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Better Homes

Basement conversions in London

Make more of the space beneath your home.

A place to watch a film together, work in peace or give guests their own space. A basement can open up new possibilities at home. We help you explore what is practical, with careful attention to daylight, comfort and the ground beneath your house.

5.0/5 · across all review platformsExtensions, lofts and renovations

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Basement conversions project by Better Homes in London
Rated by homeowners
5.0 / 5Across all review platforms
Completed work
Specialist buildersExplore our projects →
Insurance cover
Up to £10 millionRequest insurance details →
Workmanship guarantee
Up to 10 yearsCover by work type
Guide budget
Existing cellars £2,000 to £4,000+ per m²; new basements £4,000 to £7,000+ per m²
Typical construction programme
A new basement journey can take 6 to 12 months or more
Workmanship aftercare
10 years structural; 2 years kitchen and bathroom installation; 1 year decoration

Life in your finished home

More room for life, without giving up the garden.

Start with the moments you would like to make easier. We will help you think through the possibilities, the space you have and what feels right for your budget.

Space with a purpose

A family room, workspace or guest room. Start with what you need the space to do, then explore what your house can support.

Comfort comes first

Daylight, fresh air and keeping moisture out all need careful planning. We work with your specialists to understand those needs before building.

Enjoy the home above

Create room for another part of life while keeping the garden and the upstairs spaces you already enjoy.

Explore your options

Existing cellar conversion

Turn an underused cellar or lower-ground floor into comfortable living space, with headroom, damp protection, insulation, services and finishes resolved together.

New basement excavation

Create a new storey beneath the existing footprint. This is the most structurally involved route and needs careful feasibility, temporary works, logistics and approvals.

Basement extension

Extend an existing lower-ground level beneath part of the house, rear garden or side area where planning policy, trees, drainage and site conditions allow.

Shell, waterproofing and fit-out

Take a basement from structural shell through waterproofing, mechanical and electrical services, joinery, bathrooms, flooring, decoration and final commissioning.

Your quotation

Know what is included before we begin

Your quote explains the work, what it costs and the choices still to make. We talk it through with you, so you feel comfortable with the plan before work begins.

  • Feasibility and scope definition

    We start with the property, access, existing structure, drainage, neighbours, likely approvals and your intended use. The aim is to identify costly assumptions before they become drawings or contracts.

  • Design and consultant coordination

    Architectural design, structural input, waterproofing strategy and building-services planning are coordinated around one buildable scheme rather than developed in isolation.

  • Planning and pre-construction

    We help coordinate the correct route for planning, Building Regulations, structural calculations, Party Wall matters and the information needed before site starts.

  • Excavation and structural shell

    Temporary works, excavation, underpinning or alternative structural solutions are sequenced to the engineer's design, with access and spoil removal planned around the site.

  • Waterproofing and drainage

    The waterproofing approach is designed for the ground conditions and intended use, with drainage routes, maintainable pump access and failure points considered at design stage.

  • Services, fit-out and handover

    Heating, ventilation, lighting, electrics, plumbing, walls, floors, joinery and decoration are brought together into a finished space, followed by snagging and a documented handover.

Design and construction

Your choice of architect. Support either way.

You need design support

If your project needs an architect, we can recommend one. They prepare the drawings. We help you understand what the options mean for the build and your budget, and can look after the conversations and follow-up questions. You choose the design and approve the cost.

You have your own architect

We are happy to work with them, whether your drawings are underway or complete. If you wish, we can speak with them on your behalf and keep the plans and building work moving together. You stay informed and make the decisions that matter to you.

Your architect prepares the drawings and agreed professional submissions; we manage construction. Our proposal sets out the coordination support you want, each appointment and the fees before you commit.

How we work

From your first ideas to feeling at home

  1. 01Tell us what you have in mind

    We listen to what you want from your home, talk through your budget and explain the next steps. You do not need every detail decided.

  2. 02Make a plan you feel good about

    We work through the drawings and choices with you and your design team, then agree the work, price and timing before building starts.

  3. 03Stay informed while we build

    Your project lead updates you each week and explains any decisions you need to make. We check the finishing details with you and give you a clear aftercare contact.

Cost planning

A clearer picture of what it could cost

Existing cellars £2,000 to £4,000+ per m²; new basements £4,000 to £7,000+ per m². Scope and specification determine the final price. Check the written quotation for VAT, professional fees, product allowances and contingency. Planning ranges are not a fixed offer.

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Built on trust

Care during the build. Support afterwards.

We want you to feel looked after while we work and once you are settled in. Your project lead keeps you informed, and you have a clear contact for questions afterwards. Your workmanship cover is matched to the work we have done and explained before you commit.

Manufacturer warranties and insurance are separate. Read about our guarantee and read independent homeowner reviews.

Useful to know

Questions you may be considering

Do I need planning permission for a basement conversion in London?
It depends on the work and the property. An internal conversion of an existing cellar may not need planning permission if there is no material external change or change of use. New excavation, enlarging a basement, adding a visible lightwell, creating a separate dwelling, or working on a listed building commonly changes the route. London boroughs can also apply their own basement policies, so the correct answer should be checked for your address.
How much does a basement conversion cost in London?
For early planning, converting existing cellar space may fall around £2,000 to £4,000+ per square metre, while creating a new basement can start around £4,000 to £7,000+ per square metre before premium fit-out. Access, depth, groundwater, structural method, spoil removal, lightwells, bathrooms, joinery, professional fees and VAT can materially change the total. A site-specific feasibility and cost plan is more useful than relying on one generic rate.
How long does a London basement project take?
A straightforward conversion of existing below-ground space may take several months on site. A new excavation is a larger structural project and the full journey often runs 6 to 12 months or more once surveys, design, planning, Party Wall matters, construction and fit-out are included. The programme should be built around the specific structural sequence and approvals rather than a generic promise.
Can you convert a cellar without digging it deeper?
Sometimes. If the existing headroom, floor construction, damp condition, access and intended use all work, the project may focus on waterproofing, insulation, services and fit-out. Where finished headroom is inadequate or the floor build-up needs to change, excavation or structural lowering may be required.
How do you prevent damp and water ingress?
The waterproofing strategy should be designed for the site's water risk and the intended use of the room. Depending on the property, that may involve a drained-cavity membrane, barrier protection, integral waterproof concrete, or a combined approach, with maintainable drainage and pump systems where required. The design should follow current professional guidance, including BS 8102 principles.
Will I need a Party Wall agreement?
Basement work frequently falls within the Party Wall etc. Act because it may deepen a party wall or excavate below and near a neighbour's foundations. The exact notices depend on the design and distances involved. Party Wall matters should be addressed early, with the necessary drawings and engineering information, rather than left until the planned start date.
Do basement conversions need Building Regulations approval?
Yes, habitable basement work needs Building Regulations approval. The review can cover structure, fire safety and escape, ventilation, thermal performance, damp protection, drainage, electrical work, stairs and guarding. Planning permission and Building Regulations are separate processes.
Can we stay in the house during the basement works?
It can be possible, but it depends on the structural method, access route, utilities, dust and noise tolerance, and whether the house can be separated safely from the work. We discuss the practical reality during pre-construction so you can decide based on the actual programme rather than optimism.
What ceiling height should a converted basement have?
There is no single comfortable height that suits every layout, but finished headroom has a major effect on whether the room feels like genuine living space. Floor build-up, services, structure and Building Control requirements all reduce the available height, so the finished dimension–not the current excavation height–should guide feasibility.
Does a basement conversion add value to a London home?
It can, particularly where the space is bright, dry, useful and proportionate to the house. The commercial case is property-specific: build cost, local ceiling values, quality of natural light and how well the new floor connects to the rest of the home all matter. We recommend testing value with a local agent or valuer before committing to a major excavation.
Which areas of London do you cover?
Better Homes works across Central, West, North, North West, East and North East London, including Kensington, Chelsea, Westminster, Camden, Hampstead, Islington, Hackney, Walthamstow, Leytonstone, Woodford and surrounding neighbourhoods. Project fit, access and scope are reviewed at enquiry stage.
What happens at the first basement consultation?
We discuss your property, the space you want to create, any existing surveys or drawings, your budget, timing and likely constraints. From there we can recommend the right next step, which may be a site feasibility review, measured survey, planning advice or an outline scope and cost exercise.

Your next step

What could the space below your home become?

Whether you have drawings ready or just the beginnings of an idea, we would love to hear about it. Tell us about your home and your budget, and we will help you work out a sensible next step.

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