Basement construction in Mayfair.
Mayfair · W1 · Mayfair apartmentCompleted work, photograph
Basements under Mayfair townhouses, within Westminster’s one storey rule. We study the whole building before anything is drawn.
A Mayfair basement starts with the building.
- Policy 50
- Westminster’s basement rule, January 2026
- 1.8 metres
- The most a vault may reach under the highway
- W1K · W1J · W1S
- Georgian townhouses, many split into flats
NU Projects is a design and build company in Fulham SW6, founded in 2010. We handle basement conversion and construction in Mayfair W1, 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.
Mayfair is mostly Georgian townhouses, many now split into apartments. Gardens are few.
So a Mayfair basement often starts with the lower ground floor and the vaults.
Westminster sets one storey below the lowest original floor. A listed house must keep its original hierarchy of spaces.
Lightwells, vents and plant must be discreet. A landscaping scheme goes in with the application.
We refitted a Mayfair apartment room by room, with Cochrane Bespoke. Our basements are in Fulham and Chelsea.
What the council allows in Mayfair.
- Council
- City of Westminster. Kensington and Chelsea’s CD11 does not apply here.
- Depth
- Policy 50 of the City Plan, adopted January 2026. One storey below the lowest original floor.
- The garden
- No more than half of it. Where a garden is 8 metres or less, a basement may reach 4 metres.
- Listed buildings
- Heritage assets must be protected. A listed house must keep its original hierarchy of spaces.
- Conservation areas
- Lightwells, vents, skylights and plant must be sensitively designed and discreetly located.
- Under the pavement
- Up to 1.8 metres below the highway. 900mm must stay above the vault.
- The application
- A structural methodology statement, certified by a qualified engineer. Plus a signed Code of Construction Practice checklist.
Source: Westminster’s City Plan, January 2026 edition, Policy 50. Read on 16 October 2026. Policies change, so we read them again for your address.
Our work in Mayfair, and below ground.
Mayfair·Apartment
Mayfair apartment
Our Mayfair apartment, refitted room by room. The joinery is by Cochrane Bespoke.
See the project
Fulham·Basements
Fulham basements
Basements dug, waterproofed and finished by our own team, under Fulham houses.
See the projectCompleted work, photographs
What a basement costs in Mayfair.
£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.
The guide figures are whole project totals. Fees, party wall costs, contingency and VAT sit outside them.
A Mayfair lower floor is priced after a survey of the whole building.
Open the calculatorThe 2026 cost guideBasement costs in full
What Mayfair owners ask about basements.
In Mayfair
- Every service in Mayfair
- Interior design in Mayfair
- Luxury refurbishment in Mayfair
- Basement swimming pools in Mayfair
- Basement gyms in Mayfair
- Basement cinema rooms in Mayfair
- Basement golf simulator rooms in Mayfair
Basements nearby
- Basement construction across London
- 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 Marylebone
- Basement construction in Holland Park
- Basement construction in Hampstead
- Basement construction in Notting Hill
- Basement construction in Clapham
- Basement construction in Weybridge
- Basement construction in Cobham
- Basement construction in Oxshott
- Belgravia
- Marylebone, Bayswater and Maida Vale
- Knightsbridge
Further reading, from the journal
How deep can a Mayfair basement go?
A single level beneath the original lowest floor, under Policy 50.
We survey the lower ground floor and the vaults first.
Can a listed Mayfair townhouse have a basement?
Policy 50 has no outright ban.
The work must not unbalance the building’s original hierarchy of spaces.
Listed building consent runs alongside planning.
Can a Mayfair basement reach under the pavement?
Up to 1.8 metres under the highway, under Policy 50.
At least 900mm must stay between the road surface and the vault.
Who signs off the structure of a Mayfair basement?
A qualified engineer certifies the structural methodology statement.
A signed Code of Construction Practice checklist travels with it.
What does a Mayfair basement cost?
A new dig runs £500k to £900k and more, in our 2026 cost guide.
Converting an existing basement runs £180k to £300k as a project total.
Tell us about your home in Mayfair.
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