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 Buckinghamshire?
In Buckinghamshire, 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. The guide for Buckinghamshire reflects typical costs in the South East, roughly 12% above the UK-wide figure. 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 |
Your quote will depend mainly on:
- Lightwells
- Party wall surveyor fees
- Existing cellar or new excavation
- Ground water and access
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 Buckinghamshire?
The approval route for Buckinghamshire is set by planning law 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.
Our first visit includes a check of your planning history, so you know the route before paying for drawings.
What we handle
What we take care of:
- Lightwells and windows
- Waterproofing design (tanking or cavity drain membrane)
- Underpinning or new structure where needed
- Building control sign-off
- Structural and ground survey
- Party wall notices
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 Buckinghamshire
Commuter towns across the South East have many 1930s and post-war semis that suit rear extensions and hip-to-gable loft conversions.
Towns we cover in Buckinghamshire include Milton Keynes, High Wycombe, Aylesbury, Bletchley, Amersham and Chesham.
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 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 Buckinghamshire
How much does a basement conversion cost in Buckinghamshire?
In Buckinghamshire, 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.
Do I need party wall agreements?
In England and Wales, excavating near a neighbour’s foundations usually triggers the Party Wall etc. Act 1996.
Who approves a basement conversion in Buckinghamshire?
Planning matters in Buckinghamshire go to the council covering your address, and the work needs building control approval. We prepare and submit the applications for you.
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.