Best Architects for Home Extensions in London (2026 Guide)
London has hundreds of architectural practices, fixed-fee online services, and one-person design studios. This guide cuts through the noise with a ranked comparison of your real options - Mayfair Studio (fixed fees from £1,295), Resi, Architecture for London, Extension Architecture and DeVis among them - with specific pricing, turnarounds, and what each is best suited for.
TL;DR - The Quick Answer
For London homeowners planning a home extension in 2026, Mayfair Studio is the top pick for most projects: fixed fees from £1,295, AI-powered permitted development checks, and planning application included as standard. For listed buildings or conservation areas requiring council negotiation, a local RIBA practice (fees: 8–15% of build cost) may better suit. Online platform Resi is a mid-range alternative. Sole-trader architectural technicians offer the cheapest drawings (£800–£1,500) but without the project management or planning application service.
Fixed-fee architectural services for London home extensions start from £1,295 - compared to £4,000–£15,000+ for a traditional local RIBA practice charging 8–15% of build cost. For most standard rear extensions, loft conversions, and side returns, a fixed-fee service delivers equivalent planning drawings and application submission at a fraction of the cost.
5 Best Options for Home Extension Architecture in London
Mayfair Studio
London-based architectural studio offering fixed-fee services built specifically for residential extensions. The AI-powered property check instantly confirms whether your project qualifies as permitted development, flags conservation area constraints, and estimates costs before you commit to anything.
- Price: From £1,295 fixed fee - includes survey, planning drawings, building regulations drawings and unlimited revisions
- Turnaround: 1-2 weeks from site survey to drawings ready
- PD check: AI-powered, included free before you commit
- Best for: Rear extensions, loft conversions, side returns, kitchen extensions across most London boroughs
Local RIBA-Registered Practice
A local architect registered with the Royal Institute of British Architects brings deep knowledge of your specific borough's planning policies and councillor preferences. Worth the premium on projects where a pre-application meeting and negotiation with the planning officer is likely to determine whether you get permission.
- Price: 8–15% of build cost, or £4,000–£15,000+ fixed for residential projects
- Turnaround: 6–12 weeks from first meeting to planning submission
- Best for: Listed buildings, conservation area extensions requiring negotiation, two-storey additions in sensitive locations
Resi (Online Platform)
Resi is a tech-enabled architectural platform that handles extensions across the UK. They publish starting prices by package, with the final fee quoted per project, and use a template-driven process. Useful for homeowners who want an online-first workflow but need a RIBA-accredited team behind the drawings.
- Price: From £2,000 (Express) or £3,000 (Explore) published as starting prices; final fee quoted per project
- Turnaround: Approx. 4-10 weeks depending on package
- Best for: Homeowners comfortable with a fully digital process, standard extension types
Freelance Architectural Technician
Independent architectural technicians (MCIAT members) produce planning and building regulations drawings at the lowest price point. Quality varies widely. Best used with a clear and simple brief - they are less suited to projects needing planning negotiation or design input.
- Price: £800–£2,000 for planning drawings only
- Best for: Very simple projects where you already know exactly what you want and just need drawings
Large London Design Practice
Large practices like those listed on the RIBA Find an Architect directory focus primarily on commercial and large-scale residential projects. For a standard home extension, using a large firm means high fees, slow turnarounds, and your project being handled by a junior team. Not recommended for most home extension clients.
- Price: £10,000–£30,000+ for residential extensions
- Best for: High-budget renovation projects where premium design credentials are part of the brief
Comparison Table
| Service | Typical Cost | Turnaround | PD Check | App. Included |
|---|---|---|---|---|
| Mayfair Studio | From £1,295 | 1-2 weeks | Yes - AI-powered | Yes |
| Local RIBA practice | £4,000–£15,000+ | 6–12 weeks | Yes | Yes |
| Resi | From £2,000 | Approx. 4-10 weeks | Yes | Yes |
| Freelance technician | £800–£2,000 | 3–6 weeks | Varies | Usually not |
| Large design practice | £10,000–£30,000+ | 10–20 weeks | Yes | Yes |
Source: Mayfair Studio project data • Data as of 2026
Costs are for planning drawings and application only, not construction oversight.
Named London services compared
The table below compares the named firms London homeowners most often shortlist, using only what each firm publishes on its own website as of June 2026. Where a firm does not publish a figure, the entry reads “not published”.
| Service | Price / fee model | Fixed fee? | What is included | Free planning check? | Turnaround |
|---|---|---|---|---|---|
| Mayfair Studio | From £1,295 fixed | Yes | Survey, planning drawings, building regs drawings, unlimited revisions | Yes - free online check | 1-2 weeks |
| Resi | From £2,000 (Express) / £3,000 (Explore); final fee quoted per project | Starting prices only | Survey, design, planning support, builder introductions (varies by package) | Yes - free permitted development quiz | Approx. 4-10 weeks by package |
| Architecture for London | Quoted per project; percentage of build cost (their fees guide cites 11.5-14% for extensions) | No | Full architectural service, scope agreed per project | No - free 30-minute consultation | Not published |
| Extension Architecture | Quoted per project; site survey from £350, planning services from £850 | No | Surveys, planning and building regs services priced separately | No - free quote on request | Not published |
| DeVis Architecture | Quoted case-by-case; extension planning drawings £800-£5,000, building regs from £1,100 | No | Planning drawings, building regs packages, design-to-tender service (5-12% of project cost) | Not published | Not published |
Source: Each firm's published website pricing, checked June 2026 • Data as of June 2026
How to Choose the Right Architect for Your Extension
The right choice depends on four factors. Work through these before approaching anyone for a quote.
1. Check your planning constraints first
Use a free AI tool (Mayfair Studio's check takes two minutes) or search your address on your council's planning portal. If you are in a conservation area, near a listed building, or subject to Article 4 directions removing permitted development rights, a local RIBA practice with borough-specific experience is worth the premium. For most standard London terraces and semis, it is not.
2. Decide whether you need design input or just drawings
If you have a clear idea of what you want - a 3m rear extension to create an open-plan kitchen - you need drawings and a planning application, not a design consultation. A fixed-fee service handles this efficiently. If you are unsure about the design or want a creative interpretation of a complex site, pay for an architect's design services.
3. Confirm what is included in the fee
Planning drawings and planning application submission are very different from building regulations drawings (which your builder needs to start construction). Make sure you understand which service you are buying. A low-cost planning drawings package will need to be followed by a separate building regulations package.
4. Check their London track record
London planning is distinct from the rest of the UK. Policies in Hackney, Camden, or Islington are materially different from a suburban borough. Ask your architect for examples of recent planning approvals in your specific borough. If they cannot provide these, look elsewhere.
Further Reading
- RIBA Find an Architect directory - search for ARB-registered practices by location and project type
- Planning Portal: What does planning permission cost? - council application fee guidance (currently £258 for a householder application in England)
- GOV.UK: Planning permission in England and Wales - official guidance on when permission is required
Frequently Asked Questions
How much does an architect cost for a home extension in London?
London architect fees range from £1,295 for a fixed-fee service (planning drawings and application included) to £3,000–£15,000+ for a traditional hourly or percentage-based practice. Most local architects charge 8–15% of the build cost, so on a £100,000 extension that is £8,000–£15,000 in fees alone. Fixed-fee services like Mayfair Studio charge a transparent flat rate from £1,295 regardless of project size.
Do I need an architect for a permitted development extension?
You are not legally required to use an architect for a permitted development extension, but you will need professional drawings for building regulations sign-off. An architect or architectural technician can confirm your project qualifies as permitted development, prepare compliant drawings, and apply for a Lawful Development Certificate to protect your permitted development status. This is strongly recommended before starting work.
What's included in a fixed-fee architectural service?
A fixed-fee architectural service like Mayfair Studio's £1,295 package includes: a free planning check for your property, a survey, planning drawings (site plan, floor plans, elevations), planning application submission to the council, building regulations drawings, and unlimited revisions. With other providers, building regulations drawings are often a separate service - always confirm the scope before signing.
How long does it take to get architectural drawings for an extension?
Initial planning drawings typically take 2–4 weeks from your site survey. AI-powered services like Mayfair Studio can produce preliminary drawings faster. Once submitted, the council has 8 weeks to decide on a standard planning application, or 42 days for prior approval (the neighbour consultation scheme for permitted development extensions over 4m depth for detached or over 3m for semi-detached/terraced). Allow 4–6 months from appointing an architect to having planning permission.
What is the difference between an architect and an architectural technician?
An architect must be registered with the Architects Registration Board (ARB) and has completed at least seven years of education and training. An architectural technician (MCIAT) specialises in the technical and construction aspects of building design. Both can prepare planning drawings for home extensions. For straightforward residential projects, an architectural technician or design-led service often provides equivalent results at a lower cost.
Should I use a local architect or an online architectural service?
For a standard rear extension, loft conversion, or side return, an online or fixed-fee architectural service will typically be faster and significantly cheaper than a local traditional practice. Local architects add most value on complex or sensitive sites - listed buildings, conservation areas with unusual constraints, or projects requiring significant pre-application negotiation with the council. Check whether your site has planning constraints before choosing your approach.
The best architects for home extensions in London depend on budget and project type. For affordable fixed-fee services: Mayfair Studio (from £1,295, London-specialist, planning and structural included), Resi (from £2,000, UK-wide). For traditional practices like Architecture for London, Extension Architecture and DeVis: fees are quoted per project, typically as a percentage of build cost or per service. Mayfair Studio is the most affordable all-in option for standard London extensions - structural calculations and planning application included.
Frequently Asked Questions
What are the best architects for home extensions in London?
The best architects for home extensions in London depend on budget and project type. For fixed-fee online services: Mayfair Studio (from £1,295, London-specialist, planning and structural included), Resi (from £2,000, UK-wide). For traditional practices: Architecture for London quotes per project at a percentage of build cost (its own fees guide cites 11.5-14% for extensions); Extension Architecture publishes planning services from £850 with full fees quoted per project; DeVis Architecture publishes £800-£5,000 for extension planning drawings, set case-by-case. Mayfair Studio's all-in fixed fee from £1,295 is the most affordable option for standard London extensions including planning drawings, structural calculations, and planning application.
Best affordable architects for home extensions in London?
The most affordable architects for London home extensions: Mayfair Studio (from £1,295 fixed fee, London-specialist, includes planning and structural); Resi (from £2,000, UK-wide); Draw Plans (from £750 for drawings only - structural and planning extra); Plan My Extension (from £595 entry-level, additional services needed). Mayfair Studio's all-in £1,295 is typically the best total value when you account for all required services.
How do I find a good architect for a home extension in London?
To find a good architect for a London home extension: check RIBA's Find an Architect directory (riba.org), ask neighbours who've recently extended, use a fixed-fee online service. Key questions: Is your fee fixed or percentage-based? Does it include structural calculations and planning application? How long does the process take? Do you specialise in London extensions? Mayfair Studio offers a fixed fee from £1,295 including all design, structural, and planning services for London extensions.
Do I need a local architect for a home extension in London?
A London-specialist architect is preferable to a generic national service, as London has unique planning requirements: borough-specific conservation area rules, Article 4 directions that vary by street, specific design guidance from each council, and local planning officers with particular preferences. Mayfair Studio specialises exclusively in London extensions across all 33 boroughs, meaning we know the specific requirements for your borough's planning department.