House Extensions London 2026: Complete Guide to Costs, Types and Planning
Updated: Nov 2
House extensions in London are one of the most popular ways to add space and value to your home without the cost and disruption of moving. Whether you need a larger kitchen, an extra bedroom, a home office or a bigger living space, a well-designed and well-built house extension can transform how you use your home. LCCL Construction is a specialist design and build company based in Finchley, North London, delivering house extensions across London and Hertfordshire for over 20 years.
Not sure whether your project needs planning permission? Enter your postcode and tick what you want to build — we look up the conservation areas, Article 4 directions and listed buildings for you, and you see which parts are permitted development and the from-price for each. Lawful Development Certificate included on every permitted development job.
Types of House Extensions in London
Rear house extension: The most popular type across London. Extends the back of the ground floor to create a larger kitchen, dining or living space. Costs from £42,000 inc. VAT (£35,000 + VAT). See our rear house extension guide.
Side return extension: Popular for Victorian and Edwardian terraced houses with a narrow side alley. Fills the side return to create a wider kitchen or living space. Costs from £42,000 inc. VAT (£35,000 + VAT). See our side return extension guide.
Kitchen extension: A rear or side return extension specifically designed around a new kitchen layout. Costs from £48,000 inc. VAT (£40,000 + VAT). See our kitchen extension guide.
Wraparound extension: Combines a rear and side return extension to maximise ground floor space. Costs from £72,000 inc. VAT (£60,000 + VAT). See our wraparound extension guide.
Double storey extension: Extends on two floors to add maximum space. Costs from £80,000. See our house extension types guide.
How Much Do House Extensions Cost in London in 2026?
House extension costs in London vary depending on the type, size and specification. Here is a guide to typical costs for a full design and build service in London in 2026:
Rear extension £42,000 – £90,000 inc. VAT (£35,000 – £75,000 + VAT).
Side return extension £42,000 – £93,600 inc. VAT (£35,000 – £78,000 + VAT).
Kitchen extension £42,000 – £153,600 inc. VAT (£35,000 – £128,000 + VAT).
Wraparound extension £72,000 – £153,600 inc. VAT (£60,000 – £128,000 + VAT).
Double storey extension £90,000 – £198,000 inc. VAT (£75,000 – £165,000 + VAT).
All costs include architectural design, planning permission, building regulations, structural calculations, construction, electrics, plumbing, plastering and decoration.
Do I Need Planning Permission for a House Extension in London?
Most single storey house extensions in London fall under permitted development rights and do not require planning permission. Double storey extensions and extensions in conservation areas always require planning permission. LCCL Construction checks all planning requirements as part of our free consultation. See our full guide to planning permission for house extensions in London.
How Long Does a House Extension Take in London?
A single storey house extension in London typically takes 10 to 14 weeks on site. The full project timeline from initial consultation to completion including design, planning and building regulations is usually 5 to 8 months. A double storey extension takes 14 to 18 weeks on site with a full project timeline of 7 to 10 months.
How to Choose House Extension Builders in London
When choosing house extension builders in London look for: 50+ verified reviews at 4.5 stars or above, LABC Registered Partner or NFB membership, a full design and build service, a detailed written estimate and a dedicated project manager. See our full guide: 7 things to check when choosing home extension builders in London.
Why Choose LCCL Construction for Your House Extension in London?
LCCL Construction is a specialist design and build company based in Finchley, North London. Over 20 years experience, 200+ verified reviews at 4.7 out of 5, LABC Award Winners 2024 for Best Residential Extension, LABC Registered Partners and members of the National Federation of Builders. We deliver house extensions across all of London and Hertfordshire. One company, one estimate, one point of contact from design to completion.
Can it be done under permitted development?
A single-storey rear extension of 3 m on a terrace or semi (4 m on a detached house), a side-return infill and a side extension up to half the original width are permitted development on a house outside a conservation area or Article 4 street — no planning application, just a Lawful Development Certificate, which we apply for on every one. Fixed-price permitted development extensions start from £42,000 inc. VAT (£35,000 + VAT) at economy specification, design and build inclusive, and the 6 m / 8 m larger home extension goes through a 42-day prior approval notification rather than a full application. See our permitted development projects page for every product with its from-price and the checks we run before we confirm a project qualifies.
Not sure whether your project needs planning permission? Enter your postcode and tick what you want to build — we look up the conservation areas, Article 4 directions and listed buildings for you, and you see which parts are permitted development and the from-price for each. Lawful Development Certificate included on every permitted development job.
Frequently Asked Questions About House Extensions in London
How much does a house extension cost in London in 2026?
Costs range from £42,000 inc. VAT (£35,000 + VAT) for a small single storey extension to £150,000 for a large double storey extension with high specification finishes. The typical single storey extension costs £42,000 – £90,000 inc. VAT (£35,000 – £75,000 + VAT) for a full design and build.
What is the best type of house extension in London?
The best type depends on your property, garden space and budget. For terraced houses, a rear or side return extension offers the best value. For semi-detached properties, a wraparound or double storey extension maximises the return on investment.
To get a free consultation and detailed estimate from LCCL Construction call 020 8037 7332 or get an instant quote online.
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