Sagging floor joist repair cost when buying a house

How much does it cost to fix a sagging floor joist?

Sistering, which fastens a new joist against the sagging floor joist, runs $100 to $300 or more per joist. Replacing every joist in a 300-square-foot room runs $5,000 to $20,000, and can run higher if all the flooring comes up. Have a structural engineer name the cause and the scope first. Then ask the seller for the amount on a contractor's written bid.

Key takeaways

• Ask whether your joists can be sistered. Replacing a sound joist costs more and can tear up the subfloor above it.
• No notch is allowed in the middle third of a joist's span. Bored holes can be up to a third of its depth.
• Joists reached from a crawl space or unfinished basement cost less to fix. A finished floor above can add $1,800 to $3,000 a room for new subfloor.

Is a sagging floor joist serious?

It depends on whether the floor is still moving. The International Association of Certified Home Inspectors (InterNACHI) frames the question as whether the problem was "built into the home, which has remained stable," or comes from foundation or soil movement, "which may continue, eventually causing serious and/or expensive-to-repair damage."

Treat it as a structural finding. Book a structural engineer before your deadline, before you set any number. Hiring one can cost $343 to $724, and the engineer can determine the best repair route.

How do you fix a sagging floor joist?

Ask about sistering first. The contractor slowly raises the frame, then fastens a new joist against the damaged one to share the load. The job includes clearing rot and treating the wood. HomeAdvisor advises choosing sistering over full replacement whenever the joist is still structurally sound.

A foundation contractor serving Indiana and nearby states doesn't usually recommend replacing joists. The subfloor is nailed and glued to them, so pulling one out can tear the subfloor and damage the flooring above.

Access and room size set the final price. If the joists are exposed from a crawl space or unfinished basement, a contractor can reach them without touching the finished floor. Under a finished floor, such as a second-story room, the crew removes flooring and subflooring first. Subfloor replacement alone runs $1,800 to $3,000 per room.

If rot or insects caused the sag, ask for a bid that fixes that cause too. HomeAdvisor advises dealing with moisture or insect problems promptly to prevent further damage. If the report names termites, ask the seller for any treatment records.

Is it okay to notch a floor joist?

Only within limits. InterNACHI's inspection reference sets them out:

• Notches at the ends of a joist can go up to one-fourth of its depth.
• Notches in the outer thirds of the span can go up to one-sixth of its depth.
• No notches in the middle third of the span.
• Bored holes no wider than one-third of the joist's depth.

Notched joists are common in older homes, where joists were cut to fit newer pipes or ductwork. The same contractor says those notches weaken the joists and can cause them to crack, split or fail. If your report flags a notched joist, have the engineer check it against these limits. Your local building department decides what the code requires at your address.

How much does sagging floor repair cost?

Most of the spread is scope, from one joist to a whole room.

The first three rows price one joist, or one foot of it. The rest price a whole job, up to every joist in a room. Ask your contractor to bid the same scope as the row you compare against. How to get repair estimates during the inspection period covers how to get a figure while your window is open.

What should I ask the seller for?

Sistering is a structural change, so a permit is likely required. Building permits run $50 to $2,000, depending on the project.

Say the engineer finds eight sagging joists over a crawl space and calls for sistering. At HomeAdvisor's rate, that's $800 to $2,400 (8 × $100 and 8 × $300). Add the engineer's visit and the permit, and the total is $1,193 to $5,124 ($800 + $343 + $50, and $2,400 + $724 + $2,000). No flooring comes up, because the joists are reached from below.

Bob Vila's $200 to $500 per repaired joist would put the same eight joists at $1,600 to $4,000 (8 × $200 and 8 × $500). With the engineer and the permit, that's $1,993 to $6,724 ($1,600 + $343 + $50, and $4,000 + $724 + $2,000). The contractor's bid replaces all of these numbers once you have it.

Write the request as one line: the engineer's scope, a licensed contractor, the permit, and the amount on the contractor's bid. Ask for the work done with the permit and receipts, or a credit sized to the bid. Put the line in your buyer repair request letter. See what to ask for after a home inspection for how it sits with the rest of your list.

What if the seller says no?

You can accept it, ask for a credit or price cut instead, or walk away if your contract allows it. A sistering job with a bid is a known cost. A sag the engineer ties to foundation movement is a bigger unknown, and when to walk away after a home inspection walks through that call.

Your contract sets the deadline and your options, so confirm them with your agent or attorney.

Does homeowners insurance cover sagging floor joists?

Usually not when rot caused it. Progressive says sagging floors caused by rotting floor joists "are typically not covered by homeowners insurance." It says dwelling coverage may pay for foundation damage from covered perils, such as tornadoes or falling trees. Your policy wording decides, so settle a slow sag in your repair request rather than counting on a claim after closing.

Do you need a structural engineer to replace floor joists?

Ask your local building department whether the permit needs an engineer's design. Even where it doesn't, the engineer's visit is what tells you whether sistering is enough.

How do I know what the rest of my list is worth?

Get bids on the lines that need them, like this one, and price the rest. Kept prices every line of an inspection report for $79, usually under 4 hours. That tells you where the engineer's time and your days matter most.

If the joists are one line of many, upload your inspection report to Kept and spend your remaining days on the engineer and the bid.

Sources

• InterNACHI, Evaluating Structural Framing
• InterNACHI, Cutting, Notching, and Bored Holes in Floor Joist
• HomeAdvisor, Floor Joist Replacement Cost
• Bob Vila, Sagging Floor Repair Cost
• Acculevel, Costs for Sagging Floors
• Progressive, Does Home Insurance Cover Foundation?