Subfloor Repair Types Under Hardwood
Hardwood is only as flat and quiet as the layer it is nailed to. These are the four jobs that come up most when a floor is opened.
Rotted Plywood or Plank Subfloor Sections
Soft, dark or crumbling sections get cut back to sound wood and replaced with a panel of matching thickness, so the new piece doesn't leave a step. HomeGuide calls 3/4-inch plywood the best choice under hardwood. The older NWFA guidelines ask for at least 5/8-inch plywood, or 23/32-inch OSB, over joists spaced 16 inches or less.
- Plywood: $2.50 to $3.00 a sq ft installed; OSB: $2.20 to $2.80 (HomeGuide)
- Repairing a section in place: $35 to $80 a sq ft in HomeGuide's repair guide
Sistering and Shimming Joists Under Raised Floors
A floor that sags or bounces across a room points at the framing. Sistering, where new lumber is fastened alongside a cracked or sagging joist, is the common fix, and gaps between joist and plywood get glued shims. Crawlspace work is slower: HomeGuide says tight crawlspaces add 20 to 50 percent to labor.
- Sistering: $200 to $1,000 a joist; replacement: $500 to $2,500 a joist
- Simple sistering: 1 to 2 days; several joists with subfloor removal: 3 to 7 days
- Structural engineer, if the sag is serious: $300 to $800
Ask the contractor whether they do framing themselves or bring in a carpenter, and whether the job needs a permit.
Leveling Dips and Humps Before New Wood
New boards copy every hollow under them. Under a nailed floor NWFA allows 1/4 inch of deviation across 10 feet; under a glue-down floor, 3/16 inch. Highs get sanded down and lows filled with a leveling compound approved for use under wood. Fixr's range for uneven-floor repair, $5 to $60 a sq ft, shows how much depends on the cause. Concrete slabs are handled differently: see Hardwood Floors Over Concrete Slab.
Subfloor Under Old Bathrooms and Laundry Rooms
Wet rooms rot from the fixtures out. HomeGuide notes that bathroom leaks often rot the subfloor and loosen the screws holding the toilet flange, so a toilet that rocks is worth a look underneath. Washer hoses and water heaters do the same in a laundry room. A small bathroom subfloor runs $100 to $380, and a larger primary bath up to $570. If the leak has also stained or cupped nearby wood, see Water-Damaged Hardwood Floor Repair.
Why Torrance homeowners call Torrance Wood Flooring
- Free to call or use the form; the referral costs you nothing
- Your request goes to one independent contractor, not a bidding list
- Ask for a moisture reading and a written line-item estimate
- California caps the down payment at 10% or $1,000, whichever is less
Subfloor Repair Costs at a Glance
| Work | Typical national range | Source |
|---|---|---|
| Small damaged area | $100 to $300 | HomeGuide |
| Replace subfloor | $2.20 to $4.75 / sq ft | HomeGuide |
| One bedroom (100 to 180 sq ft) | $220 to $850 | HomeGuide |
| Sister one joist | $200 to $1,000 | HomeGuide |
| Replace one joist | $500 to $2,500 | HomeGuide |
| Rotted floor repair | $50 to $250 / sq ft | Fixr |
The flooring that goes back on top is priced separately; see Hardwood Floor Installation for that range and the moisture checks a subfloor should pass first.
Before the Floor Is Opened
Find the cause
HomeGuide lists damaged joists, water, drainage, termites and soil settlement behind failing floors, and a patch over an active leak or live termites won't last.- Ask how hidden damage will be priced once the old floor is up, per sheet or per hour, in writing.
- In a pre-1978 house, old vinyl tile or black glue under the floor should be tested before anyone cuts through it (see Hardwood Floor Removal).
- Check the license through the CSLB lookup explained on Hardwood Floor Repair.