An RSJ installation is a structural alteration, not a building task you can not size by eye or leave to a builder’s best guess. It requires a chartered structural engineer to produce calculations and drawings, Building Control sign-off, and temporary propping before a single brick is touched. On-site steel work typically takes one to two days, but the full programme from engineer appointment to Completion Certificate runs three to six weeks. Budget realistically: a straightforward single opening commonly costs from several hundred to a few thousand pounds once supply, labour, temporary works, and padstones are included.
- Appoint a chartered structural engineer first — do not rely on a builder’s estimate of beam size.
- Notify Building Control before work starts, either by Building Notice or Full Plans submission.
- Allow three to six weeks for the full programme, including steel lead time of one to three weeks.
- Keep all records: engineer calculations and your Completion Certificate matter when you sell or insure the property.
Key takeaways
A competent RSJ installation requires a chartered structural engineer, Building Control approval, and a Completion Certificate — cutting corners on any of these creates legal and financial risk when you sell.
| Point | Details |
|---|---|
| Engineer before contractor | Appoint a chartered IStructE or ICE engineer first; never let a builder guess the beam size. |
| Budget for the full scope | Typical small-opening jobs run £1800–£3,000+; include temporary works, padstones, and a contingency. |
| Building Control is mandatory | Submit before work starts and keep your Completion Certificate — it matters at conveyancing. |
| Allow three to six weeks | Engineer calculations, steel lead time, and making good all add to the programme beyond the one to two days of steel work. |
| Complete-Property-Solutions | Manages engineer liaison, Building Control, and fixed-price structural work across Warrington, St Helens, Wigan, and the wider North West. |
Table of Contents
- How much does RSJ installation cost in the UK?
- What is the RSJ installation process, step by step?
- Who should you hire for steel beam work?
- Key technical details you need to understand
- Do you need planning permission or Building Regulations approval?
- Common complications that increase cost and risk
- How to estimate costs and what to ask for in a quote
- How long does RSJ installation take?
- Complete-Property-Solutions’ approach to structural work in the North West
- What the conventional advice on RSJ work gets wrong
- Planning a structural alteration? We can help
- Sources
How much does RSJ installation cost in the UK?
Steel beam costs break down into several distinct line items, and understanding each one helps you read a quote clearly.
Material and fabrication depend on beam weight (measured in kg per metre), steel grade, and overall length. Suppliers price structural steel by the kilogram, so a heavier universal beam for a wider span costs noticeably more than a lighter section for a short opening. Published cost guides note that total job costs for residential RSJ work range from around £2,00 for a basic small opening to £5,000 or more for larger spans once labour and temporary works are included.
Labour and temporary works cover the Acrow props and strongboys needed to support the structure while the opening is formed, any lifting equipment or hoist required, and the skilled time to bed and level the beam. Access matters: a tight terraced house in Wigan or a rear extension in St Helens with no side access can add cost quickly if a crane or specialist lifting rig is needed.
Padstones and masonry making good are often underestimated. Concrete padstones, plastering, and reinstating finishes around the new beam add both material and labour costs that should appear as separate line items on any honest quote.
| Item | Indicative range |
|---|---|
| Steel supply (small beam, 3–4 m) | £250 |
| Fabrication and delivery | £250 |
| Temporary propping and labour | £500 |
| Padstones and masonry making good | £1000 |
| Typical small job total | Approx, £2,000 or more |
Structural steel beam installation to form a wider rear opening ready for new bi-folding doors.
Larger spans, difficult access, or hidden complications push totals higher.
What is the RSJ installation process, step by step?
- Structural survey and calculations. A chartered structural engineer visits the site, assesses the load path, and produces drawings and calculations specifying the exact beam size, grade, bearing lengths, and padstone requirements. These documents go to Building Control.
- Building Control notification. Submit a Building Notice or Full Plans application before work begins. The inspector will visit at key stages: before the opening is formed, when the beam is in, and at final completion.
- Temporary propping. Acrow props and strongboys are installed on both sides of the wall to carry the load above. Props are tested under load before any cutting begins — a step that professional teams consistently emphasise as the most critical safety stage.
- Padstone preparation and beam lift. Padstones are cast or bedded into the masonry at each end of the opening to the engineer’s specification. The RSJ is then lifted into position, seated on the padstones, and checked for level.
- Curing, prop removal, fire protection, and making good. Padstone concrete typically requires 24–72 hours to cure before props are removed. Once the engineer or Building Control inspector confirms the installation, fire protection is applied — usually intumescent paint or two layers of 15 mm fire-rated board — and the opening is plastered and finished.
Who should you hire for steel beam work?
The two non-negotiable appointments are a chartered structural engineer and an experienced main contractor.
Structural engineer: look for membership of the Institution of Structural Engineers (IStructE) or the Institution of Civil Engineers (ICE), and confirm they hold professional indemnity insurance. Their calculations are the legal and technical foundation of the whole project.
Pro Tip: Ask your engineer for their IStructE or ICE membership number and verify it on the relevant institution’s online register before signing anything.
Main contractor: check that your builder has demonstrable experience with RSJ and structural steel work, holds public liability insurance of at least £2 million, and can provide references from comparable jobs. Ask specifically who will manage Building Control liaison and who arranges the propping.
Steel supplier: request mill certificates confirming BS EN 10025 conformity for the grade specified. Delivery lead times of one to three weeks are typical; confirm this before fixing your programme. For broader context on why steel is used in modern domestic construction, the structural properties that make it reliable are well established.
Key technical details you need to understand
Bearing length and padstones. A qualified engineer or surveyor should confirm whether a wall is load-bearing and specify the required bearing. Beams normally need a minimum bearing of at least 150 mm at each end. Padstones spread the concentrated load into the surrounding masonry; without them, the masonry beneath the beam end can crush over time.
Steel grade. Structural beams are specified as either S275 or S355 to BS EN 10025. S355 offers higher yield strength and is often specified for longer spans or heavier loads. Your engineer’s calculations will state which grade is required — never substitute one for the other without written approval.
Pro Tip: Always request the mill certificate from your steel supplier before the beam is delivered. It confirms the grade and traceability of the steel, and Building Control may ask to see it.
Fire protection. In domestic properties, a 30-minute fire rating is the standard expectation. Intumescent paint applied to the correct thickness achieves this for exposed beams; alternatively, two layers of 15 mm fire-rated plasterboard encasing the beam meets the same standard.
Do you need planning permission or Building Regulations approval?
Most RSJ installations fall under Building Regulations, not planning permission. Planning permission relates to changes in the external appearance or use of a building. Removing an internal load-bearing wall and installing a steel beam is structural work, so Building Regulations apply regardless of whether planning permission is needed.
Your Completion Certificate is the document that proves the work was inspected and approved. Without it, you may face difficulties when selling the property or making an insurance claim. Keep your engineer’s calculations and all Building Control correspondence alongside it.
You can submit either a Building Notice (simpler, faster, but the inspector has more discretion on site) or a Full Plans application (calculations and drawings reviewed before work starts, giving greater certainty). For most RSJ projects, Full Plans is the safer route.
Common complications that increase cost and risk
- Hidden services: pipes, drainage runs, and electrical cables inside or immediately above a wall are discovered only when the wall is opened. Rerouting them adds cost and time.
- Uneven or sloping floors: these can affect how props are set up and may require packing or levelling before the beam can be bedded correctly.
- Existing steels or previous alterations: a wall that has already been partially altered, or that conceals an earlier beam, may need additional structural assessment before the new RSJ can be specified.
- Undersized beams or insufficient bearing: using a beam that is too light, or seating it on too short a bearing, risks cracking above the opening, movement in the structure, and potential insurance or conveyancing complications.
- Missing Completion Certificates: undocumented structural work is one of the most common issues flagged during conveyancing. Buyers’ solicitors routinely request evidence of Building Control approval for any structural alteration.
How to estimate costs and what to ask for in a quote
A reliable quote breaks costs into clear line items. When tendering the work, ask each contractor to price the following separately:
| Line item | What to confirm |
|---|---|
| Steel supply (grade, weight, length) | Mill certificate and BS EN 10025 conformity |
| Fabrication and cutting | Included or separate charge |
| Delivery to site | Access requirements and offloading method |
| Temporary propping (supply and removal) | Who supplies props, how long they remain |
| Padstones (supply and installation) | Concrete grade specified by engineer |
| Labour (installation and making good) | Day rate or fixed price |
| Building Control liaison | Who submits, who attends inspections |
Ask directly: “Who arranges the structural engineer, and is that cost included?” A quote that bundles everything without itemising is harder to compare and easier to dispute later.
How long does RSJ installation take?
The on-site steel work itself is fast — typically one to two days for lifting, bedding, and initial checks. The wider programme takes longer:
- Engineer calculations: one to two weeks from appointment.
- Steel fabrication and delivery: one to three weeks, depending on the supplier and section size.
- On-site structural work: one to two days.
- Making good, plastering, and decoration: several days to a week.
- Overall programme: three to six weeks from engineer appointment to a finished, inspected result.
For homeowners in Warrington, St Helens, or Wigan, plan for dust and noise on installation day. Prop up internal doors to contain dust, arrange for children or vulnerable residents to be elsewhere during the cutting and lifting stage, and confirm with your contractor how waste masonry will be removed from the site.
Complete-Property-Solutions’ approach to structural work in the North West
Complete-Property-Solutions is a family-run building company with more than 35 years of experience delivering structural alterations, house extensions, and full home renovations across Warrington, St Helens, Wigan, Rainhill, Great Sankey, Penketh, Culcheth, Lowton, and Haydock. The company is a member of the Guild of Master Craftsmen and manages every project from initial design through to final Building Control sign-off, including engineer liaison, temporary works, and Completion Certificate.
Fixed-price quotations, clear communication, and professional project management are at the heart of how we work. If you are planning a structural alteration or an extension that involves RSJ work, we can arrange an engineer-led site survey and provide a transparent, itemised quote.
What the conventional advice on RSJ work gets wrong
Most online guides focus on cost and process, which is useful. What they underplay is the sequence risk: the single most common mistake homeowners make is appointing a contractor before appointing an engineer. The contractor then guesses the beam size, or uses a section they have left over from another job, and the whole project proceeds without proper calculations. Building Control may not catch this until the final inspection — or it may surface years later during a sale.
The second underplayed issue is the Completion Certificate. Homeowners routinely treat it as paperwork. It is not. It is the only document that proves the structural alteration was designed, installed, and inspected to the required standard. Without it, a buyer’s solicitor will either require an indemnity policy or pull out of the purchase entirely.
Get the engineer first. Get the Completion Certificate at the end. Everything in between is manageable.
Planning a structural alteration? We can help
Complete-Property-Solutions handles the full scope of RSJ and structural alteration work across the North West, from engineer coordination and Building Control submission through to plastering, fire protection, and final sign-off. Whether you are opening up a kitchen in Warrington, creating an open-plan living space in St Helens, or extending into a garage in Wigan, we provide a fixed-price quote and manage every stage on your behalf.
Our house extensions service includes all structural steelwork, and we handle Building Control liaison and Completion Certificates as standard. Get in touch to arrange a site survey and engineer-led quote — no obligation, just honest advice from a team that has been doing this for over 35 years.
Sources
The resources below are the primary references for RSJ installation guidance, Building Regulations, and structural standards in England and Wales.
