What is a basement conversion?
A basement conversion turns an existing cellar into living space, or excavates a new basement under the house or garden. Waterproofing, structural support and daylight are the main design challenges.
How much does a basement conversion cost in Acton?
In Acton, a basement conversion typically costs £2,450–£4,150 per m² for converting an existing cellar, including VAT at 20% (standard rate). For a typical 30 m² project that is roughly £73,500–£124,500. That range is adjusted for London, where domestic building work typically costs around 30% above the national average. Design, structural calculations and council fees are extra.
| Size or type | Guide range |
|---|---|
| Smaller project (21 m²) | £51,500–£87,000 |
| Typical project (30 m²) | £73,500–£124,500 |
| Larger project (42 m²) | £103,000–£174,500 |
| Rate per m² | £2,450–£4,150 |
What moves the price most:
- Lightwells
- Ground water and access
- Floor lowering and underpinning
- Party wall surveyor fees
Use the guide price tool to see how size and specification change the figure, then ask for a written, itemised quote.
Do you need planning permission for a basement conversion in Acton?
The approval route for Acton is set by planning law in England. In England converting an existing cellar with no external change usually does not need planning permission. New excavation, lightwells and changes to the front often do, and some councils, particularly in London, have specific basement policies.
Building regulations approval comes from the council’s building control service or a registered building control approver. The work is inspected at key stages, such as foundations, drainage and insulation, and a completion certificate is issued at the end.
If the answer is not clear-cut, we can apply for formal confirmation before you commit to the build.
What we handle
On a typical basement conversion we handle:
- Lightwells and windows
- Party wall notices
- Structural and ground survey
- Electrics, heating and plastering
- Underpinning or new structure where needed
- Insulation, ventilation and drainage pumps
How long does it take?
Expect 8 to 16 weeks for a cellar conversion; longer for new excavation. Design and approvals come first and typically take 3 to 5 months, depending on the approval route.
Building in Acton
Space is at a premium in London, so homeowners often build out into the side return or up into the roof rather than move.
Our Acton coverage includes postcode districts W3, and we also work in nearby places such as Chiswick, Hammersmith and Willesden.
How it works
- 01
Visit and measured survey
A free visit to understand the project, check access and take measurements.
- 02
Design and fixed quote
Drawings, structural calculations and an itemised, fixed price for the agreed specification.
- 03
Approvals
Planning or permitted development confirmation, building regulations and any party wall matters.
- 04
Build and handover
Work follows the agreed programme, with inspections along the way and a completion certificate at the end.
Questions about basement conversions in Acton
How do you keep a basement dry?
With a waterproofing system designed to BS 8102, typically a cavity drain membrane with a sump pump, or a tanking system.
Do I need party wall agreements?
In England and Wales, excavating near a neighbour’s foundations usually triggers the Party Wall etc. Act 1996.
Is new excavation worth it?
It can be in high-value areas, but costs are high. We give a feasibility view before design starts.
Who approves a basement conversion in Acton?
Planning matters in Acton go to the council covering your address, and the work needs building control approval. We prepare and submit the applications for you.
How much does a basement conversion cost in Acton?
In Acton, a basement conversion typically costs £2,450–£4,150 per m² for converting an existing cellar, including VAT at 20% (standard rate). A typical 30 m² project comes to roughly £73,500–£124,500. Your fixed price depends on the survey and drawings.