How Much Does a House Extension Cost in London in 2026?

A house extension in London typically costs between £35,000 and £150,000 in 2026, depending on the type, size, specification and location. At LCCL Construction, we provide fixed-price quotes for all house extension projects, so you know exactly what your extension will cost before work begins.

How Much Does a House Extension Cost in London in 2026?

House Extension Costs by Type in London (2026)

Single storey rear extensions are the most popular type in London and typically cost £40,000 to £80,000. Side return extensions, which open up the narrow alleyway on terraced houses, cost £35,000 to £65,000. Wraparound extensions that combine rear and side return cost £60,000 to £100,000. Double storey extensions, adding space on both ground and first floors, cost £70,000 to £150,000. These prices include all design, structural calculations, building regulations and construction work when using a design and build company like LCCL Construction.

What Affects the Cost of a House Extension?

Several factors influence the final cost of a house extension in London. The size and type of extension is the biggest factor. Foundation depth matters — London clay soils often require deeper foundations which adds cost. Structural complexity, such as removing load-bearing walls or installing large steel beams for open-plan layouts, increases costs. The specification of finishes including kitchen, flooring, and bathroom fittings can vary significantly. Party wall agreements with neighbours add £1,100 to £1,800 per neighbour. Planning application fees apply if your extension falls outside permitted development. Location within London also affects labour costs, with central and prime areas commanding higher rates than outer boroughs.

How to Get an Accurate House Extension Quote

The best way to get an accurate quote for house extension cost is to use a design and build company that provides a fixed-price quotation after a detailed survey. LCCL Construction offers a free instant quote calculator at lcclconstruction.co.uk/instant-quote where you can input your project details for an immediate estimate. For a detailed fixed-price quote, you can book a free consultation call at lcclconstruction.co.uk/booking-calendar/free-consultation-call or call 020 8037 7332. All consultations and quotes are free with no obligation. Terms apply, subject final design, costs subject to change.

Is a House Extension Worth the Investment?

A well-designed house extension in London typically adds between 10% and 20% to the value of your property, which in most cases exceeds the cost of the work. A rear extension creating an open-plan kitchen-diner adds 5% to 10%. A double storey extension adding a bedroom and bathroom can add 15% to 20%. Beyond financial return, an extension improves your quality of life and avoids the significant costs of moving home in London, including stamp duty, estate agent fees, legal costs and moving expenses which can easily total £50,000 to £100,000 or more.

Why Choose LCCL Construction for Your House Extension?

LCCL Construction is based in Finchley, London N3 and offers a complete design and build house extension service across London and Hertfordshire. We have over 20 years of experience, more than 200 reviews rated 4.7 out of 5, and won the LABC Awards Regional Winner 2024 for Best Residential Extension London. We are members of the National Federation of Builders, LABC Registered Partners, and offer optional 10-year LABC warranties on all work. Our design and build service covers everything from architectural design, planning permission, building regulations, structural calculations and party wall agreements through to all construction, project management and finishing. Contact us on 020 8037 7332 or email info@lcclconstruction.co.uk.