BasementsChelsea SW3 · SW10
Basement conversion in Chelsea.
New basements and conversions under Chelsea houses, within CL7’s one storey. Designed, engineered and built by one team.
What a Chelsea basement can be.
NU Projects is a design and build company in Fulham SW6, founded in 2010. We handle basement conversion and construction in Chelsea SW3, 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.
Chelsea is terraces and garden squares, with studio houses and riverside streets between them. Most of it is conservation area.
The borough changed basements here in January 2015. Policy CL7 allows one storey, under no more than half the garden.
So a Chelsea basement is designed to make one storey count. Height, light and where the plant goes are settled early.
We built a new basement and a kitchen extension in Chelsea, under one contract. One team ran the structure, the design and the fit-out.
What the council allows.
- Council
- Royal Borough of Kensington and Chelsea. Chelsea sits wholly inside it.
- Policy CL7
- Adopted 21 January 2015. One storey only, under no more than half the garden.
- Basements SPD
- Adopted April 2016. The storey cannot be split in two later. A pool may earn a little extra depth.
- The garden
- The garden left over must stay as one area. It is usually the end furthest from the house.
- Planning
- The April 2016 Article 4 direction closed the last permitted route. Every basement here now needs planning.
- On site
- A Construction Traffic Management Plan goes in with the application. The Code of Construction Practice, revised 2019, governs the site.
Source: Policy CL7, the 2016 Basements SPD and the Article 4 direction. Read on 6 September 2026. Policies change, so we read them again for your address.
Basements in the borough.
Chelsea·Townhouse
Chelsea basement and extension
A new basement and a kitchen extension in Chelsea, with the interior renovated throughout.
See the project
South Kensington·New build
South Kensington new-build houses
Two houses in the same borough, three floors down, consented before CL7.
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.
These are two kinds of figure. The band is a rate per square foot, construction only.
The cost guide figures are whole project totals.
Fees, party wall costs, contingency and VAT sit outside them.
Open the calculatorThe 2026 cost guideBasement costs in full
Basements in Chelsea, answered.
Can I build a double basement in Chelsea?
Not any more. CL7 has limited new basements to one storey since 2015.
Our South Kensington houses went three floors down, consented before the rule.
Today we design one generous storey instead.
How much of a Chelsea garden can a basement go under?
No more than half of it, under CL7.
The garden left over must stay as one area.
It is usually the end furthest from the house.
Does a Chelsea basement need planning permission?
Yes. Since April 2016 an Article 4 direction has closed the permitted route.
The application carries a Construction Traffic Management Plan.
We prepare it with the drawings and the structural design.
Can a Chelsea basement have a pool?
Sometimes. The borough’s 2016 guidance allows a little extra depth for one.
It is still one storey, under half the garden.
We test it against the site before you commit.
What does a Chelsea basement cost?
Our basement band is £450 to £500 a sq ft, construction only.
Our 2026 cost guide puts a new dig at £500k to £900k and more.
Converting an existing cellar runs £180k to £300k as a project total.
From the journal358 notes, free to read
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Basements, Chelsea
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