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RSJ Cost: 2023 Steel Beam Installation Price Comparison UK

An RSJ, also known as a Rolled Steel Joist, is a length of steel used in the building industry to replace a loadbearing wall with a steel beam. The RSJs have a specific profile or shape to produce the greatest loadbearing capacity using the minimum amount of steel. They are massproduced in various lengths and profiles to keep RSJ installation costs as low as possible.  Usually, on average a 1 metre RSJ installation costs around £200 to buy, whereas the labour costs around £400 per day. This makes a total installation cost of around £600. But, we’ll talk more about this later on. 

Mechanical engineers calculate the profile of an RSJ to produce the strongest possible shape. Youll find RSJs commonly made using three basic cross-sectional shapes. Namely, an ‘I or ‘H beam, a ‘Channel’ which looks like ‘П’, and a ‘T’ beam. Each one has a specific application. But, for this article, we’ll talk about the most common, an ‘H’ or Universal Beam. 

If you’re adding an extension to your home or adding extra doors and windows, you have to cut into loadbearing walls. To ensure the load safely transfers to the building’s foundations, you must support the load above, using an RSJ. 

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How Much Does an RSJ Cost?

Steel supports, such as universal beams, have widespread use in the building industry. Theyre strong, relatively easy to make, and cheap to install. You can buy them in standard lengths to suit almost any application. However, it’s not only the length thats important. Also, mechanical engineers perform RSJ calculations to increase the size of the cross-sectional profile as the length increases. This means, the RSJ won’t bend more than the safety limits allow, as it becomes longer. 

So, the cost of a steel ‘I Beam’, increases as its profile and length increase. Furthermore, the larger amount of steel that goes into the manufacture increases the universal beam’s weight. If it’s heavier, it’s harder to lift and requires mechanical lifting equipment. Therefore, the labour charges increase, and finally so does the cost of an RSJ installation. 

In the following table, we’ll break down the installation costs using typical scenarios to show the steel beam prices as well as labour cost. In addition, you can also use the figures as an RSJ cost calculator to benchmark against your own workings.

TaskRSJ lengthDurationMaterial costLabour charge
External single doorway 1m 1 to 1.5 days £200 to £300 £400 to £450 
External window opening 2m 1.5 to 2 days £350 £600 
Bifold doors3m 2 days £400 £650 to £700 
House extension4m 2 to 3 days £500 £800 
Loft conversion5m 3 days £700 £850 to £900 

Remember, the labour charges will vary depending on where you are in the country. So, London and Southeast areas will be more expensive than elsewhere. Also, a structural engineer must calculate the steel beam sizes, and prices will vary with profile dimensions and length.

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Additional Considerations

Structural alterations always need a structural engineer’s input to comply with the Building Regulations. They will charge depending on the amount of work, but for a typical straightforward calculation, the fees will be about £300 to £400. 

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Removing a loadbearing wall will produce a large amount of rubble. So, you’ll need a waste skip to remove this. Legally, you must use a registered waste carrier to ensure they dispose of the rubble according to local and national regulations. A waste skip costs up to about £200. 

As we’ve already said, the Building Control Officer will be involved in any work involving RSJs. The Inspector’s fees should be between £150 and £200. 

Never remove loadbearing walls or use RSJs if you’re not a professional. This isn’t a DIY job and the Building Inspector must be satisfied that the builder doing the job knows how to do it. So, use a professional builder with many years of experience.  

A small RSJ should be light enough for one or two people to lift into position. However, if you’re using one longer than 2m, you’ll probably require mechanical lifting aids to ease it into position. The builder will know the best lifting equipment for your situation, so take his advice. Or, even better, leave it up to him to organise. 

Once the metal support beam is in position, and the brickwork reinstated, you’ll require a plasterer and decorator to finish off the surface. Probably, you can save money by decorating it yourself but use a professional to get a smooth finish to the plaster.

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What is an RSJ?

An RSJ is a length of steel of a specific profile. It’s used as a substitute for a loadbearing wall in many different situations. A structural engineer calculates the necessary length and profile to ensure the building stays structurally sound. We’ve already mentioned the different profiles ‘H’, ‘П’, and ‘T’. And, you can use these for a variety of different applications, ranging from a simple door lintel to steel girders bolted together to create a building or roof framework. 

An RSJ has a very simple operating principle. It supports a specified weight above and transmits the load through ‘padstones’ supporting the RSJ at either end. Initially, the builder creates a slot in the wall, large enough to fit the RSJ. If the brickwork isn’t very stable, he might cast a concrete padstone at either end. Then, once the cement and concrete have cured, with the RSJ fixed in place, he’ll slowly remove the brickwork beneath the RSJ lintel. The lintel must overlap the opening by at least 150mm at both ends to provide good support.

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Commonly used RSJ dimensions

The following table lists those RSJs commonly used in the UK, together with the dimensions and weight. You can use this table to also work out the cost per metre.

NameDepth (mm)Width (mm)Weight per metre (kg/m)
152x89x16 UB 152.4 88.7 16 
178x102x19 UB 177.8 101.2 19 
203x102x23 UB 203.2 101.8 23.1 
203x133x25 UB 203.2 133.2 25.1 
254x146x31 UB 251.4 146.1 31.1 
254x146x37 UB 256.0 146.4 37 
254x146x43 UB 259.6 147.3 43 

There are many more sizes available, over 60 in fact. And, the maximum standard Universal Beam measures 914mm x 419mm with a weight of 388kg/m. However, those won’t be used in normal domestic situations.

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In practice, a structural engineer will calculate the dimensions of the RSJ based on the original load of the wall. Furthermore, the engineer will decide if the wall below the 150mm overhang is strong enough to accept the added load. You might have to install an area of dense concrete as a padstone, or even build a blockwork pillar to support the RSJ. Usually, these instructions will come from the structural engineer, based on the specific calculations for your property. 

Building Regulations & Planning Permissions

Usually, you won’t need Planning Permission unless you live in a listed building or intend changing the outside of the propertyHowever, projects along the lines of loft conversions or kitchen extensions will need permission. 

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Building Regulations, however, are a different matter entirely. Generally, people use RSJs when removing loadbearing walls and other structural alterations. So, Building Control will always be involved in projects with structural stability and safety considerations. 

Building Regulation compliance must have structural engineer’s calculations based on your specific situation. Therefore, the engineer will calculate a basic size of RSJ, add on a factor of safety. And then, round it up to the next commercially available RSJ. 

Furthermore, all RSJs must be suitably fireproofed so they have at least 30 minutes resistance. Usually, we achieve this by covering the steel with a minimum of two plasterboard layers, depending on the manufacturer’s specifications.

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Top 5 Tips: Hiring A Structural Engineer

Hire a structural engineer 

Finding a structural engineer isn’t easy if you don’t know where to look. Use personal recommendations from family and friends, or the architect drawing up your plans. You can find a reputable structural engineer for your project using the form on the top of this page, we will put you in contact with up to 3 local professionals.


The Building Regulations require a suitably qualified structural engineer for compliance. So, ensure the engineer has the letters C.Eng. after his or her name. This means, they are a Chartered Engineer and, in this case, will be a member of The Institute of Structural Engineers (ISE) or Institution of Civil Engineers.  Building Control will usually accept either of these qualifications as suitable for compliance. 


Usually, structural engineers advertise their previous projects. Often, you’ll find them, either on their website or in a physical portfolio of photos, reviews and references.  Look through the list to find any similar to your project.  

Generally, some engineers specialise in commercial projects, while others specialise in domestic projects. If all you only want a lintel over a doorway, youll probably be overcharged by an engineer who normally works on large commercial projects like bridges or office blocks. Choose your engineer appropriately.

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Also, consider experience as another factor. Always, look for an engineer who has a long and consistent track record. An experienced engineer will always ask to inspect the site, before making any decisions. Whereas, an inexperienced engineer might just give you a price over the phone. Site visits are very useful and often show up a problem that changes the calculations from straightforward to complicated. So, an experienced engineer will make use of the visit to notice things that might not always be obvious to the layman. 

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Ask questions

Always ask a range of specific questions to set your mind at rest. 

  1. Find out how they calculate fees and whether there are any non-obvious extras. Usually, Structural Engineer fees vary depending on experience. So, make sure you know the fees, upfront. 
  2. Are site surveys included in the price as standard? Or, are they charged as an extra? 
  3. Are there any previous customers you can contact? You want to know if the engineer is easy to work with and whether everything went to plan. 
  4. How long has the engineer been working? And, if they’re selfemployed, how long have they worked on their own? 
  5. Is the engineer insured? The company should have Professional Indemnity insurance. This covers you and the engineer in case anything goes wrong as a result of mistakes on their part. Also, make sure you know the limit of cover. And, whether they’ve ever made a claim. 
  6. Where is the engineer based?  Ask this, so you can hire a local who won’t travel vast distances, and charge you for it.
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Can an RSJ Bend? 

Yes. RSJs bend slightly when accepting the load. This is called deflection and the engineer allows for it when calculating the RSJ dimensions.  But, it’s not anything to worry about, because the engineer designed the beam to carry bending loads in the vertical plane. And, any deflection won’t be large enough to cause cracking in the masonry or steel. 

Can RSJ be left exposed? 

No. Steel must be protected from fire and heat. If you don’t bother fireproofing an RSJ, it won’t comply with the Building Regulations and your household insurance will be invalid. To comply, it must be protected to at least half an hour fireproofing.  In practice, this means at least two layers of plasterboard must protect the steel, depending on the manufacturer’s specifications. 

Do I need a structural engineer to remove a wall? 

That depends on whether it’s a load-bearing wall or not. If it’s not load-bearing, then you can remove the wall without having any calculations or contacting Building Control. However, if it is load-bearing, you must notify Building Control and have a structural engineer’s calculations and report before removing any part of it. The report must specify the loads bearing on a proposed beam and the RSJ dimensions needed to replace the wall. 

How far should an RSJ overhang? 

An RSJ must overhang the opening by at least 150mm at each end. In practice, the overhang depends on the structural stability of the supporting wall. If the brickwork crumbles easily, the builder must cast an in-situ padstone of dense concrete to support the RSJ and might increase the overhang. 

Can you install an RSJ yourself? 

You could do it, but youll need the engineer’s calculations and you must be able to convince the Building Control Inspector that you know how to do the job. Although it’s possible, we don’t recommend that you do this project yourself.  

Do RSJs need Padstones? 

This depends on whether the load on the RSJ is more than that which will crumble the masonry. Even if the calculations say you don’t need to, it’s probably better to be safe than sorry, and cast concrete padstones for support, in case the masonry cracks in future. 

Should an RSJ be painted? 

An RSJ already comes painted with red primer to prevent rust. Usually, an RSJ won’t require any more decoration because it’s hidden behind fireproof plasterboard, to comply with the Building Regulations. However, if you want to make the beam a feature, you can paint it with ‘intumescent’ paint. This type of paint swells with heat and protects the steel for 90 minutes. Although useful if you want an exposed RSJ conversation piece in your home, the paint is very expensive at around £52 per 2.5L container. Additionally, you’ll need a primer at £26 per 2.5L and a special topcoat which costs £52 per 2.5L and comes in a variety of colours. You might wonder whether the cost of paint is worth it when you can use plasterboard costing about £10. 

How much wall does an RSJ need to sit on 

If you have a solid masonry wall, in good condition, you need at least 150mm of cast concrete to make a padstone at each end. Ask your structural engineer for advice. 

Find RSJ Installers Near You

Using an RSJ in place of a supporting wall is often the only way you can provide a solution. If you want to find out how much an RSJ costs to install, complete the form on this page and you’ll receive 2 to 3 quotes for your project.

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