RSJ Costs Explained: Supply Only vs Supply & Install
- southwesttradestee
- Jan 21
- 3 min read
If you’ve been told you need an RSJ (Rolled Steel Joist), the next question is almost always:
“How much is this going to cost?”
The answer depends on whether you’re looking for supply only or supply and install, and understanding the difference early can save time, money and frustration.
This guide explains typical RSJ costs, what affects the price, and which option suits your project best.
What Is an RSJ and Why Does Cost Vary?
An RSJ is a structural steel beam designed to support loads where walls or structural elements have been removed or altered.
RSJ costs vary because every project is different.
Price is influenced by:
Beam size and weight
Span length
Steel grade
Fabrication requirements
Delivery and access
Whether installation is included
There is no “one price fits all” — and that’s where confusion often starts.
Typical RSJ Costs in the UK (Guide Only)
As a rough guide:
Small RSJs (short spans, lighter loads):£200 – £500 + VAT (supply only)
Medium RSJs (open-plan knock-throughs, extensions):£500 – £1,200 + VAT (supply only)
Large or bespoke RSJs:£1,200 – £3,000+ + VAT (supply only)
Installation, temporary supports and associated works are additional.
These figures are indicative — structural engineer specifications always take priority.
Supply Only RSJs: What You Need to Know
Who supply-only is best for
Builders
Developers
Experienced contractors
Projects with labour already in place
What supply-only usually includes
Fabricated steel beam to engineer’s specification
Primed or painted finish (as specified)
Delivery to site
What supply-only does NOT include
Installation
Temporary propping
Padstones
Building Control coordination
Typical supply-only cost range
👉 £200 – £3,000+, depending on beam size and complexity.
Supply & Install RSJs: What’s Included
Supply & install is a turnkey option, commonly chosen by homeowners and developers who want peace of mind.
What supply & install typically includes
Supply of the RSJ
Temporary supports (acrow props, needles)
Safe installation
Padstones where required
Coordination with Building Control
Compliance with engineer’s details
Typical supply & install cost range
👉 £1,500 – £4,000+, depending on:
Beam size
Access
Number of steels
Site conditions
This option costs more upfront, but reduces risk and coordination issues.
Why Supply & Install Costs More (And Why That’s Normal)
The extra cost isn’t just labour.
It covers:
Temporary structural support
Skilled installation
Liability and insurance
Compliance with Building Regulations
Risk management if issues arise
Cutting corners here is one of the most common causes of delays and failed inspections.
Hidden RSJ Costs People Often Miss
This is where budgets can creep if not planned properly:
Structural engineer revisions
Padstones or additional bearings
Restricted access or manual handling
Multiple steels instead of one
Unexpected load changes
A clear scope from the start helps avoid surprises.
Do You Need Building Control for an RSJ?
In almost all cases, yes.
Building Control will typically require:
Structural calculations
Inspection during installation
Confirmation that the RSJ has been installed correctly
Skipping this step can cause serious issues later, especially when selling or refinancing a property.
Supply Only or Supply & Install: Which Should You Choose?
Choose supply-only if:
You’re a builder or contractor
You already have labour on site
You’re comfortable managing compliance
Choose supply & install if:
You’re a homeowner
You want a single point of responsibility
You want reduced risk and hassle
Both options are valid — the right choice depends on experience and project complexity.
RSJ Supply & Installation in the South West
For projects in Somerset, Devon, Dorset and the wider South West, reliable RSJ supply and clear lead times are essential to keep builds moving.
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