The 254×146×31 is one of the most commonly specified steel beams in UK domestic construction. It offers a practical balance between depth, weight, and load-carrying capacity, making it a go-to choice for loft conversions, kitchen diners, garage openings, and internal wall removals. But how far can it actually span? What loads can it safely carry? And how much will it cost you in 2026?
This guide provides accurate dimensions, a clear load capacity table, real-world design examples, and up-to-date pricing. If you are still unsure which size you need, our beam size calculator can help you narrow it down before you speak to a structural engineer.
What Is a 254×146×31 RSJ Beam?
Despite the popular name “RSJ” (Rolled Steel Joist), the 254×146×31 is technically a Universal Beam (UB) manufactured to BS EN 10365. The naming convention tells you exactly what you are getting:
- 254 — the overall depth of the beam in millimetres (254 mm).
- 146 — the width of the flange in millimetres (146 mm).
- 31 — the nominal self-weight in kilograms per metre (31.1 kg/m exactly).
Universal Beams have an “I” or “H” shaped cross-section with relatively wide flanges compared to older joist sections. This geometry gives them excellent resistance to bending in the vertical plane, which is why they are used horizontally to support floors, roofs, and masonry walls.
The 254×146×31 sits in the middle of the domestic range. It is deeper than the 203×133×25 often used for small openings, but lighter and more economical than the 305×165×40 required for heavy two-storey loads. If you are removing a load-bearing wall and the span is in the 3.5 m to 5.5 m range, your engineer will almost certainly consider this section.
254×146×31 Dimensions and Weight
Knowing the exact physical size is essential for two reasons: you must ensure there is enough vertical clearance for the beam to fit, and you need to know the total weight for handling, transport, and crane hire.
Section Properties
| Property | Value |
|---|---|
| Overall depth (D) | 251 mm (approx. 254 mm nominal) |
| Flange width (B) | 146 mm |
| Web thickness | 6.0 mm |
| Flange thickness | 10.9 mm |
| Self-weight | 31.1 kg/m |
| Second moment of area (Iy) | 4,410 cm⁴ |
| Elastic section modulus (Wel,y) | 351 cm³ |
Note: Exact rolled dimensions vary slightly between mills. Always allow a 5–10 mm tolerance when checking headroom.
For a full comparison of standard UK sections, see our complete RSJ size chart.
Total Weight by Length
Because steel is priced by weight and lifted by the tonne, the total mass matters on site.
| Length | Total Weight (kg) |
|---|---|
| 3.0 m | 93 kg |
| 3.5 m | 109 kg |
| 4.0 m | 124 kg |
| 4.5 m | 140 kg |
| 5.0 m | 156 kg |
| 5.5 m | 171 kg |
| 6.0 m | 187 kg |
At 156 kg, a 5 m beam is manageable for a small telehandler or a two-man team with a genie lift, provided access is good. Anything over 5 m usually requires a mini-crane or a hiab lorry for safe installation.
254×146×31 Load Capacity and Safe Span Table
Load capacity depends on more than just the beam size. The grade of steel (usually S275 or S355), the end connections, the deflection limit, and whether the load is uniformly distributed or concentrated all affect the final design. The table below gives indicative maximum uniformly distributed loads (UDL) for a simply supported 254×146×31 beam in S275 steel, assuming a standard residential deflection limit of span/360 and typical load factors.
These figures are a useful rule of thumb, but they are not a substitute for a structural calculation. For a beam-specific check, use our load capacity calculator.
Safe UDL Table (254×146×31 UB, S275, Simply Supported)
| Span | Maximum Indicative UDL |
|---|---|
| 2.5 m | 29 kN/m |
| 3.0 m | 23 kN/m |
| 3.5 m | 17 kN/m |
| 4.0 m | 13 kN/m |
| 4.5 m | 10 kN/m |
| 5.0 m | 8 kN/m |
| 5.5 m | 7 kN/m |
| 6.0 m | 6 kN/m |
What Do These Numbers Mean in Practice?
A kN/m is a kilonewton per metre. In rough domestic terms, 1 kN/m ≈ 100 kg per metre of beam. So a 5 m span carrying 8 kN/m is supporting the equivalent of roughly 800 kg on every metre of its length.
That sounds like a lot, but a typical concrete floor with finishes, furniture, and people can easily generate 6–9 kN/m once you factor in the safety margins required by the design codes. This is why the allowable load drops off sharply as the span increases. For openings longer than 5.5 m, your engineer will often specify a deeper 305 series beam or a heavier 254×146×37 section to keep deflection within acceptable limits.
Real-World Example: 5m Garage Opening Supporting a Concrete Floor
Let us look at a scenario we see on site almost every week.
The project: You want to open up a 5 m wide garage wall to create a double-width opening. Above the garage is a ground-floor kitchen/diner with a 150 mm concrete floor slab. The beam will support a 2.5 m wide strip of that floor (the “tributary width”).
The loads:
- Dead load (permanent weight of the floor, finishes, ceiling, and the beam itself): approximately 4.5 kN/m².
- Live load (people, furniture, appliances): approximately 1.5 kN/m².
With the standard 1.35 safety factor on dead load and 1.5 on live load, the design load on the beam becomes:
- UDL on the beam = (4.5 × 1.35 + 1.5 × 1.5) × 2.5 m tributary width
- Design UDL ≈ 20.8 kN/m
For a 5 m span, our table shows the 254×146×31 can carry roughly 8 kN/m under typical residential deflection limits. Even if we look only at bending strength, 20.8 kN/m over 5 m produces a bending moment of 65 kNm. The plastic moment capacity of a 254×146×31 in S275 is about 109 kNm, so it does not fail in bending. However, the long-term deflection of the concrete slab above the garage would be noticeable and could cause cracking in the plasterwork above.
The engineer’s decision: In this case, a 254×146×31 would be borderline. Most chartered engineers would upgrade to a 254×146×37 or a 305×102×28 to control deflection and provide a safety margin for any future alterations. This example shows why you cannot rely on bending strength alone; serviceability (deflection) often governs the design.
When Is 254×146×31 the Right Choice?
This beam size is an excellent, cost-effective solution for a wide range of typical domestic projects:
- Loft conversions where the new floor joists span onto steel beams. For guidance specific to loft projects, read our article on what size RSJ for loft conversion.
- Internal wall removals in bungalows or single-storey extensions where the span is 3.5 m to 5.0 m and the load is a timber floor plus light roof load.
- Wide doorways or patio openings in single-storey rear extensions.
- Supporting a first-floor timber floor where the load is modest and the span is under 4.5 m.
- Kitchen knock-throughs where a chimney breast or a narrow partition is being removed.
In all these cases, the 254 mm depth gives you enough strength without eating too much headroom, and the 146 mm flange width provides good lateral stability during installation.
When Should You Upgrade to 254×146×37 or 305×165×40?
There are three main reasons to specify a heavier or deeper beam:
- The span is over 5.5 m. Deflection increases with the cube of the span. At 6 m, a 254×146×31 will sag excessively under normal domestic loads.
- The load is heavy. Concrete floors, blockwork walls sitting directly on the beam, or two-storey loads all push the UDL well above the safe limits of the 31 kg/m section.
- You need a stiffer floor. Even if the beam is technically strong enough, excessive “bounciness” or vibration can be annoying. A deeper 305 mm beam is roughly twice as stiff as a 254 mm beam, giving a much more solid feel underfoot.
254×146×37 is the obvious upgrade if you want to keep the same 254 mm depth (for example, because of restricted headroom) but need roughly 20% more strength and stiffness.
305×165×40 is the standard step up when headroom allows and you are supporting a two-storey masonry load over a 4.5 m to 6.0 m opening.
254×146×31 Price and Supply in 2026
Steel prices fluctuate with global demand, energy costs, and transport surcharges. As of 2026, indicative pricing for a 254×146×31 RSJ supplied cut to length in the UK is as follows:
| Length | Indicative Price (2026) |
|---|---|
| 3.0 m | £320 – £420 |
| 4.0 m | £420 – £560 |
| 5.0 m | £520 – £700 |
| 6.0 m | £620 – £840 |
These prices assume S275 steel, standard cutting, and delivery within a 50-mile radius of the supplier. S355 steel, drilling, shot-blasting, or priming will add 10–20% to the cost.
For a more detailed cost breakdown including VAT and installation labour, use our RSJ beam cost calculator.
What Affects the Final Price?
- Raw steel market: Base steel prices have remained volatile since 2022. Mills typically adjust their list prices quarterly.
- Delivery distance: Beams over 6 m often require special transport and can incur £100–£200 delivery surcharges.
- Extras: Drilling for end plates, cambering, intumescent fire protection, and galvanising all add cost.
- VAT: Standard 20% VAT applies to the supply of steel in the UK.
Always request a firm quotation from a structural steel fabricator. Do not rely on “per metre” prices from general builders’ merchants, as they rarely include cutting, marking, or certification.
Installation and Handling Notes
A 5 m 254×146×31 weighs 156 kg. That is too heavy to manhandle through a house without mechanical assistance and too risky to lift above head height without proper lifting gear.
Safe Handling
- Mechanical aid: Use a mini-crane, telehandler, or a genie lift. Never attempt to lift a beam of this weight with ropes and manpower alone.
- Slings: Use certified webbing slings positioned to avoid crushing the web. Do not use chains directly on the edges of the flange without edge protectors.
- Access: Check door heights and corridor widths. A 254 mm deep beam on its side is only 146 mm high, but it is 5 m long. Turning corners in tight Victorian terraces can be impossible without a crane over the roof.
Structural Installation
- Bearing length: The beam must bear onto a minimum of 100 mm of masonry at each end, preferably 150 mm. This usually means 215 mm padstones or concrete bearings built into the wall.
- Level and plumb: The beam must be installed level and straight. A twisted beam induces torsion and can overload the connections.
- Lateral restraint: The top flange must be restrained by the floor structure above. If it is not (for example, in a long-span roof beam), lateral torsional buckling can reduce the capacity by 30% or more.
- Fire protection: If the beam is part of a fire-resistant structure (for example, supporting a separating floor), it may need 30 or 60 minutes of fire resistance. This is usually achieved with intumescent paint or fire-resistant board enclosures.
FAQs
Q: How far can a 254×146×31 span?
For typical domestic floor loads, a 254×146×31 can span up to 5.5 m as a general rule of thumb. At 6 m, deflection usually becomes the limiting factor, and most structural engineers will specify a deeper or heavier section. The exact safe span depends on the load, the steel grade, and the end support conditions.
Q: What is the total weight of a 5m 254×146×31?
A 5 metre length weighs 156 kg (31.1 kg/m × 5 m). Add roughly 5–10 kg for weld plates or end cleats if they are fitted by the fabricator.
Q: Is 254×146×31 enough for a loft conversion?
Often, yes. Loft conversions usually involve supporting a new timber floor and a light roof load over spans of 3.0 m to 4.5 m. The 254×146×31 is a very common specification for this type of work, provided the structural engineer has calculated the exact loads. See our dedicated guide on what size RSJ for loft conversion.
Q: Can a 254×146×31 support a two-storey load?
Only over relatively short spans (up to about 3.5 m). A two-storey masonry load generates a high UDL, and over a 4.5 m or 5 m opening, the beam would be overstressed. For two-storey loads, engineers usually specify a 305×165×40 or a 356×171×45 section.
Q: How much does a 254×146×31 cost in 2026?
As of 2026, expect to pay roughly £100–£140 per metre for the raw steel, cut to length, plus delivery and VAT. A typical 5 m beam therefore costs in the region of £520–£700 supplied. Installation, padstones, and fire protection are additional. Use our cost calculator for a full project estimate.
Important Disclaimer
The information in this article is provided for general guidance only. Steel beam selection is a critical structural engineering decision that affects the safety and stability of your building. You must appoint a chartered structural engineer or an approved engineer to calculate the correct beam size, load path, and connection details for your specific project.
All structural alterations in the UK require Building Regulations approval. Installing an incorrectly sized beam, omitting padstones, or failing to provide adequate fire protection can lead to structural failure, invalidate your insurance, and create serious legal liabilities. Always obtain the necessary calculations and approvals before ordering steel or commencing building work.
