Kitchen Extension Cost in London (2026): Price, Glazing & Planning
A kitchen extension in London costs roughly £2,800–£5,000 per m² to build in 2026 — about £80,000–£150,000 all-in for a typical 20–30 m² single-storey rear or side-return extension once glazing, the kitchen itself, professional fees, VAT and contingency are included. The shell is rarely what moves the budget: your glazing (roof lantern vs bi-folds vs structural glass) and the kitchen fit-out are where a London kitchen extension gets expensive. This guide breaks down the 2026 numbers, where the money actually goes, and the planning and structural rules that catch people out.
How much does a kitchen extension cost in London in 2026?
A "kitchen extension" is almost always a single-storey rear or side-return extension built to create a bigger open-plan kitchen-diner. The build rate depends far more on specification — glazing, structure and finish — than on raw floor area.
| Specification | Build cost (per m², excl. VAT, fit-out & fees) | What you get |
|---|---|---|
| Standard | £2,800 – £3,400 | Solid shell, blockwork or timber frame, standard windows/doors, a rooflight, plastered and decorated, ready for the kitchen |
| High | £3,400 – £4,200 | Larger glazing (roof lantern + bi-folds), underfloor heating, better insulation and finishes |
| Premium | £4,200 – £5,000+ | Structural glazing, sliding or Crittall-style screens, high-end MEP and bespoke detailing |
Indicative 2026 London figures, exclusive of VAT, kitchen fit-out and professional fees.
For a typical London kitchen extension of 20–30 m², that puts the build shell alone at roughly £56,000–£120,000, before the kitchen, glazing upgrades, professional fees and VAT — which is why the all-in figure lands so much higher.
Where does the money actually go on a kitchen extension?
This is what separates a kitchen extension from a plain rear extension: two line items — glazing and the kitchen itself — can swing the budget by tens of thousands, and they sit outside the £/m² build rate. On a typical £120,000–£150,000 project, roughly:
- Structural shell and roof — around 45–55% of the budget. The foundations, walls, roof, and the steel to open up the back of the house.
- Glazing — 6–15%. A rooflight is cheap; a wall of structural glass is not (see the table below).
- The kitchen — 10–20%. Units, worktops, appliances and an island are a project inside the project.
- MEP (electrics, plumbing, heating, underfloor heating) — 8–12%.
- Professional fees and party wall — 10–14%.
The lesson: the size of the room barely moves the number. The glazing spec, the kitchen spec, and how much of the existing house you open up do.
How much do the glazing options cost in 2026?
Glazing is the single most emotive — and most variable — choice in a kitchen extension. Here are realistic 2026 London fitted costs:
| Glazing option | Typical fitted cost (2026) | Best for |
|---|---|---|
| Rooflight / roof lantern | £1,500 – £4,000 | Flooding a deep-plan kitchen with daylight on a budget |
| Aluminium bi-fold doors (standard 3–4 m span) | £3,150 – £7,200 | Opening the kitchen out to the garden |
| Sliding / large-span doors, Crittall-style screens | £8,000 – £15,000 | Wide openings, a heritage look, slim sightlines |
| Structural glazing / frameless glass box | £15,000+ | Premium architect-led extensions |
Indicative 2026 UK/London supply-and-fit figures. Spans, specification and access change the price.
A roof lantern plus a standard run of bi-folds — the most popular London combination — typically adds £6,000–£12,000 to the build. Push to structural glazing and you can add £20,000 or more.
Do you need planning permission for a kitchen extension in London?
Often not — a single-storey rear kitchen extension is frequently permitted development (PD), provided it stays within the limits:
- Rear projection: up to 3 m beyond the original rear wall for a terraced or semi-detached house, or 4 m for a detached house.
- Larger Home Extension scheme: you can go to 6 m (terrace/semi) or 8 m (detached) via a prior approval application — a neighbour-consultation process, not a full planning application. You must apply and receive approval before starting; building the larger depth without it makes the work unlawful.
- Height: maximum 4 m to the ridge, with eaves no higher than the existing eaves; within 2 m of a boundary, eaves are capped at 3 m.
- Side-return extensions must be single-storey, no wider than half the original house, and no higher than 4 m.
- Not on "Article 2(3) land": in conservation areas — and under an Article 4 direction (common across Islington, Hackney, Camden and Kensington & Chelsea) — PD rights are removed or reduced, so most inner-London period homes need full planning.
- Flats and maisonettes have no PD rights at all.
"Original house" means the property as it stood on 1 July 1948 (or as first built, if later), so earlier extensions eat into your allowance. Where PD applies, it is worth securing a Lawful Development Certificate to put the status beyond doubt before you build. See our London planning permission guide and our planning application service.
One point competitors get wrong: a 2026 kitchen extension must meet the current Part L building regulations (2021 edition, in force since June 2022) — not the Future Homes Standard. The Future Homes and Buildings Standards come into force in England on 24 March 2027 and apply mainly to new dwellings, so they do not govern a 2026 extension, though they signal where insulation and low-carbon heating are heading.
What structural work does going open-plan need?
The defining feature of a kitchen extension is knocking the old back wall through so the new space flows into the existing house. That means:
- A structural steel (RSJ) to carry the load above the new opening, sized by a structural engineer and signed off by building control. Budget £1,500–£4,000+ per opening depending on span.
- Foundations to current standards — often deeper than the existing house, especially near trees or drains.
- A Thames Water build-over agreement if you are building over or near a public sewer — common in London, and easy to miss. See our 7 hidden renovation costs guide.
- Party wall awards on a terrace or semi — £1,000–£2,500 per neighbour, with notice served around two months before work starts. See our party wall service.
Do not value-engineer the structure or the waterproofing detail at the wall junction — that is exactly where kitchen extensions later crack and leak.
How long does a kitchen extension take?
Design, planning (or prior approval) and party wall typically take 2–4 months before you start on site. The build itself is usually 10–16 weeks for a single-storey kitchen extension, plus kitchen fit-out. Plan for roughly 5–8 months end to end — longer if you need full planning in a conservation area.
Worked example: a 25 m² kitchen extension in a London terrace (2026)
| Item | Cost |
|---|---|
| Build shell & roof — 25 m² @ £3,200/m² (high standard) | £80,000 |
| Glazing — roof lantern + bi-fold doors | £8,000 |
| Kitchen — units, worktops, appliances (supply & fit) | £15,000 |
| Party wall awards (2 neighbours) | £2,400 |
| Professional fees (design, structural, building control) ~10% | £8,000 |
| Subtotal (ex VAT) | £113,400 |
| VAT @ 20% | £22,680 |
| Contingency (10%) | £11,340 |
| Indicative all-in | ~£147,000 |
Indicative 2026 London figures. A smaller standard-spec extension comes in lower; premium or larger projects run higher.
A smaller, standard-spec 18–20 m² kitchen extension with a simple rooflight can come in around £90,000–£110,000 all-in; a larger or premium project (30 m²+, structural glazing, a high-end kitchen and island) can run £180,000–£220,000+. The biggest swing factors are glazing, the kitchen spec, and ground conditions.
Does a kitchen extension add value in London?
A well-designed open-plan kitchen-diner is consistently one of the strongest returns on a London home — it is the room buyers judge a house on, and the space families use most. On the right property it can add more to the sale price than it costs to build.
The constraint is the ceiling price for your street: every road has a realistic maximum even a beautiful finish will not beat. If you are already near it, spec lighter; if you are well below it, a kitchen extension is usually where the money is best spent. Get a local estate agent's view on your ceiling price before you fix the glazing and kitchen budget.
How to keep a kitchen extension on budget
- Get a proper Bill of Quantities so every builder prices the exact same scope — no apples-to-oranges quotes.
- Choose your glazing and kitchen before you tender. Switching from bi-folds to structural glass, or a mid-range kitchen to a bespoke one, mid-build is where budgets run.
- Use a fixed-price contract, not day rates.
- Keep the kitchen and interior fit-out on the same drawings as the build — get interior design involved early so services, lighting and the island are coordinated, not retrofitted.
- Decide early whether a side-return extension or a loft conversion would hit your goal for less.
Related guides
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Get a free estimateFrequently asked questions
- How much does a kitchen extension cost in London in 2026?
- Roughly £2,800–£5,000 per m² to build, or about £80,000–£150,000 all-in for a typical 20–30 m² single-storey extension once glazing, the kitchen, professional fees, VAT and contingency are included.
- Do I need planning permission for a kitchen extension?
- Often not. A single-storey rear extension up to 3 m (terrace/semi) or 4 m (detached) is usually permitted development, extendable to 6 m/8 m via prior approval. But PD rights are removed in conservation areas and under Article 4 directions, and flats have none.
- What's the most expensive part of a kitchen extension?
- Not the floor area — it's the glazing and the kitchen itself. A roof lantern plus bi-folds adds £6,000–£12,000; structural glazing adds £20,000+. A bespoke kitchen can cost more than the shell it sits in.
- Do I need a structural engineer to open up the back of my house?
- Yes. Knocking the rear wall through to go open-plan needs a steel beam (RSJ) sized by a structural engineer and signed off by building control, typically £1,500–£4,000+ per opening.
- How long does a kitchen extension take?
- Around 5–8 months end to end — 2–4 months for design, planning and party wall, then 10–16 weeks on site plus kitchen fit-out.
- Is VAT charged on a kitchen extension?
- Most extension work on an existing home is standard-rated at 20%. Limited reliefs exist for listed buildings and homes empty for two years or more — check eligibility before assuming.