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
Kensington's basement conversion experts
Many Kensington properties, from the stucco terraces of Holland Park to the mansion blocks near Kensington High Street, already have a cellar or lower ground floor with real potential. Beams matches you with vetted builders who specialise in cellar conversions, basement lowering and new excavations, with proper waterproofing and a fixed price agreed before work begins.
Cellar conversion, basement conversion or new basement?
Cellar conversion: Converting an existing cellar into usable living space, the lightest-touch option.
Basement lowering: Digging down to increase headroom in an existing basement or cellar.
New basement excavation: Digging a new basement beneath a home that does not currently have one.
How basements are waterproofed
Every basement conversion needs a proper waterproofing strategy, designed to BS 8102, whether that is a tanking system, a cavity drainage membrane, or a combination of both depending on ground conditions. Getting this right from the design stage, rather than as an afterthought, is what keeps a basement dry and usable for the long term.
What your Kensington basement could become
A converted basement in Kensington can become a self-contained media room, a gym, a guest suite, a wine cellar, or additional bedrooms with en-suites, and in larger stucco terraces and mansion houses, a full lower ground floor extension with a lightwell and its own kitchen. Given the borough's high property values, a well-executed basement conversion is one of the more efficient ways to add genuine living space without altering the footprint or roofline of a period property.
What a basement conversion costs in Kensington
There is no flat rate. What a basement conversion costs in Kensington depends on whether you are converting an existing cellar, lowering the floor, or excavating a new basement, alongside waterproofing, structural work and finish. Kensington is one of London's most expensive property markets, with the Royal Borough of Kensington and Chelsea recording an average house price of around £1,233,000 in the year to July 2026 (ONS and HM Land Registry, provisional), and basement projects here tend to sit toward the top of the London range given the scale of work RBKC requires for larger excavations.
Project size | Typical estimate |
|---|---|
Cellar conversion | £85,000 |
Most projects | £145,000 |
Basement lowering / larger dig | £240,000 |
Top 10% of projects | £380,000 |
Based on Beams estimates for London basement conversion projects, these figures are a general guide rather than a fixed quote. Converting an existing cellar sits at the lower end, while a new excavation with underpinning and a lightwell sits considerably higher. Your builder confirms a fixed price once a structural engineer has assessed the ground conditions and design.
How a Beams basement conversion works
1. Design and structural assessment: Our team designs the scheme and arranges a structural engineer's assessment of your property and ground conditions.
2. Planning and party wall: We handle planning permission where needed and coordinate any party wall agreements with neighbours.
3. Fixed-price build: A vetted builder delivers the excavation, waterproofing and fit-out under one fixed-price contract.
Why a basement conversion is worth it
Basement conversions add genuine, useable floor area without changing the footprint or height of a property, which matters in areas where extensions and loft conversions face tighter restrictions. Done well, the extra space adds both day-to-day comfort and resale value, particularly in a market where property is at as much of a premium as it is in Kensington.
Converting a basement in Kensington
Kensington and Chelsea has historically taken a stricter line than most London boroughs on very large basement excavations, sometimes called 'iceberg basements', following years of local concern about the scale, disruption and structural risk of the biggest schemes. RBKC's planning policy generally restricts new basements to a single storey beneath the footprint of the existing house and garden, with tighter controls on excavation depth, light wells and construction management in conservation areas, which cover most of the borough. This does not rule out a well-designed cellar conversion or basement lowering project, but it does mean the planning and structural strategy needs to be right from day one. Our team works with vetted builders across Kensington, Chelsea and Hammersmith who understand the local requirements.
Other services in Kensington
We also help Kensington homeowners with:
House extensions in Kensington
Bathroom renovation in Kensington
Kitchen renovation in Kensington
Basement conversion in nearby areas:
Basement conversion in Chelsea
Ready to start your Kensington basement conversion?
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