RSJ Installation Calculator — Bearing, Padstone & Support

NHBC Standards clause 6.5.5 requires a minimum of 100mm bearing of the steel onto a padstone (each end of the beam resting on at least 100mm of solid support). 150mm is a widely used good-practice convention that gives extra tolerance for line and level. BS EN 1996 (Eurocode 6) does not set a fixed minimum bearing length — it governs the bearing-strength check, not the length. For heavily loaded beams or weaker masonry a longer bearing or a larger padstone may be needed, and the structural engineer's specification always governs.

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. One is needed when the bearing stress would exceed the allowable bearing capacity of the wall material. NHBC 6.5.5 requires a padstone with a minimum compressive strength of 10 N/mm²; a precast or cast-in-situ C30-C40 concrete padstone is typical, and for smaller padstones (under about 215 × 100mm) engineering bricks (Class A or B) are suitable. The padstone should project beyond the beam flange on each side.

Temporary support is needed during wall removal until the beam is installed and loaded. A common rule of thumb is roughly one prop per metre of opening width plus one near each end (minimum 3), positioned on scaffold boards or strongboys to spread the load — so a 3m opening typically needs about 4 props and a 5m opening about 6. This is practice guidance, not a code figure: the temporary-works arrangement should be checked by the structural engineer or temporary-works designer. Props must be placed on both sides of the wall being removed and left in until the beam is fully packed and loaded.

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.

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.