What is the minimum bearing length for a steel beam?

The minimum bearing length for a steel beam on masonry is 150mm per BS EN 1996. This means the beam must sit at least 150mm onto the wall at each end. For heavily loaded beams or weaker masonry, a longer bearing or a padstone may be needed to spread the load. The structural engineer's specification should always be followed.

What is a padstone and when do I need one?

A padstone is a concrete or engineering brick bearing pad placed under a steel beam to spread the concentrated end reaction over a larger area of masonry. Padstones are needed when the bearing stress exceeds the allowable for the wall material. Typically C40 concrete, 215mm deep, precast or cast in-situ. Engineering bricks (Class A or B) can also be used.

How many temporary supports (Acrow props) do I need?

Temporary support is needed during wall removal until the beam is installed and loaded. Typically: one prop per metre of opening width, positioned on scaffold boards to spread the load. For spans up to 3m, 3-4 props; 3-5m, 4-6 props. Props must be positioned on both sides of the wall being removed and left in place until the beam is fully packed and loaded.

How do I level and pack a steel beam?

Steel beams are levelled using steel packing plates (not timber, which can crush). Place the beam on the padstone, check level in both directions, and insert 3mm or 6mm thick steel plates to achieve level. The void between the beam and padstone is then dry-packed with a 1:3 cement:sand mortar. Never use expanding foam — it is not structural.

Do I need Building Regulations approval for an RSJ installation?

Yes, any structural alteration (removing a wall and installing a beam) requires Building Regulations approval. You need: (1) a structural engineer's calculation and beam specification, (2) a Building Notice or Full Plans application to your local authority, (3) the work inspected by Building Control at key stages. A completion certificate is issued when satisfactory.

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RSJ Installation Calculator — Bearing, Padstone & Support

Plan your RSJ/steel beam installation: calculate bearing lengths, padstone sizes, temporary support requirements, and bearing stress checks for common wall types.

Clear Beam Span

Opening width between supports

Total UDL on Beam

From your structural engineer's calculation

Wall Type at BearingsDetermines allowable bearing pressure

Beam Weight

From beam specification (last number in UB designation)

How We Calculate This

This calculator helps plan the installation of a steel beam (RSJ) into an existing structure, calculating bearing requirements and padstone sizing.

Key calculations

End reaction: R = wL/2 (half the total load for simply supported beam)
Bearing stress: Reaction ÷ bearing area (must not exceed wall capacity)
Padstone area: Reaction ÷ allowable bearing stress of masonry
Total beam length: Clear span + 2 × bearing length

Frequently Asked Questions

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Last updated: March 2026

All calculations are estimates. Verify with your supplier.