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 £57,000 to £70,000 including VAT, or £2,300 to £2,800 per m² at Welsh prices. Monmouthshire’s own published charge for building control on a 10 to 40 m² extension is £1,056 (full plans, including VAT): the 17th dearest of the 91 councils we checked, 26% above the typical council (£840). With a measured survey, building regulations drawings, a structural engineer, Monmouthshire’s own building control charge and a 15% contingency, plan for £70,000 to £89,000.
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 | £57,000 to £70,000 | £70,000 to £89,000 |
| Double-storey extension, 40 m² | £82,000 to £104,000 | £99,500 to £129,000 |
| Dormer loft conversion, 30 m² | £42,500 to £52,000 | £52,500 to £68,000 |
| 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 to 60 m² (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’s own published charge for building control on a 10 to 40 m² extension is £1,056 (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. The charges apply from 1 April 2026. The page shows each charge plus VAT, and the total including VAT, which is the figure we use.
Private building control firms (registered building control approvers) 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
Monmouthshire publishes its charges on its own page and in its guidance, with one charge for full plans or a building notice, in bands of up to 10 m², 10 to 60 m² and 60 to 80 m².
Planning
If your extension needs planning permission, a householder application in Wales costs £585. Many single-storey rear extensions are permitted development and need no application, and a lawful development certificate (£292.50) confirms it in writing.
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: £885.60
Questions people ask
How much does an extension cost in Monmouthshire?
A mid-range 25 m² single-storey extension in Monmouthshire costs about £57,000 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 a measured survey, design, a structural engineer, Monmouthshire’s own building control charge and a 15% contingency, plan for £70,000 to £89,000.
How much is building control in Monmouthshire?
Monmouthshire’s own published charge for full plans approval of a 10 to 40 m² extension is £1,056 (including VAT). The charges apply from 1 April 2026.
How much does a loft conversion cost in Monmouthshire?
A mid-range 30 m² dormer loft conversion in Monmouthshire costs about £42,500 to £52,000 including VAT for the building work, and about £52,500 to £68,000 with fees, Monmouthshire’s own building control charge 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
- When quotes arrive, check each one against the typical range for your area
Work in Monmouthshire? Firm listings on Estiquote’s map of checked local firms open soon: see what you’ll need. Listing will be free while we build the map, with at least 30 days’ notice before any charge.