Planning a house extension is exciting. But before the bricks go up, there’s a decision that shapes the entire project: who designs it? Specifically, how do you choose the right person or company to handle your drawings, planning permission, and building regs?
It’s a question that trips people up more than you’d think. And it matters — get it wrong and you could end up with poorly prepared plans, drawn-out delays, or bills that spiral well beyond the original quote.
This guide breaks it all down simply, so you can make a confident decision and get your extension moving.
What Does an Architect Actually Do for an Extension?
First, let’s clear something up: you don’t always need a fully registered architect (chartered, RIBA-qualified) to get your extension designed. The term “architect” is legally protected in the UK — only those registered with the ARB can legally use the title. But the actual work of drawing up plans and submitting to the council? That can be done by an architectural designer or architectural technologist too.
What any of them should do for your extension project:
- Survey your existing property
- Produce architectural drawings (existing and proposed)
- Submit your planning application to the local council
- Handle building regulations drawings (for the structural/construction detail)
- Liaise with the council, structural engineer, and sometimes the builder on your behalf
Some companies handle all of this in-house. Others outsource large chunks of it. That distinction matters more than the letters after their name.
Registered Architect vs Architectural Designer: Which Do You Need?
For most residential extensions — rear extensions, loft conversions, side returns — a registered architect isn’t a legal requirement. What you need is someone competent who understands UK planning policy, building regs, and your local council’s preferences.
Fully chartered design professionals tend to charge more, and for a straightforward extension, much of that premium goes on professional overhead rather than added value to your project. Most companies handling extension drawings at volume are specialist architectural design firms — and they’re often significantly faster and more affordable.
That said, if your project is genuinely complex — listed building consent, unusual site constraints, structural complexity — a chartered architect’s experience may be worth the extra cost.
For the vast majority of homeowners building a standard extension, though, the key is finding someone who knows what they’re doing, communicates clearly, and handles the process end to end. See how Arkiplan handles extension drawings — drawings, planning permission, and building regs, all in-house.
What to Look for When Choosing
1. Do they handle everything in-house?
Some companies take your money, outsource the drawings to a third party, and act as a middleman. That creates delays, communication gaps, and less accountability. You want a company where the person designing your extension is the same company submitting your planning application.
2. Is the pricing clear and fixed?
Many companies quote low and then add on extras — revisions, additional drawings, structural calculations, resubmission fees. Ask specifically: what’s included in the price? Is it fixed? What would cost extra?
A good design company should give you a fixed price upfront and stick to it. Vague “from” prices with no ceiling are a warning sign.
3. What’s their track record with local councils?
Planning permission isn’t just about good drawings — it’s about understanding what your local council will and won’t approve. Ask how many planning applications they submit each month and what their approval rate is. A company doing this at volume, across England and Wales, will have seen most scenarios and know how to present your project in the strongest light.
4. Do they include structural calculations?
Building regulations drawings need to be backed up by structural engineer calculations — for things like RSJ steel beams, foundations, and load-bearing walls. Some design companies exclude these and expect you to find your own structural engineer. Make sure you know what’s included before you sign anything.
5. How do they communicate?
Will you deal with the same person throughout? Can you book a call or video meeting to discuss your plans? Or will you be sending emails into a void? Clear communication throughout the design process is what separates a smooth project from a stressful one.
Questions to Ask Before You Hire Anyone
These are the ones that actually matter:
- Who will be working on my project specifically?
- What does the fee include, exactly? What isn’t included?
- Do you handle structural calculations in-house, or do I need to arrange that?
- What happens if planning is refused? Do you resubmit?
- How long will the drawings take?
- How many revisions are included?
- Do you operate in my local council area?
If a company gives vague answers to any of these, that tells you something.
Red Flags to Watch Out For
There’s no shortage of design companies operating in the UK, and quality varies enormously. Watch out for:
- No fixed pricing — “depends on complexity” with no ballpark is a red flag
- No clear timeline — if they can’t tell you when your drawings will be ready, that’s telling
- Slow initial response — if it takes them a week to reply to your initial enquiry, imagine what the project will be like
- No examples of their work — ask to see planning applications they’ve prepared or approved projects they’ve handled
- No mention of building regs — some companies only do planning drawings and leave you to deal with building control yourself
How Much Does It Cost to Get Extension Drawings Done?
Costs vary widely depending on who you use and what’s included. As a rough guide:
- Local sole trader/architectural designer: £500–£2,000+ (often excludes structural calcs and building regs drawings)
- Mid-size design firm: £1,500–£4,000 (more likely to be full-service)
- Larger specialist extension companies: Fixed-price packages, typically £1,698–£5,498 depending on project complexity
The cheapest option isn’t always the best. A low quote that excludes structural calculations, resubmissions, or building regs drawings can end up costing more in the long run when you factor in those extras.
For loft conversion work specifically, the process is slightly different — see our loft conversion drawings and planning service for what’s involved.
Why Turnaround Time Matters More Than You Might Think
Many homeowners underestimate how long the design and planning phase takes. Once you’ve submitted a planning application, your local council has 8 weeks to decide (sometimes longer for complex applications). That 8 weeks only starts once your drawings are submitted — which means slow design work at the front end adds to an already long process.
Some companies take 3–6 months just to get your drawings ready. Others, with a more streamlined process, can have them ready in 3–6 weeks. If you’ve got a builder in mind, or a project start date in your head, that difference is significant.
Ask upfront: when will I receive my drawings? Get it in writing if you can.
The Arkiplan Approach
At Arkiplan, we do things differently to most companies. We use LiDAR 3D scanning technology to survey your home remotely, so there’s no need for multiple site visits. Meetings happen via Zoom, which means you can see your designer face-to-face from the comfort of your kitchen without anyone needing to travel.
We handle everything in-house: architectural drawings, planning application, structural calculations, and building regulations submissions. Fixed price from the start — no surprises. And we work across all of England and Wales, so wherever you are, we’ve got you covered.
Curious what that looks like for your project? Get an instant online quote for your extension drawings — it takes about two minutes.
Summary: How to Choose an Architect for Your Extension
To recap, here’s what to prioritise when choosing who designs your extension:
- Full-service company (planning + building regs + structural calcs all in one place)
- Fixed, transparent pricing
- Clear timeline for drawings
- Strong track record with local councils
- Good communication throughout
You don’t need to pay top-end fees for a simple extension. You do need someone who knows what they’re doing, communicates well, and takes the process off your plate.
Get that right, and the rest of the project is a lot less stressful.