The short answer
Usually not. For a small, standard extension — a modest single-storey rear or side addition that follows a familiar pattern — you rarely need a full architect. You still need accurate drawings (for planning, if it's not permitted development) and technical drawings plus structural calculations for Building Regulations, but those can come from an architectural technologist, an architectural designer, a structural engineer, or even your builder's own plans. "Architect" is a protected title, not a legal requirement for the work. An architect can still add value on a small extension if the design is tricky, the site is sensitive, or you want a more ambitious result — but for a simple box on the back, paying full architect fees is often more than the job needs.
Small extensions are where the "do I need an architect?" question matters most, because the fees can be a big share of a small budget. Here's an honest look at when you can skip the architect and when even a modest extension benefits from one.
Small extension drawings
- Architect required?No
- Often falls underPermitted development
- Building RegsStill needed
- Cheaper routeTechnologist / designer
- Architect worth it ifDesign-led or sensitive site
Why small extensions often don't need an architect
A small, conventional extension is a well-trodden problem, which is exactly why it's often the wrong place to spend full architect fees. Two things usually keep it simple:
- It may not need planning permission at all. Many single-storey rear and side extensions fall under permitted development, within set size limits. If yours does, you can often proceed without a full planning application — a Lawful Development Certificate is a sensible way to prove it.
- The design is fairly standard. When the layout is obvious — extend the kitchen, add a utility, square off the back — you mainly need compliant, accurate drawings rather than design exploration.
You still must satisfy Building Regulations, with technical drawings and usually structural calculations for any beam over an opening. But none of that is reserved to architects — a technologist or designer handles it routinely and more cheaply.
Who can design a small extension
For a small job, the routes mainly differ on cost and how much design thinking you want. The cheaper options are perfectly capable of producing compliant drawings.
| Route | Suits | Relative cost |
|---|---|---|
| Architectural technologist | Compliant technical drawings | Mid |
| Architectural designer | Simple standard extensions | Lower |
| Builder's own plans | Very simple, well-trodden jobs | Lowest |
| Architect (ARB/RIBA) | Design-led or sensitive small jobs | Higher |
Indicative comparison for guidance only. Sources: HomeOwners Alliance and Checkatrade guidance.
When even a small extension benefits from an architect
"Small" doesn't automatically mean "simple". There are cases where a modest extension still rewards an architect's input:
- You want it to be more than functional — lots of glazing, a considered roofline, a careful relationship to the garden, or a design that lifts the whole house.
- The site is constrained or sensitive — a conservation area, listed building, tight urban plot or awkward levels — where design quality affects both planning success and the result.
- The extension is reorganising how the ground floor works, not just adding area, so the layout decisions are worth getting right.
- You're close to a neighbour's boundary or windows and a well-judged design helps the planning case.
The honest summary: for a simple small extension, a technologist, designer or your builder's plans will usually give you everything you legally need at a fraction of architect fees, and that's a sensible saving. Reserve the architect for the small jobs that are design-led or genuinely tricky, where the fee buys a better result rather than just compliant paperwork. Either way, budget for a structural engineer if there's a beam or opening involved.
Frequently asked questions
Does a small extension need planning permission?
Often not. Many single-storey rear and side extensions fall under permitted development within set size limits. If yours does, you can usually proceed without a full planning application, though Building Regulations still apply. A Lawful Development Certificate proves it's lawful.
What's the lowest-cost way to get drawings for a small extension?
An architectural designer or your builder's own plans are usually the lowest-cost routes for a simple extension, with an architectural technologist a step up for more technical confidence. All can produce drawings that satisfy Building Regulations.
Do I need a structural engineer for a small extension?
Usually yes if there's a steel beam or a new opening into the house, since those need structural calculations for Building Regulations. A purely simple addition with no structural change to the existing house may need less, but most extensions involve some structural work.
Sources & further reading
- Planning Portal — extensions and permitted development
- HomeOwners Alliance — do I need an architect?
- Checkatrade — extension cost guide
Figures on this page are typical UK ranges drawn from published sources and depend on your specific project. They are guidance, not a quotation.