Having the Beams team on hand to manage the project and provide extra reassurance on build decisions was incredibly helpful and made the whole experience stress free.
Kerry
London
They have been extremely efficient and reassuring. It was a complex project but they took it all in their stride. They recommended very good contractors who were all punctual, polite and capable.
Andrew
London
All about trust. I felt comfortable with my money, my project, and my home knowing that the outcome would be to my satisfaction or would be made good.
Chris
London
Barnet extension builders who design and build
Most extension projects in Barnet involve an architect, a separate planning consultant and a builder found later, each handing off to the next. Beams runs it as one project. Our in-house designers draw up the extension, handle the planning submission where one is needed, and hand a build-ready design to a vetted builder who prices and delivers it for a fixed sum agreed before work starts.
That single thread of responsibility matters in Barnet, where a good number of streets sit inside a conservation area or under an Article 4 direction, and getting the design right first time avoids costly resubmissions.
Types of house extension we build
Side-return extension: Reclaim the wasted alley beside a Victorian or Edwardian terrace.
Rear extension: Extend the kitchen or living space into the garden.
Wraparound extension: Combine side and rear for a much larger open-plan space.
Double-storey extension: Add space on both floors for maximum value.
What a house extension costs in Barnet
Cost depends on footprint, storeys, structural complexity and specification. Barnet's average house price of £601,000 (ONS/HM Land Registry, July 2026 provisional) sits below many inner-London boroughs, which is one reason extending is often a better move than moving here. Beams gives you a free estimate range upfront, and your builder confirms a fixed price once the design is finished.
Extension type | Typical cost range |
|---|---|
Side-return extension | £40,000 - £75,000 |
Single-storey rear extension | £60,000 - £110,000 |
Wraparound extension | £90,000 - £160,000 |
Double-storey extension | £120,000 - £220,000 |
Based on Beams estimates for London extension projects. Your fixed price depends on footprint, structure and finish.
Planning permission for extensions in Barnet
Many single-storey rear extensions in Barnet can be built under permitted development, without a full planning application, provided they stay within volume and height limits. That changes inside one of the borough's roughly 16 conservation areas, which include Totteridge, Mill Hill and Monken Hadley along with the part of Hampstead Garden Suburb within Barnet. Several of these, including Totteridge and Mill Hill, have Article 4 directions that remove permitted development rights for things like external alterations, so an extension there is more likely to need full planning permission. Wraparound, double-storey and larger extensions usually need planning permission regardless of location. Our design team checks your address against Barnet's planning constraints before drawing anything up.
Our design and build process
1. Design and plan: Our team designs your extension and handles any planning submission.
2. Match with a builder: Compare up to three like-for-like quotes from vetted builders.
3. Build to a fixed price: Contract and milestone payments agreed before work begins.
Why an extension is worth it
Moving house comes with stamp duty, estate agent fees and the upheaval of leaving a home and area you know. An extension lets you stay put while gaining the space that made you think about moving in the first place, often for a fraction of the cost of moving to a bigger property in the same area.
Extending a home in Barnet
Barnet's mix of Edwardian and Victorian terraces in Finchley and Hendon, 1930s semis and detached houses in Mill Hill, Totteridge and Whetstone, and larger plots around High Barnet all extend differently. Side-return extensions suit the narrow alleys beside terraced houses, while the wider gardens common in Mill Hill and Totteridge often support a bigger wraparound or double-storey build. With an average house price of £601,000 (ONS/HM Land Registry, July 2026 provisional), extending is frequently the more affordable route to extra space compared with moving to a larger home nearby.
We cover the whole of Barnet plus neighbouring Muswell Hill and Hampstead, with the same vetted builder network and design team behind every project.
Other services in Barnet
We also help Barnet homeowners with:
Ready to extend your Barnet home?
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