A beam is the main load-bearing structural element of a roof. It supports the weight of joists and other building elements. A joist is a horizontal member that generally runs across a building and is supported by a beam. What’s the difference between a beam and a joist?

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

The beam supports the joists. There’s usually only one beam supporting many joists, but they’re both as important as each other. Looking up at a roof from the shell of a house, for example, you’d see one long beam running through the length of the home with multiple joists ‘leaning’ to it for support.

Roof beams

A roof beam is a load-bearing member that is integral to the strength of the building. It supports the floor or roof above while adding integrity to walls. It also supports joists, trusses and other roofing elements. A roof beam will be the thickest and most important element of a roof or levels within a property.

There may be more than one roof beam, but they will usually span the entire length of the space. Typically, roof beams are made of timber but can also be made from steel, concrete or manufactured wood. Roof beams may support the weight of the floor above or roof, but they are also a vital component in structural integrity. Roof beams attach to walls and stop them from spreading or leaning in.

This image below shows metal beams supporting many timber joists.


Roof joists

A roofing joist is a horizontal member that runs across an open space. Depending on the construction, they may lie flat or be pitched. They can be concealed or exposed, and there will be more joists than beams. Roof joists generally join opposing walls and support the ceiling below and/or the floor above. Joists are typically made of timber, and come in a variety of thicknesses and lengths depending on the specifications of the building. Steel, concrete and manufactured wood are also commonly used to create roof joists.

Roof joists also support walls, but to a lesser degree. They are secured to the ‘side’ walls of a property and help stop those walls spreading or leaning in. Replacing beams and joists is something that is best left to a professional contractor, as sufficient support must be in place during replacement, and the correct thickness, length, etc of beam and joist must be installed.

For advice on your next roofing project and working with beams and joists, call our friendly team on 01752 692 760. Alternatively, use the live chat function in the bottom right-hand corner of our website.

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