How Much Do Structural Repairs to Floor Joists Cost?

Nick P. Cellucci
Written by Nick P. Cellucci
Updated October 27, 2021
Photo: Pixel-Shot / Adobe Stock

The typical cost to repair joists and other parts of your flooring is $10 to $67 per square foot

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If you notice uneven floors, sagging floors, or a floor rotting from moisture damage, you may have a damaged floor joist under your feet. Joists are long beams under your floors that support the weight of your home and provide vital stability.

It will typically cost between $1,000 and $10,000 or more to repair floor joists, depending on the extent of the damage and the size of your room. Noticeable issues should be addressed so you know whether the damage needs to be repaired immediately. 

How Much Does It Cost to Repair a Floor Joist per Square Foot?

Photo: / Adobe Stock

Between materials and labor, structural repairs to your flooring run $40 to $60 per square foot. Joist repairs tend to run $10 to $67 per square foot, depending on the extent of the damage. You may spend more than $20,000 if all the flooring in a room needs to be replaced.

Labor Costs to Repair Floor Joists

Because structural damage to your floor joists often requires professional tools and knowledge, you’ll likely need to hire a contractor. When repairing hardwood floor joists, expect to pay $65 to $100 per hour on labor alone. Projects tend to take anywhere from 5 to 24 hours.

Cost Breakdown to Repair Floors by Layer

If the joists were damaged by rot or mold caused by flooding, repairs or replacements may need to be done to the entire floor, including the top layer and subfloor. In unfinished basements where first floor joists are visible overhead, you’ll likely only need to pay $100 to $300 per joist.

We break down each layer and the associated installation costs for each layer below.

Floor Covering

This is your top layer that usually consists of carpeting, ceramic tile, hardwood plank, vinyl, or laminate. Repair costs $130 to $2,300 to install per room or $2 to $30 per square foot, depending on the type of flooring you own. Full replacement costs $800 to $10,000 or more per room, depending on your install type.


An optional layer installed to help with squeaky floors, under-floor heating, or leveling, underlayment installation costs $0.50 to $5 per square foot.


Under your floor covering is a surface, usually of plywood, that covers your joists. Subfloor repair costs $500 to $700 per room or $2 to $10 per square foot. Full subfloor replacement costs $1,800 to $3,000 per room.


The long beams that provide the main structural support for the floor can cost $200 to $500 per room or $10 to $67 per square foot to repair. A full replacement costs $5,000 to $20,000. If you’re only repairing individual joists, expect to pay $100 to $300 per joist.

How Much Does It Cost to Do Floor Joist Repairs Yourself?

Before taking on any DIY repairs to the structure of your floors, have a contractor inspect them for structural issues like rot, mold, undersized joints, or added weight from a heavy object. An inspection can cost $300 to $500. These issues often require professional work, for which you’ll get a scope and a cost estimate.

Occasionally, you can remedy slight sagging or bouncing problems in one or a few joists through a process called sistering. The job involves adhering and nailing new joists alongside the damaged ones and may require a hydraulic jack to level the structure. Expect materials to cost $100 to $300.

If there are electrical cables, plumbing pipes, and other obstructions that make it difficult to access the damaged joist, or if you don’t have the proper tools or knowledge to do the job yourself, your best option is to hire a contractor. If you improperly address problems with your floor joists, it can lead to more severe and costly structural damage throughout your home.

How Much Do Floor Joists Cost by Type?

There are several different types of wooden floor joists.

Engineered floor joists

Engineered floor joists are made from plywood, OSB (orientated strand board), particle, or fiberboard between standard lumber. Beam-shaped or truss-type engineered joists can span greater distances with little to no sagging over time. On average, you’ll pay $40 for a 16’ engineered I-beam.

2x10 joists

2x10 joists of softwood lumber reign as the most popular choice for floor joists due to their lower cost and their ability to be cut according to length. While 2x10s are easier to cut and manipulate than engineered floor joists, they tend to warp or bow over time due to their natural wood construction.

On average, you’ll pay $30 for a 16’ 2x10. Keep in mind that 2x10s do not come in sizes that span the entire length of an average home, so you’ll often need to purchase twice as many joists as you would I-beams. This can increase your overall installation cost.

FAQs About Floor Joist Repair

Have additional questions about your damaged floor joists? We’ve answered some frequently asked questions below to provide you with more guidance.

How do I repair floor joists?

Many homeowners will choose to hire a contractor to handle the work. However, you can take some DIY steps if a single joist is cracked or multiple joists are undersized but in otherwise good shape. Below are the basic steps in the sistering process.

  1. Jack up your floor frame from below and place a beam across the damaged joist and neighboring joists for additional support. If your sag is significant, do this slowly at about one-eighth of an inch per month.

  2. With your jack in place, adhere a full-length sister joint flush alongside the damaged joist with construction adhesive.

  3. Clamp the joists together and nail the new joist to the old one with columns of three nails every 16 inches. Place nails at the top, middle, and bottom of the joist at every nailing point.

  4. If the joist was cut to accommodate wiring or plumbing, you’ll also need to cut the sister joist. Disconnect any pipe or wiring, then feed it through the holes or notches in the sister.

What should I consider when hiring a contractor to repair floor joists?

Woman removing old tiles
Photo: Guido Mieth / STONE / Getty Images

Once you’ve discovered joist problems in your basement or crawl space, you should call the proper professionals to assist you. A plumber can assess mold, mildew, or water damage for leaks, while an exterminator can assess the damage caused by insects. Complete these inspections before starting any repairs.

A general contractor should have no problem repairing your floor joists, but you’ll want to ensure quality craftsmanship from the person you hire for such a vital part of your home’s structure. Before you hire, consider the following:

  • Ask friends for recommendations for who to work with or avoid

  • Look online for positive reviews

  • Get at least three estimates from different contractors

  • Have contractors provide recent references

What other projects should I do at the same time as floor joist repair?

As we mentioned above, what starts as a floor joist repair may come to involve tearing up your flooring and subflooring to access any problems. If that’s the case, you may wish to replace your floor completely as part of the project. If you have wanted new hardwood, tile, carpet, laminate, or vinyl, expect to pay $800 to $10,000 or more per room, depending on your desired surface type.

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