Do I Need an Architect for an Extension?

The honest answer: no, not by law

For most home extensions in England there is no legal requirement to use an architect, or any designer at all. You could, in principle, draw the scheme yourself and submit it. The word "architect" is protected by law — only someone registered with the Architects Registration Board (ARB) may call themselves one, and you can check any name for free on the public ARB register — but nothing obliges a homeowner to appoint an architect on the ARB register to extend a house.

So the real question is not "am I allowed to proceed without an architect?" — you are. It is "will the outcome be good, will it get approved, and will it cost me more in the long run to have skimped on design?" That is a judgement about your specific project, not a rule. The rest of this guide is written to help you make it honestly.

What the law actually requires

The legal obligations attach to the works, not to who designs them. In practice a London extension has to clear two separate gates, and both usually apply regardless of who prepares the drawings.

• Planning: you need either planning permission, or confirmation that the works are permitted development (often worth fixing in writing with a [[service:lawful-development-certificates|lawful development certificate]]). Much of prime London is in a conservation area or under an Article 4 direction, which restricts or removes permitted development, so this cannot be assumed.
• Building regulations: almost every extension needs building control approval for structure, insulation, drainage, fire safety and more — this is separate from planning and applies even when no planning permission is required.
• Party wall: where you build near or on a shared boundary, the Party Wall etc. Act 1996 imposes its own notice and surveyor process, again independent of who designs the extension.

Architect, architectural designer or design-and-build?

"Do I need an architect?" often really means "who should design this?" There are three common routes, and the honest position is that each suits different projects rather than one being universally right.

An architect on the ARB register has completed accredited training and is regulated by the ARB. An architectural designer or technician (sometimes called an architectural technologist) may be equally skilled at producing extension drawings but is not on the ARB register and cannot use the title "architect" — the label tells you about regulation and training, not automatically about the quality of any given individual. A design-and-build contractor bundles design and construction under one roof, which can be convenient but places the designer on the builder's side of the table rather than yours.

• Architect — regulated title, typically suited to design-led, planning-sensitive, listed or higher-value work where independent advice matters most.
• Architectural designer / technician — can be well suited to straightforward, technically-driven extensions; check the individual's experience and examples rather than the label.
• Design-and-build — one point of contact, but weigh the loss of an independent eye acting purely for you, particularly on quality and cost.

The drawings you need regardless

Whoever you appoint — or if you attempt it yourself — an extension cannot be approved or built well on a sketch. The information falls into two distinct sets that serve different purposes and are produced at different stages.

Planning drawings show what the extension looks like and how it sits on the site: existing and proposed plans, elevations and sections, drawn to scale. They answer the planning authority's question about acceptability. Building regulations drawings come later and answer a different question — how the thing is actually built — with construction detail, structural design (usually with a structural engineer) and specification. A common and costly misunderstanding is treating the two as interchangeable; a planning consent does not mean you have anything a builder can price or construct from. Our guide on planning drawings versus building regulations drawings covers the distinction in full.

When professional design genuinely pays

There are projects where paying for experienced design is not a nicety but the single best-value decision you make. The honest signal is risk and value: the more that can go wrong, or the more the finished home is worth, the more design earns its fee.

Equally, we would not pretend every project needs a full architectural service. A modest, clearly permitted-development rear extension on a standard house may need little more than competent drawings and a certificate. The point is to match the depth of design to the actual demands of the project.

• Planning-sensitive sites — conservation areas, listed buildings, Article 4 directions or a history of refusals nearby, where how the case is designed and argued materially affects whether it is approved.
• Structurally significant work — removing walls, going up a storey, or [[service:side-return-extension-architects|side-return]] and wraparound schemes where the structure is a major cost and safety variable.
• Contested or overlooked settings — where neighbour amenity, overlooking or daylight will be scrutinised and a considered design defuses objections.
• High-value homes — where design quality, light and flow move the finished value by far more than the fee, and a poor extension is an expensive mistake to live with.

Approvals still need managing

Even where you are content to keep design light, someone has to run the approvals. A planning application has to be prepared and submitted correctly, conditions discharged before work starts, and building control satisfied during construction. The statutory fees are set by government, not by the designer: a householder planning application is £548 (from 1 April 2026), a lawful development certificate is £274, and listed building consent carries no council fee — though it demands more drawings and a heritage justification. These are the same in every London borough, and sit on top of any design fee.

Getting an application refused, or building something that later fails to demonstrate compliance, is far more expensive than doing the drawings properly first. This is often where homeowners who started out planning to "just do the drawings myself" decide that focused professional help is worth it.

Buying design stage by stage

The practical answer to "do I need an architect?" is rarely all-or-nothing. You can buy design in stages and stop when you have what you need, which is exactly how our fixed-fee packages are structured — so you are never committing to a full service to get started.

Most projects begin sensibly with a £395 Planning Route Review: a fixed-fee assessment of what your property actually allows, which route to take, and what it will involve — and the £395 is credited against the work if you proceed. From there you can commission planning drawings, then building regulations and tender drawings, each as a separate fixed-fee step. We charge fixed fees rather than a percentage, so you know the number before committing, and larger, listed or complex schemes are quoted after the review. The full packages and prices are set out on our packages page.