New for 2025: Based on survey data from over 100 practising residential architects across the UK, this guide provides clear, current cost benchmarks for hiring an architect and budgeting for home extension.
What You’ll Learn
- Typical construction cost benchmarks for home extensions
- How much architects charge
- Typical consultant and engineer fees to factor in
Kitchen extension pictured above by Ana, architect from Richmond upon Thames, London. See her profile on Design for Me.
How Much Does an Architect Cost?
Our 2025 survey found that most UK architects charge between 7% and 15% of the construction cost for full architectural services for a typical small extension.
National average: ~11%
Many also offer fixed-fee packages for smaller projects, especially for early design and planning stages – typically £2,500 to £6,000.
Summary: Extension & Architect Costs (2025)
Note: All construction costs include VAT, kitchen fittings, finishes, lighting and heating. Fees are shown separately where applicable.
UK (Excluding London/SE)
These are the average prices given from the architects surveyed for the starting price for a typical project.
- 10m² Extension (incl. kitchen): £45,563
- Kitchen Cost: £11,888
- Double-Storey Extension (20m²): £74,950
- Loft Conversion: £55,821
- Mansard Roof Extension: £97,385
- Architect Fees (est.): ~11%
- Other Consultant Fees: £3,466
London & South East
These are the average prices given from the architects surveyed for the starting price for a typical project.
- 10m² Extension (incl. kitchen): £90,719
- Kitchen Cost: £18,975
- Double-Storey Extension (20m²): £137,074
- Loft Conversion: £88,000
- Mansard Roof Extension: £109,804
- Architect Fees (est.): ~13%
- Other Consultant Fees: £6,421
What’s Included in Architect’s Fees?
- Feasibility and concept design
- Planning application drawings and support
- Building Regulations / technical design
- Tender assistance and contractor selection
- Site visits and contract administration (if full service)
Architect Fee Examples by Project Type
These are the average prices given from the architects surveyed for the starting price for a typical project.
- 10m² Kitchen Extension: £45k–£90k → Architect fee £5k–£10k
- Double-Storey Extension: £75k–£137k → Architect fee £8k–£15k
- Loft Conversion: £55k–£88k → Architect fee £6k–£10k
- Mansard Roof Extension: £97k–£110k → Architect fee £10k–£12k
Other Professional Fees to Budget
Most projects need additional consultants, including:
- Structural engineer
- Party wall surveyor
- Planning consultant
- Building control inspector
Typical combined cost: £2,500 – £6,000 for a small house extension project
Factors That Affect Architect Fees
How much do architects charge? Architect’s fees for a home project vary depending on the type and scale of the job. There are no official standards or guidelines for architect’s fees, so it’s between the client and the architect to negotiate the fee, often dependant on the following:
- The extent of the architect’s services (see ‘splitting the fee up into stages’ below)
- Size of project
- Complexity of project & specific project requirements
- Extent of works to existing buildings
- Repair and conservation of historic buildings
- Degree of design repetition
- The type of practice e.g. a small office or freelancer may have fewer overheads
- The experience and expertise of the architect or firm.
Typical Fee Breakdown (Full Service)
- Outline Design: 35%
- Technical Design / Tender: 35%
- Construction Phase: 30%
Do I Need an Architect?
Not every project requires an architect, but they can help you:
- Save money by avoiding design errors
- Unlock the best layout and long-term value
- Guide you through planning and regulations
See our full guide: Do I need an architect for an extension?
Not Sure Which Design Professional You Need?
- Architect or interior designer?
- Structural engineer or architect?
- Architect vs. architectural designer
More Cost Planning Guides
Get Matched with an Architect, Interior Designer or Garden Designer
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- Shortlist design pros
- Arrange consultations – for free!
Emily Barnes,
Architect & Founder of
