Janine Stone & Co — Since 1987
Basement Extensions London
Specialist basement design and build for prime London homes — pools, spas, cinemas, gyms and more, managed end to end.
Begin a ConversationSpecialist Basement Contractors
Basement extensions, end to end
A prime London basement extension is one of the most complex residential projects there is — planning policy, structural engineering, party-wall awards and specialist build all in play. We coordinate the lot under one roof: architecture and planning consent, open-book construction, and the interior design that makes the new space feel inevitable rather than added on.
One Studio, Three Disciplines
Architecture, construction and interiors
Residential Architecture
Feasibility, design and planning consent for the new basement footprint.
Explore architecture →Construction Management
Open-book delivery, specialist structural sub-contractors, party-wall coordination.
Explore construction →Interior Design
Light, finishes and bespoke joinery so the basement feels as considered as the floors above.
Explore interior design →Buy & Refurbish — Prime London
Prime London homes currently for sale
A selection of prime London homes we have identified for their design and refurbishment potential — many with basement-extension scope. Through our Clarity pre-purchase service we can assess feasibility before you commit.
21 Manresa Road, SW3
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Trevor Place, Knightsbridge, SW7
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Winnington Road, Hampstead, N2
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Chesterford Gardens, NW3
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Cadogan Place, SW1X
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Horbury Crescent, W11
View property →Our Portfolio — Completed Work
A selected basement project
A recent London basement extension and home spa. See the full architecture portfolio for more.
Common Questions
Basement Extensions London, answered
How much does a luxury basement extension in London cost?
Costs vary widely with depth, footprint, ground conditions and finish. Single-level basements in standard ground typically start in the high hundreds of thousands; multi-level basements with pools, spas, cinemas or below-water-table excavation reach well into the millions. We provide an open-book cost framework early, so you understand the investment before committing.
How long does a basement extension take in London?
From first design to completion, expect twelve to twenty-four months — planning consent and party-wall awards typically account for the first six to nine, with construction following. We set a realistic programme at the outset.
Will my London borough allow a basement extension?
Most prime London boroughs (Westminster, Kensington and Chelsea, Camden) have specific basement policies. Single-level basements are generally feasible; multi-level and full-garden excavations face tighter scrutiny. We assess feasibility before committing to a design.
Do you handle party-wall and structural engineering?
Yes. Our in-house architects work with specialist structural and party-wall engineers we have worked with for years — all coordinated as part of the project rather than across separate appointments.
Planning a London basement extension?
Whether at feasibility stage or ready to build, we would be glad to discuss how we can take your basement extension from design to completion under one roof.
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