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 Cheltenham?
In Cheltenham, a basement conversion typically costs £1,950–£3,250 per m² for converting an existing cellar, including VAT at 20% (standard rate). For a typical 30 m² project that is roughly £58,500–£97,500. Prices in the South West sit near the national average for this kind of work, and the range for Cheltenham reflects that. Design, structural calculations and council fees are extra.
| Size or type | Guide range |
|---|---|
| Smaller project (21 m²) | £41,000–£68,000 |
| Typical project (30 m²) | £58,500–£97,500 |
| Larger project (42 m²) | £82,000–£136,500 |
| Rate per m² | £1,950–£3,250 |
The biggest cost drivers are:
- Lightwells
- Ground water and access
- Existing cellar or new excavation
- Waterproofing system
A guide range is only a starting point: the guide price tool gives an instant figure for your size, and a free survey turns it into a fixed quote.
Do you need planning permission for a basement conversion in Cheltenham?
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
From survey to sign-off, the job normally involves:
- Underpinning or new structure where needed
- Lightwells and windows
- Building control sign-off
- Party wall notices
- Waterproofing design (tanking or cavity drain membrane)
- Structural and ground survey
How long does it take?
Allow 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 Cheltenham
In parts of the South West, protected landscapes and conservation areas shape what can be built, so materials and roof forms are chosen carefully.
Cheltenham sits in Gloucestershire, about 7 miles east of Gloucester. We cover the whole of Cheltenham, including postcodes GL50 and GL52.
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
Approvals in place
We handle planning, building control and neighbour notices before work starts.
- 04
Build and sign-off
We run the build to a written programme and hand over the completion certificate.
Questions about basement conversions in Cheltenham
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 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.
How long does it take?
A cellar conversion takes around 8 to 16 weeks; new basements take longer.
Do you build basement conversions in Cheltenham?
Yes. We build basement conversions across Cheltenham, including postcodes GL50 and GL52. Every project starts with a free home visit.
How much does a basement conversion cost in Cheltenham?
In Cheltenham, a basement conversion typically costs £1,950–£3,250 per m² for converting an existing cellar, including VAT at 20% (standard rate). A typical 30 m² project comes to roughly £58,500–£97,500. Your fixed price depends on the survey and drawings.