the same picture: decking around the toilet that has gone soft or vanished entirely, a joist top with rot on its upper face, and a smell that arrived before anybody noticed a problem.

The sequence is always the same. Trace the source, close it or have it closed by the trade that owns it, then let the area dry and meter it, then cut the damaged decking back to the joist centres and rebuild with blocking under every new seam. Replacing the wood first and finding the leak second is how the same repair gets booked twice.

Subfloor repair prices at $1 to $4 per square foot in Toronto, and on an older house the subfloor component of a flooring project commonly adds $800 to $2,000 to the total. Levelling is quoted separately at $2 to $4 per square foot, roughly $1,000 to $1,500 flat for a whole floor, and $3 to $6 over a concrete slab. Keeping those two apart on the quote is deliberate: strength and flatness are different problems, and a floor can badly need one and not the other.

Subfloor questions

Does oriented strand board have to be thicker than plywood?

For the same fastener holding power, yes. Industry guidance for wood flooring puts oriented strand board at 23/32 inch where plywood is acceptable at 5/8 inch for joists at 16 inches on centre, and at 1 inch where plywood is 7/8 inch beyond 19.2 inch spacing. The Ontario Building Code table also lists the materials in separate columns rather than treating them as equivalent. The practical consequence is that a house with OSB decking at a thickness that would be fine in plywood may need an overlay before a nail-down floor goes on it.

What is a soft spot in a floor?

A section where the deck under the finish floor has lost strength, so it gives under weight in a way the surrounding floor does not. The usual causes are water that has been arriving slowly for a long time, particleboard or OSB that has swollen and delaminated, or a section spanning a gap where a joist or blocking is missing. It is not a cosmetic issue. A fastener will not hold in soft material, so a new floor laid over one will move, squeak and eventually open at the seams. We cut soft sections back to sound material on the joists rather than patching over them.

Can you replace part of a subfloor instead of all of it?

Yes, and that is what most subfloor repair is. Sections are cut back to the joist centres so the new panel has support at every edge, blocking is added where a seam would otherwise land in a bay, and the replacement is matched in thickness to what is around it so the finished surface stays level. What decides whether a partial repair is honest is the cause. Localised damage from one leak is a partial job. A whole floor of undersized or swollen decking is not, and we will say so rather than patching around a problem that is everywhere.

Why is the bathroom subfloor always the worst one?

Because it takes water from more directions than any other room and hides it longer. A toilet flange that has been weeping slightly, a shower pan that leaks at one corner, a tub surround with a failed caulk joint and steam condensing on every surface all feed the same deck. Under a tiled floor the damage is invisible until the tile grout cracks or the floor feels soft, by which point the decking around the toilet is often gone entirely. This is also why we trace the source first. Replacing the deck under a toilet without fixing the flange means doing it twice.