Guide
How much does an RSJ cost? Steel, calcs and fitting (2026)
Updated
The steel is the cheap part. Here is the whole RSJ job priced line by line, at typical 2026 quotes, and where not to economise.
The four lines on an RSJ job
| Line | Typical 2026 cost |
|---|---|
| Steel beam supplied (small domestic sections) | £150–£300 |
| Structural engineer's calcs | £250–£500 |
| Builder installation: props, padstones, fitting, making good | £1,000–£2,000 |
| Building control application (set by each council, no national scale) | £200–£400 on the 2026 council scales we checked |
| Typical all-in total | £1,600–£3,200 |
What moves the price
- Beam size and weight: a 3 m beam in the light UC range sits at the bottom of the supplied band; long or heavy UBs cost more to buy and much more to handle, sometimes needing lifting kit.
- Access: a beam walked through a front door prices differently from one craned over a roof.
- Temporary works: propping two floors while a wall comes out is real labour, and it is where cheap quotes cut corners.
- Making good: plastering, flooring and decorating around the new steel often costs as much as fitting it.
Where not to save
The calcs and the sign-off. Skipping the engineer to use a span table or a free online calculator saves a few hundred pounds and costs it back with interest: building control has to be satisfied the beam meets Part A and in practice will not take a bare span table for it, an oversized 'safe guess' beam wastes steel and headroom, and a missing completion certificate resurfaces at sale, when the buyer's conveyancer asks for it and the fix is a retrospective regularisation application with opening-up works. All figures here are typical 2026 quotes, they vary by region and job, so treat them as a sanity check on real quotes.
Start with the checker for the indicative range, then get an engineer to run the real numbers, that is the order that keeps the total at the bottom of the band.