Basement conversion and construction in Belgravia.
Fulham · SW6 · Fulham basementsCompleted work, photograph
Belgravia basements, under strict rules and, in places, a high water table. We tell you what is likely before anything is drawn.
A Belgravia basement, honestly.
- Policy 50
- One storey, no more than half the garden
- March 2024
- The Belgravia Neighbourhood Plan was made
- SW1X · SW1W
- Stucco terraces, squares and mews
NU Projects is a design and build company in Fulham SW6, founded in 2010. We handle basement conversion and construction in Belgravia SW1, under one contract. A new basement dig typically runs £500k to £900k. Converting an existing basement runs £180k to £300k. Call 020 7731 6841, and a budget estimate typically follows within seven days.
Belgravia was built to a strict order of house sizes, around its garden squares.
Westminster’s Policy 50 allows one storey below the lowest original floor.
It may run under no more than half the garden.
The Belgravia Neighbourhood Plan, made in March 2024, adds a local view.
It prefers new space added upwards, by a mansard, where that suits the house.
It discourages basements in mews. Most mews were never built with cellars.
We read both before we advise. Sometimes the better answer is up, not down.
What the council allows in Belgravia.
- Council
- City of Westminster. Kensington and Chelsea’s CD11 does not apply here.
- Extent
- City Plan Policy 50, adopted January 2026. One storey below the lowest original floor.
- The garden
- No more than half the garden. An undeveloped margin stays around the whole boundary.
- Listed houses
- A basement must not unbalance a listed building’s original order of rooms.
- Neighbourhood plan
- Made March 2024. It favours upward additions and discourages basements in mews.
- Construction
- Policy BEL4 asks how noise, dust and vibration on neighbours will be limited.
- The application
- A structural methodology statement, certified by a qualified engineer. A signed Code of Construction Practice checklist goes in too.
- Ground
- The plan notes a high water table in parts. Basements flooded there in July 2021.
Source: Westminster’s City Plan Policy 50, and the Belgravia Neighbourhood Plan of March 2024. Read on 3 October 2026. Policies change, so we read them again for your address.
Basements we have built.
Fulham·Basements
Fulham basements
Basements dug, waterproofed and finished by our own team, under Fulham houses.
See the project
Chelsea·Townhouse
Chelsea townhouse, opened up and fitted out
A basement under the full footprint of a Chelsea townhouse, with its gym.
See the projectCompleted work, photographs
What a basement costs in Belgravia.
£180k to £300kConverting an existing basement. A project total, from our 2026 cost guide.
£500k to £900k+Digging a new basement. A project total, from our 2026 cost guide.
A listed Belgravia house often needs more design and monitoring below ground.
The guide figures are project totals.
Fees, party wall costs, contingency and VAT sit outside both.
Open the calculatorThe 2026 cost guideBasement costs in full
What Belgravia owners ask about basements.
In Belgravia
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Basements nearby
- Basement construction across London
- Basement construction in Fulham
- Basement construction in Chelsea
- Basement construction in Kensington
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- Basement construction in Weybridge
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- Knightsbridge
- Chelsea
- Pimlico and Westminster
- Mayfair
Further reading, from the journal
Does the Belgravia Neighbourhood Plan allow basements?
It does not ban them. Westminster’s Policy 50 still sets the limits.
But the plan prefers new space added upwards, where that suits the house.
We weigh both before we advise you.
How much of a Belgravia garden can a basement use?
It can run under no more than half the garden.
A margin of undeveloped garden must remain around the whole site boundary.
Can I dig a basement under a Belgravia mews house?
It is hard. The plan discourages basements in mews.
Most mews were stables and service buildings, built without cellars.
We would usually look at the roof or the layout first.
Can I extend the vaults under a Belgravia pavement?
Within limits. Westminster allows up to 1.8m under the highway.
At least 900mm must stay between the road surface and the vault.
Where the estate owns the freehold, its licence is needed too.
What does Westminster ask for with a Belgravia basement application?
A structural methodology statement, certified by a qualified engineer.
A signed Code of Construction Practice checklist is also needed.
A flood risk assessment is added in flood zones 2 and 3.
Is the ground in Belgravia difficult for basements?
In parts, yes. The neighbourhood plan records a water table close to the surface.
Heavy rain flooded several basements there in July 2021.
We start with a ground investigation, then design the waterproofing and drainage.
What does a Belgravia basement cost?
A new dig is £500k to £900k and more, in our 2026 cost guide.
Listed fabric and wet ground push a Belgravia job up the range.
Tell us about your home in Belgravia.
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