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's basement conversion experts
Basement work is specialist, structural and unforgiving of mistakes, which makes the choice of builder the single biggest decision on the project. Beams matches Barnet homeowners with vetted builders who have a genuine track record in cellar conversions, basement lowering and new excavations, not a general builder taking on a basement for the first time.
Every project runs on a fixed-price contract with milestone payments and a 12-month workmanship warranty, so you know the cost and quality are agreed before excavation starts.
Cellar conversion, basement conversion or new basement?
Cellar conversion: Turning an existing cellar into usable, watertight living space.
Basement lowering: Digging down to increase headroom in an existing basement.
New basement excavation: Creating a basement where none currently exists.
How basements are waterproofed
Every basement is waterproofed to BS 8102, usually combining a structural waterproof concrete system with a cavity drainage membrane and a sump pump to manage any water ingress. Your builder specifies the right combination for your site conditions, and it is designed in from the start rather than added as an afterthought.
What your Barnet basement could become
Extra bedroom or guest suite: Popular in family homes across Finchley and Hendon.
Home cinema or gym: Make use of space without extending the footprint.
Home office or studio: A quiet, self-contained space away from the main house.
Utility or storage space: Free up ground-floor rooms for living space.
What a basement conversion costs in Barnet
Cost depends heavily on whether you are converting an existing cellar, lowering a floor, or excavating a new basement, plus ground conditions and access on your street. Barnet's average house price of £601,000 (ONS/HM Land Registry, July 2026 provisional) means many homeowners here look to a basement as a way to add significant space without extending the footprint. Beams gives you a free estimate range upfront, with a fixed price confirmed once a structural survey and design are complete.
Project type | Typical cost range |
|---|---|
Cellar conversion | £40,000 - £80,000 |
Basement lowering | £70,000 - £140,000 |
New basement excavation | £150,000 - £300,000+ |
Based on Beams estimates for London basement projects. Ground conditions, access and structural work strongly affect the final price.
How a Beams basement conversion works
1. Survey and design: A structural survey confirms what is possible, then we design the space.
2. Match with a specialist: Compare quotes from vetted builders experienced in basement work.
3. Build to a fixed price: Contract and milestone payments agreed before excavation begins.
Why a basement conversion is worth it
A basement adds significant floor area without changing your footprint or your garden, which makes it one of the few ways to add real space on a constrained plot. Done well, it can add a bedroom, an entertainment space or a home office that would otherwise mean moving to a bigger house.
Converting a basement in Barnet
Many of Barnet's Edwardian and Victorian houses in Finchley and Hendon already have a cellar or partial basement, which is often the most cost-effective starting point for a conversion. In areas with an Article 4 direction or inside a conservation area, such as Totteridge or Mill Hill, basement work is usually less visually intrusive than an extension, though structural changes still need planning permission and Building Regulations approval, and a party wall agreement is needed wherever you share a wall or foundation with a neighbour.
We cover the whole of Barnet plus neighbouring Muswell Hill and Hampstead, with the same vetted builder network behind every project.
Other services in Barnet
We also help Barnet homeowners with:
Basement conversion in nearby areas:
Ready to convert your Barnet basement?
Get a free estimate and take the first step. No commitment, no sales pressure.