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Sagging Floor Repair Cost in Ontario (2026): Overspanned and Notched Joists, Failed Posts and Footings, Rot, Sistering, New Beams and Teleposts, and When It Is the Foundation
Framing & Building Systems
A Sagging Floor Is Telling You Something. Find Out What Before You Pay to Fix It
Most sagging floors are old and stable: a joist that was a bit small in 1955 and has been a bit small ever since. Some are not: a post sinking into a soft footing, a joist a plumber cut through in 1994, a beam that is still moving. The fix and the price depend entirely on which one you have. The honest news on price is that Ontario contractors publish almost nothing for this work, so this page says plainly where the numbers are thin and where they come from out of province.
First: Is It Moving?
If a floor or beam is sagging more each month, cracking, or bouncing where it used to be solid: keep weight off it now. Move the piano, the aquarium and the bookcase full of encyclopedias, and get an engineer or a qualified contractor in now, not after the holidays. A floor that has been the same for 30 years can wait for an appointment. A floor that changed since spring cannot.
Signs that it is moving: new cracks in drywall or plaster upstairs, doors that used to close and now rub, tile that has started to crack along a line, a basement post that is no longer plumb, or a gap opening between a beam and its post. Take dated photos with a tape measure in them. An engineer will want to know what changed and when.
Why Floors Sag
- Overspanned joists. Joists too small or too far apart for the distance they cover. Plenty of older houses were framed before today’s span tables, and an overspanned joist can stand for 70 years while sagging the whole time.
- Notched, cut and drilled joists. The plumber needed a drain through, the electrician needed a hole, the duct guy needed room. Engineered I-joists may only be cut where the maker’s hole chart allows, and nobody cuts, notches or drills a truss except as the manufacturer allows. In an old house you will often find the one joist that got sawn halfway through, right under the bathtub.
- Failed posts and footings. A steel post set on a thin basement floor with no footing under it, a wood post rotting at the bottom, a footing that has settled.
- Rot and insects. Around the toilet, under the tub, at the sill plate over a damp crawlspace.
- Loads nobody planned for. A stone counter on a new island, a cast iron tub, a wall upstairs that lands in the middle of a span.
- Shrinkage and time. Lumber shrinks across the grain like bacon after you fry it, and wood under load for decades slowly bends further. Small, slow and usually harmless on its own; it adds up with everything above.
A floor that is merely bouncy is a stiffness problem, not a strength problem. That is on the bouncy and squeaky floors page, and the joist types themselves are on the I-joists vs floor trusses page.
What an Engineer Looks At, and What the Fix Might Be
An engineer measures how far the floor is out and over what length, finds the joist size, spacing and span, checks what the joists bear on, and follows the load path down through the beam, the posts and the footings to the ground. They look for moisture, rot and cuts, and at the foundation walls for cracks. The most useful thing they tell you is whether it is stable or still moving. Then they write the fix as a letter or a drawing, which is what goes with your permit application.
- Sistering. A new joist fastened alongside a weak or damaged one, to the engineer’s length and fastening. A GTA contractor notes that sistering or replacing joists needs a permit.
- A new beam and posts under the middle of the span, which cuts the span in half. The posts then need footings that can carry them, and a footing inspection.
- New posts and footings where the old ones failed.
- Replacing rotted joists and subfloor, usually in a bathroom, after fixing the leak that caused it.
A floor that took 60 years to sag does not come back in an afternoon. A good contractor raises one slowly, in small amounts, to the engineer’s plan, because lifting fast cracks the plaster, tile and door frames upstairs. Some sags are better stopped than straightened. This is not a bottle jack and a Saturday.
What It Costs, and Where the Numbers Run Out
| Line | Range | Level | Source |
|---|---|---|---|
| Engineer, structural inspection | $600 to $1,200+ | line in a Level 4 job | a GTA engineering firm |
| Engineer, hourly | $150 to $300 an hour | line in a Level 4 job | same firm |
| Permit to sister or replace joists | $180 to $500+ | line in a Level 4 job | a GTA contractor |
| Minor joist reinforcement | $1,000 to $5,000 | Level 4 job | a BC foundation company, not Ontario |
| Subfloor replacement in a renovation | adds $2 to $5 a sq ft | line in a Level 4 job | a GTA contractor |
| Sistering job, Ontario | quoted per job | Level 4 job | no Ontario price found |
| New basement beam and teleposts, Ontario | quoted per job | Level 4 job | no Ontario price found |
October 2026, before HST. The only repair range we found is from British Columbia, and we show it because it is the only one, not because Ontario labour costs the same. A new beam with posts on new footings is quoted per job; expect the engineer, the permit and the footing inspection on that quote.
Why Ontario prices are all over the map: for this job they are barely on the map at all. The contractors and engineers we checked quoted very different prices, and almost no Ontario contractor publishes a repair price. The one range we found, $1,000 to $5,000 for minor joist reinforcement, is a BC foundation company’s. Engineers ran from $600 for a structural inspection at a GTA engineering firm to $3,500 at a national marketplace for wall-removal engineering. The gap is two sistered joists versus a new beam on new footings, an open basement ceiling versus a finished one, and whether the ceiling is put back. Budget $4,500 for a minor repair with engineer and permit, our planning number, and get two or three quotes on the same written scope: the engineer’s letter.
A minor repair, added up. Say the basement ceiling is open and two joists under the bathroom were cut for a drain years ago. An engineer inspects for $900, the middle of $600 to $1,200, and writes a sistering fix. The permit is $340, the middle of $180 to $500. The repair is $3,000, the middle of the BC range. That is $900 + $340 + $3,000 = $4,240, our estimate. If 40 sq ft of soft subfloor around the toilet comes out too, add 40 x $2 to 40 x $5, or $80 to $200, before the new flooring.
When It Is the Foundation
Sometimes the floor is fine and the thing under it is not. Cracks in a foundation wall that are getting wider, stepped cracks in a block wall, a sag that follows the line of a wall all the way across the house, floors sloping toward one corner, or water in the basement where the post footings sit. Those point below the framing, and the engineer you want is one who does foundations. Sistering joists over a sinking footing is putting a new roof on a house with no walls.
If your house is under seven years old, check your Tarion warranty coverage before you pay anyone. Major structural defects are covered in years 3 to 7, and the first year covers workmanship, materials and Code violations. The Tarion warranty page explains the 1, 2 and 7 year coverage, and the structural engineer page explains how to brief one.
- Moving floor: weight off, engineer now. Stable floor: photos, measurements, then an engineer when you are ready.
- Pay for the diagnosis before the fix. A $900 inspection that finds a $3,000 repair beats a $3,000 repair that missed a footing.
- Get the fix in writing from the engineer, and give the same letter to every contractor quoting.
- Permit before the work, and inspection before anything gets covered.
Questions people ask
How much does it cost to fix a sagging floor in Ontario?
Ontario contractors rarely publish it. The only range we found is $1,000 to $5,000 for minor joist reinforcement, from a BC foundation company. Add an engineer’s inspection, $600 to $1,200 and up from a GTA engineering firm, and the permit, $180 to $500 and up from a GTA contractor. Bigger jobs are quoted per job.
Do I need a permit to sister joists?
A GTA contractor says sistering or replacing joists needs a permit, at $180 to $500 and up. Check with your building department before work starts.
Is a sagging floor dangerous?
A sag that has not changed in years is usually a comfort and appearance problem. A sag that is getting worse, cracking or bouncing is a keep-weight-off-it, call-an-engineer-now problem.
Can a sagging floor be made level again?
Often partly. A contractor raises it slowly to the engineer’s plan, because fast lifting cracks finishes upstairs. Sometimes the right answer is to stop it moving and level the floor surface instead.
How do I know if it is the foundation?
Widening foundation cracks, stepped cracks in block, sticking doors along one line and floors sloping to a corner all point below the framing. Have an engineer look before anyone sisters a joist.
Price the structural work
The beam and wall removal calculator prices the engineer, permit, beam, posts and footings line by line, which is most of what a bigger floor repair is made of. If you have repair quotes, the $99 review reads up to three of them and tells you whether they are fixing the same problem.
Sources and further reading
- Trusses and engineered wood products declaration (Arran-Elderslie): how a municipality accepts trusses and engineered floor joists, and who is responsible for bracing and anchorage.
- Do I need a building permit? (Niagara Falls): a municipal list that includes adding or removing load-bearing walls, beams and lintels.
- Tarion: new home warranty coverage: the one-year, two-year and seven-year warranties on a new Ontario home.
