— Service Details

Basement Conversion London

End-to-End Design & Build

From architectural drawings and planning applications to excavation, waterproofing, and fit-out, we manage every stage of your basement conversion in-house.

Transparent, Fixed-Price Quotes

We provide detailed, itemised quotes. No hidden costs, no nasty surprises, just honest pricing from the start.

Specialist Basement Contractors

Unlike general builders, we specialise exclusively in basement conversions. Our team has completed hundreds of projects across London and the home counties.

London's Leading Basement Conversion Company

At Basement Conversion London, we specialise entirely in converting and creating basement spaces for homeowners across London and the surrounding home counties. With years of hands-on experience and hundreds of successful projects completed, we are one of London’s most trusted basement conversion companies.

We offer a fully comprehensive design-and-build service, meaning you deal with one expert team from the very first consultation all the way through to the final finishing touches. Our in-house architects, structural engineers, and construction teams handle everything: planning permission, excavation, underpinning, waterproofing, and fit-out.

We don’t use salespeople. When you meet us, you meet the people who will actually be working on your project.

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Basement conversions have gained popularity in London for several reasons and if you’re considering this option rest assured that you’re not the only one. Moving to a house may seem like a solution but it comes with its own set of challenges and expenses such as high moving costs and stamp duty. So what’s the alternative? Choosing a basement conversion in London is a way to expand your living area without the need to move.

As the property market in London continues to soar, we are increasingly seeing homeowners realizing the potential of their existing properties. Many London properties often reach their extension limit above ground which leaves us wondering, “Where to extend?” The answer lies beneath our feet – a basement conversion. By converting basements, homeowners in London can effectively maximize their living space without the need to relocate to a new property, a move that could present financial burdens or necessitate leaving a prime location

Our Basement Conversion Services

New Basement Construction

Don't have an existing cellar? No problem. We excavate and construct new basements beneath your property from scratch, including all structural and waterproofing work.

Cellar Conversion

Transform a dark, damp, and underused cellar into a bright and beautiful living space. We handle damp-proofing, waterproofing, insulation, and full fit-out.

Basement Waterproofing

We install the industry-leading Delta Membrane waterproofing system on every project, giving you lasting protection from water ingress and damp, backed by our 10-year guarantee.

Basement Extensions

Extend your basement beyond the footprint of your property, out under the garden or to the side, subject to planning permission and site feasibility.

Planning Permission & Party Wall

Our in-house architects manage the entire planning process, including planning applications, building regulations approval, and party wall agreements with neighbours.

Basement Fit-Out & Interior Design

Once the shell and core structure is complete, our fit-out team transforms it into your dream space, whether that's a home gym, cinema room, bedroom, office, or open-plan living area.

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London's Leading Basement Conversion Company
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Why Homeowners Across London Choose Us

London’s property market is one of the most competitive in the world. Moving to a larger home means stamp duty, estate agent fees, and the upheaval of leaving an area you love. A basement conversion gives you the extra space you need — in the home you already love — at a fraction of the cost of moving.
Here’s why so many London homeowners trust Basement Conversion London with their project:

  • We specialise exclusively in basements — not loft conversions, extensions, or general building work. Basements are all we do.
  • We never subcontract. All work is carried out by our own in-house team of basement specialists.
  • We offer a free, no-obligation site survey — you’ll receive a full written quote within 2–5 working days.
  • We install the Delta Membrane waterproofing system, one of the most effective basement waterproofing solutions available.
  • All works are backed by a 10-year guarantee.
  • We cover London and the home counties — including Surrey, Essex, Hertfordshire, Buckinghamshire, and Berkshire.

Basement Conversion Services Across London & the Home Counties

We carry out basement conversion projects across London and the surrounding home counties. Our most popular areas include:

Central London

North London

South London

East London

West London

Essex

Surrey

Hertfordshire

Buckinghamshire

Frequently Asked Questions About Basement Conversions

Do I need an existing cellar to have a basement conversion?

No — an existing cellar or underground space is not a requirement. We regularly excavate and create brand new basements beneath properties that have no existing below-ground space whatsoever.

Do I need planning permission for a basement conversion in London?

In most cases, yes. Converting a basement into a habitable living space requires planning permission because it involves significant structural changes. Planning policies also vary by London borough, so it is important to check with your local authority. Our in-house architects manage the entire application process for you.

How long does a basement conversion take?

The construction and waterproofing phase typically takes between 7 and 20 weeks, depending on the size and complexity of the project. Including the planning and design stages, you should expect the full project to take between 6 and 12 months from initial consultation to completion.

How much does a basement conversion cost in London?

Costs vary significantly depending on the type, size, and specification of your project. As a guide: converting an existing cellar ranges from approximately £2,000 to £4,000 per square metre; building a new basement ranges from £3,000 to £5,500 per square metre; extending an existing basement typically falls between £2,800 and £4,300 per square metre. Professional fees and fit-out finishes will add approximately 15–20% on top. We always recommend requesting a detailed, site-specific quote.

Can I stay in my home during the basement conversion?

Yes, in most cases. Our clients typically remain living in the property during construction. There will be noise, dust, and some disruption, and certain utilities may need to be temporarily disconnected during specific phases. Our team works hard to keep disruption to a minimum.

What guarantee do you offer?

We provide a 10-year guarantee on all building works completed by Basement Conversion London.

What is the minimum ceiling height for a basement conversion?

We recommend a minimum ceiling height of 2.3 to 2.4 metres for a comfortable, habitable space. If your existing basement or excavation depth does not achieve this, we can dig further down to create the required headroom.

Will my basement be affected by damp?

Not if it is built correctly. We install the Delta Membrane waterproofing system on every project — one of the most effective waterproofing solutions available for below-ground construction. Combined with regular maintenance and pump checks, your basement will remain dry and protected long-term.
The Next Space is Yours

Let’s Design What’s Next

— Address

71-75 Shelton Street Covent Garden London WC2H 9JQ

— Hours

Mon-Fri: 9 AM to 5 PM
Sun: Closed

— Phone

02039250953

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