Extending your home in Isleworth
We design and build house extensions for homes in Isleworth and the surrounding Greater London area, with guide prices adjusted for the region.
- Postcode districtsTW1, TW3, TW4, TW5, TW7, TW8
- Price regionLondon (×1.3)
- Planning rulesEngland
- Site visitFree, no obligation
Planning rules in Isleworth
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).
Choosing the right extension in Isleworth
London's housing is dominated by Victorian and Edwardian terraces, many with a rear outrigger and a side return, and 1930s semis in the outer boroughs. Conservation areas are common, so the planning check comes first.
The types we would usually look at first for a home in Isleworth are wraparound extensions, kitchen extensions and glass box extensions, depending on the garden and how the house is laid out.
Covering Isleworth and nearby
Our survey diary covers Isleworth, including TW1, TW3, TW4, TW5, TW7, TW8. Nearby, we also take on projects in Hounslow (1 mile), Heston (2 miles), Richmond (2 miles), Southall (3 miles), Hanworth (3 miles). East Molesey, in Surrey, is roughly 5 miles from Isleworth and also on our list.
Popular extension prices in Isleworth
Use these Isleworth guide prices to sense-check a budget; the guide-price tool narrows them to your own size, and the site visit turns them into a written figure.
| Extension type | Example size | Standard spec (inc VAT) |
|---|---|---|
| Orangery extensions | 16 m² | £58,000 – £73,000 |
| Single-storey rear extensions | 20 m² | £53,000 – £68,000 |
| Double-storey extensions | 32 m² | £74,500 – £98,000 |
| Conservatory replacement extensions | 14 m² | £39,000 – £50,500 |
| Kitchen extensions | 20 m² | £54,500 – £69,000 |
| Wraparound extensions | 25 m² | £74,500 – £94,500 |
| Side return extensions | 11 m² | £34,000 – £43,000 |
Every extension type in Isleworth
- Side extensions · from £28,500
- Kitchen extensions · from £35,000
- Planning permission for extensions · from £450
- Annexe extensions · from £71,500
- Utility and boot room extensions · from £18,000
- Side return extensions · from £23,000
- Extensions over a garage · from £31,000
- Flat roof extensions · from £27,000
- Conservatory replacement extensions · from £26,000
- Single-storey rear extensions · from £27,000
- Bungalow extensions · from £34,000
- Glass box extensions · from £39,000
- Building regulations for extensions · from £1,150
- Extension plans and drawings · from £1,550
- Pitched roof extensions · from £28,500
- Home office extensions · from £20,500
- Timber frame extensions · from £27,000
- Double-storey extensions · from £49,000
- Porch extensions · from £5,200
- Wraparound extensions · from £46,500
- Orangery extensions · from £39,000
- Bedroom extensions · from £33,500
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
Once the layout is agreed, we deal with the council: planning permission or written confirmation that none is needed, plus building control.
Fixed written price
We confirm the build price in writing, based on the approved drawings and the finishes you have chosen.
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 Isleworth
How much does an extension cost in Isleworth?
Using our London factor (×1.3), a standard-spec single-storey extension of 20 m² is a guide £53,000 to £68,000 including VAT, and a 32 m² two-storey extension £74,500 to £98,000. Your written price follows the survey.
Do I need planning permission for an extension in Isleworth?
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.
Do you cover all of Isleworth?
Yes, including the surrounding parts of Greater London. Site visits are free and there is no obligation.
Who do I contract with?
Your contract is with S&K Property Investments and Improvement Ltd, which designs and manages the project and the build teams who carry it out.
Book a free site visit in Isleworth
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.