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 Dunstable?
In Dunstable, 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 |
The biggest cost drivers are:
- Floor lowering and underpinning
- Lightwells
- Waterproofing system
- Ground water and access
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 Dunstable?
Approvals for a basement conversion in Dunstable 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.
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.
Our first visit includes a check of your planning history, so you know the route before paying for drawings.
What we handle
The work we manage on a basement conversion:
- Structural and ground survey
- Waterproofing design (tanking or cavity drain membrane)
- Party wall notices
- Lightwells and windows
- Underpinning or new structure where needed
- Electrics, heating and plastering
How long does it take?
The build itself usually takes 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 Dunstable
Across the East of England, 1930s and post-war semis, newer estates and rural cottages all feature, each with different extension and loft options.
We work across Dunstable and neighbouring areas such as Luton, Leighton Buzzard and Harpenden. Postcodes we cover in Dunstable include LU6.
How it works
- 01
Free visit
We look at the property, talk through what you want and measure up. There is no charge and no obligation.
- 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 Dunstable
How much does a basement conversion cost in Dunstable?
In Dunstable, 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.
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.
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 long does a basement conversion take in Dunstable?
Typically 8 to 16 weeks for a cellar conversion; longer for new excavation. Design and approvals beforehand usually take 3 to 5 months.