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 Cambridge?
In Cambridge, a basement conversion typically costs £2,000–£3,400 per m² for converting an existing cellar, including VAT at 20% (standard rate). For a typical 30 m² project that is roughly £60,000–£102,000. We start from a UK-wide guide and adjust it for the East of England, where labour and materials are typically about 6% above average. Design, structural calculations and council fees are extra.
| Size or type | Guide range |
|---|---|
| Smaller project (21 m²) | £42,000–£71,500 |
| Typical project (30 m²) | £60,000–£102,000 |
| Larger project (42 m²) | £84,000–£143,000 |
| Rate per m² | £2,000–£3,400 |
What moves the price most:
- Lightwells
- Floor lowering and underpinning
- Ground water and access
- Existing cellar or new excavation
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 Cambridge?
Before anything is built in Cambridge, we confirm which approvals apply 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
What we take care of:
- Waterproofing design (tanking or cavity drain membrane)
- Insulation, ventilation and drainage pumps
- Structural and ground survey
- Building control sign-off
- Electrics, heating and plastering
- Lightwells and windows
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 Cambridge
Across the East of England, 1930s and post-war semis, newer estates and rural cottages all feature, each with different extension and loft options.
If your home is in Cambridge or close by in Newmarket, Ely and Huntingdon, 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
Design and pricing
Design options, then a fixed quote based on the chosen drawings and specification.
- 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 Cambridge
Do you build basement conversions in Cambridge?
Yes. We build basement conversions across Cambridge, including postcodes CB5, CB21, CB22 and CB23. Every project starts with a free home visit.
Do I need party wall agreements?
In England and Wales, excavating near a neighbour’s foundations usually triggers the Party Wall etc. Act 1996.
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.
Can a basement be a bedroom?
Yes, with a suitable escape route such as a lightwell window or protected stair.
How much does a basement conversion cost in Cambridge?
In Cambridge, a basement conversion typically costs £2,000–£3,400 per m² for converting an existing cellar, including VAT at 20% (standard rate). A typical 30 m² project comes to roughly £60,000–£102,000. Your fixed price depends on the survey and drawings.