RSJ Installation Costs UK — What to Charge to Fit a Steel Beam in 2026

What an RSJ Installation Actually Costs in 2026

When a customer asks "how much to put a steel beam in?" they're usually picturing the cost of the steel. In reality the beam is often the smallest line on the job. A typical single-beam knock-through for a standard internal load-bearing wall — steel, engineer, labour and making good, but not finishes — lands somewhere around £2,000–£5,000 all-in. Break that down and you can see where the money goes.

• The steel beam (RSJ / UB) itself: £200–£600 depending on span and section size
• Structural engineer's calculations and beam spec: £300–£750
• Building Control (building notice or full plans): a few hundred pounds
• Labour to install a single beam: £1,500–£3,500

Larger openings change the picture sharply. Double beams, heavy padstones, extensive temporary propping, needling through an external wall, and steel for a rear extension opening can push a job to £5,000–£10,000+. The variance between a tidy internal knock-through and a full-width rear opening is enormous, which is exactly why you should never quote a steel beam job off a phone description.

What Affects the Price

Two beam jobs that look identical from the kitchen door can differ by thousands once you understand the loads involved. These are the factors that move your number.

Span and Section Size of the Beam

The longer the opening and the more load above it, the deeper and heavier the steel needs to be. A 3m opening under a single floor might take a modest 152x89 UB; a 5m opening carrying a floor and a roof above could need a 254x146 or larger. Heavier steel costs more per metre, is harder to manoeuvre into position, and often needs three or four people rather than two — all of which feeds into both your material and labour lines.

Single vs Double Beam

Wide openings or heavy loads frequently call for two beams bolted together (a flitched or twinned beam) rather than a single section. That doubles the steel cost, adds the bolting and packing labour, and increases the weight you're lifting into place. A double-beam opening is a meaningfully bigger job than a single and should be priced as such.

Padstones and Bearing

A steel beam can't simply sit on brickwork — it needs an adequate bearing onto a concrete padstone or spreader that distributes the point load into the wall below. The engineer specifies the padstone size and the minimum bearing length (commonly 150mm each end). Cutting pockets, casting or fitting padstones and ensuring level bearing all take time, and getting it wrong is a structural failure waiting to happen.

Temporary Propping and Needling

Before any masonry comes out, the load above has to be supported. For an internal wall that usually means Acrow props and Strongboys; for an external wall or a heavier load it means needling — passing steel or timber needles through the wall above the opening and propping each end. Propping is the single biggest safety element of the job and is covered in more detail below under temporary works.

Access

Getting a 5m length of heavy steel into a back room through a Victorian terrace with a tight hallway is a different proposition from carrying it through wide bifold doors. Restricted access can mean craning steel over a roof, splicing beams on site, or simply a much slower, more labour-heavy lift. Survey the route the steel will physically travel before you price.

Which Floor and Whether It's Load-Bearing

A beam on the ground floor carrying the full weight of the structure above is a heavier spec than one removing a non-structural stud — though if a wall is genuinely non-load-bearing you may not need a beam at all. Working at first floor or in a loft adds platform and lifting complexity. Always confirm what the wall is actually carrying before committing to a price; assume load-bearing until the engineer says otherwise.

Making Good and Plastering

Once the steel is in and the props are out, you're left with a chased ceiling, broken plaster, exposed beam ends and a floor to reinstate. Boxing in or fire-protecting the steel, re-plastering, making good the ceiling line and tidying the floor junction is real work that customers forget about. Be explicit about whether your quote includes making good and where finishes (skirting, decoration, flooring) start and stop.

The Legal Bits: Engineer's Calcs and Building Control

Removing or altering a load-bearing element is notifiable structural work. You cannot legally just put a beam in and hope. Two things are non-negotiable on virtually every RSJ job.

A structural engineer's calculations. A qualified structural engineer must calculate the loads, specify the beam section, the bearing, the padstones and the connection details. This typically costs £300–£750 and produces a stamped calculation package and often a sketch. Building Control will want to see these calcs. Never substitute your own judgement for an engineer's spec on a structural beam — if it deflects or fails, the liability is yours.

Building Control sign-off. The work must be notified to Building Control, either via a building notice or full plans application, with fees usually running to a few hundred pounds. An inspector visits at key stages — typically to see the opening propped and the bearings before the beam is hidden, and again at completion. The customer ends up with a completion certificate, which is essential when they come to sell or remortgage. Make clear in your quote who is arranging and paying for the engineer and the Building Control application; these are commonly handled by the customer or passed through at cost.

Temporary Works and Propping Safety

The most dangerous moment on a beam job is the window between cutting the opening and the new steel taking load. During that window the structure above is held up entirely by your temporary works — Acrow props, Strongboys, needles and sole plates. Get this wrong and you risk a partial collapse with people underneath.

On anything beyond a small internal opening, temporary works should be designed, not improvised. The number, position and capacity of props, the size of the needles, and the sole plates spreading the load onto the floor below all matter. For larger or external openings a temporary works designer or the structural engineer should specify the propping arrangement. Key principles to price and plan around:

• Prop both sides of the wall, not just one, so the floor or roof above is fully caught
• Use adequate sole plates and head plates to spread load — props punching through a floor is a real failure mode
• Check what's below — propping on a suspended floor or over a basement may need its own support
• Don't remove props until the beam is fully bedded, padstones are set and the bearing has gone off
• Keep the area clear and never work alone under a propped opening

Propping is also a cost line. Acrow props, Strongboys and adjustable steels are either hired or tie up your own kit for the duration of the job. Build hire and the labour of erecting and striking the props into your price — it's often underestimated. For a fuller treatment of designing and pricing temporary support, see the related concept of temporary works and propping, which applies to underpinning, lintel replacement and chimney breast removal just as much as it does to beam installation.

Day Rate vs Fixed-Price Quoting

There are two ways to price a beam job, and choosing the wrong one is how builders lose money on steels.

Fixed price is what most customers want and what wins most jobs. It gives them certainty and lets them compare quotes. The risk sits with you: if the opening hides a surprise — a buried lintel, a second skin, a chimney flue running through the wall, rotten joist ends at the bearing — you absorb the extra unless your quote carves it out. Fixed-price beam work only makes sense once you've surveyed properly and the engineer's spec is in hand. Always include clear exclusions and a provision for unforeseen structural conditions.

Day rate shifts the risk to the customer and suits jobs with genuine unknowns — older properties, openings where you can't see what's above, or work that's part of a larger renovation. A typical small gang day rate plus materials at cost keeps you whole if the job runs long, but customers are warier of open-ended pricing and you'll need to set a sensible expectation of duration. Many builders run a hybrid: a fixed price for the defined steel installation, with a clearly stated day rate for any additional structural work uncovered once the wall is open.

Quoting Tips — What to Check Before You Price

Steel beam quotes go wrong when the builder prices off a doorway and a description rather than a survey and an engineer's spec. Before you commit a number, check the following:

• Get the engineer's calcs first where you can. The section size and bearing detail dictate the steel cost, the lifting effort and the padstone work. Pricing before you know the spec is guessing.
• Confirm what the wall carries. A floor only, a floor and roof, or a wall above changes everything. Look in the loft and at the floor direction above.
• Plan the propping. Work out how many props, where, and what's underneath. Price the hire and the time.
• Survey the access route. Walk the steel in your head from the road to the wall. Tight access can add a day or a crane.
• Separate the steel, engineer, Building Control, install and making good as distinct lines so the customer sees the value and you don't bury costs.
• State exclusions clearly. Decoration, flooring, electrical or plumbing diversions, and unforeseen structural conditions should be named, not assumed.
• Allow for muck-away. Removing a wall generates a surprising volume of rubble. Skip hire and labour to clear it is a real cost.

A quote that breaks the job into clear elements, names who's arranging the engineer and Building Control, and spells out exclusions will win more often than a single lump-sum figure — and it protects you when the wall comes down and reveals a surprise.

Quick Reference: RSJ / Steel Beam Costs UK 2026

Figures are typical UK ranges for 2026 and exclude finishes (decoration, flooring) unless stated. Always price from the engineer's spec and your own survey.