A Complete Guide on Floor Joist Repair and Replacement

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The floors in your home take a lot of abuse and are often subject to spills, wear and tear from hauling heavy furniture and appliances, and moisture from water damage. Over time this can lead to sagging or warped floors or even severe damage to floor joists.

The floor joist in your crawl space acts as a horizontal structural beam to which floor sheathing and subflooring are attached. While minor damage can often be repaired with reinforcement, major damage will require a floor joist repair or replacement.

Although the task sounds complex, Guardian foundation repair experts have the skill and experience to tackle the job quickly and efficiently.

In this guide, we’ll discuss the following:

  • Causes of floor joist damage
  • How assessing the joist helps determine the repair needed
  • How to fix your floor joist

What Causes Floor Joist Damage?

Many threats can cause damage to floor joists, including:

Moisture and Humidity:

Moisture & Humidity for Floor Joist Damage

Excess moisture in the air or a flooding event are the leading causes of floor joist damage. Since joists are made of wood, moisture will cause them to swell, weaken, and eventually decay, making them structurally unsafe. 

Poor Support Design: 

When joists are poorly designed, or the support beams below them are inadequate, they become incapable of supporting the weight of flooring and furniture placed above them. It can cause them to bend, warp or crack. Some common support design issues are inadequate hangers, undersized joists, and improper nailing.


Wood-eating insects such as termites can also cause damage to floor joists if their activity is left untreated. In addition, the presence of wood-boring beetles or other insect infestations can weaken the structural integrity of the joist and make them unsafe.

Adding Extra Loads:

Floor joists can only support a certain amount of weight. In some cases, adding too much weight to your floor joists can cause them to sag or even break. It is particularly true of older homes with thinner joists that may not be able to handle the extra load from added furniture or appliances.

How Assessing the Floor Joist Helps Determine the Repair Needed:

Floor joists hold up your floors, and it is important to ensure they are in good condition. Besides impacting the level of your floors, a damaged joist can also lead to sticking doors, creaky floors, drywall cracks, and other significant issues.

The first thing you will want to determine when assessing a floor joist is the extent of the damage. It will help you decide whether a repair or replacement is needed.

Common signs of joist damage include:

  • Sloping, bending or sagging
  • Cracks in the wood
  • Evidence of insect infestation
  • Visible water damage

Other than assessing your floor joist, it is also important to check your crawl space beams and footers because if these are damaged, then no repair to other support beams will solve the issue. However, these beams can be repaired and supported, just like a joist.

If you feel that assessing the joist is too complex for you, then calling a professional foundation repair expert in Knoxville is always a good idea. Guardian Foundation Repair experts have the skill and experience to assess floor joists and determine if there is any structural damage, as well as the best approach for repairing it.

How to Fix Your Floor Joist?

Depending on the extent of damage, you can take a few different approaches to repair your floor joist.

Reinforcement of Joist:

Reinforcement of joists.

Compromised joists only sometimes need to be replaced. For instance, if you see rot only around the area where screw or nail penetrations have been made, you can reinforce the weakened area with sister joists. 

A sister joist is an additional joist that is screwed or nailed to the side of a damaged joist to provide stability and reinforcement.

The second option for reinforcement is installing girders or beams with heavy-duty floor jacks in a location where the joists have sagged. Just like car jacks, heavy-duty jacks lift the floor joist back into place. You can also combine this option with sister joists for extra reinforcement.

Replacing of Joist:

If you are dealing with more extensive damage, replace the damaged joists instead of repairing them. It is also recommended if your floor joists are undersized or not up to building code standards. In this case, you will need to remove the existing joist and install a new one.

Floor joist repair is a far more economical and efficient approach than having to replace the entire structure. With proper inspection and timely action, you can ensure that your floor joist is in perfect condition and avoid major damage or renovations in the future. Also, to prolong the life of your joist and maintain its stability, ensure to keep your crawl space dry and free of moisture and check for any insect infestations.

Looking for Professional Floor Joist Repair Near Me? 

Guardian Foundation Repair offers all kinds of crawl space repair and floor joist repair services. Contact us today to get the best solution if you need help assessing your damaged floor joists or other foundation issues.

We provide you with a free inspection and no-obligation quote to ensure that your home is in perfect shape!

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