Floors
Subfloor repair cost
Patching a soft spot in a subfloor is about $518 — one sheet of plywood and a carpenter's half-day — and about $870 under a bathroom floor with the tile taken up and a joist sistered. Replacing a 12 × 12 ft room's subfloor is about $1,368, $9.50 a square foot. The plywood is the cheap part; the floor on top, the leak that caused it and the joists underneath are what move the price, and a floor that sags across the room needs a beam, about $1,970.
Written and edited by Pablo Ruiz Quintero
Last reviewed 2026-09-27 · Nothing you type leaves your browser
Subfloor repair cost calculator
The soft floor, what is on it, and what is under it
A subfloor repair is the plywood, the floor that has to come up to reach it, and the joists underneath if the water got that far.
The soft section cut back to the nearest joists.
Out to the sound wood.
20 sq ft · 1 sheet.
The most expensive removal there is — the mortar bed fights back and the debris is heavy..
Soft or split joists.
0 if level.
Basement or crawl space.
A carpenter.
Used only to pick a regional labour rate. It stays in your browser.
20 sq ft of subfloor patched, 1 joist
$870
$44 a sq ft · 1 sheet · ceramic or stone tile up first
Stop the water first
A soft subfloor is nearly always a slow leak: a toilet seal, a tub drain, a dishwasher, a door sill. New plywood over a live leak rots again — fix the leak, dry the joists, then close it up.
Cut back to the joists
Every edge on wood.
A patch is cut out to the nearest joists, and every edge of the new panel sits on a joist or a block. A panel that floats between joists deflects, squeaks and cracks the tile laid over it.
From a patch to a beam
The usual repairs, by a carpenter, with the ceramic or stone tile taken up.
What the carpenter charges for
- 1 sheet of subfloor
23/32 in (3/4 in) tongue-and-groove plywood or OSB, with subfloor adhesive and screws or ring-shank nails for a sheet.$68 - Taking up the ceramic or stone tile
The most expensive removal there is — the mortar bed fights back and the debris is heavy.$52 - Laying the new subfloor
Cutting, fitting, blocking, gluing and screwing new panel, per square foot.$80 - Up to the half-day minimum
A carpenter's half-day minimum: a small patch costs this whatever its size.$370 - 1 joist sistered
A full-length joist bolted or glued and nailed alongside a damaged or notched one, per joist.$300
What it costs
National average. 20 sq ft of subfloor patched, the ceramic or stone tile taken up, joists sistered. Not included: the new floor on top, fixing the leak, or mold remediation. Permit about $200 for structural work.
The new floor, on the flooring page; tile, on the tile page; if the wet wood has grown mold, the mold removal page.
Worth knowing
- 20 sq ft of subfloor: 1 sheet of 23/32 in (3/4 in) tongue-and-groove plywood or OSB, with 15% for cutting back to the joists. A patch this size is priced by the carpenter's half-day, about $450, not by the foot.
- Find and fix the water first: a toilet wax ring, a tub drain or overflow, a dishwasher, a door sill. New plywood over a live leak rots again, and wood that has been wet for years is worth checking for mold before it is closed up.
- The ceramic or stone tile on top comes up first — about $52 — and a new floor goes down after; that is priced on the flooring pages.
- 1 joist sistered — a full-length member fixed alongside each damaged one — from the basement or crawl space.
On this page — 4 sections
The plywood is the cheap part
The short version
- Patch: $518 — a carpenter’s half-day.
- Bathroom, tile up, a joist: $870.
- A room: $1,368, $9.50 a sq ft.
- A sagging floor: $1,970 for a beam.
A sheet of subfloor is about $60. What a repair costs is everything around it: the tile or hardwood that has to come up to reach it, the carpenter’s minimum on a small patch, cutting back to the joists so every edge has wood under it, and — when the water went far enough — the joists themselves. A soft spot the size of a doormat is priced by the half-day; a whole room by the square foot; a floor that sags across the middle is not a subfloor problem at all, but framing.
$518
Patch
5 × 4 ft
$870
Bathroom
Tile up, a joist
$1,368
A room
12 × 12 ft
$1,970
Sagging floor
12 ft beam
MaterialsEstimator, Subfloor and floor framing repair price survey · checked 2026-09-27
MaterialsEstimator, Flooring price survey · checked 2026-09-16
Patching it right
The damaged panel is cut out back to sound wood and out to the centre of the nearest joists, so the new piece has something to bear on at its ends; blocking goes between the joists under the long edges. The new panel is the same thickness, glued and screwed, flush with the old. Swollen or delaminated panels are replaced, not sanded flat — sanding leaves a weak spot under the tile. The water came from somewhere, and it is fixed first.
International Code Council, IRC R503 — Floor sheathing, and R502 — Wood floor framing (2021) · checked 2026-09-27
APA — The Engineered Wood Association, APA guidance on glued floor systems and subfloor installation · checked 2026-09-27
| Patch | Replace the room | |
|---|---|---|
| Priced by | The carpenter's half-day | The square foot |
| 5 × 4 ft / 12 × 12 ft | $518 | $1,368 |
| When | Damage in one place | Soft in several places, or particleboard |
Joists and sags
When the water reached the joists, a soft or split one is sistered — a new full-length joist fixed alongside it — rather than cut out; from a basement or crawl space that is about $300, from above with the floor open about $390. A floor that dips across the middle of a room is a different problem: joists overspanned or a beam or post below failing. The fix is a beam under the joists on adjustable steel posts, raised a turn at a time over weeks so the plaster and tile above do not crack.
What goes wrong
Before the carpenter comes
- The leak found and fixed.
- The soft area probed out to sound wood.
- The floor on top and whether it is being replaced.
- The joists looked at from below.
- Any dip across the room measured with a long level.
01A patch between joists
Edges with nothing under them flex and crack the tile.
Instead — Cut back to the joists and block the edges.
02New plywood over a live leak
It rots again.
Instead — Fix the leak and dry the framing.
03Sanding a swollen panel flat
The layers are delaminated underneath.
Instead — Replace it.
04Cutting too deep
Pipes and wires run just below.
Instead — Saw depth set to the subfloor.
05Jacking a sag in one go
Everything above cracks.
Instead — A little at a time over weeks.
- 01Find the causeA soft spot by a toilet, tub, dishwasher or door is a leak; fix it before anything is closed up.
- 02Measure the damageProbe outward until the wood is firm, then out to the nearest joists on each side.
- 03Note the floor on topTile, hardwood, vinyl or carpet all come up first, at very different prices.
- 04Check the joistsFrom below where possible: soft, split or notched joists are sistered.
- 05Look for a sagA dip across the middle of a room is framing, not subfloor, and wants a beam and posts.
- 06Price the new floorWhatever came up goes back down, priced by the flooring.
Whatever came up to reach the subfloor goes back down: carpet, vinyl, laminate, hardwood or tile, priced by the square foot.
The floor on top- Subfloor
- The structural panel layer — plywood or OSB, or boards in old houses — nailed to the joists, under the finished floor.
- Underlayment
- A thinner layer over the subfloor, under tile or vinyl, for a smooth surface. Not structural.
- Tongue and groove
- Panel edges that lock into each other between joists, so the floor does not deflect at the seams.
- Joist
- The horizontal framing member the subfloor sits on, usually 16 in apart.
- Sistering
- Fixing a full-length new joist alongside a damaged one, instead of cutting the old one out.
- Blocking
- Short pieces of lumber between joists, so every edge of a patch has wood under it.
- Sagging floor
- A floor that dips in the middle — undersized or overspanned joists, or a failing beam or post below.
- Adjustable steel post
- A screw-jack column on a footing pad under a beam, raised a little at a time to lift a sag.
Common questions
- How much does subfloor repair cost?
- About $518 to patch a 5 × 4 ft soft area — one sheet of plywood and a carpenter's half-day minimum of about $450 — and $570 with tile taken up first. Under a bathroom floor, with a joist sistered, about $870; the tub pages allow about $780 for the same discovery.
- How much does it cost to replace a subfloor?
- About $1,368 for a 12 × 12 ft room — $9.50 a square foot to tear out the old subfloor and lay new tongue-and-groove panels, glued and screwed — and $1,462 with the carpet taken up. With three joists sistered while it is open, $2,268.
- How much does floor joist repair cost?
- About $300 to sister one joist from the basement or crawl space, and $390 from above with the floor open. Each additional joist on the same visit is about $300.
- How much does it cost to fix a sagging floor?
- About $1,970 for a 12 ft beam under the joists on 3 adjustable steel posts with footing pads and a permit, raised a little at a time over weeks so nothing above cracks. Sagging from rotted joists or subfloor adds their repair.
- How much does plywood subfloor cost?
- About $45–$80 a 4 × 8 sheet of 23/32 in tongue-and-groove plywood or OSB, plus about $8 of adhesive and screws. Installed, about $4 a square foot on top.
- How much does a bathroom subfloor replacement cost?
- About $870 for the usual case — a 5 × 4 ft area round the toilet or tub, the tile taken up, a joist sistered. The whole bathroom floor, 5 × 8 ft, runs higher, and the new tile and toilet reset go on top.
- How much does mobile home subfloor replacement cost?
- About $1,464 for a 14 × 10 ft room with the old floor covering up. Mobile homes often have particleboard decking, which swells and crumbles when wet; it is replaced with plywood or OSB.
- Can I repair a subfloor myself?
- A patch, yes: about $68 in materials. Cut back to the joists with the saw set to the subfloor's thickness — pipes and wires run just below — add blocking under every edge, and glue and screw the new panel. Sagging floors and structural joists are for a carpenter and a permit.
- What causes a soft subfloor?
- Almost always water over years: a toilet's wax seal, a tub drain or overflow, a dishwasher or ice-maker line, a leaking door sill. Fix the leak first and let the joists dry; new plywood over a live leak rots again.
Send this to whoever is paying
The link carries your measurements, so whoever opens it sees the same numbers you are looking at — and you can come back to it yourself tomorrow with the delivery note in front of you.
Plain links, no tracking scripts. Nothing here reports back that you shared it.
About the author
Pablo Ruiz Quintero — Editor
Editor of MaterialsEstimator. Decides which documents count as a source, what every default value is, and where the line sits between what the reader parses and what the engines compute.
More about how this site is edited