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 Daventry?
In Daventry, a basement conversion typically costs £1,800–£3,050 per m² for converting an existing cellar, including VAT at 20% (standard rate). For a typical 30 m² project that is roughly £54,000–£91,500. Prices across the East Midlands are typically 5% below the UK average for this kind of work, which is reflected in the range for Daventry. Design, structural calculations and council fees are extra.
| Size or type | Guide range |
|---|---|
| Smaller project (21 m²) | £38,000–£64,000 |
| Typical project (30 m²) | £54,000–£91,500 |
| Larger project (42 m²) | £75,500–£128,000 |
| Rate per m² | £1,800–£3,050 |
Your quote will depend mainly on:
- Waterproofing system
- Existing cellar or new excavation
- Floor lowering and underpinning
- 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 Daventry?
Before anything is built in Daventry, 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.
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
From survey to sign-off, the job normally involves:
- Insulation, ventilation and drainage pumps
- Electrics, heating and plastering
- Party wall notices
- Lightwells and windows
- Structural and ground survey
- Underpinning or new structure where needed
How long does it take?
Build time is typically 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 Daventry
In the East Midlands, many estates built since the 1960s have integral garages that convert well into a study or bedroom.
From NN11 outwards, we take on projects throughout Daventry and the surrounding parts of Northamptonshire.
How it works
- 01
Survey and brief
We visit, discuss your ideas and budget, and survey the property or site at no cost.
- 02
Drawings and written quote
We prepare the design and give you a written, itemised quote with inclusions and exclusions.
- 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 Daventry
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.
How much does a basement conversion cost in Daventry?
In Daventry, a basement conversion typically costs £1,800–£3,050 per m² for converting an existing cellar, including VAT at 20% (standard rate). A typical 30 m² project comes to roughly £54,000–£91,500. Your fixed price depends on the survey and drawings.
Who approves a basement conversion in Daventry?
Planning matters in Daventry go to the council covering your address, and the work needs building control approval. We prepare and submit the applications for you.