Kitchen Extension Cost UK: What Affects the Price in 2025?

A kitchen extension is consistently one of the highest-value home improvements a UK homeowner can make — it adds usable space, improves the flow between kitchen and garden, and typically delivers strong returns when you sell. It is also one of the more complex projects, involving groundworks, structural engineering, glazing, electrics, plumbing, and a full kitchen fit-out all in sequence.

Costs vary enormously depending on size, specification, location, and site conditions. This guide gives you realistic 2025 figures, a clear breakdown by trade, and practical advice on getting quotes and managing contracts.

Types of Kitchen Extension

Single-Storey Rear Extension

The most common type for UK homes. A single-storey rear extension extends the back of the house to create a larger open-plan kitchen/dining space or kitchen/family room. It works with most property types — semi-detached, terraced, and detached.

Depth typically ranges from 3 metres to 5 metres under permitted development rights, with Prior Approval allowing up to 6 metres (semi/terraced) or 8 metres (detached). Any extension requiring full planning permission will add 8–12 weeks and £258 to the process.

Side Return Extension

Common in Victorian and Edwardian terraces, the side return fills in the narrow alleyway that runs alongside the kitchen. Often combined with a rear extension to create an L-shaped ground floor. Because the depth is limited by the existing layout, side return extensions tend to cost proportionally more per square metre than straight rear extensions — groundworks and structural work are similar, but the usable area gained is smaller.

Wrap-Around Extension

A combination of a rear and side extension, creating a substantial new ground floor addition. This typically requires full planning permission rather than permitted development. Costs are proportionally higher but the transformation to living space is significant.

Orangery

An orangery is a more traditional structure with brick pillars, a substantial lantern roof, and large glazed sections — sitting between a full extension and a conservatory. Orangeries require the same planning and building regulations approvals as a full extension and typically cost more per square metre due to bespoke glazed elements and the quality of materials expected.

Kitchen Extension Cost Table: Size × Quality Tier (2025)

All figures are for a single-storey rear extension in England, including groundworks, structure, roof, windows/doors, internal finishes (plastering, basic flooring), electrics, and plumbing first fix — but excluding kitchen units and appliances.

Budget tier: Standard brickwork matching existing, uPVC frames, flat or lean-to roof, basic finishes. Functional but no design features.

Mid-range tier: Matching brick or render, aluminium or timber frames, pitched or flat roof with lantern, underfloor heating rough-in, better insulation to meet Part L.

Premium tier: Bespoke glazing (bi-fold or sliding doors, roof lights), high-quality materials, architectural specification, structural steel exposed internally, premium finishes throughout.

Add 10–15% to all figures for London and the South East.

Detailed Cost Breakdown by Trade

1. Groundworks (£3,000–£10,000+)

Groundworks includes demolition of the existing rear wall section, excavation of foundations, laying the concrete slab or beam-and-block floor, drainage connections, and making good. Costs rise significantly if:

• Ground is unstable or requires deeper strip foundations
• There are tree roots requiring special foundations or root barriers
• Existing drains run under the extension footprint (requires diversion)
• The ground level changes significantly (steps required)

2. Structure (£8,000–£20,000+)

This covers the walls, structural steelwork, roof construction, and the structural opening from the existing house into the new space. A structural engineer's calculations are always required for the opening — budget £300–£800 for the calculations and £1,000–£3,000 for the steel beam and installation.

If you're knocking through a load-bearing wall, a structural engineer must specify the beam size and bearing pads. Never let a builder size this by eye.

3. Roof (£4,000–£15,000+)

Options include:

• Lean-to or flat roof (EPDM or GRP) — the most cost-effective; allow £4,000–£8,000
• Pitched roof to match existing — more material and labour; £6,000–£12,000
• Lantern or rooflight — adds £2,000–£8,000 per unit over the base roof cost
• Glazed roof (conservatory-style) — not recommended for kitchens due to heat gain and condensation

4. Glazing and External Doors (£3,000–£20,000+)

This is one of the biggest variables. A basic aluminium double door costs £1,500–£3,000 supplied and fitted. Bi-fold doors in aluminium typically cost £800–£1,200 per panel, so a 4-panel set could be £4,000–£6,000 before fitting. Large sliding doors or bespoke frameless glass systems can reach £15,000–£25,000.

All glazing must comply with Part K (protection from falling) and Part L (thermal performance) of the Building Regulations. Specify thermally broken aluminium or timber frames — never standard uPVC bifolds for large openings.

5. Electrics (£2,500–£5,000+)

First and second fix electrical work, including new consumer unit circuits if needed, underfloor heating wiring, external lighting, and kitchen-specific circuits (hob, oven, dishwasher, fridge). All work must be completed by a Part P registered electrician (NICEIC, NAPIT, or similar) who self-certifies.

6. Plumbing and Heating (£2,000–£6,000+)

First fix includes extending the central heating to the new space, positioning for radiators or underfloor heating manifold, and running water supply and waste for the kitchen sink and dishwasher. If the existing boiler doesn't have capacity for the additional load, a boiler upgrade adds £2,000–£4,000.

Underfloor heating (UFH) first-fix materials for a 20m² space add approximately £1,500–£3,000 for a water-fed system (more for electric).

7. Plastering and Internal Finishes (£1,500–£4,000)

Skim coat plastering of all new walls and ceilings, making good where the new extension connects to the existing house. Budget £12–£18 per square metre for skimming.

8. Flooring (£1,500–£8,000+)

The cost range is wide: basic porcelain tile (including adhesive and grout) sits at £40–£80 per square metre installed; engineered oak flooring £60–£120 per square metre; bespoke large-format tiles or marble can exceed £200 per square metre.

9. Kitchen Units and Appliances (£5,000–£50,000+)

This is a separate budget line. A standard IKEA kitchen with integrated appliances for a 3m × 5m kitchen space starts at around £5,000–£8,000 installed. A mid-range Howdens or Wren kitchen sits at £10,000–£20,000. A bespoke hand-painted shaker kitchen from a specialist company could easily reach £30,000–£60,000 for a large space.

Factors That Push Costs Up

Basement work: If the extension footprint overlaps an existing basement, or if you want to excavate beneath the new extension, costs rise dramatically. Underpinning and waterproofing alone can add £30,000–£80,000+.

Structural steel: Any large open-plan design requires significant steelwork. Exposed steel I-beams for an industrial aesthetic are not just cosmetic — they're structurally required for long spans and cost £2,000–£8,000 per beam including installation.

Bi-fold and large glazed doors: As noted above, premium glazing systems are one of the fastest ways to escalate costs. Every extra panel or metre of glass adds to both materials and the structural requirement to support it.

Underfloor heating: A fully zoned, water-fed UFH system adds £3,000–£6,000 to the build cost for a medium-sized extension but significantly improves comfort and running efficiency.

Party wall work: If you are extending close to a shared boundary, the Party Wall etc. Act 1996 may require a formal Party Wall Award. Surveyor fees (£700–£2,000+) are an additional cost the building owner must bear.

Unusual ground conditions: Made ground, high water tables, or proximity to trees can require specialist foundations (piled, raft, or reinforced strip), adding £5,000–£20,000.

Project Timeline

How to Get Quotes and What to Check in a Builder's Contract

Getting Quotes

Always get at least three quotes from different builders. Ask each to price against the same specification — if you let builders define their own scope, you'll be comparing different things.

Useful platforms to find builders:

• Federation of Master Builders (FMB) — members are independently vetted: fmb.org.uk
• TrustMark — government-endorsed scheme: trustmark.org.uk
• Checkatrade and TrustATrader — self-reporting but include verified reviews

If the cheapest quote is significantly below the others (more than 15–20%), ask why. It usually means the builder has missed scope, is planning to use cheaper materials, or will cut corners.

What to Check in a Builder's Contract

A written contract is essential. At a minimum it should include:

• Full scope of works — a detailed specification referencing drawings
• Price — fixed price where possible, or a maximum budget with any provisional sums clearly identified
• Payment schedule — milestone-based, not time-based (see below)
• Start and end dates — with a clause for what happens if the builder overruns
• Variations — how changes to scope are agreed and priced
• Materials — who supplies what, and to what specification
• Public liability and employer's liability insurance — minimum £2m public liability
• Retention — a standard 3–5% of the contract sum held for 6–12 months after practical completion, released when snagging is resolved
• Dispute resolution — how disagreements are handled; look for reference to an ADR scheme

Payment schedule advice: Never pay more than 10–20% upfront. Stage payments should be tied to measurable milestones (foundations inspected, walls to plate level, roof watertight, first fix complete) — not to calendar dates. A builder asking for 50% up front is a red flag.

For projects above £25,000–£30,000, consider a JCT Minor Works contract (available from the Joint Contracts Tribunal for around £30–£50) — it provides a standard framework for both parties.

Key Takeaways

• A kitchen extension in 2025 typically costs £25,000–£55,000 for a 3m single-storey in budget–mid spec; premium finishes and large extensions can easily reach £100,000+
• The biggest cost variables are glazing (bi-folds, rooflights), ground conditions, and kitchen specification — these can double the base build cost
• Always get three quotes and insist on a written contract with milestone-based payment
• Don't forget to budget separately for kitchen units and appliances — this is often omitted from builder quotes
• Allow 5–9 months from initial design to completion for a project requiring planning permission; 4–6 months if within permitted development limits
• A Completion Certificate from Building Control is essential — without it, you may have difficulty selling or remortgaging the property

Related Guides

• Single vs Double Storey Extension Cost UK — a side-by-side cost and value comparison to help you decide which is right for your property
• How to Project Manage a Kitchen Extension UK — phase-by-phase project management guide from brief to Building Control sign-off
• House Extension Costs UK 2025 — full regional cost table, professional fees breakdown, and cost-per-m² benchmarks
• How to Find and Manage Tradespeople for a UK Renovation — vetting builders, writing a watertight contract, and managing payments and snagging
• Permitted Development Rights UK: The Complete Homeowners Guide — check whether your extension needs planning permission or falls within PD limits