Kitchen Extension Cost UK 2026: Full Breakdown

Build costs, kitchen fit-out, hidden extras — and what actually makes the price go up

Buildcostr.ai · July 2026 · 8 min read

What does a kitchen extension cost in 2026?

A kitchen extension is really two projects in one: the structural build (the box), and the kitchen fit-out (what goes inside it). Most people focus on one and underestimate the other. Here are realistic figures for both.

A single-storey rear kitchen extension in the UK typically costs £1,800–£3,200 per square metre for the structural build. A 25m² extension therefore runs £45,000–£80,000 before the kitchen itself. Add a well-specified kitchen and you are looking at a total project cost of £60,000–£120,000.

Full cost breakdown

The kitchen itself: the most variable cost

The structural build cost is the easier number to pin down. The kitchen fit-out is where the range is enormous — from a functional flat-pack kitchen at £5,000 to a bespoke hand-painted in-frame kitchen with stone worktops and integrated appliances at £50,000 or more.

Budget kitchen (£5,000–£12,000)

IKEA, Wren or B&Q kitchens with laminate worktops and mid-range appliances. Perfectly functional and widely chosen by homeowners who plan to sell within 5 years. Installation typically included in the quoted price.

Mid-range kitchen (£12,000–£25,000)

Howdens, Magnet or smaller independent suppliers. Solid wood doors, composite or quartz worktops, integrated appliances. The sweet spot for most homeowners — durable, attractive and not ruinously expensive.

Premium kitchen (£25,000–£60,000+)

Bespoke cabinetry from specialist makers — Neptune, deVOL, Tom Howley or similar. Hand-painted finishes, stone worktops, Quooker taps, Bora or Miele appliances. Designed to last decades and to become a genuine selling point.

Glazing: where kitchen extensions get expensive fast

The most common reason kitchen extension costs exceed initial budgets is glazing. Bi-fold doors, roof lanterns and large skylights transform the space — but they are expensive. Here is a rough guide:

• Bi-fold doors (3m wide): £3,500–£8,000 supplied and fitted
• Bi-fold doors (4–5m wide): £6,000–£14,000
• Roof lantern (1.5m × 1m): £2,500–£5,000
• Roof lantern (2m × 1.5m): £4,000–£8,000
• Fixed skylights (per unit): £800–£2,500

A kitchen extension with a large roof lantern and full-width bi-fold doors can easily spend £15,000–£25,000 on glazing alone. Build this into your budget before you fall in love with the design.

Wrap-around extensions

A wrap-around extension extends across the full rear and one side of a property, creating an L-shaped footprint. These are popular for kitchen-diners as they maximise light from multiple directions and often allow for a much larger open-plan space.

Wrap-around extensions almost always require planning permission as the side extension element typically falls outside permitted development limits. Budget 20–30% more than a straight rear extension of the same floor area, reflecting the additional structural complexity and planning costs.

Single-storey vs double-storey kitchen extension

Some homeowners add a bedroom or bathroom above the kitchen extension, making it double-storey. The additional cost per square metre for the upper floor is lower than for the ground floor — you already have the foundations and structure — making double-storey extensions excellent value per square metre overall.

A double-storey extension adds roughly 40–60% to the cost of a single-storey build of the same footprint. So a single-storey at £60,000 becomes roughly £85,000–£95,000 double-storey — while roughly doubling the floor area gained. Read our full guide to single vs double storey extension costs.

Regional cost differences

Labour costs drive significant regional variation. A kitchen extension that costs £65,000 in a Midlands town could cost £85,000–£95,000 in London for the same specification. The South East sits 10–20% above national averages; the North and Wales tend to sit 5–15% below.

If you are in London specifically, read our dedicated guide to house extension costs in London for more precise figures.

Do I need planning permission for a kitchen extension?

Many single-storey rear kitchen extensions fall under permitted development rights in England and do not require a planning application, provided the extension does not exceed 3m in depth for terraced or semi-detached properties, or 4m for detached houses. Extensions beyond these limits, side returns, and any project in a conservation area will need full planning permission.

Building regulations approval is required regardless — covering structural design, insulation, ventilation and electrics. Budget £600–£1,200 for building regulations fees. Read our full guide to planning permission costs for more detail.

How to get an accurate kitchen extension cost

The most common reason kitchen extensions go over budget is not the build — it is the kitchen itself. Homeowners underestimate how much they will spend on units, worktops, appliances and glazing once they start making choices they love.

A professional cost plan produced before you start — covering the full build and a realistic kitchen budget — protects you from that creep. Buildcostr.ai produces a complete, itemised cost plan from your architectural drawings in 30 minutes, covering all 15 NRM2 cost sections including finishes and fit-out allowances. See a sample report or order yours from £99.

Also useful: our guides to house extension costs in 2026 and how to read a builder's quote.