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Homeowner’s Guide to Floor Joists

A floor joist is an integral part of a floor’s structural assembly and creates a platform for floor installation.

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As with everything that stays out of sight, floor joists can go unnoticed for many years until they rot or fail. Many homeowners are unaware of their presence or what role they play in the subfloor. The truth is, without joists, you wouldn’t have a functional floor above the crawl space

Let’s explore the different types of floor joists, problems that affect them, and how you can protect yours. 

floor joists

Understanding Floor Joists

Floor joists are horizontal structural elements that bear some of the weight from your floor and the house above. They span from wall to wall or beam to wall. A common fixture in homes with a crawl space or basement, floor joists help stiffen the subfloor sheathing. 

Their load capacities depend on:

  • Grade of the lumber
  • Wood species
  • Length of the joist span
  • Load placed on the floor
  • Width and thickness of the boards

Builders usually space joists evenly and cover them with subfloor panels. When properly installed, joists can help keep your floors level and steady. The choice of lumber and spacing will depend on the prevailing conditions. If headroom is a problem, they can install smaller joists and space them closer using a shorter span. 

Types of Floor Joists

Several options are available for supporting the floor. Here are the most common types.

I-Joists: It’s a type of engineered wood joist. They have a long span, are eco-friendly, and can carry higher loads than solid lumber. On the flip side, these joists aren’t resistant to fires or water.

Solid lumber: Made from wood, solid lumber joists also happen to the most affordable. Their cost depends on board size and wood grade, which are factors that determine their longevity.

Open-web floor trusses: If you’re looking for joists that offer a range of depth, have longer spans, or greater load capacities, go for this type. Wood trusses have low moisture levels and shrink less.

Are My Floor Joists Failing?

If your crawl space contractor spots any of the signs below, your floor joists are likely failing.

  • Damp, rotting wood
  • Jamming crawl space door
  • Bowing crawl space supports
  • Sagging or sinking beams
  • Cracks on the crawl space walls

One or more of these signs is bad news for your crawl space. Make sure they’re addressed promptly.

Common Floor Joist Problems

Your floor joists are under constant assault from different forces. Let’s look at things that can damage these structural components or lower their integrity.

Wood rot: When you leave your crawl space open, moisture will build up and create the perfect conditions for wood-damaging fungi. Mold will weaken the joists and cause your floors to sag or sink.

Poor construction: Some builders do a shoddy job when building the crawl space. For instance, they can install fewer joists than can support your floors and everything above. This will cause your beams to sag and floors to sink, making your home unsafe.

Termite damage: These wood-boring insects will chew up your floor joists, beams, and anything that contains cellulose. With time, your floors will grow weaker and cave in.

Protecting Your Floor Joists

Even slight damage to the joists can pose safety issues. Ask your carpenter to inspect and repair any broken wood joists. If the floors are still wobbly after the joists are repaired, install additional joists to reinforce your subfloor.

Next, address potential water problems or moisture issues around your crawl space. This is an area Complete Basement Systems can help you with. We recommend that you seal open crawl space vents and encapsulate the crawl space with a plastic vapor barrier. This will lock out outside moisture.

Schedule a free crawl space repair inspection to find out which the condition of your joists and the crawl space area is.