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 Wandsworth?
In Wandsworth, 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 |
Your quote will depend mainly on:
- Existing cellar or new excavation
- Party wall surveyor fees
- Floor lowering and underpinning
- Ground water and access
Your exact price depends on the survey and drawings. The guide price tool gives a quick range in the meantime.
Do you need planning permission for a basement conversion in Wandsworth?
Here is how the rules work for a basement conversion 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.
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.
At the survey we check your house’s planning history and any restrictions, and tell you which route applies.
What we handle
On a typical basement conversion we handle:
- Building control sign-off
- Structural and ground survey
- Lightwells and windows
- Insulation, ventilation and drainage pumps
- Party wall notices
- Electrics, heating and plastering
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 Wandsworth
Victorian and Edwardian terraces dominate many London streets, which is why side return, wraparound and mansard projects are so common here.
If your home is in Wandsworth or close by in Battersea, Chelsea and Fulham, a free home visit is the first step.
How it works
- 01
Visit and measured survey
A free visit to understand the project, check access and take measurements.
- 02
Drawings and written quote
We prepare the design and give you a written, itemised quote with inclusions and exclusions.
- 03
Permissions sorted
Applications, building control and neighbour arrangements, all before the start date.
- 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 Wandsworth
Is new excavation worth it?
It can be in high-value areas, but costs are high. We give a feasibility view before design starts.
How long does a basement conversion take in Wandsworth?
Typically 8 to 16 weeks for a cellar conversion; longer for new excavation. Design and approvals beforehand usually take 3 to 5 months.
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.
How much does a basement conversion cost in Wandsworth?
In Wandsworth, 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.
Do I need party wall agreements?
In England and Wales, excavating near a neighbour’s foundations usually triggers the Party Wall etc. Act 1996.