Architect percentage fees vs fixed fee: which saves you more?

How percentage fees 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.

How our fixed-fee model works

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

The difference between percentage fees and fixed fees becomes stark when you run the numbers on real London projects. Here are five common scenarios:

On every project type, the fixed-fee model saves the homeowner thousands of pounds. The savings increase as the build cost rises, because the percentage fee scales up while the fixed fee stays constant.

On a typical London extension costing £80,000, you save between £4,650 and £6,775 by using our fixed-fee service compared to a 10% architect. 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.

The scope creep problem with percentage fees

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.

With a fixed-fee model, the price you agree at the outset is the price you pay. 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

A fixed fee gives you certainty from day one. 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 a percentage-fee architect makes 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.

When fixed fee is the better choice

Our fixed-fee service is designed for homeowners who need professional, council-approved drawings at a fair price. 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, a fixed-fee service delivers the same regulatory outcome at a fraction of the cost.
• 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.

Get a free fixed-fee quote →

Hidden costs 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.

Hidden costs with fixed-fee services

• 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 (£258 householder), LDC fees (£129), 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.

The key difference: with a fixed-fee model, you know the drawing cost upfront and the additional costs are clearly identified. With a percentage model, the drawing cost itself is uncertain until the build is complete.

Frequently asked questions