BasementsBelgravia SW1X · SW1W
Basement construction in Belgravia.
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.
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 basement runs £450 to £500 a sq ft, construction only. 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 allows one storey below the lowest original floor, under 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.
- Council
- City of Westminster. Kensington and Chelsea’s CD11 does not apply here.
- Extent
- City Plan Policy 50. One storey below the lowest original floor, under half the garden.
- 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.
- 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.
Below ground, nearby.
Kensington·New build
Kensington new-build houses
Our dig for two new houses in Kensington and Chelsea, three floors down.
See the project
Chelsea·Townhouse
Chelsea basement and extension
A new Chelsea basement, built by one team with the extension above.
See the projectCompleted work, photographs
What it costs.
£450 to £500a sq ft, construction only. Our basement band.
£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 band is per square foot, construction only. 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
Basements in Belgravia, answered.
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.
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.
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?
Our basement band runs £450 to £500 a sq ft, construction only.
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.
Related pages.
In Belgravia
Basements nearby
- Basement conversion across London
- Basement conversion in Fulham
- Basement conversion in Chelsea
- Basement conversion in Kensington
- Basement conversion in St John’s Wood
- Basement conversion in South Kensington
- Basement conversion in Knightsbridge
- Basement conversion in Holland Park
- Knightsbridge
- Chelsea
- Pimlico and Westminster
- Mayfair
From the journal358 notes, free to read
Belgravia, written up.
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Everything London homeowners need to know about basement extensions. Planning, costs, party walls, and construction advice from NU Projects.
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