Floor Joist Repair Cost (2026)
Floor joist repair is priced per joist: $100 to $400 each to sister a damaged joist, $250 to $800 each to replace one. Most homeowners are dealing with several at once, which puts a typical job between $1,500 and $7,000. Where the water came from usually costs more to fix than the joists do.
- How much does floor joist repair cost?
- Floor joist repair costs $100 to $400 per joist to sister and $250 to $800 per joist to replace. A typical job covering eight to twelve joists runs $1,500 to $7,000. Replacing a main girder costs $2,500 to $12,000.
- What is sistering a floor joist?
- Sistering means bolting a new joist alongside the damaged one so the new member carries the load. It is cheaper and far less disruptive than removing the original, and it is the standard repair whenever the existing joist is still structurally present — even if it is cracked, notched or partly decayed.
- Can I repair floor joists myself?
- Sistering a single accessible joist is within reach for an experienced DIYer, at $40 to $90 in lumber and hardware. Anything involving shoring, a girder, or more than a couple of joists should not be — the floor above is being held up during the work, and getting the temporary support wrong is how people are injured.
- What causes floor joists to fail?
- Nearly always moisture. Sustained crawl space humidity above 60%, a plumbing leak, or groundwater produces fungal decay that softens the wood. Termites are the second cause, and over-notching by a plumber or electrician the third. Repairing the joists without fixing the moisture guarantees a repeat.
| What you're pricing | Low | Typical | High |
|---|---|---|---|
| Sister a damaged joistNew member bolted alongside the old one | $100 | $250 | $400 |
| Replace a joist outrightRequires shoring; more disruptive | $250 | $500 | $800 |
| Add a support jack under a joistAdjustable steel column on a footing | $150 | $300 | $500 |
| Typical job: 8–12 joists sisteredThe most common real-world scope | $1,500 | $4,000 | $7,000 |
| Girder / main beam replacementWhole-beam job, includes temporary shoring | $2,500 | $5,500 | $12,000 |
| Subfloor replacement above repaired joistsPer affected area | $1,200 | $3,000 | $7,000 |
What drives the price
- How many joists
- This is a per-unit job, so the count is the price. Get the number of affected joists in writing — it is the one figure that makes two quotes comparable.
- Sister or replace
- Sistering is roughly half the cost of replacement and is appropriate in most cases. A joist that has lost its bearing at the end, or is decayed through, has to come out.
- Whether the girder is involved
- A failed main beam is a different job — shoring, heavier material, sometimes new footings. It is what turns a $4,000 quote into a $12,000 one.
- The water source
- Drainage and encapsulation to stop the recurrence often cost more than the framing repair. Budget for both or expect to do this twice.
Get the joist count, then compare
Floor joist repair is one of the few home repairs with a clean unit price, which makes it unusually easy to sanity-check. Sistering is $100 to $400 per joist installed. If a quote says $6,800 and the contractor says "about ten joists", the implied $680 each is high and worth asking about — low headroom and difficult access can justify it, but it should be stated rather than assumed.
Conversely, an unusually cheap per-joist number often means the sister is being face-nailed rather than through-bolted, or is not running to full bearing at both ends. Both are common shortcuts and both leave the floor no stronger than before.
Fix the cause in the same project
Joists rot because the crawl space is wet. A repair that does not address drainage, ground moisture or the leak that started it is a repair with a known expiry date, and the second round costs more because more members are affected by then.
The economical sequence is one mobilisation: dry the space, repair the framing, then encapsulate. Splitting it into three visits over three years means paying setup and access costs three times, on a steadily growing scope.
Common questions
- How much does floor joist repair cost?
- Floor joist repair costs $100 to $400 per joist to sister and $250 to $800 per joist to replace. A typical job covering eight to twelve joists runs $1,500 to $7,000. Replacing a main girder costs $2,500 to $12,000.
- What is sistering a floor joist?
- Sistering means bolting a new joist alongside the damaged one so the new member carries the load. It is cheaper and far less disruptive than removing the original, and it is the standard repair whenever the existing joist is still structurally present — even if it is cracked, notched or partly decayed.
- Can I repair floor joists myself?
- Sistering a single accessible joist is within reach for an experienced DIYer, at $40 to $90 in lumber and hardware. Anything involving shoring, a girder, or more than a couple of joists should not be — the floor above is being held up during the work, and getting the temporary support wrong is how people are injured.
- What causes floor joists to fail?
- Nearly always moisture. Sustained crawl space humidity above 60%, a plumbing leak, or groundwater produces fungal decay that softens the wood. Termites are the second cause, and over-notching by a plumber or electrician the third. Repairing the joists without fixing the moisture guarantees a repeat.
How we price this. Figures are national 2026 estimates built from contractor quote ranges, material pricing and regional labour rates, then cross-checked against published industry cost data. Reckon Home does not sell, broker or perform this work. Use these numbers to judge whether a quote is reasonable — not as a quote.