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
Chelsea's basement conversion experts
Many Chelsea properties, particularly the period terraces around King's Road and Cheyne Walk, already have a cellar that can be converted, while others have room to lower an existing basement floor or excavate a new one. We match you with builders who specialise in this kind of work and understand what the ground conditions and neighbouring properties in a dense central London street demand.
Cellar conversion, basement conversion or new basement?
A cellar conversion turns existing storage space into habitable rooms. Basement lowering digs down within the existing footprint to create full-height ceilings. A new basement excavation goes further, extending under the garden or footprint entirely. Each has a different cost, timeline and structural approach, and we help you work out which fits your property.
How basements are waterproofed
A proper basement conversion is waterproofed to current British Standard guidance, typically combining a structural waterproof concrete system with an internal cavity drainage membrane and sump pump, so the space stays dry even where the water table is high.
What your Chelsea basement could become
A media room, home gym, extra bedroom with en-suite, home office, wine store, or a self-contained space for guests or staff. In a market like Chelsea, where garden space is often limited, a basement is one of the few ways to add significant square footage without changing the footprint above ground.
What a basement conversion costs in Chelsea
Basement projects are among the most complex renovations, and Chelsea's premium market and dense terraced streets push costs toward the top of London ranges. Based on Beams estimates for London basement projects, typical fixed-price ranges look like this.
Project type | Typical estimate |
|---|---|
Cellar conversion | £70,000 - £130,000 |
Basement lowering | £150,000 - £280,000 |
New basement excavation | £300,000 - £600,000+ |
Final pricing depends on ground conditions, party wall requirements and access, and is confirmed once a structural survey and design are complete.
How a Beams basement conversion works
1. Survey and design — a structural survey and design confirm what is achievable.
2. Fixed price and planning — planning, party wall and building control matters are handled.
3. Build and waterproof — a vetted specialist builds and waterproofs the space, with milestone payments and a 12-month warranty.
Why a basement conversion is worth it
A basement conversion adds significant floor area without extending the footprint of the house above ground, which is often the only way to gain real space in a dense central London street with a fixed building line and limited garden.
Converting a basement in Chelsea
Chelsea covers postcodes SW3, SW10 and parts of SW1, and much of it, including areas around King's Road and Cheyne Walk, sits within one of the Royal Borough of Kensington and Chelsea's 38 conservation areas. RBKC has historically taken a cautious approach to large basement excavations, with policies designed to protect neighbouring properties and the structural integrity of terraces, so it is worth involving a specialist early and understanding the council's basement policy before committing to a design. The average property price across the borough reached £1,233,000 in the year to July 2026 (provisional, ONS/HM Land Registry), which reflects the premium nature of the local market.
Other services in Chelsea
Bathroom renovation in Chelsea
Basement conversion in nearby areas
Ready to convert your Chelsea basement?
Get a free estimate and see what a specialist basement builder would charge before you commit to anything.