Architect stages for your extension project

Please note that these stages are for a guideline purpose only, to get a clear extension cost breakdown of each stage please post your extension project and get up to 5 free quotes in your area

Preparation & Concept Design

Defining your vision and understanding what's possible

Spatial Coordination & Planning

Refining your design and securing planning approval

Technical Design & Tendering

Turning your approved design into a build-ready package

Construction & Handover (Site Management)

Overseeing the build and ensuring quality every step of the way

How much an architect cost for extension project?

Extension Project – Roles & Responsibilities

(Architect • Structural Engineer • Builder)

Please note that these rough guides only, to get a clear extension cost breakdown of each stage please post your extension project and get up to 5 free quotes

Preparation & Brief (The Concept)

Define your vision, understand your home's potential, and establish a strong design foundation.

Spatial Coordination & Planning

Refine the design, prepare for planning, and coordinate early structural advice.

Technical Design & Tendering

Create a coordinated, regulation-compliant design package for accurate pricing and a smooth build.

Construction & Handover (Site Management)

Deliver the project safely, on budget, and to the agreed design standard.

How They Work Together

Architect

Designs, documents, and coordinates the overall project.

•Liaises with planning, Building Control, and the client.
•Oversees quality, design integrity, and communication.

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Structural Engineer

Ensures the structure is safe, compliant, and efficient.

•Provides calculations and beam/foundation designs.
•Supports the architect and builder with technical guidance during construction.

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Builder

Delivers the project on site to the agreed design and quality.

•Manages trades, sequencing, and on-site quality.
•Keeps the client updated on progress and practical matters.

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Together, these three professionals ensure your extension is thoughtfully designed, structurally sound, and beautifully built — from the first idea to the final completion certificate.

Architect step-by-step cost guide for your extension project

Please note that these are rough guides only. To get a clear extension cost breakdown of each stage, please post your extension project and get up to 5 free quotes.

(Helping you understand what you'll pay and when)

Architects' fees for home extensions can vary depending on the project size, complexity, location, and the level of service you choose. This simple guide explains what your architect does at each stage — and what costs to expect.

Preparation, Brief & Concept Design

(Turning your ideas into a clear, achievable plan)

Planning & Design Development

(Refining the design and securing planning approval)

Technical Design & Building Regulations

(Preparing detailed drawings for construction and compliance)

Construction & Site Support (Optional)

(Overseeing the build and protecting your interests)

Summary – Typical Architect Fees for an Extension

Level of Service	Estimated Cost Range	What's Included
Basic Design Service	£1,500 – £3,000	Concept + Planning drawings only
Design + Building Regs Package	£2,500 – £4,500	Full planning and technical drawings
Full Service (Concept to Completion)	8% – 15% of total build cost	Design, planning, technical, tender & site support

Basic Design Service

£1,500 – £3,000

Concept + Planning drawings only

Design + Building Regs Package

£2,500 – £4,500

Full planning and technical drawings

Full Service (Concept to Completion)

8% – 15% of total build cost

Design, planning, technical, tender & site support

Example: For a £75,000 extension, full architectural services typically range from £6,000 – £11,000, depending on complexity and location.

Key Factors That Affect Cost

•Project size & complexity: Larger or double-storey extensions cost more to design and coordinate.
•Planning constraints: Conservation areas or listed buildings need extra documentation and time.
•Location: Fees are generally higher in London and the South East.
•Level of involvement: Full project management adds reassurance and value but increases total fees.

✅In summary:

A skilled architect will help you shape your ideas into a well-designed, compliant, and buildable extension — guiding you smoothly from concept to completion while protecting your time, budget, and investment.

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