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Thinking about a kitchen extension in London? Get realistic 2026 pricing for every type of extension, understand what drives costs, and learn how to budget effectively.
A kitchen extension is arguably the single most popular home improvement project in London. It addresses the main shortcoming of many period homes — a small, dark, separate kitchen tucked away at the back of the house — by creating a bright, spacious, open-plan kitchen-diner that becomes the heart of the home. Whether you are extending into the rear garden, building out to the side (a side-return extension), or wrapping around both, the result can be transformative. But kitchen extensions in London are a significant investment, and understanding the costs involved is essential for effective budgeting.
Good to Know
These figures include the building work, structural steels, foundations, roofing, glazing, plastering, electrics, plumbing, and decoration — but they do not include the cost of the kitchen itself, which should be budgeted separately. A good-quality kitchen installation adds £10,000–£30,000 to the total.
The headline cost per square metre for a kitchen extension in London ranges from around £2,000 to £3,500, depending on the specification and complexity. However, this per-square-metre figure can be misleading because certain fixed costs apply regardless of size — such as structural steels, building control fees, professional fees, and the cost of connecting utilities. A very small extension may have a higher per-square-metre cost than a larger one because these fixed costs are spread over a smaller area.
Foundations are one of the biggest variables in extension costs. In most of London, standard strip foundations are sufficient, but if the site has poor ground conditions, is near trees (particularly on clay soil), or is close to a boundary, deeper or more complex foundations may be required. Piled foundations, which are sometimes needed in London due to nearby trees or unstable ground, can add £5,000–£15,000 to the cost. If there are existing drains beneath the footprint of the extension, these will need to be diverted, which is another significant cost.
Most kitchen extensions in London involve removing part or all of the rear wall of the house, which is usually load-bearing. This means structural steelwork (RSJs or universal beams) must be installed to support the structure above. The cost of steelwork depends on the span — a single opening to a small extension might require a steel costing £1,500–£2,500 installed, while a large opening spanning the full width of the house could cost £3,000–£5,000 or more. Structural engineer fees for designing the steelwork are typically £500–£1,000.
The type of glazing you choose has a major impact on both the cost and the feel of the finished extension. Standard bi-fold doors in aluminium cost from around £3,000 for a 3-panel set, while premium systems from brands like Schuco or Origin can cost £6,000–£10,000. Sliding doors are increasingly popular as an alternative to bi-folds, offering larger panes of glass and a more contemporary look. Roof glazing — whether a flat rooflight, a glazed lantern, or a full glass roof — is another significant cost item, ranging from £1,500 for a single rooflight to £10,000+ for large structural glazing.
Top Tip
Consider a large fixed pane of glass with a single opening door rather than full bi-fold doors. This approach is often cheaper, provides better thermal performance, and gives you a cleaner view of the garden without the visual interruption of multiple frames.
The number one rule for staying on budget with a kitchen extension is to have a clear, detailed specification before you get quotes. Vague plans lead to vague quotes, which lead to unexpected extras. Work with your architect to produce a comprehensive set of drawings and a specification document that covers every material and finish. Get at least three quotes from reputable builders and compare them on a like-for-like basis. Set aside a contingency of 10–15% for unexpected costs — in renovation work, surprises are almost guaranteed.
The cost per square metre for a kitchen extension in London in 2026 ranges from £2,000 to £3,500, depending on the specification, site conditions, and level of finish. This is the building cost only and does not include professional fees, the kitchen installation, or VAT.
Many single-storey rear extensions can be built under permitted development rights without planning permission, provided they meet the size and height limits. Extensions up to 3 metres (semi-detached/terraced) or 4 metres (detached) from the original rear wall typically qualify. Larger extensions of up to 6 or 8 metres may be possible through the prior approval process.
A typical single-storey kitchen extension takes 8–14 weeks on site from breaking ground to completion. Allow additional time before construction for design (4–8 weeks), planning permission if needed (8–12 weeks), building regulations (2–4 weeks), and party wall agreements (2–3 months).
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