Do I need an architect for a house extension?

Legally no, but in practice you need someone qualified to produce accurate scaled drawings and prepare building control documents. For anything more complex than a basic conservatory replacement, that means a professional rather than a back-of-an-envelope sketch.

What is the difference between an architect and an architectural technologist?

An architect is a legally protected title requiring seven years of training and registration with the ARB, with strengths in design and planning negotiation. An architectural technologist holds a degree in architectural technology and tends to be stronger on construction detail and building regulations, often at a lower fee.

How much does an architect charge for an extension?

For a standard single-storey extension the typical total is around £1,500 – £2,500, with the fee spread across the stages from outline drawings through to building control submission. A full RIBA-registered architect usually costs more than a technologist or a building designer.

Can anyone call themselves a building designer?

Yes, "building designer" is an unregulated title with no required qualification, professional body, or mandatory insurance. If a mistake in their drawings leads to faulty construction you may have limited recourse, so always check whether they carry professional indemnity insurance.

Where can I find a qualified architect for my extension?

The RIBA "Find an Architect" directory lists chartered practices, and CIAT maintains its own register of architectural technologists. Your council's planning register is also useful, because it shows who designed approved extensions near you and therefore knows the local context.

Back to Single Storey Rear Extension

Phase 1 · Planning & Permissions · Task 04 of 17

Finding an Architect for Your Extension

How to find, appoint, and manage an architect for your extension. Covers fees (typically £1,500 – £2,500), what each stage costs, and the questions to ask before you commit.

12 min readUpdated 2026Free with email

Six-stage architect pipeline infographic showing the journey from initial consultation through outline drawings, detailed plans, planning submission, building control documents, and BC submission, with typical fees and timeline at each stage

Prerequisites

Complete this first

Do You Need Planning Permission?

The drawings your architect produces will determine what your extension looks like, what it costs to build, and whether building control approves it. Get the wrong drawings, and your builder prices the wrong job. Get incomplete drawings, and your structural engineer can't size the steels. Your planning application gets bounced back if information is missing. Every professional and tradesperson downstream depends on what your architect puts on paper.

That makes this appointment the most consequential decision in the entire planning phase. Not the most expensive. The most consequential.

What this guide covers

01Do You Actually Need an Architect?
02Three Types of Professional
03How to Find One
04What to Look For
05What They Actually Produce (and What It Costs)
06How to Brief Your Architect
07Managing the Relationship
08Surprises in the Existing Structure
09The Modification Trap
10When Architect and Builder Disagree
11What This Costs in Total

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