Basement contractors and builders in London.
Kensington · W8 · A basement pool, engineered from the startCompleted work, photograph
Basement contractors in London, for new basements and conversions. Engineered, monitored and built by one team.
Bloomberg filmed Nick Jeffries at a Kensington super-basement dig in 2015.
A basement is engineering first, then a room.
A basement adds a floor below the house, dug new or converted. We are NU Projects, design and build in Fulham SW6 since 2010. A basement runs £450 to £780 a sq ft, construction only. Call 020 7731 6841, and a budget estimate typically follows within seven days.
NU Projects has built London basements since 2010. Work runs by underpinning or by piling, chosen for the property. Movement risk is managed by engineering, temporary works and monitoring.
Basements become bedrooms, utility rooms, cinemas, wine cellars, pools, gyms and saunas. Some become self-contained flats. Waterproofing and drainage are designed together, from the start.
Each London borough sets its own conditions for a new basement. Traffic and site management plans, soil testing and structural calculations are often needed. Flood risk and eco-home assessments follow where they are asked for.
What the work includes
- Underpinning or piling, chosen for the property
- Movement managed by engineering and monitoring
- Waterproofing and drainage designed in together
- Borough conditions, plans and assessments handled
- Bedrooms, cinemas, wine cellars, pools, gyms and saunas
- A basement built to feel like any other floor
- Applies most in
- Chelsea, Kensington, Knightsbridge, Notting Hill and Holland Park
- Basements by area
- Basement construction in Fulham, Basement construction in Chelsea, Basement construction in Kensington, Basement construction in St John’s Wood, Basement construction in South Kensington, Basement construction in Knightsbridge, Basement construction in Belgravia, Basement construction in Holland Park, Basement construction in Hampstead, Basement construction in Notting Hill, Basement construction in Clapham
- What it costs
- See a range in a minute. Then send us the address for a proper number. Open the calculator. Basement cost in London, the 2026 figures
- Where we work
- Fulham, Chelsea, Kensington, Knightsbridge, Belgravia, Mayfair, Notting Hill and Holland Park, Chiswick, Wandsworth, Putney and Barnes, Hampstead and St John’s Wood, Weybridge, Cobham and Oxshott, South Kensington, Marylebone, Bayswater and Maida Vale, Pimlico and Westminster, Battersea and Clapham, Richmond, Twickenham and East Sheen, Islington, Highgate and Primrose Hill, Greenwich, Dulwich, Camden, Wimbledon, Bermondsey, Brixton, Ealing, Acton, Hammersmith and Brook Green, Earl’s Court, Queen’s Park and Kensal Rise, Fitzrovia and Bloomsbury
A basement should feel like any other floor. Waterproofing and drainage are designed together, from the start.
A gym, a media room and the stair down.
The whole process was smooth and well managed. The standard of finish is excellent and every detail was carefully considered.
Three levels below the street.
Two new-build houses in Kensington, W8, cut through from roof to foundation.
- Garage At street level, off the road.
- Kitchen and dining One floor below the street.
- Pool and gym Two floors below the street.
How a London basement is dug, then built.
- 01
Survey and feasibility
Soil, water table, drainage and the neighbours’ walls, checked against the borough’s basement rules.
- 02
Design and planning
Our RIBA architects draw it. Engineers size the structure. We submit the plans and the borough’s reports.
- 03
Party walls and site plan
Notices served and awards agreed. A construction and traffic plan agreed with the council.
- 04
Temporary works
Propping, monitoring points and access set up before any digging starts.
- 05
Dig and structure
Underpinning or piling, chosen for the house. Movement is monitored throughout.
- 06
Waterproof and fit out
Waterproofing and drainage designed in together. Then services, joinery and finishes, by the same team.
Ten checks before you appoint a basement contractor.
- 01
Comparable completed basements
Ask for finished basements of similar depth, access and finish. Ask what the firm designed and built itself.
- 02
One schedule of design responsibility
Structure, temporary works, waterproofing, drainage and services each need a named owner.
- 03
A method for this house
Ask how the house is supported, and how movement is monitored. A generic programme is a warning.
- 04
Waterproofing as one system
Structure, joints, drainage, pumps and alarms are designed together. Ask who designs, installs and tests it.
- 05
The borough’s basement rules
Each borough sets its own limits on depth and garden. Check them before design starts.
- 06
Party walls and neighbours
Notices, awards and a traffic plan need time in the programme. Ask who handles each.
- 07
Services planned early
Ventilation, heating, lighting, pumps and fire safety shape ceiling heights. Coordinate them before the dig.
- 08
Like for like prices
Ask every firm to price the same drawings, with exclusions stated. Similar totals can hide different scopes.
- 09
Reporting through the dig
Ask how often you will hear, and for the monitoring readings. We report every week, with photographs.
- 10
Warranty and aftercare in writing
Ask who stands behind the waterproofing, and for how long. Get it in writing.
What owners ask before they dig.
Further reading, from the journal
Is my property suitable for a basement?
Suitability depends on planning, ground and water conditions, existing foundations, neighbours, utilities and access. Feasibility work sets out the main constraints before we develop a detailed layout.
How is basement waterproofing designed?
It is a coordinated specialist design for the intended use and ground conditions. The construction method is designed in alongside it.
Structure, joints, penetrations, drainage and maintenance access all need to work together.
Can a basement include a cinema, gym or wine room?
Each use needs its own structural, acoustic, ventilation and environmental requirements. A wine room and a gym should not share assumptions about temperature or humidity.
Our Chelsea townhouse basement, 1,200 sq ft, holds a mirrored gym.
What belongs in a basement shell package and what is fit-out?
We define the boundary explicitly for every package. Structure, waterproofing, drainage, slab, stairs, services and finishes can be allocated differently.
A shell price should never be compared with a fully finished living floor.
What ongoing maintenance does a basement need?
We follow the actual waterproofing, drainage, pump and ventilation maintenance schedules.
Keep inspection access clear and keep service records. Warranty terms can depend on this maintenance being kept up.
Does the Royal Borough of Kensington and Chelsea limit new basements?
Its rule began as CL7 in 2015. It is now Policy CD11, in the July 2024 Local Plan.
It allows one storey, and no more than half the garden.
We check it against your property before design starts.
Which basement rules apply in Westminster?
Westminster’s City Plan, Policy 50, covers Belgravia, Mayfair, Marylebone and St John’s Wood.
It allows one storey below the lowest original floor.
The basement may run under no more than half the garden.
At least one metre of soil must sit over any part under the garden.
Which basement rules apply in Fulham?
Hammersmith and Fulham’s Local Plan, Policy DC11, sets the limits.
One storey, and no more than half the depth of the garden.
It may reach no further than half the depth of the house.
A construction method statement and a traffic plan go in with the application.
What kinds of basement do you build?
There are three kinds, and each one goes further than the last.
The first fits out a cellar that is already there.
The second lowers or widens an existing cellar, usually by underpinning.
The third digs a new floor under the house or the garden.
Each step adds structure, waterproofing and party wall work, and cost.
How should I choose a basement contractor?
Ask what they have built on the same ground, and what the groundwater did.
Ask who designs it, who digs it and who fits it out.
Every split between firms is a place where blame can land later.
Ask for the warranty in writing, and who stands behind it.
We carry design, excavation, waterproofing and fit-out under one contract.
Why build down rather than move?
Moving can mean giving up the street, the schools or the location.
A basement adds a whole floor without leaving the house.
It takes a cinema, a gym or the plant away from the family floors.
Tell us about the basement.
Your name and one way to reply are enough. It goes straight to the studio.
- Already have an architect or designer? We build to their design. Working with your designer
- An NDA on request, and your home is never published without your consent. How we work in confidence