Extensions in Windsor: design, planning and build
Looking to extend your home in Windsor? Start here: extension types, guide prices for Windsor, the planning rules that apply and how a project runs.
- Postcode districtsSL1, SL3, SL4
- Price regionSouth East England (×1.12)
- Planning rulesEngland
- Site visitFree, no obligation
Which extension suits a Windsor home?
In the South East, plenty of houses have already been extended once, which makes checking the remaining permitted development allowance an important early step.
Start by comparing double-storey extensions, single-storey rear extensions and orangery extensions: between them they cover most of the layouts we see requested for houses like these.
Windsor extension prices at a glance
Every figure below is a guide for Windsor, adjusted for South East England build costs (×1.12) and including VAT. Design and council fees are shown separately on each page.
| Extension type | Example size | Standard spec (inc VAT) |
|---|---|---|
| Conservatory replacement extensions | 14 m² | £33,500 – £43,500 |
| Single-storey rear extensions | 20 m² | £45,500 – £58,500 |
| Double-storey extensions | 32 m² | £64,500 – £84,500 |
| Side return extensions | 11 m² | £29,500 – £37,000 |
| Kitchen extensions | 20 m² | £47,000 – £59,500 |
Do extensions in Windsor need planning permission?
In England a single-storey rear extension can usually go up to 3 m beyond the original rear wall of a semi-detached or terraced house, or 4 m on a detached house, without a planning application, provided it is no more than 4 m high, keeps eaves to 3 m within 2 m of a boundary and, with other buildings, covers no more than half the land around the original house. The larger home extension prior approval scheme raises those depths to 6 m and 8 m, with neighbours notified and a 42-day decision.
In England a two-storey rear extension is permitted development only if it projects no more than 3 m from the original rear wall, sits at least 7 m from the rear boundary, matches the roof pitch and uses obscure, non-opening side windows upstairs. Most two-storey extensions therefore go through a householder planning application, which costs £548 from 1 April 2026 and normally takes about 8 weeks.
In a conservation area, national park, National Landscape, the Broads or a World Heritage Site the permitted development limits are tighter (no side or two-storey extensions without an application). Listed homes need listed building consent, and if permitted development rights have been removed, any extension needs an application.
Building regulations approval is separate from planning. In England you can use the council's building control team or a registered building control approver; a full plans application gets the drawings checked before work starts, and the inspector signs the work off with a completion certificate.
Applications are decided by the local planning authority (your district, borough or unitary council).
Areas we cover around Windsor
We cover Windsor and the postcode districts SL1, SL3, SL4. Nearby, we also take on projects in Slough (2 miles), Maidenhead (6 miles), Bracknell (8 miles), Wokingham (11 miles), Crowthorne (11 miles). Egham, in Surrey, is roughly 4 miles from Windsor and also on our list.
Every extension type in Windsor
- Double-storey extensions · from £42,500
- Conservatory replacement extensions · from £22,000
- Orangery extensions · from £33,500
- Side return extensions · from £20,000
- Wraparound extensions · from £40,000
- Bungalow extensions · from £29,000
- Bedroom extensions · from £29,000
- Planning permission for extensions · from £350
- Timber frame extensions · from £23,500
- Building regulations for extensions · from £1,000
- Extensions over a garage · from £26,500
- Pitched roof extensions · from £24,500
- Glass box extensions · from £33,500
- Kitchen extensions · from £30,000
- Annexe extensions · from £61,500
- Flat roof extensions · from £23,500
- Extension plans and drawings · from £1,300
- Utility and boot room extensions · from £15,500
- Single-storey rear extensions · from £23,500
- Porch extensions · from £4,450
- Side extensions · from £24,500
- Home office extensions · from £17,500
Free site visit
First, a site visit: we look at the house, garden, access and drains and listen to what you need.
Design and approvals
We produce the drawings and structural design, and manage the approvals so they are in place before work starts.
Fixed written price
You receive a written, itemised price and programme. Nothing starts until you are happy with it.
Build and sign-off
Work is carried out to the agreed programme, inspected by building control and signed off at the end.
Questions about extensions in Windsor
How much does an extension cost in Windsor?
Using our South East England factor (×1.12), a standard-spec single-storey extension of 20 m² is a guide £45,500 to £58,500 including VAT, and a 32 m² two-storey extension £64,500 to £84,500. Your written price follows the survey.
Will my neighbours need to be told?
If you apply for planning or prior approval the council notifies them, and in England party wall notices may be needed for work near a shared boundary.
How long does an extension take in Windsor?
Usually 2 to 4 months of design and approvals, then 10 to 16 weeks on site for a single-storey extension or 16 to 24 weeks for two storeys.
Do I need planning permission for an extension in Windsor?
Not always. It depends on the size, position and your property's history. Many single-storey rear extensions in England are permitted development or can use prior approval.
Book a free site visit in Windsor
We will measure up, check the planning position and give you honest guide figures.
- Free, no-obligation site visit
- Planning route checked before you spend on drawings
- Written price once the design is agreed
- Building control sign-off at the end
Prefer to talk? Call 0800 088 6341 or .
Book a free site visit
Tell us a little about the project and we will arrange a time.