What are the main types of house extension in London?

The three most common are rear extensions (extending into the garden), side return extensions (filling in the narrow passage alongside a terraced house) and wraparound extensions (combining both for an L-shaped footprint). Double storey extensions add space on two floors simultaneously. The right option depends on your property layout, garden size, budget and planning situation.

Which house extension is right for my London home?

A side return extension is ideal if you want to widen your ground floor without losing garden space. A rear extension suits most property types and is the most cost-effective way to create a larger kitchen or living area. A wraparound is best when you want the maximum possible ground floor transformation and have the budget for it. We'll recommend the right approach during your free site visit.

Do I need planning permission for a house extension in London?

Not always. Single-storey rear extensions up to 3 metres beyond the original rear wall (terraced and semi-detached) or 4 metres (detached) often fall under permitted development rights. However, PD rights have been removed in many London conservation areas, so it's important to check before assuming. LLAC confirms your planning situation at the initial consultation.

How long does a house extension take?

Build time depends on the extension type and scope. A single-storey rear extension typically takes 10 to 16 weeks on site. A wraparound or double-storey extension takes longer, often 16 to 24 weeks, due to the additional structural work and build programme. Your overall timeline should also factor in any planning permission required, which can add several months before work begins.

What changes the price of your house extension in London?

The main factors are the size and type of extension, the amount of structural work, ground conditions, glazing, and your chosen finish level. Site access and waste removal can also affect the cost in London. If you need planning, party wall work, or extra groundwork, that can add time and budget too. We price the full scope clearly after your site visit, so you know what is included.

Extension cost per m2 in London?

As a rough guide, extension cost per m2 in London sits between £2,000 and £3,500 for a standard build. High-specification finishes, complex structural work, or premium glazing can push that figure higher. Cost per m2 is useful for rough budgeting but can be misleading on smaller extensions, where fixed costs like foundations, steelwork, and connection to the existing house are spread across fewer square metres. A 15m2 rear extension will typically cost more per m2 than a 30m2 one, even with an identical specification.

What does a house extension quote include?

A full extension quote from LLAC covers structural work, foundations, roofing, insulation, windows and external doors, first and second fix, plastering, and decoration. What varies between builders is whether the kitchen, bathroom, bespoke joinery, and external landscaping are included or treated as separate allowances. When comparing extension quotes, make sure you are comparing like for like. A lower headline figure can simply mean more items have been excluded. Ask each builder to confirm what is and is not in scope before you compare numbers.

What is permitted development for house extensions?

Permitted development allows certain extensions to be built without a full planning application. For rear extensions, the standard limit is 3 metres for terraced and semi-detached houses, or 4 metres for detached properties. Extensions must not exceed 4 metres in height, must not cover more than half the original garden and must use materials that match the existing house. Local councils can remove PD rights in conservation areas, so always check first.

What is a Party Wall Agreement and will I need one?

If your extension is within 3 to 6 metres of a neighbouring property's structure, you will likely need a Party Wall Agreement under the Party Wall Act 1996. This involves formally notifying your neighbours before work begins. LLAC will advise whether this applies to your project and can recommend a party wall surveyor. Starting this process early is important — neighbours have up to 14 days to respond and disagreements can add several weeks to your timeline.

How disruptive is a house extension?

The most disruptive phase is the initial groundworks and when the rear wall is opened up — usually 1 to 3 weeks. Once the new structure is weathertight the build becomes progressively less disruptive. We plan carefully to keep your home as liveable as possible throughout, particularly during the connection between old and new.

How much does a house extension cost in London?

Q: How much does a house extension cost in London?

Costs vary depending on the type of house extension and the specification of the project. As a guide: Side return extension: £35,000 – £90,000; Rear extension: £30,000 – £80,000; Wraparound extension: £50,000 – £120,000; Double-storey extension: £80,000 – £180,000+. All costs are approximate and subject to a site survey.

If you're planning an extension in London, cost is almost always the first question. It's also one of the harder ones to answer, because extension prices vary significantly depending on your property type, how much structural work is involved, and what level of finish you want.

This guide gives you realistic 2026 figures to plan with before you start getting quotes. For most London homes, a house extension cost falls somewhere between £30,000 and £180,000 or more. A single-storey rear extension, which is the most common starting point, typically comes in between £30,000 and £80,000.

Extension cost by type in London

The extension type you build has the biggest single impact on cost. Below are guide ranges for the most common options in East and North London. All figures are subject to a site survey and your specific requirements.

Rear extension:
£30,000–£80,000

The most popular extension type in London. A single-storey rear extension adds floor space at the back of the property, typically creating a larger kitchen, an open-plan kitchen-diner, or a better connection to the garden. The range is wide because the cost depends heavily on how much structural work is required, the size of the extension, and your kitchen and glazing specification.

Side return extension: £35,000–£90,000

Common in Victorian and Edwardian terraces, where a narrow alley runs along the side of the property. Infilling this side return widens the ground floor and can transform a cramped kitchen into something properly usable. The structural work involved in bridging the existing side wall and foundations pushes the base cost slightly higher than a straightforward rear extension.

Wraparound extension: £50,000–£120,000

A wraparound combines a rear extension and a side return in one build. It creates the largest ground-floor transformation available to most terraced houses, typically resulting in a big open-plan kitchen-diner with space for a utility room, downstairs WC, and strong garden connection. The higher house extension cost reflects the increased footprint, additional steelwork, and longer build programme.

Double-storey extension: £80,000–£180,000+

Adds space on both the ground and first floors, making it the most cost-effective option per square metre when you need multiple rooms. Typically used to create a larger kitchen-diner downstairs alongside new bedrooms or bathrooms above. The structural complexity and the requirement for planning permission (as opposed to permitted development for single-storey) contributes to the higher cost.

Frequently asked questions

Comparing house extension quotes?

If you are getting quotes for a house extension in London, it is important to look beyond the final price. A cheaper quote may not always include the same level of specification, structural work, materials, project management or finish.

Before choosing a builder, check what is included, what is excluded, how changes will be priced and whether the quote allows for the kind of result you actually want. Items such as glazing, steelwork, drainage, electrics, kitchen installation, flooring and decoration can make a big difference to the final cost.

At LLAC, we help homeowners understand the full scope of their extension before work begins, so the quote is clear, realistic and suited to the property. If you are comparing options, we can talk you through what to look for and help you understand what is achievable for your budget.

Get a house extension quote in London

LLAC works with homeowners across East and North London, including Hackney, Waltham Forest, Islington, and Haringey. Whether you have a clear brief or are still working out what is possible for your property and budget, the next step is a conversation.

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