Do I need an architect for an extension?
3 min
7
September 2026
Key figures in this guide
One-minute decision
What are you trying to work out?
Use the checker first, then turn the result into a clearer brief before speaking to professionals.
Open the checkerNo, you are not legally required to use an architect for a house extension in the UK. Anyone can draw and submit plans. But for anything structural, visible from the street, or in a conservation area, an architect usually pays for itself in planning success and usable space.
The real question is who produces your drawings, because you do need drawings: for planning permission if it is needed, for building regulations always, and for builders to price accurately.
When an architect is worth the fee
- The extension changes how the house works, not just its size
- You are in a conservation area, or the house is listed
- Planning is likely to be contested, or a previous application was refused
- The design involves glazing, levels, rooflights or a difficult roof junction
- You want someone independent inspecting the build and signing off valuations
- The budget is large enough that a 10 per cent design improvement is worth more than the fee
When you can do without one
- A small rear extension well inside permitted development limits
- A simple box with a standard roof, matching brick and no layout change
- A conservatory or garden room from a specialist supplier
- A like-for-like rebuild in the same footprint
Your options, and what they cost in 2026
| Who | 2026 fee for a typical extension | Best for |
|---|---|---|
| Architect (ARB registered) | £4,500 - £18,000 full service, £2,200 - £5,500 planning only | Design quality, tricky planning, site oversight |
| Architectural designer | £1,200 - £3,500 for planning and building regs drawings | Straightforward extensions on a budget |
| Architectural technologist | £1,500 - £4,000 | Technical drawings and building regs detail |
| Design-and-build contractor | Bundled into the build price | Speed and a single point of contact |
| Yourself | £328 planning fee only | Very simple work, if you can draw to scale |
Only ARB-registered professionals may call themselves an architect. A designer or technologist can be excellent, but the title, insurance and complaints route are different, so check qualifications and indemnity cover.
What you still need, architect or not
- 01Planning permission, or a lawful development certificate if you rely on permitted development
- 02Structural engineer calculations for beams, foundations and any opening
- 03Building regulations approval, with drawings and a specification
- 04A party wall notice if you build on or near a shared boundary
- 05A written scope of works, so every builder prices the same job
What architects actually improve
Better light and circulation for the same footprint, roof and glazing details that do not leak or overheat, drawings clear enough that builders stop pricing risk, and a planning submission written for the officer who will read it. On a £120,000 extension, a fee of £8,000 is easily recovered if it prevents one refusal or one wasted structural redesign.
The practical route
Start with a feasibility visit from one architect, typically £600 - £1,800 in 2026. You get two or three options and an honest view of what planning will accept. After that you can decide whether to buy the full service or take the drawings elsewhere.
Get the right people on your extension
Create your project brief on Renovome first: what you want, the constraints, the budget. Then compare architects, designers and engineers near you against that single brief, so the fee proposals you receive are actually comparable.
Last reviewed: September 2026