Estiquote

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 £72,500 to £89,500 including VAT, or £2,900 to £3,600 per m² at South East prices. Windsor and Maidenhead charges £990 for building control on a 10 to 40 m² extension (full plans, including VAT): 18% above the typical council (£840). With design, a structural engineer, building control and a 15% contingency, budget £89,500 to £115,000.

By Estiquote · Prices reviewed · Council fees from Windsor and Maidenhead's published schedule · How we calculate

Work out your project in Windsor and Maidenhead

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Typical prices in Windsor and Maidenhead

Mid-range finish, South East prices, including VAT. The budget adds design and engineering fees, Windsor and Maidenhead's building control charge and a 15% contingency.
ProjectBuilding workBudget to plan for
Single-storey extension, 25 m²£72,500 to £89,500£89,500 to £115,000
Double-storey extension, 40 m²£105,000 to £132,000£128,000 to £167,000
Dormer loft conversion, 30 m²£65,000 to £80,000£80,000 to £102,000
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 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

Windsor and Maidenhead council charges including VAT (plan and inspection combined)
WorkCharge
Extension up to 10 m² (full plans)£780
Extension 10 to 40 m² (full plans)£990
Larger extension, 40-100 m² (full plans)£1,275
Extension 10 to 40 m² (building notice)£1,138
Loft conversion up to 40 m²£1,092
Garage conversion£690

Windsor and Maidenhead charges £990 for building control on a 10 to 40 m² extension (full plans, including VAT): 18% above the typical council (£840). Source: Windsor and Maidenhead's building control charges, 1 April 2026. Inc VAT ("inclusive of VAT at 20.0%").

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 Windsor and Maidenhead compares with every council we checked.

Notes on Windsor and Maidenhead's schedule

Own schedule. Loft figure is with dormer (without dormer 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.

Other councils in South East

Building control for a 10 to 40 m² extension:

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 £72,500 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 fees and a 15% contingency, budget £89,500 to £115,000.

How much is building control in Windsor and Maidenhead?

Windsor and Maidenhead charges £990 (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 Windsor and Maidenhead?

A mid-range 30 m² dormer loft conversion in Windsor and Maidenhead costs about £65,000 to £80,000 including VAT for the building work, and about £80,000 to £102,000 with fees and a 15% contingency.

Before you get quotes