Royal Borough of Windsor and Maidenhead
22.4% of homes in the Windsor area were built before 1919, against 12.6% across Berkshire.
25.7% of households in the Windsor area live in terraced houses, against 21.7% across Berkshire.
Planning and building control here are handled by the Royal Borough of Windsor and Maidenhead.
Sources: ONS 2021 Census (TS044 accommodation type, TS052 occupancy rating, TS061 travel to work), households; VOA Council Tax stock of properties, 31 March 2025 (build period and bungalows, rounded by the VOA, homes with unknown build period excluded); HM Land Registry Price Paid Data, standard sales in 2025. Area defined by ONS built-up areas and 2021 census neighbourhoods (LSOAs).
Build costs for Berkshire, from published cost guides adjusted for the South East. They are estimates to help you budget, not quotes, and we review them regularly.
| Conversion type | Floor area | Typical build cost | Build time |
|---|---|---|---|
| Velux or rooflight | 30m² | £26,000 to £39,000 | 4 to 6 weeks |
| Rear dormer | 30m² | £46,000 to £78,000 | 10 to 12 weeks |
| Hip to gable | 30m² | £57,000 to £91,000 | 10 to 14 weeks |
| Mansard | 30m² | £57,000 to £104,000 | 12 to 16 weeks |
| Bungalow | 50m² | £72,000 to £114,000 | 10 to 12 weeks |
Ranges, not quotes. Build cost only: excludes VAT, professional fees, planning and building control. Last updated September 2026.
Sources: Checkatrade, Loft conversion cost: 2026 UK price guide (March 2026 (table), August 2026 (breakdown)); Homebuilding & Renovating, Loft conversion costs (Tim Phillips, quantity surveyor) (29 July 2026).
A typical 30m² rear dormer (£46,000 to £78,000 to build, before VAT and fees) is about 9% to 15% of the 2025 median price of a terraced house in the Windsor area (£505,000).
Work out a cost for your own loft with the calculator, or read the full cost guide.
These are tendencies based on the local mix of homes, not advice for your house. A specialist survey confirms what your roof allows.
Both older homes (22.4% built before 1919) and terraces (25.7% of households) are above the Berkshire average here. Rear dormers are the usual route for terraces, and L-shaped dormers can add more space on houses with a rear wing. Mansard conversions are an option on some period terraces, but usually need planning permission.
| Type | Median | Sales | Value added* |
|---|---|---|---|
| Detached | £800,000 | 87 | £96,000 to £200,000 |
| Semi-detached | £595,000 | 111 | £65,000 to £149,000 |
| Terraced | £505,000 | 175 | £51,000 to £126,000 |
| Flat or maisonette | £325,000 | 146 | - |
| Year | Median | Sales |
|---|---|---|
| 2021 | £480,000 | 730 |
| 2022 | £520,000 | 582 |
| 2023 | £475,000 | 463 |
| 2024 | £483,000 | 504 |
| 2025 | £520,000 | 519 |
| 2026 (to date) | £497,000 | 168 |
* A rough guide, not a valuation. The low figure applies Nationwide's estimate for adding a fourth bedroom to this type of house (10% terraced, 11% semi-detached, 12% detached); the high figure applies its "as much as 25%" for a large bedroom and bathroom. Nationwide's figures come from its 2023 national model, not Berkshire data. Prices are HM Land Registry standard market sales; medians from fewer than 20 sales are not shown.
Many loft conversions can be built without planning permission under permitted development rights, within limits: up to 40m³ of extra roof space for a terraced house and 50m³ for other houses, nothing higher than the existing roof, and nothing beyond the front roof slope facing a road. These rights do not apply in conservation areas. Read more in our planning guide for Windsor and Maidenhead.
If your home is in one of these, a dormer or other roof enlargement will normally need planning permission:
From each council's official list. Check Windsor and Maidenhead's conservation areas. Boundaries can change, so check your address on the council's map.
Every loft conversion needs building regulations approval. The council's published charges for a loft conversion (including VAT):
Royal Borough of Windsor and Maidenhead
Effective from 1 April 2026. Source.
This page covers Windsor, Eton and Datchet. Postcode districts: SL4, SL3.
The area follows the ONS built-up areas for Windsor, Eton and Datchet; the postcode districts are the ones that make up at least 5% of home sales here since 2021. Some districts also reach neighbouring areas.
As a guide, a typical 30m² rear dormer costs £46,000 to £78,000 to build in Berkshire, before VAT and fees, based on published cost guides adjusted for the South East. Velux conversions cost less and hip-to-gable or mansard conversions more. Windsor and Maidenhead's building control charge for a loft conversion is £912 to £1,092 for a full plans application, including VAT. Every house is different, so get quotes before you budget.
Usually, yes. Permitted development rights for roof enlargements, such as dormers, do not apply in conservation areas, so you will normally need planning permission. There are 6 conservation areas in the Windsor area, including Inner Windsor, Windsor Town Centre and Trinity Place/ Clarence Crescent, Windsor. Check your address on the council's map. Outside conservation areas, many loft conversions can go ahead under permitted development, within size limits.
Rear and L-shaped dormers for period terraces. Terraced houses are the most common type here (25.7% of households), and most homes were built between 1945 and 1972. A specialist survey will confirm what your roof allows.
It can. The median terraced house in the Windsor area sold for £505,000 in 2025. Nationwide's 2023 research suggests adding a bedroom adds about 10% for this type of house, and a bedroom with a bathroom as much as 25%. On that median, that is roughly £51,000 to £126,000. This is a rough guide from national research, not a valuation.
Last reviewed 22 September 2026. The figures on this page come from public datasets and published guides. We update them as new data is released.
Tell us about your project and we’ll pass it to up to three local loft conversion specialists.