Local costs · South East · September 2026
How much does an extension cost in Windsor and Maidenhead?
A mid-range 25 m² single-storey extension in Windsor and Maidenhead costs about £73,000 to £89,500 including VAT, or £2,900 to £3,600 per m² at South East prices. Windsor and Maidenhead’s own published charge for building control on a 10 to 40 m² extension is £990 (full plans, including VAT): 18% above the typical council (£840). With a measured survey, building regulations drawings, a structural engineer, Windsor and Maidenhead’s own building control charge and a 15% contingency, plan for £89,000 to £113,000.
Work out your project in Windsor and Maidenhead
Loading the calculator…
Typical prices in Windsor and Maidenhead
| Project | Building work | Budget to plan for |
|---|---|---|
| Single-storey extension, 25 m² | £73,000 to £89,500 | £89,000 to £113,000 |
| Double-storey extension, 40 m² | £105,000 to £132,000 | £126,000 to £164,000 |
| Dormer loft conversion, 30 m² | £54,000 to £66,500 | £66,500 to £86,000 |
| Kitchen, medium | £9,700 to £17,200 | £11,100 to £19,800 |
| Bathroom refit | £6,500 to £9,800 | £7,500 to £11,300 |
Building prices in the South East run about 15% above the UK average outside London. Kitchens and bathrooms vary less from place to place than extensions and lofts.
Building control fees in Windsor and Maidenhead
| Work | Charge |
|---|---|
| Extension up to 10 m² (full plans) | £780 |
| Extension 10 to 40 m² (full plans) | £990 |
| Larger extension, 40 to 100 m² (full plans) | £1,275 |
| Extension 10 to 40 m² (building notice) | £1,138.50 |
| Loft conversion up to 40 m² | £1,092 |
| Garage conversion | £690 |
Windsor and Maidenhead’s own published charge for building control on a 10 to 40 m² extension is £990 (full plans, including VAT): 18% above the typical council (£840). Source: Windsor and Maidenhead’s building control charges. The charges apply from 1 April 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 Windsor and Maidenhead compares with every council we checked.
Notes on Windsor and Maidenhead’s schedule
Windsor and Maidenhead publishes its own schedule. The loft figure is for a loft with a dormer; without one it is £912.
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 East
Building control for a 10 to 40 m² extension:
- Milton Keynes: £840
- Horsham: £858
- Crawley: £858
- Folkestone and Hythe: £941.64
- Hart: £960
- Rushmoor: £960
- Maidstone: £1,023
- West Berkshire: £1,055
- Wokingham: £1,055
- Winchester: £1,085 (building notice)
- Oxford: £1,125
- Runnymede: £1,182
- Waverley: £1,280
Questions people ask
How much does an extension cost in Windsor and Maidenhead?
A mid-range 25 m² single-storey extension in Windsor and Maidenhead costs about £73,000 to £89,500 including VAT for the building work, or £2,900 to £3,600 per m², based on South East prices reviewed in September 2026. With a measured survey, design, a structural engineer, Windsor and Maidenhead’s own building control charge and a 15% contingency, plan for £89,000 to £113,000.
How much is building control in Windsor and Maidenhead?
Windsor and Maidenhead’s own published charge for full plans approval of a 10 to 40 m² extension is £990 (including VAT). The charges apply from 1 April 2026.
How much does a loft conversion cost in Windsor and Maidenhead?
A mid-range 30 m² dormer loft conversion in Windsor and Maidenhead costs about £54,000 to £66,500 including VAT for the building work, and about £66,500 to £86,000 with fees, Windsor and Maidenhead’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 Windsor and Maidenhead? 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.