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What Is a Floor Joist?

Floor joist
Floor joist

Are you a homeowner looking to learn more about floor joists? If so, you’ve landed on the right page. In crawl space foundations, floor joists are integral structural elements that provide necessary support for the floors. They come in different shapes and sizes, and in residential construction, they’re usually made from wood. In this blog post, we’ll explore what floor joists are precisely, how to determine if yours need replacing or repairing, and other considerations when it comes to maintaining them.

What Is a Crawl Space Foundation?

A crawl space foundation is a type of foundation commonly used in residential properties. It creates a space beneath the house that’s typically 1-3 feet tall and elevates the home off the ground. It’s just tall enough to crawl around in and provides access to the home’s plumbing and other utilities. The crawl space is usually accessed through a small opening on the house’s exterior or in a closet.

A crawl space foundation is a type of foundation commonly used in residential properties. It creates a space beneath the house that's typically 1-3 feet tall and elevates the home off the ground. It's just tall enough to crawl around in and provides access to the home's plumbing and other utilities.

What Is a Floor Joist?

A floor joist is a horizontal structural member that supports the weight of the flooring system. More specifically, floor joists are wooden or steel framing members spaced regularly on top of beams/girders. The best way to describe floor joists is with an illustration:

6 Types Of Floor Support

Floor joists help provide the support necessary to hold up the weight of the floor, as well as any additional loads that may be placed on it, such as furniture, appliances, or people.

Floor joists differ from both beams and support posts in several ways. Firstly, beams are much larger and more robust than floor joists. They’re placed under the floor joists and are supported by support posts. Support posts are vertical load-bearing members used to support the beams and the floor joists.

For more information, see Signs Your Crawl Space Might Need Floor Joist Reinforcement.

Common Problems With Floor Joists

The most common problems with floor joists include the following:

  • Wood rot – Wood rot is caused by moisture in the crawl space and, if left untreated, can weaken the structural integrity of the floor joists, leading to costly repairs and potential safety hazards.
  • Termites – These pesky insects can quickly and easily infiltrate wood structures, causing extensive damage in a short amount of time. It’s crucial to regularly inspect for termite presence and address any infestations promptly to avoid significant damage to the floor joists.
  • Not enough floor joists – If there aren’t enough floor joists installed, the floor can sag. It’s essential to adhere to local building codes and standards to ensure the proper number of floor joists are installed.
  • Floor joists that are too small – Floor joists that are too small can also lead to problems since they can’t support the floor properly. They can bow, crack, or even break if the load is too heavy.

Signs There Might Be A Problem With Your Floor Joists

Signs there might be a problem with your floor joists include the following:

  • Sagging floor – If you notice the floor above the crawl space is sagging or sloped in certain areas, this could be a sign the underlying support structure is failing.
  • Bouncy floor – Similarly, if you notice that your floors feel bouncy or unstable when you walk on them, it could indicate that the joists cannot support the weight of the floor above them.
  • Problems with doors and windows – If you find that doors and windows are sticking or difficult to open and close, this could indicate a problem with the wooden support structures in the crawl space.
  • Wall cracks – These cracks can indicate that your home’s foundation is shifting or settling due to weakened floor joists or other structural issues.

If you see any of the above, contact an experienced foundation repair contractor right away and ask for an inspection. Foundation issues spotted early cost less to repair.

Read more about – Crawl space jack.

How Are Problems With Floor Joists Repaired?

The process of repairing damaged floor joists typically involves a thorough assessment of the extent of the damage. Professional contractors use specialized instruments like moisture meters and laser levels to assess the condition of the joists. If the joists are salvageable, the repairs can be performed through sistering, which involves adding new joists alongside the existing damaged ones. The new joists are then bolted and glued to the damaged ones, reinforcing them and distributing the load more effectively.

However, if the damage to the joists is extensive, replacement may be the only viable option. In such cases, the process involves the removal of the damaged joists and the installation of new ones.

Is Repairing Floor Joists A DIY Job?

We don’t recommend homeowners attempt to repair floor joists as a DIY project unless they already have experience doing it. Repairing or replacing floor joists can be a complex and involved process. Therefore, unless you have experience doing this, it’s better to let the pros handle it. They have the required expertise to perform a thorough assessment, design a viable repair or replacement plan, and execute it safely and efficiently while ensuring the structural integrity of the building isn’t compromised. When you hire a pro, you also get a warranty.

If you think there might be a problem with the floor joists in your crawl space, contact us today and schedule an evaluation. If we find a problem, we’ll give you a repair estimate. We serve areas in Nebraska, Iowa, Kansas, and Missouri.


Dave Epp

Dave is the President at Epp Foundation Repair with over 27 years of experience in the industry. Dave has worked on thousands of foundation, basement, concrete, and crawl space repair projects since 1993. Dave is involved in several civic and church organizations and enjoys coaching youth sports, mainly football, golfing, and elk hunting.



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