RSJ stands for rolled steel joist, and they’re sometimes called universal beams or girders. While RSJs look the same as other types of rolled steel sections, such as universal columns and t-beams, they’re used for different purposes.
You’re most likely to need an RSJ if you’re knocking out a load-bearing wall in your home. This is quite common when building an extension or loft conversion, or when expanding a door section to install a new larger window or door (such as bi-fold doors).
RSJs are simple in design, and the most common is the I-beam. Installing an RSJ is not a simple task as they’re extremely heavy and require specialist installation equipment. RSJs should only be installed with the guidance of a professional structural engineer.
This article will review the costs involved in RSJs in the UK, factors that affect the cost and other common questions surrounding RSJs.
Average Supply Only RSJ Cost
RSJs and other joints are usually sold in universal sizes but can be cut to measure. Below are the average prices of various steel sections per metre of length. The exact length will vary.
| Type of Steel | Average Cost |
|---|---|
| RSJ, Universal Beam or I-beam | £50 - £130/m |
| Universal Column | £50 - £130/m |
| Channels | £30 - £100/m |
| T-beams | £20 - £100/m |
| Lintels | £10 - £25/m |
Average Cost of RSJs and Other Sections By Project
The following are average costs of fitting RSJs and other sections by the project. By collecting quotes from 8 primary sources and 7 secondary sources, we discovered the following average costs of fitting RSJs in common home projects.
Costs include materials, labour and structural engineer costs. Note that structural engineer costs vary and may already be included in the planning fee of many extension or loft conversion projects.
| Project Type | RSJ Length | Total Project Cost For Installing RSJs + Other Steel Sections |
|---|---|---|
| Single Doorway | 1m | £1,000 - £1,500 |
| Double Doorway or Bi-Fold Doors | 2m | £1,750 - £2,250 |
| Kitchen or Other Room Extension | 2m - 5m | £1,750 - £2,500 |
| Knocking Down Single Wall | 1m - 3m | £1,500 - £3,500 (including the cost of knocking down the wall) |
| House Extension | 5m - 10m | £2,750 - £5,000 |
| Loft Conversion | 5m - 10m | £4,000 - £7,000 |
Factors Affecting The Costs of RSJs
RSJ projects may be straightforward, in the case of knocking through a single load-bearing wall, or complex, in the case of inserting new steel beams into a ceiling for an extension or loft conversion.
Size of the Beam
The beams themselves are not particularly expensive. Even a large beam measuring over 5m may only cost within the region of £400 to £600.
However, the weight, thickness and length of the beam factor into how much is needed for a certain support.
The Complexity of the Job
Inserting a beam into a ground-floor load-bearing wall is much simpler than installing beams into the second floor or walls (as would be the case for a loft conversion).
In this situation, the beams will likely need to be lifted by crane, which will incur significant extra costs.
Steelwork can be one of the pricier elements of a complex loft conversion, but the work required depends on the existing joists.
Knocking Down The Walls
If you simply want to knock down a wall, a builder will likely quote you for the entire job, including fitting an RSJ.
Knocking down a wall and fitting an RSJ will likely cost at least £2000 for the entire project.
Party Wall Agreements
If your RSJ interferes with an adjoining neighbour’s wall in any way, you will need a Party Wall Agreement.
Party Wall Agreements may require you to hire a Party Wall Surveyor if your neighbour objects or fails to provide written permission for you to carry out the work. This may cost within the region of £300 to £750.
Plastering
Removing walls and inserting RSJs will require the walls to be replastered. This might cost within the region of £300 to £750 for a small-to-medium-sized project.
When Will I Need an RSJ?
Homes are built with load-bearing walls which spread the weight of the upper floors and distribute the home’s overall weight to the foundations. When a load-bearing wall is modified or removed, it’s likely you’ll need an RSJ fitted in the wall to spread the load efficiently.
You might need an RSJ when:
- Walls are knocked out of kitchens or living rooms to build open-plan spaces.
- Walls are removed from the loft to make room for a loft conversion.
- When large bi-fold or other wide doors are fitted to a room.
- When a new large window is fitted to a load-bearing wall.
- When a new extension is erected, RSJs and other rolled steel sections may be used to create the frame and foundations.
RSJs serve a critical purpose and should never be overlooked. There are many horror stories of serious damage to homes resulting from missing RSJs, or DIY projects that involve knocking out load-bearing walls.
Your home insurance likely won’t cover you for damage caused in this way, and it could even result in a criminal or civil offence.
RSJs for Loft Conversions
Most loft conversions will require structural modifications, including steelwork. The original beams and joists will likely not be able to handle the weight of the new floor.
Large conversions will require more than one RSJ to be fitted, and these will likely need to be joined to form a new steel-reinforced ceiling.
Modifications to upstairs walls are less likely to require RSJs for W-shaped truss roofs built beyond the 1960s or so.
RSJs for Kitchen Extensions
Most major modifications to ground-floor load-bearing walls will require RSJs because the weight of the entire top floors of the home lies on top of them.
Knocking through walls to a living room or hallway may need RSJs, but it depends on the specific wall in question – the load-bearing walls may not be immediately apparent.
RSJs for Open Plan
If you want to turn your ground floor into an open-plan space, it’s highly likely that steelwork will be required to reinforce various load-bearing walls, not just downstairs but probably in the ceilings too.
Not all homes are suitable for fully open-plan designs, at least not without full-blown structural engineering works.
How Do I Know If I Need an RSJ?
If you’re planning any major home renovation project that requires modifications or removal of walls, your builder should help you determine if you need an RSJ or other steel supports fitted.
If you need an RSJ, the builder will recommend that you need a structural engineer who will come in and assess your walls thoroughly.
Not all walls that appear load-bearing are load-bearing – it depends on how your house is built and how the existing ceiling joints are assembled.
The structural engineer will determine what sort of beam you need, how the builder should install it, and whether any other modifications to your foundations are required (e.g. inserting new steelwork into a timber-framed ceiling).
They will also liaise with Building Control; any work to your home’s loadbearing walls, ceilings, or other foundations will need to be cleared by a building inspector.
Different Types of Steel Beams and Sections
While the term ‘RSJ’ has become interchangeable with a wide range of similarly-shaped steel sections, there are a few different types of steel sections available.
While your builder and structural engineer will recommend what beam(s) are required for the job, it’s worth being aware of the main options:
I-beam (RSJ)
I-beams are the most common rolled steel section and are also known as universal beams (UBs). They have a traditional ‘I’ shape (which has the crosssection of an ‘H’ when written in some fonts like Times New Roman!)
These are inserted horizontally between or under the masonry to add strong structural support when removing load-bearing walls.
Universal columns
Universal columns, or UCs, are used vertically rather than horizontally and have a slightly different profile to I-beams despite looking very similar. Specifically, their depth is greater than their width, whereas I-beam’s depth is equal to its width.
Lintels
Lintels are smaller beams that are typically inserted above windows and doors to support the load above. They’re not really designed for heavy-duty load-bearing applications and may not be a valid alternative to a more substantial beam.
Channels
Channels are U-shaped beams suitable for some ceiling supports and occasionally used as columns.
T-beams
Less common in residential construction, T-beams may be required to build certain steel frames.
How Long Does It Take to Install an RSJ?
Installing an RSJ may only take a day in simple projects when the wall has already been knocked through. For advanced projects, e.g. loft conversions or home extensions, inserting RSJs and other steelwork might take several days.
However, planning for an RSJ installation may take a while as the structural engineer will need to take measurements and make calculations of what sort of beam you need, how long, how it should be installed, etc.
Also, plans and calculations will need to be submitted to Building Control. Lastly, you’ll need an inspection at the end of the project so you can receive a completion certificate, which may prove necessary when you go to sell the house.
The entire start-to-finish process may take a month or so. It’s always wise to plan projects like this well in advance of when you wish for work to begin.
If you’re installing an RSJ as part of a wider home renovation project, then the project planning process should have already included the engineer’s calculations and fees.
Choosing a Structural Engineer
Structural engineers should be part of The Institute of Structural Engineers (ISE) or Institution of Civil Engineers – this is necessary for compliance with Building Control.
Always look for a qualified structural engineer with a strong local reputation and portfolio of projects.
Your builder may work with a structural engineer or may recommend one. Otherwise, it’ll be your responsibility to find one and hire one yourself.
Get Prices on RSJs Near You
We’ve done our best to give you a good idea of what you can expect to pay for a RSJ steel beam installation.
However, our guides are not a substitute for a fixed quote specifically for you.
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About the Author
Alex Johnson is a qualified quantity surveyor and writer with a passion for conducting original research and uncovering the true cost of jobs. His cost data has been referenced by EDF Energy and the Scottish Government.