Covering Caernarfon
Our coverage around Caernarfon (LL55) also includes Llangefni, Bangor and Pwllheli.
Homes in Gwynedd and Anglesey
Welsh homes include long terraces built into hillsides, stone cottages and modern estates, and sloping sites often shape how and where an extension can go.
What do you get with a basement conversion?
Everything below ground depends on keeping water out. We design the waterproofing system (usually a cavity drain membrane with a pump, or tanking) to the relevant British Standard guidance, then add insulation, ventilation, light and an escape route. New basements involve underpinning and a party wall process and are designed with a structural engineer.
- Planning and building regulations checks under Welsh rules
- Underpinning or lowering the floor where needed
- Ventilation, heating and electrics
What is the guide price for a basement conversion in Caernarfon?
Typical ranges for basement and cellar conversions. Ground conditions, access and specification move the final figure, which we fix in writing before work starts.
| Basement and cellar conversions | Guide price incl. VAT |
|---|---|
| Existing cellar conversion | £1,900 to £3,000 per m² |
| New basement excavation | £4,200 to £6,600 per m² |
What approvals does a basement conversion need in Wales?
Planning decisions in Wales are made by the local council, using permitted development rules set by the Welsh Government rather than England’s. Building regulations in Wales have their own approved documents, and the Party Wall etc. Act 1996 applies to work on shared walls and boundaries.
In Wales an existing cellar conversion usually does not need planning permission; new excavation and lightwells may.
What can affect a basement conversion?
- Groundwater levels drive the waterproofing design and cost.
- A pump for the drainage system needs a battery back-up.
From first call to completion
- Send us the details. Give us a postcode, a rough idea of size and some photos, by phone, form or the guide price tool.
- We visit and measure. A surveyor checks the house, the boundaries and the ground, and discusses what is realistic.
- Drawings, approvals, written quote. We prepare the design, apply for the approvals it needs, and give you a fixed price in writing.
- Construction and completion. One site lead co-ordinates every trade through to the building control certificate.
Your questions answered
How much does a basement conversion cost?
Converting an existing cellar costs about £1,900 to £3,000 per square metre including VAT. A new excavated basement is around £4,200 to £6,600 per square metre.
Will my neighbours be affected?
New basements usually need party wall agreements. We handle the notices and surveyors.
Do you work in Caernarfon?
Yes. Caernarfon is within our coverage for basement and cellar conversions, along with nearby Llangefni and Bangor.
Other towns nearby
- Basement and cellar conversions in Llangefni
- Basement and cellar conversions in Bangor
- Basement and cellar conversions in Pwllheli
- Basement and cellar conversions in Holyhead
Learn more about basement and cellar conversions, or see every project we cover in Caernarfon.