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 Abergavenny?
In Abergavenny, a basement conversion typically costs £1,750–£2,950 per m² for converting an existing cellar, including VAT at 20% (standard rate). For a typical 30 m² project that is roughly £52,500–£88,500. The guide for Abergavenny reflects typical costs in Wales, roughly 8% below the UK-wide figure. Design, structural calculations and council fees are extra.
| Size or type | Guide range |
|---|---|
| Smaller project (21 m²) | £37,000–£62,000 |
| Typical project (30 m²) | £52,500–£88,500 |
| Larger project (42 m²) | £73,500–£124,000 |
| Rate per m² | £1,750–£2,950 |
The main things that change the cost:
- Floor lowering and underpinning
- Lightwells
- Waterproofing system
- Existing cellar or new excavation
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 Abergavenny?
Whether you need planning permission depends on your house and its location in Wales. In Wales converting an existing cellar usually does not need planning permission; new excavation and lightwells may.
Building regulations in Wales are set by the Welsh Government. Approval comes from the council’s building control service or a registered building control approver, with inspections during the work and a completion certificate 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
From survey to sign-off, the job normally involves:
- Party wall notices
- Waterproofing design (tanking or cavity drain membrane)
- Building control sign-off
- Electrics, heating and plastering
- Structural and ground survey
- Lightwells and windows
How long does it take?
Expect 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 Abergavenny
Wales has many terraced valley streets, stone cottages and post-war estates, so extension designs are shaped by slopes, materials and local character.
Abergavenny sits in Gwent, about 16 miles north of Newport. We cover the whole of Abergavenny, including postcodes NP7.
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
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 Abergavenny
Do I need planning permission for a basement conversion in Abergavenny?
In Wales converting an existing cellar usually does not need planning permission; new excavation and lightwells may.
Do you build basement conversions in Abergavenny?
Yes. We build basement conversions across Abergavenny, including postcodes NP7. Every project starts with a free home visit.
Is new excavation worth it?
It can be in high-value areas, but costs are high. We give a feasibility view before design starts.
Can a basement be a bedroom?
Yes, with a suitable escape route such as a lightwell window or protected stair.
How much does a basement conversion cost in Abergavenny?
In Abergavenny, a basement conversion typically costs £1,750–£2,950 per m² for converting an existing cellar, including VAT at 20% (standard rate). A typical 30 m² project comes to roughly £52,500–£88,500. 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.