RSJ Cost: What Really Sets the Price of a Steel Beam

The beam is the smallest line on the quote

An RSJ (rolled steel joist) or universal beam is specified by depth, width and weight per metre. A short beam over a doorway-width opening is a modest piece of steel; a long beam across the back of a house, sometimes in two sections bolted together on site, is heavier and more involved to handle. Either way, the material is usually a fraction of the total.

What moves the number is the labour and sequencing needed to swap a wall for a beam without the house above ever being unsupported, and the work to make the opening look as though the wall was never there.

Span and load decide the size

The wider the opening and the more weight above it, the deeper and heavier the steel. A wall carrying only a floor is a different calculation from one carrying a floor, a wall above and part of the roof. A structural engineer works this out from the loads and the span, and also designs what the beam sits on at each end.

Engineer’s calculations are a cost in their own right, but they are not optional: building control requires them, and a future buyer’s surveyor will ask for them.

The cost factors, one by one

Each of these appears somewhere on a properly itemised quote:

• Structural engineer’s design and calculations
• Temporary support: needles, acrow props and the time to set them
• Forming the opening and removing the wall and rubble
• The steel, delivered, plus any bolted sections or plates
• Padstones or posts, and sometimes new foundations under a post
• Fire protection to the beam where regulations require it
• Building control fees and inspection
• Making good: plastering, ceiling line, skirtings, flooring and decoration

Bearings, padstones and posts

A beam is only as good as what holds it up. Each end sits on a padstone — a concrete or engineering-brick block that spreads the load into the wall below. Where the wall cannot take the load, or there is no wall at all, a steel post carries it down to a foundation. Digging a new pad foundation inside a house adds noticeably to a job, which is why it is checked at the survey rather than discovered halfway through.

Access and installation

Getting a long steel into a house is a practical puzzle. Through a front door and down a hallway is fine for some beams; others come in through a window opening, or are specified in sections that bolt together in place. Lifting a heavy beam onto its bearings needs enough hands or lifting gear, and that is priced in.

The order of work is always the same: props and needles take the load, the opening is formed, the beam goes in on its padstones and is packed tight, and only then do the props come out. Most single openings are formed in a few days, with drying and making good after.

Load bearing wall removal cost: the hidden extras

A few things change the scope of a load bearing wall removal more than the opening size. A chimney breast in the line of the wall needs its own support design. A party wall may need notice under the Party Wall Act before work starts. Services in the wall — radiator pipes, wiring, sometimes a soil pipe — need rerouting. Spotting these early is what keeps the final figure close to the quote.

Making good is where finish quality shows

Once the steel is in, the ceiling line needs boarding and skimming, the reveals plastering, the floor joining across the old wall line and both rooms decorating. Plastering and finishing are in-house trades at Mighty Oak, so the making good sits in the same quote as the structural work.