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 Berkshire?
In Berkshire, a basement conversion typically costs £2,150–£3,600 per m² for converting an existing cellar, including VAT at 20% (standard rate). For a typical 30 m² project that is roughly £64,500–£108,000. Prices across the South East are typically 12% above the UK average for this kind of work, which is reflected in the range for Berkshire. Design, structural calculations and council fees are extra.
| Size or type | Guide range |
|---|---|
| Smaller project (21 m²) | £45,000–£75,500 |
| Typical project (30 m²) | £64,500–£108,000 |
| Larger project (42 m²) | £90,500–£151,000 |
| Rate per m² | £2,150–£3,600 |
The biggest cost drivers are:
- Existing cellar or new excavation
- Ground water and access
- Party wall surveyor fees
- Floor lowering and underpinning
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 Berkshire?
Approvals for a basement conversion in Berkshire 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.
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.
We check this for your address before design work starts, so there are no surprises later.
What we handle
From survey to sign-off, the job normally involves:
- Insulation, ventilation and drainage pumps
- Lightwells and windows
- Building control sign-off
- Waterproofing design (tanking or cavity drain membrane)
- Party wall notices
- Underpinning or new structure where needed
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 Berkshire
The South East has a broad mix of housing, from Victorian terraces in the towns to post-war semis and newer estates, so extension types vary street by street.
Towns we cover in Berkshire include Reading, Slough, Bracknell, Maidenhead, Wokingham and Newbury.
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 fixed quote
Drawings, structural calculations and an itemised, fixed price for the agreed specification.
- 03
Approvals
Planning or permitted development confirmation, building regulations and any party wall matters.
- 04
Build and sign-off
We run the build to a written programme and hand over the completion certificate.
Questions about basement conversions in Berkshire
Is new excavation worth it?
It can be in high-value areas, but costs are high. We give a feasibility view before design starts.
Who approves a basement conversion in Berkshire?
Planning matters in Berkshire go to the council covering your address, and the work needs building control approval. We prepare and submit the applications for you.
How much does a basement conversion cost in Berkshire?
In Berkshire, a basement conversion typically costs £2,150–£3,600 per m² for converting an existing cellar, including VAT at 20% (standard rate). A typical 30 m² project comes to roughly £64,500–£108,000. Your fixed price depends on the survey and drawings.
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.