Do I need a structural engineer for a steel beam?

Yes. Building Regulations (Approved Document A) require that all structural alterations are designed by a competent person. A structural engineer will produce calculations and a specification drawing. Building Control will require these calculations before approving the work. This calculator provides an estimate only — never order steelwork based solely on this tool.

What is the most common steel beam for a domestic opening?

For a typical single-storey domestic opening of 2.4-3.6m span, a 152x89x16 UB or 203x102x23 UB is commonly used. For two-storey loads or longer spans, larger sections such as 254x146x31 UB or 305x127x37 UB may be needed. The actual size depends on span, loading, bearing conditions and building geometry.

What is a padstone and why do I need one?

A padstone is a concrete or engineering brick pad placed under each end of a steel beam to spread the load into the wall below. Without a padstone, the concentrated load from the beam end could crush the blockwork or brickwork. Padstones are typically dense concrete (min 40 N/mm²) or Class A engineering bricks bedded in 1:3 mortar.

How much does a steel beam cost in the UK?

Steel beams typically cost between £30-£60 per metre for common domestic sizes (up to 305 UB), plus delivery. Fabrication (end plates, fire protection) adds to the cost. Installation by a builder including temporary propping, padstones and making good typically costs £500-£2,000 depending on access and complexity.

What temporary support is needed when installing a steel beam?

For load-bearing walls, you must install temporary support (needles and Acrow props) before removing any masonry. Needles are typically placed at 900mm maximum centres, extending at least 600mm beyond each side of the opening. Props must bear onto spreader plates on a solid floor. Never remove a load-bearing wall without proper temporary works.

Steel Beam Calculator (RSJ) — Domestic Openings

How We Calculate This

This calculator estimates a suitable Universal Beam (UB) section for a domestic wall opening based on the span, load type and wall construction. It uses simplified loading assumptions derived from BS EN 1991-1-1 (Eurocode 1 — Actions on structures).

Loading assumptions

Timber floor: 0.5 kN/m² dead + 1.5 kN/m² imposed = 2.0 kN/m²
Concrete floor: 3.5 kN/m² dead + 1.5 kN/m² imposed = 5.0 kN/m²
Roof (tiles): 1.0 kN/m² dead + 0.6 kN/m² imposed = 1.6 kN/m²
Wall self-weight: ~4.0 kN/m per storey (cavity brick/block)
Tributary width: 4.0 m assumed floor span onto beam

Beam selection

The applied bending moment is calculated as M = wL²/8 for a simply supported beam under uniformly distributed load. A safety factor is applied, and the smallest suitable UB section from the standard range is selected.

Important disclaimer

This calculator is for estimation only. A qualified structural engineer must produce the final beam specification and calculations. Building Control approval is required before any structural work begins.

Frequently Asked Questions

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Last updated: March 2026

All calculations are estimates. Verify with your supplier.