RSJ stands for Rolled Steel Joist, a steel beam used to support the structure above an opening once a load-bearing wall has been removed or altered. Although modern sections are technically Universal Beams (UB), the term RSJ is still used generally in the UK to describe any structural steel beam fitted across a knocked-through wall or enlarged doorway.

Total cost depends on the beam size, span length, number of beams, labour, and any professional fees involved. Costs vary widely between a small single-storey opening with minimal finishing and a longer span needing two beams or service alterations. Use the calculator above with your own measurements and supplier quotes for an estimate specific to your project.

Beam size depends on the span, the load it carries (including floors and roof above), and the building’s construction. As a very rough guide, beam depth is often around one-twentieth of the span, but this varies significantly with loading conditions. The exact size must always be confirmed by a qualified structural engineer through proper calculations before any work begins.

Yes. A structural engineer calculates the correct beam size, the bearing required at each end, and any additional support needed, then produces calculations that your builder follows and that building control will check. Skipping this step risks an unsafe structure and will almost certainly fail building control sign-off.

Yes, removing or altering a load-bearing wall is structural work and requires building regulations approval in the UK, regardless of whether the wall is also a party wall. An inspector will usually check the work at key stages and issue a completion certificate once satisfied.

Padstones are dense concrete or stone pads placed under each end of the beam to spread its load safely into the supporting wall or pier below. They are required whenever the existing masonry is not strong enough to bear the point load from the beam ends on its own, which a structural engineer will specify.

A straightforward single-storey installation typically takes one to three days, covering temporary propping, removing the old wall section, lifting the beam into place, building padstones or piers, and making good. Larger spans, two-storey openings, or jobs involving service alterations usually take longer.

RSJ is the older, traditional name for a structural steel beam, while UB (Universal Beam) is the modern manufacturing standard most beams are now made to. In everyday conversation and quotes, the terms are used interchangeably to describe the same type of steel beam fitted across a structural opening.