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 Bolton?
In Bolton, a basement conversion typically costs £1,800–£3,000 per m² for converting an existing cellar, including VAT at 20% (standard rate). For a typical 30 m² project that is roughly £54,000–£90,000. That range is adjusted for the North West, where domestic building work typically costs around 6% below the national average. Design, structural calculations and council fees are extra.
| Size or type | Guide range |
|---|---|
| Smaller project (21 m²) | £38,000–£63,000 |
| Typical project (30 m²) | £54,000–£90,000 |
| Larger project (42 m²) | £75,500–£126,000 |
| Rate per m² | £1,800–£3,000 |
What moves the price most:
- Ground water and access
- Lightwells
- Party wall surveyor fees
- Existing cellar or new excavation
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 Bolton?
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.
If the answer is not clear-cut, we can apply for formal confirmation before you commit to the build.
What we handle
From survey to sign-off, the job normally involves:
- Party wall notices
- Lightwells and windows
- Building control sign-off
- Insulation, ventilation and drainage pumps
- Waterproofing design (tanking or cavity drain membrane)
- Underpinning or new structure where needed
How long does it take?
Expect 8 to 16 weeks for a cellar conversion; longer for new excavation. Allow time beforehand for drawings and approvals, usually 3 to 5 months.
Building in Bolton
Terraced streets across the North West often suit rear dormers and single-storey kitchen extensions.
Our Bolton coverage includes postcode districts BL1, BL11 and BL78, and we also work in nearby places such as Farnworth, Westhoughton and Radcliffe.
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 pricing
Design options, then a fixed quote based on the chosen drawings and specification.
- 03
Approvals
Planning or permitted development confirmation, building regulations and any party wall matters.
- 04
Construction and completion
We build, put right any snags and hand over the building control certificate.
Questions about basement conversions in Bolton
Do you build basement conversions in Bolton?
Yes. We build basement conversions across Bolton, including postcodes BL1, BL11 and BL78. Every project starts with a free home visit.
How long does it take?
A cellar conversion takes around 8 to 16 weeks; new basements take longer.
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.
How much does a basement conversion cost in Bolton?
In Bolton, a basement conversion typically costs £1,800–£3,000 per m² for converting an existing cellar, including VAT at 20% (standard rate). A typical 30 m² project comes to roughly £54,000–£90,000. Your fixed price depends on the survey and drawings.