By GoTaskhub Editorial Team · 13 min read · Updated March 2026
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Grounded in standard domestic opening: 203x133 Universal Beam, 2x precast concrete padstones, temporary acrow prop and Strongboy needle hire, structural calculations, local authority Building Notice, 3–4 days 2-person builder crew labour, and licensed rubble skip disposal.
Learn how to price structural steelwork accurately, account for genie-lift hire, cover heavy masonry skip weight limits, pass Building Control inspections first time, and protect your commercial profit margin.
Understand what is involved in creating an open-plan kitchen-diner, why structural engineer calculations are legally required, and why a builder cannot cut corners on propping and fireproofing.
RSJ Knock-Through Costs by Opening Width
As structural openings widen, steel beam weight increases exponentially, requiring heavier crane or lifter equipment and larger load-spreading concrete padstones:
| Opening Width | Steel Specification | Total Benchmark (Ex. VAT) | Duration |
|---|---|---|---|
| 2.0 Metres (Standard Double Doorway) | 152x89 Universal Beam (Manual lift) | £1,650 – £2,400 | 2 – 3 days |
| 3.0 Metres (Kitchen-Diner Opening) | 203x133 Universal Beam (~75kg) | £2,200 – £3,500 | 3 – 4 days |
| 4.5 Metres (Full Width Rear Wall) | 254x146 UB or Twinned Flange Steels | £3,400 – £5,200 | 4 – 6 days |
| 6.0 Metres (Large Open Plan Extension) | Heavy Universal Column + Steel Goalpost | £5,500 – £8,500+ | 6 – 9 days |
Itemised Cost Build-up: 3m Internal Load-Bearing Wall Knock-Through
Here is how a deterministic builder estimate breaks down for removing a 3-metre load-bearing wall between a kitchen and dining room:
Four Critical Traps in Structural Knock-Throughs
Structural demolition carries substantial liability. Avoid these four common pitfalls when pricing:
Never strike temporary acrows until the dry-pack mortar between the steel top flange and masonry has fully cured (minimum 48 hours). Removing props prematurely transfers loads onto wet mortar, causing ceilings and brickwork upstairs to crack.
A solid brick wall 3m wide by 2.4m high yields over 3.5 tonnes of dense brick and mortar rubble. Standard 8-yard skips carry strict highway weight limits (usually 8 tonnes max). If loaded unevenly or mixed with plaster, skip companies will refuse collection or levy £150+ excess weight surcharges.
Internal walls frequently house central heating flow/return copper pipes, boiler flues, and ring final circuits traveling between floors. Quotes must specify that plumbing drain-downs and electrical rerouting around the new opening are billed as specialist trade variations.
If the new RSJ beam bears directly into a shared party wall separating a terraced or semi-detached neighbour, the Party Wall etc. Act 1996 mandates serving written notice 2 months prior to work. If neighbours appoint surveyors, costs increase by £800 to £1,500.
UK Regional Builder Day Rates
Builder day rates and waste removal costs vary across the UK:
| Region | Builder Day Rate | 2-Person Crew Rate | Average 3m RSJ Knock-Through |
|---|---|---|---|
| London & Inside M25 | £380 – £520 | £600 – £850/day | £3,400 – £4,800 |
| South East & Home Counties | £320 – £420 | £500 – £700/day | £2,800 – £3,900 |
| Midlands, South West & East Anglia | £260 – £340 | £440 – £580/day | £2,400 – £3,400 |
| North of England, Wales & Scotland | £240 – £310 | £400 – £520/day | £2,100 – £3,000 |
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Building Regulations Inspection Process
Building Control will require two statutory inspections for an RSJ knock-through:
- Structural Inspection: The officer visits while the steel is resting on padstones and dry-packed, checking beam sizes against the structural calculation sheet before it is boxed in.
- Completion Inspection: The officer checks fire protective boarding (minimum 30 minutes fire resistance) and smoke alarms. A statutory completion certificate is then issued.
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