Basement and cellar conversions in Monmouth

Covering Monmouth

Alongside Monmouth, we also cover Ross-on-Wye, Chepstow (12 miles to the south) and Abergavenny.

Homes in Gwent

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 is 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.

Damp and structural survey
Underpinning or lowering the floor where needed
Finished floors, walls and ceilings

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

What basement and cellar conversions typically cost. These are guide ranges; the written quote for your house replaces them.

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

Do you need permission for a basement conversion in Monmouth?

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 should I think about before starting?

Groundwater levels drive the waterproofing design and cost.
Headroom of about 2.1 m or more is needed, which may mean lowering the floor.

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.
Free site visit. We measure up, look at access, drains and the structure, and talk through options and budget.
Design and fixed price. You get drawings and a written price for the agreed specification before anything is ordered.
We build it. Work follows an agreed programme, with inspections at each stage and a final sign-off.

Questions about a basement conversion in Monmouth

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.

Does a cellar conversion need planning permission?

Usually not if nothing changes outside. New basements and lightwells often do.

How do I get a price for basement and cellar conversions in Monmouth?

Use the guide price tool for a ballpark figure, then book a visit for a fixed written price for the agreed specification.

Other towns nearby

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