Architect Fees UK & London: What You Actually Pay For on an Extension or Renovation

“How much do architects charge?” is the question people type when they have a sketch of a rear extension and a mortgage that already feels tight. The search results usually offer a tidy percentage, a fee calculator, or a practice promising “transparent fees” that still leave you unsure what you are buying.

Here is the blunt version: architect fees are not a single UK tariff. They depend on what stages you appoint, how complete the information is when you start, how complex the house and the neighbours are, and whether you want drawings only or someone who stays through the build as contract administrator. London work — especially on Victorian and Edwardian terraces in SW, West and Central boroughs — often costs more to design and administer than a simpler provincial job, but that is a market reality, not a HOPM price list.

This article is education first. It is written for homeowners planning an extension, loft conversion or renovation who want to understand fee language before they sign an appointment — and who keep confusing “architect fee” with “someone running my build for me as the client.” Those are related. They are not the same.

Homeowners Project Manager is a client-side renovation project manager for SW / West / Central London homeowners. We do not sell SaaS, we do not quote architect fees, and we do not pretend one person replaces the whole team. If you mainly need a stronger architect appointment, that is a valid outcome of a conversation.

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There is no compulsory architect fee scale (and has not been for decades)

Older homeowners — and plenty of online threads — still talk as if RIBA publishes a mandatory percentage scale that every practice must use. That compulsory fee scale was abolished. Practices set their own fees. Some use a percentage of construction cost. Some use fixed fees for defined stages. Some use hourly or day rates. Many mix models across a single appointment.

So if a blog, calculator or “industry guide” shows a neat table of percentages by project type and presents it as official, treat it as someone else’s marketing or opinion, not law. Ask your shortlisted practices for a written fee proposal tied to scope and stages. Compare those proposals — not a random table on the internet.

HOPM will not invent a replacement “official” fee table for you. That would be dishonest.

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What architect fees often cover (and what they often do not)

Before you argue about percentages, ask what is in the box.

Drawings-only (or design-to-planning / design-to-Building Regulations)

Commonly includes some mix of:

• Briefing and measured survey coordination (sometimes separately priced)
• Concept and developed design options
• Planning drawings and supporting material for the application
• Sometimes Building Regulations / technical drawings to a defined level

Often does not include: structural engineer calculations, party wall surveyor, full tender package, contract administration, weekly site attendance, or chasing builder prelims and provisional sums on your behalf.

Full service (design + construction stage / contract administration)

May additionally include:

• Production information for tender and construction
• Helping you appoint a contractor (sometimes)
• Acting as contract administrator under a building contract (instructions, valuations/certificates, extensions of time, variations assessment — depending on the form of contract and the appointment)
• Site inspections at agreed intervals against the design intent

Still usually does not mean: they are your commercial buyer for kitchens and bathrooms, your day-to-day WhatsApp decision engine, or a substitute for a structural engineer, party wall surveyor or building control.

For a plain map of who sits where on a typical SW London job, see renovation team roles.

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RIBA stages in plain English (homeowner version)

Architects often talk in RIBA Plan of Work stages. You do not need to memorise the numbers. You do need to know which stages you are paying for.

Rough translation for a house extension / renovation:

1. Strategic brief / preparation — do we even have a project? Constraints, budget realism, consultants needed.
2. Concept design — options, massing, how the house might work.
3. Spatial coordination / developed design — the scheme that planning (or permitted development strategy) will hang on.
4. Technical design — the information builders and engineers need so the thing can actually be built.
5. Manufacturing / construction — site stage; if appointed, this is where contract administration and inspections live.
6. Handover — completion, defects period coordination (scope varies wildly by appointment).
7. Use — usually light-touch for homeowners; do not assume it is included.

The expensive confusion happens when a homeowner thinks they bought “the architect will run the build” and the appointment actually stopped at planning drawings. Read the appointment. Ask which stages are in, which are optional, and what “site visits” means in hours per month — not vibes.

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How fees are commonly structured (models, not a HOPM tariff)

UK practices and third-party cost guides typically describe some combination of:

• Percentage of construction cost for broader appointments (fee moves with the build cost — which can create a structural tension if the fee rises when your project gets more expensive)
• Fixed fee per stage (cleaner for drawings-only or defined packages; watch where the stage ends)
• Time charge (hourly/day) for extras, redesigns, or uncertain early work
• Hybrid — fixed to planning, then percentage or fixed for technical and construction stages

London / extension angle (industry context only — verify with your quotes): complex terraces, conservation constraints, tight access, party walls, basements, and high specification finishes generally attract higher design and administration effort than a simple single-storey rear extension on a straightforward plot. Published third-party guides and practice websites discuss bands and percentages; those figures move, and they are their claims, not Homeowners Project Manager rates. Use them only as a sense of scale before you collect real proposals.

What to do instead of hunting for the “correct” percentage on a blog:

1. Write a one-page brief: scope, live-in or empty, planning status, budget ceiling for works, not just fees.
2. Ask two or three practices for fees by stage, with inclusions/exclusions.
3. Put build cost bands in a planner so fee percentages (if used) have something honest to sit on — try the extension / loft budget planner and the London extension & loft costs 2026 overview for works context (indicative, not quotes).
4. Separate design fee, CA fee, and other consultants so you are not comparing apples to scaffolding.

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Architect fees for a house extension: what changes the number

On SW / West / Central London extensions and loft-plus-extension jobs, fee proposals usually move with:

• Information completeness — sketch brief vs measured survey and a settled layout
• Planning risk — permitted development strategy vs full application vs conservation / listed constraints
• Structural complexity — steels, openings, foundations, drainage diversions (SE is usually separate)
• Neighbour interfaces — party wall timing and design knock-ons
• Finish ambition — bespoke joinery and glass vs standard catalogue
• Construction-stage involvement — drawings only vs CA with defined visit frequency

A “cheap” architect fee that stops at pretty planning drawings can become the most expensive path if the tender package is thin and every site question becomes a variation. A higher fee that includes proper technical information and a clear CA appointment can be the calmer path — if you still have someone minding the client’s commercial seat.

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Percentage of build: useful idea, dangerous slogan

People search “architects fees percentage of build cost” because it sounds comparable. It is only comparable when:

• The construction cost base is defined the same way (works only? VAT? professional fees? client direct purchases?)
• The stages included match
• You know whether redesign, planning refusals, and extra site meetings are inside or extra

If Practice A quotes X% of build for stages through construction, and Practice B quotes a fixed fee to Building Regulations drawings only, you do not have two prices. You have two different jobs. To see sourced London ranges for drawings-only and full-service architect fees side by side with the structural engineer, party wall, building control and project management, use the renovation fees calculator.

Also name the conflict out loud: on a pure percentage of construction cost, the fee rises when the build gets more expensive. Many excellent architects manage that tension professionally. You are still allowed to ask how they handle it, and whether a fixed fee for defined stages would fit your job better.

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Architect design ± CA ≠ client-side commercial seat

This is the bridge most fee articles skip.

• Architect (design) owns the design quality and the information that makes the building lawful and buildable (within their appointment).
• Architect as contract administrator (if appointed) administers the building contract: instructions, certifications, design compliance inspections, assessing variations under the contract.
• Client-side project manager is appointed by you to protect your commercial and logistical interests: like-for-like tender quality, budget visibility, programme pressure, trade pricing on finishes, snagging pressure — the seat that notices the quote never priced temporary works.

Contract administration is about the contract. Client-side PM is about the client. Detailed comparison: client-side PM vs architect contract administration.

For how client-side PM fees are structured (and why they are not the same thing as architect fees), see renovation project manager cost.

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When both make sense on SW London jobs

You do not automatically need both. You also should not assume “we hired an architect, so the client seat is covered.”

Architect CA alone can be enough when: drawings and technical information are complete, tenders already match on scope, the CA appointment is explicit (visits, response times), and you can make weekly decisions without living on the WhatsApp group.

Add a client-side seat (with or without architect CA) when: quotes disagree after “clarifications,” loft + extension or full-house work stacks consultants, you are dual-income time-poor and living in, provisional sums are doing heavy lifting in the tender, or you are mid-build and the programme is slipping without a recovery plan.

On larger or more delicate Wandsworth, Fulham, Battersea, Chelsea and Hammersmith jobs, both is often the calmest answer: architect (and SE) protect design and, if appointed, administer the contract; client-side PM protects your money, sequence and decision quality. They should talk to each other. They should not pretend to be each other.

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Practical checklist before you appoint

1. List stages included / excluded in writing.
2. Ask what happens after planning consent — is technical design in or out?
3. If CA is included, ask visit frequency, valuation process, and who answers same-day site questions.
4. Confirm which other consultants you still need (SE, party wall, building control, etc.).
5. Run builder quotes like-for-like before you treat any percentage-of-build fee as “settled.”
6. Hold contingency against works — fees are not contingency.
7. If the unknowns cluster around money and programme rather than design beauty, get a client-side read on the drawings and quotes.

Still choosing a practice? How to choose an architect in South West London covers ARB checks, the council planning register and the questions to ask before you appoint.

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Soft close — enquire / phone

If you are in SW, West or Central London with drawings or builder quotes in hand and you want a straight read on gaps, exclusions and whether you need a clearer client-side seat — enquire or phone. There is no fee for the first conversation. If you mainly need a stronger architect appointment, a better tender process, or a different builder, that is a valid outcome. This is not a pitch to skip the architect.

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See the architect fee next to every other fee: the renovation fees calculator itemises drawings, planning, structural engineer, party wall, building control, the JCT contract and project management for a London project — ex VAT, with published sources.