How Much Does It Cost to Replace Damaged or Rotting Floor Joists?

Typical Range:

$2,000 - $30,000

Find out how much your project will cost.

Cost data is based on research by HomeAdvisor.

Updated November 17, 2021

Written by HomeAdvisor.

Floor joist replacement costs $12,500 on average, typically between $5,000 and $20,000. You might pay as little as $2,000, while the largest and most complex jobs cost up to $30,000. Expect to pay anywhere from $100 to $2,000 per joist depending on the extent of the damage and its accessibility to your contractor.

In most homes, the carpet, hardwood, or tile is only a surface layer resting on a subfloor. Underneath are floor joists, a series of parallel beams that provide the main structural support for the floor or ceiling load. When these joists become moisture- or insect-damaged, repair or replacement is essential, as is knowledge of the floor repair costs to complete the job.

Average Cost to Replace Floor Joists

Average Cost$12,500
High Cost$30,000
Low Cost$2,000

Floor Joist Prices by Type

The price you’ll pay for the floor joists themselves will vary based on the type of joist you use. There are two types of floor joists commonly used in home construction.

Engineered I-Beam Floor Joists

The average cost for a standard 16-foot engineered I-beam is $40 per joist. This type of joist comes from plywood, OSB (oriented strand board), particleboard, or fiberboard placed between standard pieces of lumber in the shape of a letter “I.” Beam-shaped or truss-type engineered joists can span greater distances than other floor joists with little to no sagging over time.

2x10 Joists

A popular choice for floor joists, 2x10s are only about $10 per joist. They’re made from softwood lumber cut to custom lengths more easily than engineered I-beams. However, their natural wood construction can cause warping or bowing over time. And, they do not come in sizes that span the length of an average home. This means you’ll often need to purchase twice as many joists as you would I-beams, increasing your overall installation cost.

Floor Joist Total Installation Cost

The total project cost for full joist replacement is typically $5,000 to $20,000 in a 300-square-foot room. That’s because replacing floor joists is a major structural repair to your floor, often requiring professional tools and knowledge that only a trained contractor will have.

Additionally, unless your joists are easily accessible from a crawlspace or the ceiling of an unfinished basement, joist replacement will likely also involve subfloor and floor covering replacement.

Floor Joist Installation Cost Per Joist

Expect to pay anywhere from $100 to $2,000 per joist depending on their accessibility to your contractor and whether additional repair or replacement work is required. You may pay only $100 to $300 per joist if your contractor can easily access the joists from below.

However, if your joists are insulated or covered by flooring and subflooring, a complete replacement will more likely cost $1,000 or more per joist. Most contractors price a full joist replacement job as a total project cost based on the number of joists replaced.

Floor Joist Replacement Cost by Extent of Damage

Joist replacement is usually necessary when a joist has rotted away due to damage from insects or moisture. The scale of your floor repair project and the repairs necessary will depend partly on the extent of this damage.


On average, sistering (or clearing rot, treating the wood and laying a new joist beside the old one) will cost you $100 to $300 or more per joist. However, these costs will increase if your contractor needs to open up a floor or ceiling to access the joists. If only a few joists have rotted, a full replacement may not be necessary.

Partial Room Replacement

A minimal joist replacement will cost you $2,000 to $5,000 if only one part of your room suffered damage.

Full Room Replacement

If damage is extensive enough that all joists in a room have been affected and require replacement, the job will usually cost $5,000 to $10,000.

Entire Level Replacement

If damage compromised the entire level of your home, expect to pay anywhere from $10,000 to $30,000 for replacement.

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Floor Joist Replacement Cost Factors

Several factors can influence the total cost of a floor joist replacement.


If possible, your contractor will replace your joists from below, either in a crawl space or the ceiling of an unfinished basement. This cuts down on time, involves much less work, and will save you money.

However, if you have rotting joists in a second-story room, your contractor will need to remove and replace the existing carpet or hardwood and subflooring on top of your joists just to expose the damage, which significantly increases the price of the job. Furniture and appliances will also need to be removed, which you can do yourself to reduce labor costs.

Flooring and Subflooring

Flooring and subflooring installation can range anywhere from $6.50 to $23.50 per square foot. You can lower flooring installation costs by installing a floating floor.

If your floors need to be removed and replaced as part of your joist replacement, the type of flooring you choose will impact your total cost. For instance, tile and natural hardwood cost more than other options and require a more complex installation with higher labor and material costs.

Extent of Damage

The cost to replace all the joists on one level of a typical home is $10,000 to $30,000, based on a 300 square foot space. If damage is only limited to one room or section, your total will likely only be $2,000 to $10,000.

The more extensive the damage to your floor joists, the higher your cost will be. Insects (such as termites) or extended water exposure can damage joists, so before replacing anything, you’ll need to pay to exterminate the insects or fix the moisture problem. These costs can vary greatly depending on the nature of the issue.

DIY vs. Hire a Floor Joist Replacement Pro

Home inspections cost about $300 to $500, but you’ll receive a cost estimate for any additional work required. Be very cautious when it comes to major structural components like floor joists. You should always have a contractor inspect for issues such as rotting wood, mold, or undersized joints, all of which tend to require professional work.

If the damage is not too severe, skilled DIY’ers can sister new floor joists alongside damaged ones using $200 to $500 worth of materials and equipment, including a hydraulic jack to level your structure. However, if electrical cables or plumbing get in your way, or if you simply lack the skills to replace a rotting joist, we highly recommend hiring a pro to do the job.


How do I know if my floor joists need to be replaced?

The following are all telltale signs of damaged floor joists in need of repair or replacement:

  • Moist or visibly rotting wood beam

  • Door and window frames that are skewed or unlevel

  • Uneven upstairs floors that sag or slope

  • Cracks in your interior drywall

  • Crawl space supports that are titled or sinking

If you notice any of these signs in your home, contact a home inspector for an assessment.

Can you replace a floor joist without removing your floor?

Technically yes, but only if your floor joists are accessible. For example, in an unfinished basement or crawl space, you can often see exposed joists in the ceiling, making it relatively easy to replace them if needed. However, if your joists are insulated or covered by flooring and subflooring, those layers will need to be removed before making repairs.

How do you sister a rotted floor joist?

If you have a single cracked or undersized joist that is otherwise in good shape, you may be able to complete a small structural repair with the sistering method. The main steps include:

  1. Slowly jacking up your floor frame from below, about one-eighth of an inch per month, and placing a beam across the damaged joist and any neighboring joists.

  2. Using construction adhesive and adhere a new, full-length joist flush alongside the damaged one with your jack still in place.

  3. Clamping and nailing both joists together with columns of three nails every 16 inches at the top, middle, and bottom of the joist.

  4. Cut the sister joist to match any cuts in the original joist; these typically accommodate wiring or plumbing. Disconnect pipe or wiring before feeding it through the cuts you’ve made.

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