The Short Answer
On our estimates, supplying and installing a steel beam (RSJ) in a house costs about £800 to £2,500 for a typical opening, including propping and padstones. On top, a structural engineer's calculations are £250 to £500 and building control £200 to £500. Most beams go in over one or two days.
The steel itself is the smaller part, about £3 to £5 per kg. Most of the cost is labour: propping the house above while the wall comes out. Making good (plaster, floor and decorating) is usually extra.
RSJ prices
| Item | Typical cost |
|---|---|
| Beam supplied and installed, with propping and padstones | £800 to £2,500 |
| Steel only, per metre | £60 to £390 |
| Steel only, per kg | £3 to £5 |
| Structural engineer: calculations | £250 to £500 |
| Building control | £200 to £500 |
| Making good: plaster, floor patch, decorating | £500 to £1,500 |
How the beam is specified
The Planning Portal sets out what building control will expect:
- the beam is designed to carry the loads the wall was carrying, on supports that take them down to the foundations;
- it normally has at least 150mm of bearing on each side of the opening;
- the wall under each end may need strengthening, often with a concrete padstone, to stop it crushing;
- a steel beam is normally fire protected to 30 minutes, most commonly with plasterboard;
- a new opening in an outside wall typically needs one or, more usually, two beams.
A structural engineer works out the size and type of beam and the padstones, which is why the calculations come first.
Building regulations, party walls and planning
Fitting a beam to replace a load-bearing wall is a structural alteration that needs building regulations approval. As an example, the Royal Borough of Windsor and Maidenhead's 2026 charge for structural work under £5,000 was £495 including VAT. You don't need planning permission for internal alterations, unless the house is listed.
Knocking through?
For the whole job, including removing the wall and the fire safety points, see cost to knock down a wall. For new openings in the back of the house for doors, see bifold doors.
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Frequently asked questions
How much does it cost to install an RSJ?
On our estimates, about £800 to £2,500 for a typical domestic beam supplied and installed, plus £250 to £500 for the engineer and £200 to £500 for building control, including VAT.
How much is a 3 metre RSJ?
For the steel alone, about £180 to £1,150 on our estimates, depending on the section the engineer specifies. Supplied and fitted, most domestic beams come to £800 to £2,500.
Do I need planning permission to install an RSJ?
Not for internal work on a house that isn't listed. You do need building regulations approval, and a party wall notice if the beam bears on a shared wall.
How much does a structural engineer charge for a beam?
About £250 to £500 for the calculations for a single domestic beam.
Do I need building regulations for an RSJ?
Yes, when it replaces a load-bearing wall: it's a structural alteration, so you need approval and an engineer's calculations.
How long does it take to fit an RSJ?
One or two days for most domestic beams, plus time for plastering and decorating.
How much is a 6m RSJ?
For the steel alone, roughly £360 to £2,350 on our estimates, or £240 to £1,550 for 4m; the section the engineer specifies decides where in that range it falls. A span that long is likely to come in at or above the top of our £800 to £2,500 fitted price for a typical domestic beam, plus the engineer (£250 to £500) and building control.
How we priced thisView sources (6, 6 official)
Rules come from the legislation and official guidance, read at source. Prices are our estimates: we check them against trade price data, retailer shelf prices and specialists' price lists, then build them up from their parts so the totals add up. Below are the sources behind the page; the trade price guides we only compare against aren’t listed. Where sources disagreed, we've said so. More on our method.
- OfficialInternal walls: building regulations, load bearing walls, Planning Portal. Checked 15 Oct 2026.
- OfficialBuilding regulations: structural opening, Planning Portal. Checked 15 Oct 2026.
- OfficialInternal walls: planning permission, Planning Portal. Checked 15 Oct 2026.
- OfficialWhat building regulations apply to internal walls?, Planning Portal. Checked 15 Oct 2026.
- OfficialBuilding control charges: domestic alterations 2026 to 2027, Royal Borough of Windsor and Maidenhead. Checked 15 Oct 2026.
- OfficialParty Wall etc. Act 1996, sections 2 and 3, legislation.gov.uk. Checked 15 Oct 2026.
