The short answer
For a typical single-storey kitchen extension (a rear or side extension creating an open-plan kitchen-diner), an architect's fee is usually a fixed fee in the four-figure range for design plus planning and building-regulations drawings, or a percentage of the construction cost (commonly around 7%–15%) for a full service that includes overseeing the build. The figure depends on the size and design (a simple box versus a glazed, design-led space with rooflights and bifolds), whether planning is needed or it's permitted development, and your location. The architect's fee is separate from the build cost, the structural engineer, the planning fee and Building Control. Kitchen extensions are popular enough that fees are fairly predictable, but design quality varies a lot, which is where an architect can add real value.
A kitchen extension is one of the most common UK home projects, and the architect's fee depends on how design-led it is and how much of the work they handle. Here's the breakdown.
Architect cost — kitchen extension
- Design + drawingsFixed fee, four figures
- Full service~7%–15% of build cost
- Separate costsEngineer, council fees
- Biggest driverGlazing & design ambition
- PlanningSometimes permitted development
What the architect's fee covers
For a kitchen extension an architect can be appointed for some or all of the work:
- Design: the layout of the new kitchen-diner, how it connects to the existing house, and how light enters — rooflights, large glazing or bifold doors are common and need careful handling.
- Planning drawings: preparing a planning application, or a lawful-development certificate where the extension is permitted development.
- Building-regulations drawings: the technical set covering structure (often a steel beam where the rear wall opens up), insulation, drainage and more.
- Construction stage (optional): overseeing the build, inspecting and handling queries.
The design of a kitchen extension matters more than its size suggests — getting the light, the ceiling height, the connection to the garden and the flow of the open-plan space right is what separates a good extension from a flat one. That's the part an architect most clearly adds to.
Typical fees and separate costs
The architect's fee is one line among several. The build is the largest cost, and the structural engineer and statutory fees are separate from the architect.
| Item | Indicative figure | Notes |
|---|---|---|
| Architect — design + drawings | Lower–mid four figures | scales with design ambition |
| Architect — full service | ~7%–15% of build | if overseeing the build |
| Structural engineer | Separate fee | beam over the opening |
| Planning / lawful-dev fee | Paid to council | if an application is needed |
| Building Control fee | Paid to council/inspector | checks the build |
Indicative UK figures for guidance only. Excludes the build cost and VAT. Source: Checkatrade and HomeOwners Alliance cost guides.
Where the value is, and how to decide
Because kitchen extensions are so common, you'll find everything from a builder's free 'we'll sort the drawings' offer to a full architect-designed scheme. The right choice depends on how much the result matters to you. If you simply want a slightly bigger kitchen in a standard box, a technologist or a builder's drawings may be enough. If you want a light-filled, well-proportioned kitchen-diner that genuinely changes how the house feels — and adds to its value — an architect's design input is usually where the money is best spent.
Whichever route you choose, be clear about scope. Confirm whether the fee covers design and drawings only, or also overseeing the build; whether planning is needed or it's permitted development; and who is arranging the structural engineer and the Party Wall matters. Budget the whole project — architect, engineer, statutory fees and the build — rather than just the design fee, so there are no surprises. A kitchen extension done well is one of the most rewarding home improvements; the fee is worth weighing against how much the finished space, and its value, matter to you.
Design choices that shape the cost
A kitchen extension's size is only part of what drives the cost — the design decisions often matter more, and they're where an architect's input shows. A few choices that significantly affect both the feel of the space and the budget:
- How you bring in light: rooflights, a glazed lantern, large sliding or bifold doors, or a glass link all transform a single-storey extension, but glazing is more expensive than wall and affects the structure and heat performance.
- The roof form: a flat roof, a pitched roof or a lantern changes the ceiling height, the light and the external look. Higher ceilings make a kitchen-diner feel far more generous.
- How far the rear wall opens up: a wide opening into the existing house creates the open-plan effect most people want, but needs a bigger steel beam and more structural work.
- The connection to the garden: floor levels meeting, the threshold detail and how the doors open all affect how usable the space is in practice.
- Finishes and services: underfloor heating, the position of the kitchen, and relocating radiators, sockets and plumbing all add to the build cost.
None of these are 'extras' bolted on at the end — they're design decisions best made early, because they're interlinked. The roof affects the light, the glazing affects the structure, the opening width affects the beam. An architect who thinks them through as a whole tends to produce a space that feels considered and generous for a given budget, rather than a plain box with money spent in the wrong places. That coherence is the real argument for design input on a kitchen extension: the same build cost can buy a very ordinary room or a genuinely good one, and the difference is largely in the design decisions made before a brick is laid.
Frequently asked questions
Do I need an architect for a kitchen extension?
Not necessarily. A technologist or a builder's drawings can suffice for a simple box extension. An architect is most worth it where you want a light-filled, well-designed open-plan space that changes how the house feels and adds value — design is where they most clearly contribute.
Does a kitchen extension need planning permission?
Often it's permitted development within size limits, so full planning permission isn't always required, but you'll still need building-regulations approval. Larger extensions, conservation areas, flats and corner plots can change this, so check with your local authority.
Is the structural engineer included in the architect's fee?
Usually not. Opening up the rear wall for an extension typically needs a steel beam, and the structural calculations for it are normally a separate engineer's appointment and fee, even if the architect coordinates them.
Sources & further reading
- Planning Portal — extensions
- Checkatrade — kitchen extension cost guide
- HomeOwners Alliance — extending your home
Figures on this page are typical UK ranges drawn from published sources and depend on your specific project. They are guidance, not a quotation.