Choosing an Architect for Your Home Extension: UK Guide to Fees, Roles, and Finding the Right Fit

Getting the design right is the single most important decision in your extension project. A good designer transforms a vague idea into a buildable plan that maximises space, light, and value. A poor one costs you money through wasted planning applications, inaccurate drawings, and missed opportunities.

This guide helps you understand the options, the costs, and how to choose the right professional.

Architect vs Architectural Technologist vs Designer

Three main types of professional design residential extensions in the UK:

Chartered Architect (RIBA / ARB)

• Training: 7+ years (university degree + professional practice)
• Registered with: Architects Registration Board (ARB) — "architect" is a legally protected title
• Strengths: Creative design, complex projects, planning expertise, full project oversight
• Typical fees: 5–12% of build cost, or £4,000–£10,000 fixed
• Best for: Complex or high-value extensions, listed buildings, sensitive planning situations, projects where design quality is the priority

Chartered Architectural Technologist (CIAT)

• Training: 3-year degree + professional experience
• Registered with: Chartered Institute of Architectural Technologists
• Strengths: Technical detailing, Building Regulations compliance, construction knowledge, cost-effective
• Typical fees: £2,000–£6,000 fixed for a standard extension
• Best for: Straightforward extensions, loft conversions, garage conversions — the majority of UK domestic projects

Architectural Designer (Unregulated)

• Training: Varies — no minimum requirement
• Registered with: No mandatory registration
• Strengths: Often the most affordable, can be perfectly adequate for simple projects
• Typical fees: £1,500–£4,000 fixed
• Best for: Very simple projects with clear scope; always check their portfolio and references carefully

Key point: The title "architect" is protected by law — only ARB-registered professionals can use it. "Architectural designer" and "building designer" are not regulated, so quality varies widely.

Service Levels and Fees

Architectural services are typically offered at different levels:

Level 1: Design and Planning Only

The most common service for domestic extensions. Includes:

• Initial consultation and site survey
• Concept design options (usually 2–3 schemes)
• Detailed planning drawings (plans, elevations, sections, site plan)
• Planning application submission and management
• Design and Access Statement (if required)

Typical cost: £2,000–£5,000

Level 2: Design Through to Building Regulations

Everything in Level 1, plus:

• Construction drawings for Building Regulations approval
• Structural coordination with your engineer
• Specification and materials schedule
• Drawings suitable for builders to quote against

Typical cost: £3,000–£8,000

Level 3: Full Service Including Construction

Everything in Level 2, plus:

• Tender management (issuing drawings to builders, comparing quotes)
• Contract administration during the build
• Regular site inspections
• Snagging inspection at completion

Typical cost: 8–12% of build cost (£5,000–£12,000 for a £60,000 extension)

What Most Homeowners Choose

For a standard single-storey or double-storey extension, Level 2 offers the best balance. You get professional design, planning and Building Regulations drawings, and a specification that builders can quote against. You then manage the build yourself or with occasional architect input.

Fee Comparison by Project

| Project | Design + Planning | + Building Regs | Full Service | |---|---|---|---| | Garage conversion | £1,500–£2,500 | £2,000–£3,500 | £3,000–£5,000 | | Loft conversion | £2,000–£3,500 | £3,000–£5,000 | £4,500–£7,500 | | Single-storey extension | £2,500–£4,000 | £3,500–£6,000 | £5,000–£9,000 | | Double-storey extension | £3,000–£5,000 | £4,500–£7,500 | £6,500–£12,000 | | Whole-house renovation | £5,000–£10,000 | £8,000–£15,000 | £12,000–£25,000 |

These are national averages. London and South East practices typically charge 20–40% more.

How to Choose the Right Practice

1. Check Their Portfolio

Look for projects similar to yours in scale, style, and property type. A practice that specialises in contemporary new-build houses may not be the best fit for extending a Victorian terrace. Ask to see:

• Before and after photos
• Floor plans showing how they solve spatial problems
• Projects at a similar budget to yours

2. Meet Face to Face

Your initial meeting should be free or low-cost (£50–£150). Use it to assess:

• Do they listen? A good architect asks about how you live, not just what you want to build
• Do they understand your budget? If you say £50k and they immediately talk about £80k schemes, move on
• Do they know the local planning authority? Local knowledge makes a real difference to planning success
• Can they explain things clearly? You'll be making decisions together for months

3. Get Fee Proposals in Writing

Ask each practice for a written fee proposal that includes:

• Scope of work (which stages are covered)
• Deliverables (what drawings and documents you'll receive)
• Fee structure (fixed, percentage, or hourly)
• Payment schedule
• What's excluded (structural engineer, surveys, planning fees)
• Timeline

4. Check References

Ask for 2–3 recent client references and actually call them. Key questions:

• Did the project come in on budget?
• Was the architect responsive and easy to communicate with?
• Did they manage the planning process effectively?
• Would you use them again?

When You Don't Need an Architect

Some projects are simple enough to proceed without professional design:

• Like-for-like replacements — new windows, boiler, roof
• Internal renovations — new kitchen or bathroom within existing walls
• Very small extensions — a simple porch or small conservatory
• Builder-led projects — some experienced builders offer a design-and-build service, producing drawings as part of their package

Even for these, ensure someone qualified produces Building Regulations drawings if required.

Getting Value From Your Architect

To make the most of the relationship:

• Be clear about your budget from day one — there's no point designing a £100,000 extension if you have £50,000
• Share your priorities — natural light, open-plan living, a specific room layout
• Trust the process — a good architect will present options you hadn't considered. Be open to ideas that challenge your initial thinking.
• Make decisions promptly — delays in approving designs delay the whole project
• Ask questions — no question is too basic. Understanding the design helps you manage the build.

Next Steps

1. Define your brief — what space do you need, what's your budget, and what's your timeline?
2. Search for local practices — use RIBA Find an Architect or CIAT's directory
3. Meet 2–3 practices — compare portfolios, fees, and personal fit
4. Agree a written fee proposal before work starts
5. Get a cost estimate — use our free quote calculator to set a realistic budget before engaging a designer
6. Read about getting builder quotes — your architect's drawings make builder quotes more accurate and comparable