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 Deeside?
In Deeside, 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 Deeside. 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 |
What moves the price most:
- Party wall surveyor fees
- Ground water and access
- Waterproofing system
- Floor lowering and underpinning
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 Deeside?
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.
If the answer is not clear-cut, we can apply for formal confirmation before you commit to the build.
What we handle
On a typical basement conversion we handle:
- Lightwells and windows
- Building control sign-off
- Structural and ground survey
- Electrics, heating and plastering
- Underpinning or new structure where needed
- Waterproofing design (tanking or cavity drain membrane)
How long does it take?
Build time is typically 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 Deeside
Terraced houses in Welsh towns often have narrow plots, which suits rear and side return extensions and rear dormers.
If your home is in Deeside or close by in Hawarden, Buckley and Flint, a free home visit is the first step.
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
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 Deeside
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 Deeside?
In Deeside, 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.
Do I need planning permission for a basement conversion in Deeside?
In Wales converting an existing cellar usually does not need planning permission; new excavation and lightwells may.
Is new excavation worth it?
It can be in high-value areas, but costs are high. We give a feasibility view before design starts.
Do you build basement conversions in Deeside?
Yes. We build basement conversions across Deeside, including postcodes CH5. Every project starts with a free home visit.