Home Extensions · Structural Engineer
A structural engineer for extension projects across the UK. We design RSJ beams, goalpost frames and foundations for single storey, double storey, side and wrap-around extensions.
The most common question homeowners ask before starting an extension. Here is a clear answer.
Building Control requires structural calculations if your extension involves any of the following:
A structural engineer is rarely needed for extensions that involve no structural changes — for example a very small conservatory or glazed lean-to where no load bearing walls are removed and no new foundations are required beyond standard strip footings.
We will always advise you honestly at the quote stage if calculations are not needed. Most extensions — even straightforward ones — do require at least beam and foundation calculations.
Building Control will not issue a completion certificate, you cannot legally sell the property and any structural failure becomes your liability. The engineer fee is a small cost relative to the risk.
What a full extension structural design calculation pack contains and how it is used on your project.
From simple single storey rear extensions to full wrap-around schemes — safe, buildable steelwork and foundations for every layout.
RSJ beams and padstones for wide garden openings, with roof and wall loads checked into the existing structure.
Full structural design from foundations up — walls, floors and roof loads checked along the full load path.
More complex schemes where rear and side elements meet — often needing goalpost frames and cranked beams.
All fees are fixed and confirmed in writing before work begins. No extras added later.
| Extension Type | Structural Engineer Fee | What Is Included |
|---|---|---|
| Single storey rear extension | £450 – £700 | RSJ beam, padstones, foundation spec, BC pack |
| Side return extension | £550 – £850 | As above plus party wall beam checks |
| Wrap-around extension | £700 – £1,100 | Goalpost frame, cranked beams, full BC pack |
| Two-storey extension | £750 – £1,200 | Full load path from roof to foundations |
| Complex / large extension | £1,000 – £1,500+ | Multiple beams, frames, unusual structure |
| Site visit (when required) | +£150 – £300 | Most projects handled remotely from drawings |
"Clear drawings, quick turnaround and no hassle with Building Control. Our rear extension steelwork was approved first time and the builder said the layout was easy to follow."
"Double storey side and rear extension with a big knock-through. The engineer explained the goalpost frame in simple terms and dealt with all structural questions from Building Control."
"We sent drawings on Monday and had the calculation pack ready to submit within two days. Fixed fee and no extras added later."
"Project involved underpinning and poor ground. The team were patient, explained the options and updated the design when site conditions changed."
Timing, costs, information needed and how Building Control uses our packs.
Yes in almost all cases. If your extension involves new openings, RSJ beams, frames, foundations or any changes to load bearing walls, Building Control requires structural calculations. We will advise if calculations are not needed for very small projects.
RSJ beam sizing, goalpost frame design, padstone specification, foundation bearing checks, roof structure and floor joist sizing — formatted for direct Building Control submission with drawings your builder follows on site.
Single storey extensions in 24–72 hours. Two-storey or wrap-around projects take 4–7 working days. Complex or large schemes up to 10 working days. We confirm the exact timeframe before you commit.
Often yes. Good photos and basic measurements are enough to confirm a fee and sometimes to start design. If we need more detail, we give you a short checklist of exactly what to send.
£450–£700 for a standard single storey rear extension. Two-storey or wrap-around extensions are £700–£1,200. All fees are fixed and confirmed in writing before work starts.
Our calculations follow current UK design codes and are formatted for Building Control officers. If your officer has questions, we answer them directly and make any clarifications needed at no extra cost.
We cover England and Wales. Most projects are completed from drawings and photos without a site visit. Recent extension calculations have been produced for homeowners in Manchester, London, Birmingham, Leeds, Bristol, Sheffield, Nottingham, Liverpool and many other locations.
Your enquiry goes straight to an engineer, not a call centre. We respond within one working day.
Share a few details so we can review the layout and confirm the right scope and fixed fee.
Fixed fees, fast turnaround, Building Control-ready. Call 07359 267907 or fill in the form above.
