Basement and cellar conversions in Penarth

Covering Penarth

We work in Penarth (CF64) and the places around it, including Cardiff, Whitchurch and Barry.

Homes in South Glamorgan

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 does a basement conversion involve?

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.

Damp and structural survey
Ventilation, heating and electrics
Finished floors, walls and ceilings

What is the guide price for a basement conversion in Penarth?

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

How is a basement conversion approved in Penarth?

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.

How does the project run?

Send us the details. Give us a postcode, a rough idea of size and some photos, by phone, form or the guide price tool.
Survey at your house. We look at the existing structure, services and access, and agree what the design needs to achieve.
Drawings, approvals, written quote. We prepare the design, apply for the approvals it needs, and give you a fixed price in writing.
Build and hand over. Our teams build to the programme, building control inspects, and you get the completion paperwork at the end.

What people ask before starting

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 Penarth?

Yes. Penarth is within our coverage for basement and cellar conversions, along with nearby Cardiff and Whitchurch.

Also covering

Learn more about basement and cellar conversions, or see every project we cover in Penarth.