House Extension Architect Fees: What I Charge, Stage by Stage
Updated: Aug 12
Níall Hedderman · ARB-registered architect · RIBA Chartered Member
I've run my own architecture practice in Edinburgh since 2009, specialising in altering, extending and renovating homes. Since 2022 I've given over 340 online consultations to homeowners and buyers across the UK.
Hiring an architect for a house extension in the UK typically costs 10% to 13% of the construction budget for a full service from first sketch to completion certificate.
On a £175,000 extension that is roughly £18,000 to £24,000.
Those are my own fees, published in full, which almost no architect does. Below I break down what each stage buys, what is not included, when you don't need an architect at all, and how to brief local practices so you can compare like with like.
Most architects don't publish fees, but I do
There are no fee scales in the UK. Every practice sets its own, and most quote privately on enquiry. Percentage fees are increasingly rare; most of the architects I know use a mix of fixed prices and hourly rates.
I publish mine because most of my clients have never hired an architect or commissioned a building before, and have no way of knowing what is normal. Putting the numbers in public gets the awkward conversation off the table before it starts. My fees are what they are and I don't negotiate.
One thing worth understanding before you look at any number: you are not buying drawings. People ring me and ask what the drawings will cost, and it is the wrong question. This is a process, not a product. Drawings happen along the way, but what you are paying for is judgement, training, experience, and access to a network — because good designers work with good builders, suppliers and consultants.
The six stages, and what each one buys
Feasibility study. I survey the existing house and draw up options. Charged by the hour, because I cannot predict how many times you will want the design revised before you are happy. Everything after this is fixed price.
Planning application. I lodge the application and handle any negotiation with the planning department. If your property is listed, listed building consent is part of the same stage at no extra cost.
Building warrant. The technical approval. I coordinate with a structural engineer and, where needed, an energy consultant, to produce a full construction package. Most people are fixated on planning, but far more work goes into this stage, which is why it costs more.
Pre-construction. I write a scope of works listing every element so it can be priced individually, then either tender it or negotiate directly with contractors.
Construction. A monthly retainer plus a fee for each site inspection, usually two a month. This covers correspondence, contractor valuations, payment certificates, instructions, cost reporting, snagging, the three-month defects inspection and the completion certificate application. Note that this is contract administration, not project management. I inspect the contractor's work; I do not supervise it. On projects this size that role belongs to the main contractor.
Post-construction. Only applies if an amendment to the building warrant is needed, where the finished building differs from the approved drawings. That happens on roughly a third to a half of projects.
Worked example: a £175,000 extension
Feasibility study — 17 to 32 hours at £125 per hour = £2,125 to £4,000
Planning application — £2,900
Building warrant — £5,000
Pre-construction — £3,300
Construction — 5 to 8 months at £500 per month, plus around £200 per site visit twice a month = £4,500 to £7,200
Total — roughly £17,800 to £22,400
Add £1,500 if an amendment to warrant is needed at the end. That is about 10% to 13% of the construction budget.
No VAT, and why that matters
I work alone and don't employ staff, and my turnover stays below the VAT registration threshold. VAT does not apply to my fees.
This is worth understanding when you compare quotes. Homeowners cannot reclaim VAT. A practice with an office and staff carries higher overheads and will usually be VAT registered, so their fee is 20% more expensive than the headline figure before you have compared anything else. That is not a criticism of them — it is a real difference in what leaves your bank account.
What the fee does not include
Council lodgement fees for planning and building warrant applications are paid on your behalf and added to your invoice at cost. They are not a fee to me.
A planning appeal, or a fresh application, if permission is refused.
Structural engineer and energy consultant fees, which are separate appointments.
Interior design, and any redesign requested after the feasibility study is signed off. Once the design is frozen, changes are charged by the hour.
Cost estimates. I used to produce these myself and stopped, because construction inflation made them unreliable. Get a proper cost before you spend money on a planning application — there is no point getting permission for something you cannot afford to build.
How to find and brief a local architect
The fees above apply to my own practice, and only to projects in Edinburgh, the Lothians and Fife. Elsewhere in the UK the number will differ. London is dearer than anywhere else. In remote and rural areas there are fewer architects to choose from, and that affects what they charge. A young practice just starting out will charge less than I do; a firm with an office and staff will charge more, plus VAT.
Every architect in the UK is registered with the Architects Registration Board, and you can check anyone's status on the ARB register before you engage them. Companies are not registered — individuals are.
When you approach practices, brief them all identically. Give the address and age of the property, what you want to achieve, the remedial work you already know about, and your maximum construction budget. Then ask each of them the same questions: is this the type and size of project you normally take on, do you offer a consultation before I commit, and how are your fees structured. If you brief three practices differently you will get three quotes you cannot compare.
Not sure whether you need an architect at all?
That is the question I am asked most often, and it is the reason I run online consultations.
Thirty minutes on a video call, anywhere in the UK, £130. I will look at your property and your plans beforehand, tell you honestly whether what you want is realistic on your budget, what approvals it will need, and what the work is likely to cost.
Afterwards I send a written summary, including guidance on how to approach local architects with a clear description of the works required, and the statutory approvals your project will need. You can take that brief to any practice in the country.
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