Local costs · Wales · September 2026
How much does an extension cost in Gwynedd?
A mid-range 25 m² single-storey extension in Gwynedd costs about £57,000 to £70,000 including VAT, or £2,300 to £2,800 per m² at Welsh prices. Gwynedd’s own published charge for building control on a 10 to 40 m² extension is £684 (full plans, including VAT): the 13th cheapest of the 91 councils we checked, 19% below the typical council (£840). With a measured survey, building regulations drawings, a structural engineer, Gwynedd’s own building control charge and a 15% contingency, plan for £70,000 to £88,500.
Work out your project in Gwynedd
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Typical prices in Gwynedd
| Project | Building work | Budget to plan for |
|---|---|---|
| Single-storey extension, 25 m² | £57,000 to £70,000 | £70,000 to £88,500 |
| Double-storey extension, 40 m² | £82,000 to £104,000 | £99,000 to £129,000 |
| Dormer loft conversion, 30 m² | £42,500 to £52,000 | £52,000 to £67,500 |
| 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 Gwynedd
| Work | Charge |
|---|---|
| Extension up to 10 m² (full plans) | £456 |
| Extension 10 to 40 m² (full plans) | £684 |
| Larger extension, 40 to 60 m² (full plans) | £820.80 |
| Extension 10 to 40 m² (building notice) | £786.60 |
| Loft conversion up to 40 m² | £684 |
| Garage conversion | £456 |
Gwynedd’s own published charge for building control on a 10 to 40 m² extension is £684 (full plans, including VAT): the 13th cheapest of the 91 councils we checked, 19% below the typical council (£840). Source: Gwynedd’s building control charges. Schedule date: Version A19 dated 4 March 2026. The charges include VAT.
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 Gwynedd compares with every council we checked.
Notes on Gwynedd’s schedule
Gwynedd publishes its own schedule. The loft figure is for up to 50 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
- Pembrokeshire: £780
- Ceredigion: £885.60
- Monmouthshire: £1,056
Questions people ask
How much does an extension cost in Gwynedd?
A mid-range 25 m² single-storey extension in Gwynedd 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, Gwynedd’s own building control charge and a 15% contingency, plan for £70,000 to £88,500.
How much is building control in Gwynedd?
Gwynedd’s own published charge for full plans approval of a 10 to 40 m² extension is £684 (including VAT). Schedule date: Version A19 dated 4 March 2026.
How much does a loft conversion cost in Gwynedd?
A mid-range 30 m² dormer loft conversion in Gwynedd costs about £42,500 to £52,000 including VAT for the building work, and about £52,000 to £67,500 with fees, Gwynedd’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 Gwynedd? 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.