Difference between Joist and Beam

Joists and Beams are the structural members used to frame the buildings. Steel has been used extensively as a common building material in various structures for decades. The steel design involves operational planning of the system in addition to the purpose it’s meant for, proportioning of structural members to carry the loads and the consideration of erection at the site.

In the end, the structure should be economical and easy to erect, and any such structural effect can easily be achieved in steel. The structural members here play a vital role in choosing the structural system of a building; joists and beams act as such structural members with differences between the both of them.

What is a Joist?

A Joist is a horizontal structural member that runs across an open space or a building and is supported by a beam. Several small beams together may make a joist. The function of a joist is primarily the same as that of a beam, except that wall framings, beams, and foundations support joists. They usually run between the walls to support the ceiling or the floor. They are used to transfer the dead load of the subfloor and floor finishes and the live load of people and furnishings to beams, headers, and foundation walls.

Joists act as the skeleton of the building that supports the load the floor is built to bear, and they are technically like beams, but they span relatively short distances compared to beams and are made of steel or wood.

Joists do not have any standard size used for ceiling or industrial buildings, but most average homes use ceiling joists on a broad size of 2-by-6 inches that can go up to 2-by-12 inches.

Types of Joists

There are four primary types of a joist, they are −

  • Floor joists - Floor joists are horizontal framing components underneath the floor. A floor joist supports the floor of a home.

  • Deck joists - Deck joists usually provide a frame for the deck surface and ensure it does not buckle under the floor.

  • Ceiling joists - These are horizontal elements that span throughout the ceiling and transfer the load of the ceiling to the studs.

  • Rim joists - These joists support joists at the opposite ends of the central beam and help prevent them from warping.

What is a Beam?

A beam is the main load-bearing structural element in a roof. They are the most common structural members that are typically horizontal. However, they can have any orientation and are prominent horizontal members carrying the floor loads from the walls, floors, or roofs to the column or foundation walls. The floor joists may indirectly rest on the beams, and even the walls and columns often sit on the floors.

The primary function of the beam is to provide a straight, level surface, which is even with the top of the mudsill and will support the floor joist system between the foundation walls. Beams are usually made of wood and steel, but they are also engineered wood these days. The term beam is generally substituted with the word girder in residential construction works.

Difference between Joist and Beam

The following table highlights the major differences between Joists and Beams −

Roof joists are horizontal structural elements that subsequently transfer loads to vertical members. These roofing joists usually connect opposing walls and support the ceiling below or the floor above.
A roof beam is usually a loadbearing member that supports the floor or the roof above, and at the same time, it adds integrity to the walls.
Joists combine several smaller beams that run parallel and support horizontal structures such as floors, decks, or ceilings. They have a high strength-to-weight ratio, making them a preferred choice of material in building long spans and multistory buildings.
Beams are generally horizontal, load-bearing structural members that bridge an area with columns and posts around it and protect the structural integrity of both residential and industrial buildings. They are used almost everywhere, from walls to roofs, ceilings to floors, and decks to garages.
Joists are small beams that run across an open space, arranged in a parallel series to support the ceiling or the floor. Their primary function is the same as that of a beam, except they are like the skeleton of a building that spans horizontally between the buildings’ foundations or the walls.
The beam is one of the most common structural members used in construction or building works to carry the floor loads from floors, walls, or roofs to columns or foundation walls. They are usually horizontal but can have any orientation that better serves the purpose.


In conclusion, although both joists and beams are horizontal structural members used to frame buildings and protect the structural integrity of the walls. While both these terms can be used interchangeably, beams are the main load-bearing structural elements of a roof, and joists usually span between two beams.

Updated on: 11-Jul-2022

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