Subfloor Repair & Replacement
Handis subfloor repair and replacement is the structural repair scope for the layer under the finish floor — rotted plywood and OSB sheathing replacement on intact joists, sistered joists where the bearing has failed, and surgical cut-and-patch around the leaks that take out a square foot at a time — from $900 for a small bath patch around a toilet flange to $4,000 for a full sagging laundry-room sheathing replacement with two sistered joists. The 1948 craftsman where the powder-room toilet has weeped at the flange for years and you can rock the bowl by hand because the OSB underneath is black and gone. The 1965 split-level where the dishwasher hose leaked behind the kick plate for an unknown period of time and the bottom of the cabinet line is soft when you stand on it. The 1922 bungalow where the original ground-floor sleeper joists have rotted at the bearing into the foundation rim because the crawlspace vapor barrier was torn open thirty years ago. APA-rated tongue-and-groove plywood replaces the failed sheathing. Sister joists go in alongside any joist that has cracked, sagged, or rotted at the bearing. Structural screws into the joists at the manufacturer pattern. Every joint sealed at the perimeter, every fastener set flush, the sheathing primed before any finish floor goes back on top.
Service
What Does Subfloor Repair & Replacement Include?
Subfloor repair and replacement is the structural repair scope for the layer under the finish floor — covering full replacement of rotted or sagging plywood and OSB sheathing on intact joists, sister joist or sister-and-replace for joists that have cracked or rotted at the bearing, surgical cut-and-patch scopes around toilet flanges, tub aprons, dishwasher leaks, and exterior-wall sill plates, structural-screw fastening at the manufacturer-specified pattern, sealed perimeter at every joint, and full sheathing prime before any finish floor goes back on top. Handis covers repair scopes from $900 on a small bath patch around a toilet flange to $4,000 on a full sagging laundry-room sheathing replacement with two sistered joists. No licensed-trade handoff is needed for subfloor structural repair — this is core Handis finish-carpentry scope.
Full Sheathing Replacement on Intact Joists
Rotted or sagging plywood and OSB subfloor sheathing replaced with APA-rated tongue-and-groove plywood (3/4 inch for primary subfloor on joists at 16 or 24 inch on-center spans). Old sheathing cut out at the nearest joist centers, fastener heads pulled from the joist tops, joist tops sanded flat where adhesive has built up, new sheathing dropped with the tongue-and-groove engaged, construction adhesive on every joist contact, structural screws (typically #8 by 2-1/2 inch or 3 inch GRK or Spax) at the manufacturer pattern (6 inches on edge, 12 inches in the field). Sheathing primed before any finish floor goes on top.
Joist Sistering and Sister-and-Replace
Sister joist (a full-length new joist fastened alongside the existing joist) when the existing joist has cracked at a notch, sagged at the bearing, or rotted at the rim. Sized to the existing joist depth and species (typically 2x8, 2x10, or 2x12 in Douglas fir or hem-fir). Full-length sister bolted or structural-screwed every 16 inches along the run, shimmed up at the bearing where the existing joist has dropped, end-bearing seated on the rim or the foundation sill plate per the prescriptive code. Sister-and-replace (cut out the existing joist and full-replace with a new one) on the rare case where the existing joist is so far gone the sister cannot bear alone — done with temporary shoring of the floor above before the existing joist comes out.
Cut-and-Patch Around Toilet Flanges and Tub Aprons
Surgical cut-and-patch on the small square-foot areas where a long-standing leak has eaten the underlayment but the surrounding sheathing is sound. Most common at the toilet closet flange (the wax ring has failed and the flange has been leaking for months or years), the tub apron (the caulk seal has failed and water has run down the apron into the underlayment), the dishwasher hose connection (a slow leak behind the kick plate), and the exterior-wall sill plate at a window (a long-failed exterior caulk has let water down the wall). The damaged sheathing is cut back to the nearest joist centers, replaced with matched-thickness plywood, and screwed to spec. The source of the leak is identified and named before the patch closes — fixing the leak source is in scope for the appropriate trade (plumber on a flange, Handis on a tub caulk, exterior trim and caulk on a wall).
Exterior-Wall Sill-Plate and Rim-Joist Repair
Rotted rim joist or sill plate at an exterior wall replaced where the rot is local (a single window leak, a failed exterior caulk run, a downspout that drained against the foundation for a decade). The rotted lumber is cut out to sound material, the new rim joist or sill plate is sized to match (pressure-treated where it contacts concrete), anchor bolts re-set or new anchor bolts epoxied into the foundation per the prescriptive code, and the wall sheathing tied back into the rim. Larger structural rim or sill rot routes to a foundation contractor with a structural-engineer review — we will tell you on the booking call which scope your house needs.
Sheathing Prime and Seam Seal Before Finish Floor
New sheathing primed with a matched primer (Zinsser BIN, Kilz Premium, or an oil-based subfloor primer where the finish floor manufacturer requires it) and every joint sealed at the perimeter so moisture cannot migrate under the new floor. The sheathing is verified flat (under 3/16 inch in 10 feet) before the finish floor install rolls in — if a leveler pour or shim plan is needed on top of the repair, that scope is named on the quote alongside the structural work.
How a Subfloor Repair & Replacement Job Works
Six sequential steps from leak-source identification to final flat check — the actual sequence on every Handis subfloor structural repair.
Identify the Leak Source Before Any Demo
Most subfloor rot is downstream of an active or recently-fixed leak. The source gets identified first — toilet wax-ring failure at the closet flange, tub apron caulk failure, dishwasher hose connection, exterior-wall flashing or caulk, washing-machine hose. The source is named on the quote alongside the structural repair so the fix sequence is right — leak source fixed first, structural repair second, finish floor third.
Cut Out the Failed Sheathing to the Nearest Joist Centers
Failed plywood or OSB cut out to the nearest joist centers with a track saw or a circular saw set to the sheathing depth so the joists below are not scored. Fastener heads pulled from the joist tops. Joist tops checked for rot and adhesive buildup; sanded flat where the new sheathing has to seat. Cut perimeter chalked square so the patch lines up clean.
Sister Joists Where the Bearing or the Span Has Failed
Each exposed joist sound-checked at the bearing and along the run. Cracked or rotted joist sistered full-length with matched-depth lumber, structural-screwed every 16 inches, shimmed up to plane where the existing joist has dropped, end-bearing seated on the rim per the prescriptive code. Sister-and-replace where the existing joist is too far gone to bear; temporary shoring of the floor above goes in before the existing joist comes out.
Drop the New Sheathing with Adhesive and Tongue-and-Groove Engaged
APA-rated tongue-and-groove plywood (3/4 inch for primary subfloor on joists, 1/2 inch for underlayment patches over sound sheathing) cut to the patch dimensions. Construction adhesive (Liquid Nails Subfloor, PL Premium) bead on every joist contact. Sheathing dropped with the tongue-and-groove engaged at the seam to the existing sheathing, tapped tight with a sledge and a sacrificial block.
Structural-Screw to Spec, Set Every Fastener Flush
Structural screws (#8 by 2-1/2 inch or 3 inch GRK or Spax) driven through the new sheathing into the joists at the manufacturer-specified pattern — typically 6 inches on edge along the perimeter, 12 inches in the field. Every fastener set flush so the new substrate is dead flat to the existing — no proud screws to read through the finish floor. Perimeter seam beaded with adhesive to seal against moisture migration.
Prime the Sheathing, Verify Flat, Hand Off to Finish Floor
New sheathing primed with the matched primer (Zinsser BIN, Kilz Premium, or oil-based subfloor primer where the finish-floor manufacturer requires it). Long straightedge walked over the repair to verify flat to the finish-floor spec (3/16 inch in 10 feet for hardwood, 1/4 inch in 10 feet for luxury vinyl plank, 1/8 inch for large-format tile). If the repair sits proud or low of the existing, the matched leveling scope goes on the quote. Customer photos before sign-off.
Subfloor Repair & Replacement Pricing
Final pricing is labor plus APA-rated plywood (typical 3/4-inch tongue-and-groove sheet runs $55 to $75 per sheet at trade pricing; 1/2-inch underlayment plywood runs $40 to $55 per sheet; product passes through transparently on the quote). Joist sistering is quoted as a separate add-on per sistered joist. Leak-source repair (plumber on a flange, exterior trim and caulk on a wall leak) is named on the quote and either self-performed by Handis or routed to the appropriate licensed sub. Asbestos in pre-1985 vinyl or mastic above the failed sheathing is identified on the booking call and abated by a licensed contractor before any Handis structural work begins. Request a free estimate for an accurate quote.
Send a phone photo of the failed sheathing and any visible water source — we will quote the cut-and-patch, the sistering, and the leak-source fix sequence on one estimate.
Why Handis for Subfloor Repair & Replacement
Most subfloor failures we are called to repair come from a small leak that nobody fixed for a long time — a toilet wax ring that has been weeping at the flange for two years, a tub apron caulk that has been failing since the previous owner painted around it, a dishwasher hose that has been dripping behind the kick plate since the appliance was installed. The honest scope on every repair is to fix the leak source first, repair the sheathing second, and lay the new finish floor third — in that order, with the leak source named on the quote and the responsible trade identified. Patching the sheathing without fixing the leak puts the homeowner back in the same chair in eighteen months. We never close a sheathing patch over an unresolved leak source.
Leak source identified before any demo, fixed in the right sequence
Subfloor rot is almost always downstream of a leak that has been going for months or years. The source gets identified on the booking call (closet flange, tub apron caulk, dishwasher hose, exterior caulk, washing-machine line) and the fix sequence is built right into the quote. Leak source fixed first, sheathing patched second, finish floor laid third. Patching over an unresolved leak puts the customer back in the same chair in eighteen months.
APA-rated tongue-and-groove plywood, never OSB on a wet area
Subfloor patches and replacements use APA-rated tongue-and-groove plywood — 3/4 inch for primary subfloor on joists at 16 or 24 inch on-center spans, 1/2 inch for underlayment over sound sheathing. We never use OSB on a wet area (kitchens, baths, laundry, mudrooms) because OSB swells at the edges when it gets wet and never recovers. The tongue-and-groove engages at the seam so the patch ties into the existing sheathing flush.
Structural screws to spec, set flush, perimeter sealed
#8 by 2-1/2 inch or 3 inch GRK or Spax structural screws driven through the new sheathing into the joists at the manufacturer pattern — 6 inches on edge along the perimeter, 12 inches in the field. Every fastener set flush so the new substrate is dead flat to the existing. Perimeter seam beaded with construction adhesive to seal against moisture migration. No proud screws to read through the new finish floor, no open seams to wick water under the floor.
Joist sistering where the dip is structural, not just a surface fix
A sagging floor that traces to a settled, cracked, or rotted joist gets the structural fix first — full-length sister joist alongside the existing joist, structural-screwed every 16 inches, shimmed to plane, end-bearing seated on the rim per the prescriptive code. Sistering the joist before the sheathing patch ensures the fix lasts. We do not patch sheathing over a sagging joist and call it done.
Primer on the new sheathing, flat-checked before finish floor
Every new sheathing patch gets a matched primer (Zinsser BIN, Kilz Premium, or oil-based subfloor primer where the finish-floor manufacturer requires it) and the patch is straightedge-checked to the finish-floor flatness spec before the finish floor install rolls in. If the patch sits proud or low of the existing sheathing, a matched leveling scope goes on the quote alongside the structural work — the customer sees both numbers together.
Insured, background-checked, one-year project warranty on structural repair
Handis carries general liability and workers' compensation; every technician has cleared a background screening. One-year project warranty on the structural repair workmanship — sheathing replacement, joist sistering, sister-and-replace, cut-and-patch. A repair failure that traces to our workmanship (a screwed pattern off-spec, a missed adhesive bead, a sistered joist that drops because the bearing was not shimmed) gets the repair redone at no cost. The leak-source fix carries its own warranty path named separately on the quote.
Estimate
Tell us the room (kitchen, bath, laundry, hallway, exterior wall), the rough size of the visible soft spot or rot, and any known leak source (toilet flange, tub caulk, dishwasher, washing-machine hose, exterior flashing). Send a phone photo of the floor with the suspect area visible and a photo of the under-floor or basement view of the same area if the joists are accessible. We send a written estimate with the leak-source fix, the sheathing repair, the joist sistering (if needed), and the matched leveling scope (if needed) itemized so you see what each scope adds.
Customer Reviews
Subfloor repair and replacement reviews from real Handis customers.
1948 Madison Park craftsman. The powder-room toilet had been wobbling for years and we could rock it by hand. Handis pulled the toilet, found the OSB underneath was black and gone, called their plumber sub for a brass flange repair, then cut out a 4-foot square patch and dropped in new 3/4-inch tongue-and-groove plywood. Toilet does not wobble. Closet next door does not smell like mildew anymore.
1965 Ravenna split-level. Dishwasher had been dripping behind the kick plate for an unknown period of time. Tech identified the dish hose connection as the source, the appliance plumber repaired the hose, then Handis cut out the soft sheathing under the cabinet line and patched with new plywood. 18 square feet of patch, two days, no more soft spot when you stand at the counter.
1922 Wallingford bungalow. Original ground-floor joists had rotted at the rim where they bear into the foundation. Tech sistered two full-length joists in pressure-treated 2x8, anchored them properly to the foundation sill, then patched the sheathing on top. Floor stopped bouncing across the dining-room run. Five years and still solid.
1971 Ballard kitchen. The whole space under the dishwasher and the adjacent base cabinet had sagged and gone soft. Handis sistered one joist that had cracked at a notch from a previous plumber run, replaced about 30 square feet of sheathing, primed everything, and the new luxury vinyl plank install on top has held flat for three years. Honest about the leak source (a slow dish hose drip) and got the plumber on the right day.
Laundry room in a 1958 Burien rambler. The washing-machine hose had failed inside the wall and water had been running for unknown weeks before we noticed. Handis pulled up the failed sheathing (about 90 square feet), sistered two joists, primed the new plywood, and the new tile floor has been dead flat since. Six months and the sub-cabinet area is bone dry.
Frequently Asked Questions
Common questions about subfloor repair and replacement — pricing, the difference between cut-and-patch and full replacement, joist sistering, leak-source coordination, and the warranty path.