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Kitchen Extension vs Rear Extension: Cost Compared (2026)
A rear extension describes the structure (a single-storey build off the back of the house); a kitchen extension is a rear extension that happens to house a new kitchen. So the shell costs the same — roughly £2,000–£3,000/m² in 2026 — and the real cost gap is the kitchen fit-out, which adds £8,000–£30,000+ depending on units, worktops and appliances. This guide compares the two line by line so you can budget accurately and decide which adds more value to your home; our guide on how much an extension adds to value and current single-storey extension costs can help you plan.
Cost per m² Shell vs fit-out Resale value
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Side by Side
Kitchen Extension vs Rear Extension (2026)
Typical single-storey build, 20 m², standard spec, England & Wales.
Which to Choose
Which Adds More Value?
- For resale, the fitted kitchen extension wins. A modern open-plan kitchen-diner is the single most requested feature by UK buyers and typically returns 60–80% of its cost at sale, more in higher-value areas.
- For pure floor-space-per-pound, the empty rear extension is cheaper. If you only need a bigger living room or playroom, you skip the £8k–£30k kitchen bill entirely.
- Watch the kitchen spec creep. The shell price is predictable; the kitchen is where budgets blow out. Set the units/worktop/appliance budget before you start.
- Both usually fall under permitted development up to 6m (terraced/semi) or 8m (detached) under the larger-home extension rules — but check before you commit.
Frequently Asked
Common Questions
Often yes. A single-storey rear extension up to 6m on a terraced or semi-detached home, or 8m on a detached home, usually falls under permitted development with prior approval, and adding a kitchen inside it does not change that. You still need building regulations sign-off for the structure, drainage and electrics, and conservation areas or listed buildings are exceptions, so check whether you need planning permission for a rear extension before you start.
Kitchen fit-out is where extension budgets usually overrun, because units, worktops and appliances vary enormously while the building shell stays the same price. Fix your kitchen specification and appliance list before work starts, keep a contingency of around 10 to 15 percent, and get like-for-like written quotes on identical drawings so you are comparing builders fairly. A clear, locked specification is the single biggest protection against cost creep.
Only by the cost of the kitchen itself. The building shell costs the same — £2,000–£3,000/m². A kitchen extension adds £8,000–£30,000+ for units, worktops, appliances and plumbing on top.
A fitted open-plan kitchen-diner extension usually adds the most resale value because it's the feature UK buyers most want. An empty rear extension adds space cheaply but less wow-factor.
Often neither — single-storey rear extensions up to 6m (terraced/semi) or 8m (detached) usually fall under permitted development with prior approval. Conservation areas and listed buildings are exceptions.
A single-storey shell is typically 8–12 weeks. A kitchen extension adds 2–4 weeks for the kitchen fit, plumbing and electrics, so budget 10–16 weeks all-in.
Get at least 3 like-for-like written quotes on the same spec and drawings. Extension prices vary 30–50% between builders for identical work, so comparing fairly is the single biggest money-saver.
Reviewed by the BestBuilders editorial team · Last updated: 10 August 2026 · See our editorial standards.
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