Local costs · South West · September 2026
How much does an extension cost in Wiltshire?
A mid-range 25 m² single-storey extension in Wiltshire costs about £66,000 to £81,000 including VAT, or £2,600 to £3,200 per m² at South West prices. Wiltshire’s own published charge for building control on a 10 to 40 m² extension is £755 (full plans, including VAT): 10% below the typical council (£840). With a measured survey, building regulations drawings, a structural engineer, Wiltshire’s own building control charge and a 15% contingency, plan for £80,500 to £102,000.
Work out your project in Wiltshire
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Typical prices in Wiltshire
| Project | Building work | Budget to plan for |
|---|---|---|
| Single-storey extension, 25 m² | £66,000 to £81,000 | £80,500 to £102,000 |
| Double-storey extension, 40 m² | £95,000 to £120,000 | £114,000 to £148,000 |
| Dormer loft conversion, 30 m² | £49,000 to £60,500 | £60,000 to £77,500 |
| Kitchen, medium | £9,200 to £16,300 | £10,600 to £18,800 |
| Bathroom refit | £6,100 to £9,200 | £7,100 to £10,600 |
Building prices in the South West run about 4% above the UK average outside London. Kitchens and bathrooms vary less from place to place than extensions and lofts.
Building control fees in Wiltshire
| Work | Charge |
|---|---|
| Extension up to 10 m² (full plans) | £609 |
| Extension 10 to 40 m² (full plans) | £755 |
| Larger extension, 40 to 60 m² (full plans) | £901 |
| Extension 10 to 40 m² (building notice) | £755 |
| Loft conversion up to 40 m² | £755 |
| Garage conversion | £409 |
Wiltshire’s own published charge for building control on a 10 to 40 m² extension is £755 (full plans, including VAT): 10% below the typical council (£840). Source: Wiltshire’s building control charges. Schedule date: 1 April 2026 (to 31 March 2027). 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 Wiltshire compares with every council we checked.
Notes on Wiltshire’s schedule
Wiltshire publishes its charges on its own page, with one fee for full plans or a building notice. Its bands are up to 10 m², 10 to 20 m², 20 to 40 m² and 40 to 60 m², so the 10 to 40 m² figure is the 20 to 40 m² charge; 10 to 20 m² costs £721. Loft conversions use the same charges as extensions.
Planning
If your extension needs planning permission, a householder application in England costs £548. Many single-storey rear extensions are permitted development and need no application, and a lawful development certificate (£274) confirms it in writing.
Other councils in the South West
Building control for a 10 to 40 m² extension:
- Bath and North East Somerset: £696
- Bristol: £735
- Exeter: £800
- Mid Devon: £896
- North Devon: £896
- Plymouth: £973
- South Hams: £1,095
- Teignbridge: £1,095
- West Devon: £1,095
- Cornwall: £1,140
Questions people ask
How much does an extension cost in Wiltshire?
A mid-range 25 m² single-storey extension in Wiltshire costs about £66,000 to £81,000 including VAT for the building work, or £2,600 to £3,200 per m², based on South West prices reviewed in September 2026. With a measured survey, design, a structural engineer, Wiltshire’s own building control charge and a 15% contingency, plan for £80,500 to £102,000.
How much is building control in Wiltshire?
Wiltshire’s own published charge for full plans approval of a 10 to 40 m² extension is £755 (including VAT). Schedule date: 1 April 2026 (to 31 March 2027).
How much does a loft conversion cost in Wiltshire?
A mid-range 30 m² dormer loft conversion in Wiltshire costs about £49,000 to £60,500 including VAT for the building work, and about £60,000 to £77,500 with fees, Wiltshire’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 Wiltshire? 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.