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Do You Need an Architect for an Extension?
The short answer is no — there is no legal requirement to use an architect for a house extension. What your council needs is accurate, scaled drawings that meet its validation standards. Here is what architects charge, when one is genuinely worth it, and what the alternative costs.
Is an architect legally required for an extension?
No. Planning law sets no requirement for who prepares your drawings. Councils assess the drawings themselves — the scale, the accuracy and whether they meet the validation checklist — not the credentials of whoever produced them.
"Architect" is a protected title held by someone registered with the Architects Registration Board. It reflects a particular training. It is not a licence that planning applications require.
What Does an Architect Cost for an Extension?
Architectural practices usually price one of two ways: a fixed fee for the drawing stages, or a percentage of the build cost. For a typical domestic extension you should expect £3,000 to £5,000 for a planning and building regulations package, or 8–12% of build cost if they are running the project through to completion.
Site visits are often billed on top, and structural calculations are normally subcontracted to a separate engineer at a further cost. Timescales of eight to twelve weeks to produce drawings are common, before the council's own eight-week determination period even begins.
Architect's practice
£3,000–£5,000 for the drawing package. Site visits billed separately. Structural engineer usually an additional appointment. Eight to twelve weeks typical.
TM Designs
£1,650 for planning drawings, or £2,300 for the full package including structural calculations and building regulations. Two weeks guaranteed. No site visit, no travel cost, revisions included.
When an architect earns the fee
Listed buildings, genuinely difficult conservation-area schemes, and bespoke new builds where the architecture itself is the point. We will say so if yours is one of those.
What Councils Actually Require
A householder planning application is validated against a checklist, and the checklist is about documents, not credentials. Every UK authority asks for broadly the same set.
- checkExisting and proposed floor plans — scaled, every affected level
- checkExisting and proposed elevations — all affected faces of the building
- checkSite plan at 1:500 — the property and its boundaries
- checkLocation plan at 1:1250 — with the application site edged red
- checkCompleted application forms and the fee
Most refusals at validation stage are about missing drawings or incorrect scales rather than the design. Getting the set right first time is a process problem, and process is what we have built the business around — 98% of our projects are approved first time across more than 150 jobs.
Qualified Drawing Work, Without the Practice Overheads
TM Designs is a father-and-son business combining formal architectural training with a process designed for one thing: producing council-ready residential drawings quickly and at a fixed price.
We do not run a studio, we do not make site visits, and we do not charge by the hour. You capture the measurements using our app or supply existing plans, we draw, you review online, and the final set is issued ready for submission. Taking the travel, the premises and the billable-hour model out of the equation is where the difference in price comes from — not from doing less work.
For a bespoke architectural statement, hire an architect. For a well-drawn, properly validated extension package at a fraction of the cost and a quarter of the time, this is what we do all day.
Extension Drawings — From £1,650
Planning drawings are £1,650. Most extensions also need structural calculations and building regulations drawings, so the Full Package at £2,300 is the usual choice — still well under half a typical architect's quote.
Architects and Extensions — Frequently Asked Questions
Do you have to have an architect to build an extension?
No. There is no legal requirement to use an architect for a house extension in the UK. Councils assess the drawings against a validation checklist — scale, accuracy and completeness — and do not ask who prepared them. An architectural designer can produce exactly the same package.
How much is an architect for an extension?
Typically £3,000 to £5,000 for a planning and building regulations drawing package, or 8–12% of build cost where the architect runs the project to completion. Site visits and structural engineering are often charged on top. Our equivalent package is £1,650 for planning drawings or £2,300 for planning, structural and building regulations combined.
What is the difference between an architect and an architectural designer?
"Architect" is a title protected by law and held by those registered with the Architects Registration Board, reflecting a specific route of training and examination. "Architectural designer" is not protected, and covers a wide range of experience. For residential extension drawings both produce the same deliverables; the difference shows most on complex or bespoke design work.
Will the council accept drawings not done by an architect?
Yes. Planning authorities validate applications on the documents submitted, not on the author. Our drawings are approved first time on 98% of projects across more than 150 extensions, lofts and new builds.
When should I use an architect instead?
Listed buildings, demanding conservation-area schemes, and bespoke new builds where the design itself is the main value. If your project falls into one of those, we will tell you rather than take the work.
Do I need an architect for permitted development?
No, and often you do not need a planning application at all. You will still need building regulations approval, which requires a technical drawing set. Many clients also obtain a Lawful Development Certificate for certainty when selling, and that needs drawings too.
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