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

Average Cost to Replace Floor Joists

Floor Joist Prices by Type

Floor joist costs vary quite a bit based on the type of joist you use. There are three main 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, oriented strand board (OSB), particleboard, or fiberboard placed between standard pieces of lumber in the shape of the 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 cost 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. Plus, they don't 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.

Open-Web Floor Truss Joists

Open-web floor truss joists feature two 2x4s that sandwich an inner wood or metal "web". These joists typically cost $30 to $70 per joist, depending on the type. They minimize shrinking, squeaking, and bowing. You can also fit electrical wires and some pipes through them, which can make construction easier. 

Floor Joist Total Installation Cost

Replacing floor joists is a major structural repair to your floor, often requiring the professional tools and knowledge of a trained contractor. The total project cost for full joist replacement is typically $5,000 to $20,000 in a 300-square-foot room.

Additionally, unless your joists are easily accessible from a crawl space or an unfinished basement ceiling, 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 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 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.

Sistering

On average, sistering will cost you $100 to $300 or more per joist. Sistering involves clearing rot, treating the wood, and laying a new joist beside the old one. However, these costs will increase if your contractor needs to open up a floor or ceiling to access the joists. 

Partial Room Replacement

A minimal joist replacement typically costs $2,000 to $5,000. If only part of your room suffered damage, you might only need to replace a few joists rather than all of them. Generally, the more joists you need replaced, the more you can expect to pay.

Full Room Replacement

Full room replacements typically cost $5,000 to $10,000, as damage extent is among the biggest factors affecting floor joist replacement costs. If your room experienced a lot of damage throughout it, you might need to replace all of the joists in the room.

Entire Level Replacement

In some cases, damage is so extensive that an entire level of a home becomes compromised. In this instance, you'll need to replace all of the joists on that level, typically costing $10,000 to $30,000. The larger your level, the more you'll likely have to pay. 

Floor Joist Replacement Cost Factors

Several factors can influence the total cost of a floor joist replacement. For instance, if your floor is tough for a pro to reach, it will require more time and labor to fix, which drives up costs.

Accessibility

If possible, your contractor will replace your joists from below, either from a crawl space or an unfinished basement ceiling. 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 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 laminate and require a more complex installation with higher labor and material costs.

Extent of Damage

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

The more extensive the damage to your floor joists, the higher your costs. Insects, like termites, or prolonged 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 DIYers 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 local pro to do the job.