Basement Conversions & Extensions in London
N10 CONTRACTORS are expert builders who can transform your unused or partially underground basement into a fully functional, stylish living space, maximising both practicality and property value. Whether you want a home office, entertainment area, or extra bedrooms, we handle every step of the conversion with precision. We can also extend your basement footprint beneath your garden, incorporating features like a 'walk-on' roof-light where space permits, creating a bright and accessible underground space.
Don’t Move! We Make Expanding Your Home Simple with a Basement Conversion
N10 CONTRACTORS can manage every step of adding a functional and stylish extension to your home—from loft conversions and single or double-storey extensions to complex basement conversions. Working closely with architects, interior designers, and local planning and building regulation officers, we oversee every stage of your project—from detailed design and planning to budgeting, construction, waterproofing, and finishing—ensuring your new basement conversion or extension is seamless and stress-free.
A Basement Conversion: Maximise Your Space and Property Value
No space to extend? If your garden is limited, your loft isn’t suitable for conversion, and moving isn’t an option, a basement conversion could be the perfect solution. Not only can it significantly increase your living space, but it can also add considerable value to your property—especially in London, where land is limited and property prices are high.
Our team has extensive experience with London basement conversions, enhancing existing cellars and, where needed, excavating beneath your property to increase ceiling height or expand horizontally under gardens.
The potential uses for basement conversions are almost endless. Whether you want a home gym, entertainment or games room, wine cellar, bar, kids’ playroom, home office, utility space, home cinema, granny annexe (complete with bedroom, living area, kitchen, and bathroom), or even an underground swimming pool, we can bring your vision to life.
Get a Quote for Your Basement Conversion
If you’re considering a basement conversion or extension in London, N10 Contractors can visit your property to discuss options, processes, and costs—completely free and with no obligation.
We can guide you through planning permission requirements, building regulations, and design options. Whether you’re thinking of a multi-level basement, extending under your garden, or adding a pool, we provide expert advice on every detail.
Our team also offers recommendations for fixtures, fittings, kitchens, bathrooms, doors, staircases, and specialist lighting solutions, including rooflights and high-level clerestory windows for partially underground spaces.
Once your plan is agreed, we provide a detailed quote. During construction, our project manager coordinates all trades and professionals from start to finish, ensuring a smooth, stress-free process. If you need architects or interior designers experienced in basement conversions, we can recommend trusted specialists.
The Typical Basement Conversion Process with N10 Contractors
Transforming your basement into a fully functional, luxury living space is what we do best. Here’s how we manage most straightforward basement conversion projects:
All existing floor and ceiling finishes are carefully removed and cleared
If ceiling height is limited, the floor is excavated and lowered to maximise headroom
All construction debris is removed, using windows or doors where accessible
If needed, a drainage channel, sump, and waterproofing system are installed
New steel supports are added where structural reinforcement is required
Above-ground openings are optimised for natural light and to provide fire escape routes
First-fix plumbing and electrical work is installed or rerouted as required
External walls are lined with cavity drainage membranes and waterproofing systems
A framework is fitted to support insulation and conceal electrics and pipework
New internal plasterboard walls are constructed and staircases to upper floors installed
Ceilings and walls are insulated to prevent heat loss and receive two coats of plaster
Windows, doors, staircases, and lightboxes are upgraded or installed as needed
Final finishes including flooring, radiators, painting, decorating, and lighting installation
If your basement extends under your garden, landscaping is managed as part of the project
High-end installations such as kitchens, bathrooms, home cinema, and telecom systems are included
Typical Basement Conversion Costs in London
The cost of a basement conversion varies depending on project complexity, existing structures, and your intended use of the space. As a general guide, London basement conversions typically range as follows:
Conversion of an existing cellar: £750 – £1,500 per m²
Lowering floor level + underpinning an existing cellar: £1,500 – £2,000 per m²
New basement excavation + underpinning: £2,000 – £3,000 per m²
