RSJ cost: what decides the price of a steel beam

The short answer

The steel itself is usually a modest part of the price. RSJ cost is mostly in the work around it: the engineer's design, temporary propping of the walls and floors above, cutting out the opening, building padstones or piers for the beam to sit on, Building Regulations sign-off and making good the walls, ceiling and floor afterwards. A short beam over a doorway is a small job; a long beam opening a kitchen into a rear extension is a much bigger one. We give a free estimate after a site visit.

Span and load

The longer the opening and the more the wall carries, the deeper and heavier the beam. A wall carrying floor joists only needs less steel than one carrying a floor, another wall and part of the roof. Very long openings may need two beams side by side, or a steel post partway along, which adds both material and labour. The beam size comes from a structural engineer's calculations, not from guesswork on site.

Structural engineer's calculations

Building control needs calculations showing the beam, its bearings and anything supporting it are adequate. The engineer checks the load path down to the foundations, sizes the steel and specifies the padstones. That design fee is part of every RSJ job and is worth paying for: it is what makes the work safe and approvable.

Temporary support and access

Before any wall is removed, the structure above is held up on adjustable props and needles through the wall. Getting a heavy steel beam into the house and lifted into position takes several people or lifting equipment, so access through the front door, hallway and around corners affects the time involved. Longer beams can sometimes be bolted together on site from shorter sections.

Padstones, piers and the ends of the beam

Each end of the beam sits on a padstone, a concrete or engineering-brick bearing that spreads the load into the wall below. Sometimes the existing wall is strong enough; sometimes a new brick pier or deeper foundation is needed under the bearing. This is bricklaying work, so it suits a builder who also lays bricks.

Load-bearing wall removal versus non-load-bearing

Removing a non-load-bearing stud wall is mostly demolition and making good, so it costs much less. Removing an internal load-bearing wall and replacing it with a beam adds the design, propping, steel, padstones, fire protection and building control inspection. Never assume a wall is not load-bearing without checking the floor and roof structure above.

Lintel replacement

A cracked or sagging lintel over a window or door is a smaller job than a full beam. The brickwork above is supported temporarily, the old lintel removed and a new steel or concrete lintel bedded in, then the brickwork made good to match. Lintels are often replaced when windows are enlarged or doorways widened.

Making good and Building Regulations

After the steel is in, it is boxed in and fire protected, the ceiling and walls are plastered, and floors where the wall used to stand are filled. Building control inspects the work and signs it off. These finishing stages are easy to leave out of a quote, so check they are included when comparing prices.

About us

D & A Brickwork & Building is a family-run firm based in Bidwell, Dunstable, with more than 26 years of building experience. We are FMB members and fully insured, and we give free estimates after a site visit.

Questions people ask