If you're opening up a kitchen, removing a wall between rooms, or adding an extension, there's a good chance you'll need a structural steel beam — commonly called an RSJ (rolled steel joist). Here's what every homeowner should know.
Why Would You Need a Steel Beam?
Any time you remove a load-bearing wall, the weight it was supporting needs to be carried by something else — and that's usually a steel beam. The beam sits in the gap where the wall was, supported at each end by padstones or posts that transfer the load down to the foundations.
The Process: Step by Step
- Structural engineer's calculation — before any work starts, a structural engineer calculates the beam size, bearing requirements, and support details. This is essential — you can't guess beam sizes.
- Building control approval — the calculation is submitted to building control for sign-off
- Installation — the beam is lifted into place (often requiring multiple people or lifting equipment), supported with Acrow props while the wall is removed, then fixed and fire-boarded
- Building control inspection — an officer inspects the installation before it's covered up
- Completion certificate — issued once all work is signed off
What Affects the Cost?
- Beam size and length — longer spans need larger, heavier, more expensive beams
- Number of beams — some jobs need more than one
- Access — getting a heavy steel beam into a house can require temporary scaffolding or even removing a window
- Fire protection — steel beams must be fire-boarded (usually with plasterboard) to meet building regulations
- Structural engineer's fee — typically £300–£800 for a residential calculation
Typical Costs
| Job | Typical Cost (incl. labour & materials) |
|---|---|
| Single RSJ installation (up to 4m) | £1,500–£3,500 |
| Single RSJ installation (4–6m) | £2,500–£5,000 |
| Structural engineer's calculation | £300–£800 |
| Fire boarding | £200–£500 |
Always Use a Qualified Professional
Installing a steel beam is not a DIY job. It involves structural calculations, building control, and physically dangerous lifting work. Always use a qualified builder working with a structural engineer — and never let anyone install a beam without a proper calculation.