Local costs · Wales · September 2026
How much does an extension cost in Monmouthshire?
A mid-range 25 m² single-storey extension in Monmouthshire costs about £56,500 to £70,000 including VAT, or £2,300 to £2,800 per m² at Welsh prices. Monmouthshire charges £1,056 for building control on a 10 to 40 m² extension (full plans, including VAT): the 17th dearest of the 91 councils we checked, 26% above the typical council (£840). With design, a structural engineer, building control and a 15% contingency, budget £71,500 to £92,500.
Work out your project in Monmouthshire
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Typical prices in Monmouthshire
| Project | Building work | Budget to plan for |
|---|---|---|
| Single-storey extension, 25 m² | £56,500 to £70,000 | £71,500 to £92,500 |
| Double-storey extension, 40 m² | £82,000 to £104,000 | £102,000 to £133,000 |
| Dormer loft conversion, 30 m² | £51,000 to £62,500 | £64,000 to £82,000 |
| Kitchen, medium | £8,600 to £15,200 | £9,800 to £17,500 |
| Bathroom refit | £5,600 to £8,500 | £6,500 to £9,700 |
Building prices in Wales run about 10% below the UK average outside London. Kitchens and bathrooms vary less from place to place than extensions and lofts.
Building control fees in Monmouthshire
| Work | Charge |
|---|---|
| Extension up to 10 m² (full plans) | £768 |
| Extension 10 to 40 m² (full plans) | £1,056 |
| Larger extension, 10-60 m² (single band) (full plans) | £1,056 |
| Extension 10 to 40 m² (building notice) | £1,056 |
| Loft conversion up to 40 m² | £1,056 |
| Garage conversion | Not published |
Monmouthshire charges £1,056 for building control on a 10 to 40 m² extension (full plans, including VAT): the 17th dearest of the 91 councils we checked, 26% above the typical council (£840). Source: Monmouthshire's building control charges, 1 April 2026. Published as fee + VAT; inc-VAT total shown on page.
Private approved inspectors set their own prices and are often competitive, so it is worth asking one or two for a quote as well. See how Monmouthshire compares with every council we checked.
Notes on Monmouthshire's schedule
Own page and guidance. Same charge for full plans and building notice. Bands <=10 / 10-60 / 60-80 m2.
Planning
In Wales, householder planning fees are set by the Welsh Government. Check the current fee on Planning Portal before you apply.
Other councils in Wales
Building control for a 10 to 40 m² extension:
- Newport: £485
- Vale of Glamorgan: £540
- Bridgend: £587
- Conwy: £648
- Gwynedd: £684
- Pembrokeshire: £780
- Ceredigion: £886
Questions people ask
How much does an extension cost in Monmouthshire?
A mid-range 25 m² single-storey extension in Monmouthshire costs about £56,500 to £70,000 including VAT for the building work, or £2,300 to £2,800 per m², based on Wales prices reviewed in September 2026. With fees and a 15% contingency, budget £71,500 to £92,500.
How much is building control in Monmouthshire?
Monmouthshire charges £1,056 (including VAT) for a 10 to 40 m² extension (full plans), according to its published schedule (1 April 2026).
How much does a loft conversion cost in Monmouthshire?
A mid-range 30 m² dormer loft conversion in Monmouthshire costs about £51,000 to £62,500 including VAT for the building work, and about £64,000 to £82,000 with fees and a 15% contingency.
Before you get quotes
- How to compare builders' quotes line by line
- Plan your whole budget, including the costs people forget
- Trades: price an extension element by element with editable unit rates