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 West Glamorgan?
In West Glamorgan, 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. Prices across Wales are typically 8% below the UK average for this kind of work, which is reflected in the range for West Glamorgan. 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 |
Your quote will depend mainly on:
- Floor lowering and underpinning
- Existing cellar or new excavation
- Party wall surveyor fees
- Waterproofing system
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 West Glamorgan?
Approvals for a basement conversion in West Glamorgan follow the rules for 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.
At the survey we check your house’s planning history and any restrictions, and tell you which route applies.
What we handle
Handled as part of most basement conversions:
- Electrics, heating and plastering
- Structural and ground survey
- Underpinning or new structure where needed
- Party wall notices
- Waterproofing design (tanking or cavity drain membrane)
- Building control sign-off
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 West Glamorgan
Wales has many terraced valley streets, stone cottages and post-war estates, so extension designs are shaped by slopes, materials and local character.
Towns we cover in West Glamorgan include Swansea, Neath, Gorseinon and Clydach.
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 pricing
Design options, then a fixed quote based on the chosen drawings and specification.
- 03
Approvals in place
We handle planning, building control and neighbour notices before work starts.
- 04
Build and handover
Work follows the agreed programme, with inspections along the way and a completion certificate at the end.
Questions about basement conversions in West Glamorgan
How long does it take?
A cellar conversion takes around 8 to 16 weeks; new basements take longer.
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 much does a basement conversion cost in West Glamorgan?
In West Glamorgan, 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.
Do I need planning permission for a basement conversion in West Glamorgan?
In Wales converting an existing cellar usually does not need planning permission; new excavation and lightwells may.
Do you build basement conversions in West Glamorgan?
Yes. We build basement conversions across West Glamorgan, including postcodes SA1, SA10, SA11, SA12 and SA13. Every project starts with a free home visit.
Can a basement be a bedroom?
Yes, with a suitable escape route such as a lightwell window or protected stair.