The Beams team removed all the stress and matched me with a wonderful contractor."
Teresa
Queen's Park
On time and on budget. A real pleasure."
Eleanor
Stoke Newington
Completed our renovation project within budget and on time."
Evelyn
Bow East
London extension builders who design and build
Beams brings your design and build together in one place — our in-house designers plan your extension, and a vetted builder delivers it, all under one fixed price and managed end to end. You get the join-up of design and build without having to coordinate an architect and a builder separately.
Design is optional: bring your own drawings and work straight with a vetted builder if you'd rather. Either way, the price is fixed before work starts and Beams keeps the whole project joined up for you.
Types of house extension we build
The right extension depends on your home, your plot and how you want to live.
Single-storey rear extension
Extends into the garden — the most popular way to open up a kitchen or living space.
Side return extension
Fills the narrow alley alongside Victorian and Edwardian terraces. A small footprint that transforms light and width.
Wraparound extension
A rear and side return combined into an L-shape — the most ground-floor space for open-plan living.
Double-storey extension
Space on two floors at once — living space below, a bedroom or bathroom above. Often the best value per square metre, sharing one set of foundations and roofing.
Kitchen extension
Most extensions are really about the kitchen. We plan the space, and you can specify the kitchen itself from our kitchen ranges as part of the same project.
House extensions gallery
Explore our completed London house extension projects.
Our design and build process
A clear path from first conversation to finished extension. The design steps are optional — if you already have drawings, you can go straight to costing and build. Most extensions take several months from first consultation to handover — see how long a house extension takes.
Step 1 — Design and plan
We visit your property, talk through what you want, and our designers develop the layout — including 3D visuals and material choices so you can see it before a brick is laid.
Step 2 — Planning and fixed price
We handle the planning application and building regs for you, covering permitted development, party wall and conservation area considerations where they apply. Once the design is set, your builder quotes a fixed price — so you know the full cost before work begins.
Step 3 — Build and handover
Your vetted builder delivers the extension, with the project managed throughout. Milestone payments held securely until you approve each stage. 12-month workmanship warranty from your builder.
What does a house extension cost in London?
Extension costs depend on type, size, specification and your borough — so the price is set once the design is agreed, not before.
As a broad guide, London extensions run from around £2,500 to £5,000 per square metre, before VAT and professional fees. Specification drives where you land: standard finishes sit at the lower end, extensive glazing and a premium kitchen towards the top. A double-storey extension costs more in total but often less per square metre, sharing one set of foundations and roof. Your builder quotes a fixed price once the design — or your own plans — and specification are agreed.
For a full cost breakdown by type, see our guide to how much a house extension costs.
Areas we cover
We work with vetted builders across every London postcode — north, south, east and west. From side return extensions on Victorian terraces in Clapham and Islington to wraparounds in Hackney and double-storey builds in Ealing, our builders understand London homes, plots and borough planning rules.
Ready to extend your London home?
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