Compare Fixed-Fee Architects for Home Extensions in London (2026)
Fixed-fee architectural services have become the go-to for London homeowners who want cost certainty. Here is an honest comparison of Mayfair Studio (from £1,295 fixed) against Resi, Architecture for London, Extension Architecture and DeVis - what you actually get, and at what price.
Why Fixed-Fee Architecture Has Taken Off in London
Traditional architects charge a percentage of your total build cost - typically 8–15%. On a standard 20m² rear extension costing £50,000 to build, that puts architect fees between £4,000 and £7,500. On a two-storey rear extension at £100,000, you're looking at £8,000–£15,000 in architect fees alone - before you've paid for structural engineering, planning fees, party wall surveyors, or building control. The total professional fee bill for a straightforward extension can easily reach £20,000–£25,000 on this model.
Fixed-fee services change this entirely. You pay a single quoted price upfront - typically £795–£1,880 - and you know exactly what you're getting. Services like Mayfair Studio from £1,295 handle planning drawings, planning application submission, structural calculations, and building regulations drawings within that fixed price. For most standard extensions and loft conversions in London, the outcome is functionally the same - a granted planning permission and a buildable set of drawings.
London homeowners are increasingly using fixed-fee online services for standard rear extensions, loft conversions, and side-return extensions, reserving traditional architects for complex projects: listed buildings, large-scale new-build work, or jobs requiring full RIBA contract administration on site. Understanding which category your project falls into is the first and most important decision you'll make.
The Comparison Table
The table below compares the main fixed-fee architectural services available to London homeowners alongside the traditional architect model. The most important column to scrutinise is “Structural Calcs” - structural engineer calculations are required for building regulations approval and are not optional. Services that exclude them will charge £1,500–£2,500 separately, often wiping out the apparent cost saving. “Revisions” refers to rounds of design changes included before extra fees apply.
| Service | Price | Structural Calcs | Turnaround | Revisions |
|---|---|---|---|---|
| Mayfair Studio | From £1,295 fixed | Included | 1-2 weeks (drawings) | Unlimited |
| Fast Plans | £1,880 inc VAT | Included | 4–8 weeks | Revisions charged |
| Draw Plans | From £795+VAT | Extra cost | 3–6 weeks | 1 round included |
| Plan My Extension | From £1,200 | Not included | 4–8 weeks | Varies |
| Traditional Architect | 8–15% of build | Included | 10–16 weeks | Included |
Source: Mayfair Studio research • Data as of 2026
Mayfair Studio vs Resi, Architecture for London, Extension Architecture and DeVis
Beyond drawing-package services, London homeowners frequently shortlist four well-known names: Resi, Architecture for London, Extension Architecture and DeVis Architecture. They follow different fee models - some publish starting prices, others quote each project individually. The table below records 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
None of these fee models is wrong. A percentage fee buys a bespoke design service, and quoted-per-project pricing reflects genuinely variable scope. The comparison matters because the totals can differ by an order of magnitude on a standard extension: a fixed £1,295 against a percentage fee that can reach £8,000–£15,000 on a £100,000 build. If your project is a standard rear extension, loft conversion or side return, paying for a bespoke design process buys you very little that a fixed-fee package does not already include.
What Should a Fixed-Fee Package Include?
Not all fixed-fee packages are equal. When comparing services, check each of the following is either included in the quoted price or clearly stated as an additional cost before you commit.
- Site survey / measured survey - required to produce accurate drawings of your existing property
- Planning drawings - floor plans, elevations, and sections for the planning application
- Planning application submission and management - completing portal submissions and liaising with the council
- Design and Access Statement - required for most full planning applications
- Structural calculations - required for building regulations; adds £1,500–£2,500 if not included
- Building regulations drawings - the detailed technical drawings your builder and building control inspector need
- One free resubmission if planning is refused - important protection if the council requests amendments
Building regulations drawings are sometimes not included at the base price on cheaper services - always confirm the full scope before signing up. A package that excludes building regs drawings will require a second engagement (and second fee) before your builder can start on site.
Mayfair Studio vs Fast Plans: Detailed Comparison
Mayfair Studio and Fast Plans are the two most commonly compared fixed-fee services for London extensions. On price, Mayfair Studio starts at £1,295 and tops out at £1,795 for larger or more complex projects. Fast Plans charges a single rate of £1,880 inc VAT regardless of project scale. Both include structural calculations and planning application submission in their headline price, so the comparison table price is genuinely all-in for standard cases.
On turnaround, Mayfair Studio produces drawings in 1-2 weeks; across the sector, 4–8 weeks from instruction to planning submission is typical. The meaningful difference lies in London-specific expertise. Mayfair Studio specialises exclusively in London, with detailed knowledge of conservation area requirements, Article 4 directions, and borough-specific Supplementary Planning Documents (SPDs) that vary significantly across the capital. Services designed for the national market tend to apply a generic approach that can miss borough-specific nuances in places like Hackney, Camden, or Wandsworth.
Before committing to any service, use Mayfair Studio's free property intelligence tool to instantly check your planning constraints - conservation area status, Article 4 directions, listed building status, and tree preservation orders. Knowing your constraints before you engage any service will help you ask the right questions and avoid paying for a package that's not suited to your property.
When Fixed-Fee Isn't Right For You
Fixed-fee services work best for:
- Standard rear extensions and loft conversions
- Projects that do not require full RIBA contract administration during construction
- Properties outside conservation areas, or where the service has documented conservation area experience
Fixed-fee may not suit:
- Listed buildings - these require specialist heritage architects with listed building consent experience
- Large complex new-build extensions - multi-unit schemes or large-footprint projects that need ongoing design management
- Projects requiring extensive conservation officer negotiation - where a pre-application relationship and iterative design process is essential
Fixed-fee architectural services for London extensions typically cost £1,295–£1,880, compared to £8,000–£25,000+ for traditional architects charging 8–15% of build cost. Mayfair Studio at £1,295 includes planning drawings, structural calculations, planning application, and building regulations drawings. For standard extensions and loft conversions, fixed-fee services offer equivalent planning success rates at a fraction of the cost.
Frequently Asked Questions
How do I compare fixed-fee architects for home extensions in London?
Compare fixed-fee architects on four criteria: (1) price - Mayfair Studio charges £1,295-£1,795, Fast Plans £1,880 inc VAT, Draw Plans from £795+VAT; (2) what's included - check whether structural calculations are included or extra; (3) turnaround - most services take 4-8 weeks; (4) London-specific knowledge - some services lack experience with London conservation areas and Article 4 directions.
Which fixed-fee architect is best for a home extension in London?
Mayfair Studio (£1,295-£1,795) is the best value fixed-fee option for standard London extensions. It includes planning drawings, structural calculations, planning application submission, and building regulations drawings. It specialises in London specifically, with expertise in conservation areas and borough-specific planning policies that affect most London extension projects.
What should be included in a fixed-fee architectural service?
A complete fixed-fee architectural service should include: planning drawings (floor plans, elevations, sections), a planning application submission, a Design and Access Statement, structural calculations, building regulations drawings, and at least one free resubmission if the application is refused. Services that charge extra for structural calcs or building regs drawings may end up costing as much as a traditional architect.
How does Mayfair Studio compare with Resi, Architecture for London, Extension Architecture and DeVis?
Mayfair Studio charges from £1,295 fixed, including survey, planning drawings, building regulations drawings and unlimited revisions, with a 1-2 week drawings turnaround and a free online planning check. Resi publishes starting prices from £2,000 (Express) and £3,000 (Explore), with the final fee quoted per project. Architecture for London quotes per project at a percentage of build cost (its own fees guide cites 11.5-14% as typical for extensions). Extension Architecture publishes a site survey from £350 and planning services from £850, with full fees quoted per project. DeVis Architecture publishes a range of £800-£5,000 for extension planning drawings, with fees set case-by-case.
How much do fixed-fee architectural services cost in London?
Fixed-fee architectural services in London cost £795-£1,880 for standard extensions. Mayfair Studio charges £1,295-£1,795 (structural calcs included). Fast Plans charges £1,880 inc VAT. Draw Plans starts from £795+VAT but structural calcs are extra. Traditional architects charge 8-15% of build cost - typically £8,000-£25,000+ for a standard London extension.
Are fixed-fee architects as good as traditional architects for planning applications?
For standard residential extensions, yes. Fixed-fee online services handle hundreds of similar applications and know local planning policies well. The key advantage of traditional architects is for complex projects - listed buildings, conservation area applications requiring extensive negotiation, or large new-build projects needing full RIBA contract administration during construction.