Loft Conversion Steel Cost UK 2026: What Will the Steelwork Cost?
Loft conversion steel cost in the UK in 2026 typically runs from around £1,500 to £4,000 for the steel supply alone, with most standard terraced or semi-detached lofts needing two or more beams. Add structural engineer fees, delivery, installation and building control and the steelwork element usually lands between £3,000 and £6,000 all-in. This guide breaks down what you're paying for, what drives the price, and includes a calculator to estimate your steel supply cost.
How Much Does Loft Conversion Steel Cost?
There are two figures that matter. The steel supply — the beams themselves, cut to size — is what you buy from a stockholder like Rackerman, and for a typical loft that's roughly £1,500–£4,000 depending on the number and size of beams. The installed steelwork cost — supply plus engineer, delivery, lifting, fitting and building control — usually totals £3,000–£6,000 for a standard house. Bigger spans, more beams, or difficult access push it higher.
Steel Beam Prices (Supply Only)
Supply-only RSJ steel costs roughly £50–£120 per metre depending on the section size and finish, so a single 3–6m loft beam is usually £150–£600. A loft conversion commonly needs more than one beam — typically a pair of spine beams plus a ridge beam — which is why the supply total adds up. See our full RSJ cost guide for the per-beam detail.
Estimate Your Loft Steel Cost
Use the calculator below for an indicative steel supply figure plus a rough all-in band. It is a guide only — your exact beam sizes must come from a structural engineer.
Loft Steel Cost Estimator
What Drives the Cost?
Several factors decide where in the range you land. Number of beams: most lofts need a pair of main beams plus a ridge beam, sometimes more. Span: longer openings need bigger, heavier sections, which cost more per metre. Section size and weight: a heavier UB carries more load but costs more. Finish: mill is cheapest, red oxide adds a little, galvanising adds roughly 20%. Access: getting steel into a loft often needs craning or a telehandler, adding to labour.
The Other Costs Around the Steel
The beams are only part of the bill. Budget for a structural engineer (£395–£900) to calculate and specify the steel; delivery (£60–£120, more if a hiab offload is needed); lifting and access (£300–£600 where a crane or telehandler is required for beams over about 4m); installation labour to seat the beams on padstones and connect them; and building control fees (£200–£400). The beams must bear onto correctly sized padstones or spreader plates, which your engineer will specify.
What Size Steel Does a Loft Need?
It depends entirely on the span and the loads above. As a rough guide, loft spine beams are often in the 178–254mm deep UB range, with longer spans needing deeper, heavier sections. Never size loft steel from a guide — a structural engineer must calculate it for your roof, floor and any walls it carries. Our guide on what an RSJ is and our RSJ size guide explain the sections involved.
How to Keep the Cost Down
Get the engineer's design before you order so the steel is cut to size and right first time. Order all the beams together to save on delivery. Choose mill or red oxide finish unless galvanising is genuinely needed (it usually isn't for internal loft steel). And book delivery with offload assistance for heavy beams so you're not paying for a second attempt. Once the beam is in, our guide on how to box in a steel beam covers the fire-protection casing.
Buy Loft Conversion Steel at Rackerman
Rackerman supplies RSJ steel beams and columns cut to size in mill finish or red oxide primer, in S355J0 structural grade, with offload assistance available for heavy sections. Browse universal beams (UB) and universal columns (UC), and use our RSJ cost calculator for per-beam pricing.
Browse RSJ steel beams at Rackerman →
Frequently Asked Questions
How much does loft conversion steel cost?
The steel supply for a typical UK loft is roughly £1,500–£4,000, depending on the number and size of beams. Once you add engineer fees, delivery, lifting, installation and building control, the steelwork element usually totals £3,000–£6,000. Larger spans and difficult access cost more.
How much is a steel beam for a loft conversion?
A single loft beam costs around £150–£600 to supply, based on roughly £50–£120 per metre for a 3–6m beam. Most lofts need more than one beam — commonly a pair of spine beams plus a ridge beam — so the total supply cost is higher.
Why does a loft conversion need steel beams?
Steel beams carry the new floor and the roof loads once the existing structure is altered, spanning between the masonry walls. They replace or support the original timber roof structure and allow the loft to be used as a habitable room. A structural engineer designs them.
What size steel beam for a loft conversion?
It depends on the span and loads, but loft spine beams are often in the 178–254mm deep universal beam range, with longer spans needing deeper, heavier sections. The exact size must be calculated by a structural engineer for your specific roof and floor.
Do I need a structural engineer for loft steel?
Yes. Loft beams are load-bearing structural elements, so building regulations require a structural engineer's design and calculations. Their fee (typically £395–£900) covers specifying the beam sizes, grade and the padstones they bear onto.
Does loft steel need to be galvanised?
Usually not. Internal loft steel is normally supplied in mill finish or red oxide primer, then boxed in with plasterboard for fire protection. Galvanising adds around 20% and is reserved for steel exposed to damp or outdoor conditions.
How are heavy loft beams lifted into place?
Beams that are too heavy to carry are lifted with a crane, telehandler or hoist, which adds roughly £300–£600 to the job for spans over about 4m. Access is a big cost factor, so discuss it with your builder and arrange offload assistance on delivery.
Does a loft beam need building control approval?
Yes. Installing structural steel is notifiable work requiring building control approval, with fees typically £200–£400. The beam, its connections and the padstones it bears onto are inspected as part of the loft conversion sign-off.