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 Putney?
In Putney, 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. We start from a UK-wide guide and adjust it for London, where labour and materials are typically about 30% above 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 |
Your quote will depend mainly on:
- Ground water and access
- Floor lowering and underpinning
- Lightwells
- Party wall surveyor fees
For a figure based on your own measurements, try the guide price tool, then book a free home visit for a fixed quote.
Do you need planning permission for a basement conversion in Putney?
Approvals for a basement conversion in Putney follow the rules for 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.
Where work involves a shared wall, building on the boundary, or digging foundations within 3 metres of a neighbour’s building and deeper than its foundations (or within 6 metres for deeper work), the Party Wall etc. Act 1996 applies and notices must be served before work starts.
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:
- Structural and ground survey
- Lightwells and windows
- Party wall notices
- Insulation, ventilation and drainage pumps
- Electrics, heating and plastering
- Waterproofing design (tanking or cavity drain membrane)
How long does it take?
Allow 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 Putney
Space is at a premium in London, so homeowners often build out into the side return or up into the roof rather than move.
From SW15 outwards, we take on projects throughout Putney and the surrounding parts of Greater London.
How it works
- 01
Survey and brief
We visit, discuss your ideas and budget, and survey the property or site at no cost.
- 02
Design and fixed quote
Drawings, structural calculations and an itemised, fixed price for the agreed specification.
- 03
Permissions sorted
Applications, building control and neighbour arrangements, all before the start date.
- 04
Construction and completion
We build, put right any snags and hand over the building control certificate.
Questions about basement conversions in Putney
Can a basement be a bedroom?
Yes, with a suitable escape route such as a lightwell window or protected stair.
Do I need party wall agreements?
In England and Wales, excavating near a neighbour’s foundations usually triggers the Party Wall etc. Act 1996.
How long does a basement conversion take in Putney?
Typically 8 to 16 weeks for a cellar conversion; longer for new excavation. Design and approvals beforehand usually take 3 to 5 months.
How much does a basement conversion cost in Putney?
In Putney, 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.
Does a basement conversion need planning permission?
Converting an existing cellar without changing the outside usually does not. New excavation, lightwells and changes visible from outside usually do.