12 Apr What Is An RSJ Beam? Uses, Sizes & When You Need One

Are you planning a structural alteration to your home or a commercial property? If so, the chances are you’ve already come across the term RSJ beam, or Rolled Steel Joist. But what exactly are they, how are they made, and do you really need one?

This handy guide covers everything you need to know about RSJ beams: from how they’re manufactured to how much they cost to supply and fit. Let’s dive right in.

What is an RSJ?

Rolled Steel Joists are structural steel beams with a distinctive I-shaped or H-shaped cross-section. RSJ beams are popular for residential remodels.Crucially, unlike a traditional timber beam, an RSJ beam won’t bend, warp or rot.

They are one of the most widely used load-bearing elements in construction, designed to span openings and carry a large amount of weight from the structure above. If you’re removing a load-bearing wall or creating a large open-plan space, an RSJ is often the go-to solution.

How Is an RSJ Beam Made?

RSJ beams are produced through a process called hot rolling, where steel billets are heated to extremely high temperatures and passed through a series of rollers to form their final shape. This method creates the characteristic flanged I-section profile that gives the beam its strength.

Because the steel is shaped rather than cut or welded, hot rolling produces a consistent, dense grain structure throughout the beam, resulting in a product that is both strong and reliable.

The finished beams are then cut to standard lengths and either used as-is or fabricated to suit specific project requirements.

What Are RSJ Beams Used For?

RSJ beams can be found in a huge range of domestic and commercial applications. In residential properties, they are most commonly installed when:

• Knocking through walls to create open-plan living spaces. They can support upper floors and roofs when load-bearing walls are removed to create open-plan kitchen-diners or larger living areas.
• Supporting upper floors during rear or side extensions
• Carrying roof loads in loft conversions
• Spanning garage openings where a lintel alone isn’t sufficient
• For lintels they are used over large windows, doors, or bifold openings to distribute weight.
• For renovation and basement reinforcement they are used to secure foundations and strengthen existing structures.

In commercial construction, RSJs form part of the primary structural framework in warehouses, offices, and retail units. Their versatility and availability in a wide range of sizes make them suitable for projects of almost any size and scale.

What Sizes Do RSJ Beams Come In?

RSJ beams are available in a wide range of standard sizes, typically defined by their depth (the vertical height of the beam), flange width, and weight per metre.

Common depths range from around 100mm up to 900mm or more for heavy industrial applications, though most domestic projects use beams in the 150mm to 305mm range.

The correct size for your project is determined by two key factors: the span (the distance the beam needs to bridge) and the load it must carry. A structural engineer will calculate these figures precisely, taking into account the weight of floors, walls, roof structures, and any live loads such as people and furniture.

Getting the size wrong, even slightly, can have serious structural consequences. These can include structural failure or collapse, excessive deflection and sagging, cracking and uneven settlement, as well as buckling or twisting.

Do I Need a Structural Engineer for an RSJ?

In almost all cases, yes you will. Installing an RSJ beam is notifiable under UK Building Regulations, which means the work must be approved by your local authority or a registered building inspector.

A structural engineer will provide the load calculations and beam specification needed to obtain that approval. Attempting to select a beam size without professional input is not only dangerous but could invalidate your building insurance and cause problems when you come to sell the property.

The total cost of supplying and fitting an RSJ in the UK typically ranges from £800 to £2,500 or more, depending on the size of the beam, the complexity of the installation, and your location.

Steel material costs are relatively modest, but the labour, temporary support works, padstones, plastering, and structural engineer fees all contribute to the final figure. As such, it is wise to always obtain at least three quotes and ensure that your contractor is experienced in structural steelwork.

Speak to an Expert about RSJ Beams

If you’re looking for high-quality, CE-marked steel fabrication that will help any domestic or commercial project in the construction industry maximise its potential, Baker Steel Trading can help.

To learn more, contact a member of our team today.