What Is a Floor Joist?

 In Floor joists

Floor joists are essential wooden elements necessary for constructing a residential or commercial building.

Understanding what joists are and what they do is important if you’re planning on building a home or carrying out an extension project such as adding a deck.

Keep reading to learn more about the basic concepts of floor joists, including joist span, and the impact of these beams on your home and any future renovation projects.

How floor joists work

Floor joists are wooden beams that are laid horizontally to support your floors and floor coverings. They link various elements of a building’s structure, filling spaces within a floor system and transmitting the load to the foundation.

Floor joists support the weight of the room, including walls, furniture, people and so on. This is why it’s important to calculate the weight your floor will have to bear before choosing the type of joist.

Generally speaking, floor joists are spaced 16″ apart on center, but this distance may vary according to local building codes and the requirements of your specific structure.

Joists help distribute the load evenly through the building and play a role in keeping the structure safe. When a load is applied to the floor, the wood fibers below the joist are stretched (go into ‘tension’), while those above are compressed (go into ‘compression’), which helps distribute weight evenly.

What’s the difference between a beam and a joist?

Beams are the main structural elements of a house or other building. Beams carry the whole, while joists link the different elements of the structure to balance the weight.

Visually, a beam is much larger than a joist. Remember, a damaged or missing joist can still leave your house intact, whereas a damaged or missing beam will put the entire structure at risk.

Practically speaking, beams support joists.

The role of joists in wood floor systems

A wood floor system is made up of various elements that work together to support your floor and the weight that will be placed on it. This is not an exhaustive list, but here are a few of the main structural wood components of a floor system:

  • Braces and bridging: These reinforce the lateral stability of the structure and are installed between the joists.
  • Rim joists: Generally located on the edge of the floor system to reinforce its structure.
  • Floor joists: Horizontal beams that provide support to the floor system.
  • Sill plate: The sill plate is installed on the foundation and is usually made from pressure-treated wood. Joists are attached to the sill plate.
  • Support beam: Support beams support the first-floor joists if they are not long enough to reach between the walls.
  • Subfloor: A flat, stable level surface made of panels of plywood or OSB that are attached to the floor joists.
  • Floor covering: Material used to cover the subfloor. The floor covering provides an attractive finish, protection against wear and tear, and a functional surface for walking on.

Floor structure

Types of wood floor joists

There are different types of wood beams and joists. The differences lie in price, service life and how difficult they are to intall. Let’s find out more.

Solid joists

This is the most common type of joist, and also the most affordable. Their span and strength vary according to the type of wood they are made from.

Unfortunately, this type of wood floor joist is not very environmentally friendly, as wood reserves are becoming increasingly depleted. They also do not last as long as other, more modern solutions.

Solid wood


I-joists take their name from their shape, which is similar to the 9th letter of the alphabet. This modern solution offers greater spans than solid wood joists, and is lighter, which optimizes construction costs for your foundations.

However, the unit cost of I-joists is higher, since it takes more work to manufacture them. Each I-joist consists of two wooden sections and a central framework of oriented strand board (OSB).

Joist floor in i

Open-web trusses

Built according to very specific calculations by the Truss Plate Institute of Canada, open-web floor joists offer many advantages, making them very popular with building contractors.

This type of floor system is made up of several sections of wood, all ingeniously joined by metal connectors. Open-web trusses include open spaces, which saves on construction time since builder don’t have to drill holes in the joists for pipes or other cables.

Open-web floor trusses are even stronger than I-joists, and allow even greater spans. They offer real time-savings during construction, but they’re also the most expensive solution. Floor trusses also require precise construction plans, as they cannot be cut to size once assembled.

Floor joist

Get floor joists fast with UsiHome

Are you looking for a wood floor joist supplier for your construction project? Trust UsiHome.

We’ve been leaders in manufacturing prefabricated wood structures since 1967, and we are certain our complete range of wooden structural components includes the solution you need. In addition to building floor joists, our teams and factories can also supply roof trusses or prefabricated wooden walls. Thanks to our expertise, you can rely on a single supplier for your entire construction project.

Contact us via our online form or directly by phone at 855-595-0666, and one of our representatives will be happy to help.

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