Supply and fit of structural steel beams (RSJs) to engineer's calculations
Steel Beam Installation (RSJ)
Steel installation is the supply and fitting of a structural steel beam, commonly called an RSJ, sized by a structural engineer to carry the load of a wall, floor or roof once an opening has been formed beneath it.
Definition
What Steel Installation covers
A steel beam (RSJ, or 'rolled steel joist') transfers the load previously carried by a removed wall down to padstones or new supporting walls either side of an opening. The size and type of beam is determined by a structural engineer's calculations based on the span and load involved, and installation typically forms part of a wider knock-through or structural alteration project.
Suitable for
- Openings formed by removing a load-bearing internal wall
- Supporting a chimney breast that has been removed at a lower level
- Widening an opening between two rooms
- Loft conversions and other projects needing additional floor or roof support
Not suitable for
- Situations without an engineer's structural design, as beam size and bearing cannot be assumed
- Spans or loads beyond what a single steel solution can support without wider structural redesign
Process
How the work is carried out
- 01
Engineer's calculations
A structural engineer specifies the beam size, type and bearing requirements based on the span and load.
- 02
Temporary support
Propping the structure above the opening before any existing wall is removed.
- 03
Padstones and installation
Forming padstones to spread the load, then lifting and fixing the steel in position.
- 04
Inspection and making good
A Building Control inspection of the installed steel, followed by making good the surrounding wall, floor and ceiling.
Typical timescale
Installing a single steel beam typically takes one to three days on site, excluding making good, depending on the beam's weight and access into the property.
Cost guidance
Steel installation typically costs £1,200–£4,000 per beam in our area, including supply and fitting to the engineer's calculations, with span and load being the main factors. We provide an itemised quotation once the structural design is confirmed.
Limitations and exclusions
- Engineer's structural calculations are a required part of the work and are provided by a qualified structural engineer, not written in-house
- Beam access into the property (through doorways, stairwells or via crane) affects programme and cost and is assessed at survey
- Making good the wall, floor and ceiling around the new steel is typically part of the wider structural alteration works rather than the steel installation alone
Areas we cover
Steel Installation across Sussex, Surrey, Kent and South London
Local property styles, planning authorities and neighbourhood coverage for steel installation in each town we work in.
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FAQs
Steel Installation FAQs
How is a steel beam sized for my opening?
A structural engineer calculates the required beam size and type based on the span of the opening and the load it needs to carry — including the floor or roof structure above and any additional loads such as water tanks. This is confirmed before ordering the steel.
Can a steel beam be installed without removing the whole wall?
Often yes — a beam can be installed to widen an existing opening or doorway rather than removing an entire wall, with the remaining sections of wall providing the bearing for the steel.
Does Building Control need to see the steel before it's covered up?
Yes. An inspection at the point the steel is installed, before plastering or boarding covers it, is a standard part of Building Regulations sign-off for structural work.
Discuss your steel installation project
Tell us about the property and what you have in mind, and we'll arrange a site visit.
Last reviewed 2026-07-28.