Steel Beam Calculator (RSJ) — Domestic Openings

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.

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.

Yes. As well as the bending-strength check, this calculator checks deflection (sag) under load and sizes the beam up if needed. The UK National Annex to BS EN 1993-1-1 (Table NA.2) limits deflection to span/360 under imposed load for beams carrying brittle finishes such as plaster, and span/250 under total load is a common overall serviceability limit. A beam can be strong enough in bending yet still sag too much, cracking ceilings and finishes — at longer domestic spans, deflection often governs the beam size rather than strength. The result shows which check governs. This remains an estimate; your structural engineer will confirm the final deflection limits for your project.

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. Use our Padstone Sizing Calculator to determine the correct size.

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.

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. See our Acrow Prop Spacing Calculator for prop requirements.