Architect percentage fees vs: which saves you more?

Why does a percentage fee cost more on a London extension?

Because the base it multiplies is the build cost, and the build cost is the number nobody controls at briefing stage. A fixed fee moves that risk to us. The statutory costs are identical either way: £548 for a householder application, £274 for a lawful development certificate.

Sources: statutory fees from the Town and Country Planning (Fees for Applications) (England) Regulations 2012 as amended, 2026 rates, retrieved 1 September 2026; our own fees are the published fixed fees on this site. Percentage ranges are the market convention rather than a published statistic, and no professional body sets a mandatory scale — mandatory fee scales were abolished for architects in 1982.

How does a percentage fee actually work?

The traditional model in architecture is to charge a percentage of the total construction cost. When a London architect quotes "10% of the build cost," they mean their fee is calculated as a fraction of whatever you end up spending on the actual building work -- materials, labour, subcontractors, and site costs.

The percentage typically ranges from 8% to 15%, depending on the complexity of the project and the scope of services provided. Here is what the ranges usually mean:

• 5–8%: Planning and building regulations drawings only (concept design, planning submission, building regs details). No site supervision or project management.
• 8–12%: Full design service through planning and building regulations, plus some contract administration (tender analysis, contractor liaison). The most common range for residential projects in London.
• 12–15%: Comprehensive service including concept design, detailed design, interior design input, planning and building regs, full project management, site inspections throughout construction, and snagging. Typical for larger or more complex residential projects.

The percentage model has a fundamental structural problem for homeowners: the architect earns more when you spend more. If the build cost increases from £80,000 to £100,000 due to specification changes, unforeseen issues, or material inflation, the architect's fee increases from £8,000 to £10,000 (at 10%). There is no inherent incentive for the architect to help you control costs -- in fact, specifying more expensive materials and finishes directly increases their fee.

This is not to say architects deliberately inflate costs. Most are professionals who want happy clients. But the structural misalignment of incentives is worth understanding when you compare fee models.

Our model is simple: we quote a fixed price for the drawings and regulatory documents you need, and that price does not change regardless of your build cost, specification, or the number of revision rounds within the agreed scope.

The reason we can charge significantly less than percentage-fee architects is scope. We are MCIAT chartered architectural technologists, not architects. We specialise in the technical drawing and building regulations side of the process. We do not offer interior design, furniture layout, lighting design, or full project management. By focusing on what we do best -- accurate technical drawings and regulatory compliance -- we eliminate the overhead that comes with running a full-service design practice.

The result: you get the same quality technical drawings that the council and building control need, at a fee that is typically 30% below London architect rates.

Worked examples: 5 project types compared

Here are five common scenarios:

On every project type. The savings increase as the build cost rises.

On a typical London extension costing £80,000. That is money you can put toward better kitchen units, improved insulation, or simply keeping in reserve for contingencies.

What is included in each model

The fee difference reflects a genuine difference in scope. Here is an honest comparison of what you get:

The items we do not include -- concept design, interior design, construction supervision -- are the expensive, time-intensive parts of an architect's service. For most standard London residential projects (loft conversions, rear extensions, mansard roofs), these services are not strictly necessary. You need accurate technical drawings that the council will approve and building control will sign off. That is what we deliver.

If you want an architect's creative input on the layout, or you need someone to manage the builder during construction, a percentage-fee architect provides that. You are paying more, but you are getting more. The question is whether you need those additional services for your specific project.

What happens to a percentage fee when the scope creeps?

One of the most common frustrations homeowners report with percentage-fee architects is scope creep -- the gradual expansion of the project scope (and therefore the fee) beyond what was originally discussed.

Here is how it typically happens:

1. Initial quote: The architect quotes 10% on an estimated build cost of £60,000 = £6,000 fee.
2. Design development: During the design process, the architect suggests premium specifications -- bifold doors instead of standard patio doors, a flat roof with parapet detail instead of a lean-to, underfloor heating, a bigger kitchen island. Each suggestion adds to the build cost.
3. Revised estimate: The build cost is now £85,000. The fee is now £8,500.
4. Additional reports: The architect recommends a party wall survey, a drainage report, and a daylight assessment. These are quoted separately, outside the percentage fee.
5. Planning resubmission: The planning application is refused. The architect charges for revisions and resubmission -- either as additional time or as an extra round of the percentage fee.
6. Final cost: The total architectural fees are £10,000+. The homeowner expected £6,000.

If the build cost increases, our fee does not change. If we need to revise the drawings to respond to council feedback, that is included. There are no percentage recalculations, no hourly uplift charges, and no hidden extras for "additional stages."

Transparency and certainty

You know exactly what you will pay before you commit. This makes budgeting straightforward and avoids unpleasant surprises.

With a percentage fee, the final cost is not known until the project is built -- because the fee is calculated on the final construction cost. This creates a moving target that can make budgeting difficult, especially for homeowners who are financing the project through savings, remortgaging, or borrowing.

Our quote process is designed to be fully transparent:

1. You tell us about your project (property type, location, what you want to do).
2. We confirm which package applies and give you an exact price.
3. You pay a deposit to instruct us. The balance is due on delivery of drawings.
4. That is it. No percentage calculations, no hourly rates, no change orders.

When does a percentage-fee architect make sense?

We believe in being honest about when our service is and is not the right choice. A percentage-fee architect is the better option when:

• You are building a new house from scratch. A ground-up new build involves extensive concept design, site analysis, building form exploration, and creative decision-making that goes well beyond technical drawings.
• You want a bespoke, architect-designed aesthetic. If the design of your extension is a primary goal -- you want a visually striking, contemporary addition that will be photographed for design magazines -- an architect's creative skills are essential.
• You need full project management. If you do not have a builder you trust and want someone to manage the tendering process, select contractors, supervise construction, and handle snagging, a full-service architect provides that.
• The project is multi-storey or commercial. Complex projects with multiple stakeholders, planning committees, and technical challenges benefit from the comprehensive service that a percentage-fee architect provides.
• Budget is not a primary concern. If you have a generous budget and want the most comprehensive service available, a full-service architect is the premium option.

It is the right choice when:

• You know what you want. You have a clear idea of the extension, loft conversion, or alteration you need, and you want someone to draw it up professionally and navigate the planning/building regs process.
• The project is standard residential. Rear extensions, loft conversions, mansard roofs, internal structural alterations, and building regulations submissions. These are well-understood project types that do not require creative exploration.
• Budget matters. If you would rather spend your budget on better construction quality rather than higher professional fees.
• You already have a builder. If you have a trusted builder who will handle construction, you do not need an architect for project management. You just need drawings.
• You want price certainty. You want to know the exact cost of your drawings before you commit, with no risk of escalation.

The majority of residential projects in London fall into this category. A three-bed Victorian terrace in Wandsworth getting a rear extension and a loft conversion does not need a £12,000 architect. It needs accurate, professional drawings that get approval first time. That is exactly what we deliver, at a fee that is 30% below typical London architect rates.

Which costs are hidden in both models?

No fee model is entirely free of additional costs. Here is what to watch for in both:

Hidden costs with percentage-fee architects

• Stage charges. Some architects quote a percentage but only for RIBA Stages 1-3 (concept through planning). Building regulations drawings (Stage 4) and construction supervision (Stages 5-6) are quoted separately, often adding another 3-5%.
• Revision charges. Some architects include only two revision rounds. Additional rounds are charged at hourly rates of £80–£150.
• Disbursements. Printing, postage, Planning Portal submission fees, travel to site, and similar costs may be charged on top of the percentage fee.
• VAT. Percentage fees are subject to VAT at 20%. A 10% fee on a £80,000 build cost becomes £9,600 including VAT.

• Structural engineer. Our fee covers architectural drawings. The structural engineer's calculations are a separate cost (£400–£1,200 depending on complexity). We can recommend engineers we work with regularly.
• Council fees. Planning application fees (£548 householder), LDC fees (£274), and building control fees (£400–£900) are paid directly to the council or building control provider.
• Party wall surveyor. If your project involves work near or on a party wall, you need a party wall surveyor (£800–£1,500 per neighbour). This applies regardless of which fee model you use for drawings.
• Additional reports. Tree surveys, flood risk assessments, contamination reports, and similar specialist reports are outside the drawing fee. We advise which reports your project needs.

With a percentage model, the drawing cost itself is uncertain until the build is complete.

Frequently asked questions