From architectural drawings and planning applications to excavation, waterproofing, and fit-out, we manage every stage of your basement conversion in-house.
We provide detailed, itemised quotes. No hidden costs, no nasty surprises, just honest pricing from the start
Unlike general builders, we specialise exclusively in basement conversions. Our team has completed hundreds of projects across London and the home counties.
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.
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
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 carry out basement conversion projects across London and the surrounding home counties. Our most popular areas include:
The team at Basement Conversion London were fantastic from start to finish. They managed planning permission, the excavation, waterproofing, and the full fit-out, we didn't have to deal with multiple contractors. Our new basement living room has completely transformed our home."
We were given a detailed, fixed-price quote within a week of the site survey. The project was completed on time and to an exceptional standard. No hidden extras, no surprises. Highly recommend."
Our Victorian terraced house in South London had a damp cellar that had been unused for 20 years. Basement Conversion London turned it into a stunning home gym and utility room. The quality of the waterproofing and finish is outstanding."
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.
Your Basement Conversion’s Waterproofing Guide in London Basement waterproofing becomes necessary when a structure or property or any part of it is constructed at ground level or below. In some cases, there tends to be an accumulation of water, in the surrounding ground causing the water table to rise and...
Congrats! Your planning application is on the way, and now you’ve arrived at the next exciting stage of your basement conversion in London journey – the technical and structural design. This isn’t just some boring paperwork, nope. It’s where you and a structural engineer sit down together and bring your...
