Planning permission for a house extension in London is the question West London homeowners ask most before starting a project — and for good reason. Get it right and you can add significant living space without council involvement. Get it wrong, however, and you risk enforcement action or complications when you sell. This guide gives you the complete, accurate answer for 2026.
At Signature Build Properties, we manage planning permission for house extensions in London and West London on every project. Based in Hayes and covering Ealing, Hounslow, Hillingdon and Richmond, we establish your planning position at the free site survey — completely free, no obligation.
Permitted Development rights allow certain house extensions in London without a full planning application. For West London homeowners in 2026, the key limits for single storey rear extensions are as follows. For independent guidance, the Planning Portal house extension guide provides a useful overview of the national rules.
This is the maximum single storey rear extension depth under standard Permitted Development for terraced and semi-detached houses — the most common property type across Ealing, Hounslow and Hillingdon.
Detached properties benefit from a larger limit. Consequently, many homeowners in Richmond and Hillingdon can extend further before needing any kind of planning involvement.
Under the Larger Home Extension Scheme, terraced and semi-detached homes can extend up to 6 metres. However, this route requires a 42-day neighbour consultation rather than standard PD.
Detached homes can extend up to 8 metres under the Prior Approval route. As with the semi-detached route, the council notifies neighbours who have 42 days to raise objections before a decision is issued.
PD limits are measured from the original house as it was built — not from any previous extensions. If a prior owner has already extended the property, those extensions count towards your total Permitted Development allowance. We check this at the free site survey, so you always know exactly where you stand before any plans are drawn up.
Although many extensions qualify under Permitted Development, several types always require a full planning application. The table below sets out the planning position for each extension type clearly:
| Extension Type | Planning Required? | Key Conditions |
|---|---|---|
| Single storey rear (within limits) | Usually No — PD | 3m (semi/terraced) or 4m (detached), max 4m eaves height, no more than half the garden covered. |
| Single storey rear (beyond limits) | Prior Approval | Up to 6m (semi/terraced) or 8m (detached) via 42-day neighbour consultation scheme. |
| Side return extension | Sometimes | Must not exceed half the original house width. Check side boundary and height rules carefully. |
| Wrap-around extension | Usually Yes | Combines rear and side — this typically exceeds PD limits, so planning permission is usually required. |
| Two storey extension | Yes — Always | All double storey rear extensions require full planning permission without exception. |
| Front extension | Yes — Always | Any extension forward of the principal elevation always requires a planning application. |
| Conservation area property | Yes — Always | PD rights are restricted here. Side extensions and all cladding require full planning permission. |
| Listed building | Yes — Always | Listed Building Consent is required in addition to planning permission for any works whatsoever. |
To help you quickly understand your position, here is a summary of the four main planning routes available to West London homeowners:
Small single storey rear extensions within 3m (terraced/semi) or 4m (detached). Most standard kitchen extensions on Victorian terraces across West London fall into this category.
Extensions between 3–6m (semi/terraced) or 4–8m (detached). The council notifies neighbours and issues a decision. This route is faster and cheaper than a full planning application.
Two storey extensions, front extensions, wrap-arounds exceeding PD limits, all conservation area and listed building work, and any extension where PD rights have been removed by the council.
Building regulations approval is always required for every extension regardless of planning status. This covers structure, waterproofing, insulation, electrics and fire safety compliance.
The side return extension is the most requested project type we handle across Ealing, Hounslow, Acton and Hillingdon. Victorian and Edwardian terraced properties have a narrow side passage alongside the kitchen that, when infilled, creates a dramatically larger ground floor living space — typically gaining 8–15 square metres without touching the garden.
A side return extension can qualify under Permitted Development, provided it does not exceed half the width of the original house, does not project beyond the rear elevation, and has a maximum eaves height of 3 metres within 2 metres of the boundary. In addition, the roof pitch must match the main house where practical. When all these conditions are satisfied, you can proceed without a planning application.
In practice, most side return extensions in West London combine with a rear extension to create a larger L-shaped or wrap-around footprint. This combination typically exceeds PD limits and therefore requires a full planning application. Conservation area properties always require planning permission for any side extension, regardless of size. Our team advises on the most efficient planning route for your specific property at the free site survey.
A neighbour cannot automatically stop your extension. For Permitted Development projects, neighbours have no right of objection — although the Party Wall Act still applies. For planning applications, the council makes decisions based on planning policy, not by neighbour vote. Although objections are a material consideration, they are not a veto on approval.
Double storey extensions always require a full planning application — there are no exceptions to this rule. West London councils assess these applications carefully, given their potential impact on neighbouring properties. To maximise the chances of approval, the design must address several key considerations.
West London has a high concentration of conservation areas, particularly in Richmond, Chiswick, Kew, Twickenham and parts of Ealing Broadway. If your property falls within one of these areas, your Permitted Development rights for extensions are significantly restricted.
In a conservation area, side extensions always require planning permission. Similarly, cladding the exterior of the house always requires a planning application. Although rear extensions at ground floor level are sometimes still possible under PD, you should always verify with the council before proceeding. The council assesses all proposals against the Conservation Area Character Appraisal, which sets out the architectural character of the area and the design standards required.
You can check conservation area status using your local council's planning portal. Ealing homeowners should visit ealing.gov.uk/planning. Hounslow residents can check at hounslow.gov.uk/planning, while Richmond homeowners should visit richmond.gov.uk/planning. Alternatively, we confirm your status at the free site survey, so there are no surprises when work begins.
If your extension requires a full planning application, here is exactly what the process looks like. Although it involves more steps than the PD route, we manage every stage on your behalf:
To begin with, our project manager visits your property, assesses the feasibility of your extension, and checks your PD eligibility. We also identify any conservation area or Article 4 restrictions affecting your property. This visit is always free and carries no obligation whatsoever.
Next, our in-house team produces existing and proposed floor plans, elevations and a site plan to the standard required for planning submission. There is no additional cost for drawings when you build with Signature Build Properties.
We then submit through the Planning Portal — whether that is a Lawful Development Certificate (£200), Prior Approval (£120) or a full householder planning application (£258). Throughout the process, we track progress and liaise with the planning officer so you do not need to.
Prior Approval decisions arrive within 42 days. Full planning applications take 8–12 weeks in most West London boroughs. On approval, planning permission is valid for 3 years. We notify you immediately when the decision arrives.
Finally, we submit building regulations drawings, appoint the structural engineer and begin construction. A building control inspector visits at key stages to verify compliance. On completion, the inspector issues the completion certificate — a document you must keep safe, as solicitors will request it on any future property sale.
Understanding the full cost of your extension — including planning and building regulations costs — helps you assess the overall investment clearly. Here are realistic West London build costs for 2026, all of which include planning management as part of the Signature Build service:
| Extension Type | Typical Cost | Build Time | Planning Route |
|---|---|---|---|
| Single storey rear | £25,000 – £45,000 | 8–12 weeks | Usually PD |
| Side return (kitchen) | £30,000 – £55,000 | 10–14 weeks | PD or Planning |
| Wrap-around extension | £55,000 – £85,000 | 12–16 weeks | Full Planning |
| Double storey extension | £65,000 – £110,000 | 14–20 weeks | Full Planning |
| Kitchen extension with bi-folds | £35,000 – £65,000 | 10–14 weeks | PD or Planning |
All prices are indicative for West London 2026 and include structural works, roofing, insulation, glazing, electrics and standard finishes. We provide a fixed-price written contract after every free site survey, so there are no surprises once work begins.
Can I build a 4 metre extension without planning permission in London?
A detached house can build a single storey rear extension up to 4 metres under Permitted Development. For terraced and semi-detached houses, however, the limit drops to 3 metres. Both property types can extend further — up to 6 metres (semi/terraced) or 8 metres (detached) — using the Prior Approval route, which requires notifying the council and allowing a 42-day neighbour consultation period before work begins.
Do I need planning permission for a kitchen extension in London?
Whether you need planning permission depends on the size and configuration. A single storey kitchen extension to the rear within PD limits — 3 metres for terraced and semi-detached, 4 metres for detached — usually qualifies as Permitted Development. A side return kitchen extension may also qualify, provided it does not exceed half the width of the original house. Larger or wrap-around kitchen extensions, and any extension in a conservation area, always require full planning permission.
How long does planning permission take for a house extension in West London?
A full householder planning application takes 8 weeks statutorily, although West London councils commonly take 10–12 weeks in practice. A Prior Approval application takes 42 days. A Lawful Development Certificate typically takes 6–8 weeks. Throughout the process, Signature Build submits and tracks all applications on your behalf.
Can a neighbour stop my house extension?
A neighbour cannot automatically stop your extension. For Permitted Development extensions, neighbours have no right of objection — although the Party Wall Act still applies. For planning applications, the council makes the decision based on planning policy and material planning considerations. Although neighbour objections are considered, they are not a veto on the outcome.
Do I need a Party Wall Agreement for a house extension?
Yes, in most cases. The Party Wall Act 1996 applies to most house extensions in West London where the build involves work on or near a shared wall, excavation within 3 metres of a neighbouring building, or foundations deeper than the neighbour's. Consequently, Signature Build Properties serves all party wall notices on your behalf as a standard part of the project process.
My extension was built without planning permission — what should I do?
If the extension was completed more than 4 years ago, the council generally cannot take enforcement action. In that case, you can apply for a Lawful Development Certificate for an existing use. If it is less than 4 years old, however, you can apply for retrospective planning permission. We strongly advise regularising this before selling, as solicitors will request evidence of planning compliance during the conveyancing process.
Which West London boroughs do you cover for house extensions?
We build house extensions across Hayes, Hillingdon, Ealing, Hounslow, Richmond, Harrow, Brent, Acton, Southall, Uxbridge, Twickenham and all surrounding West London areas. Based in Hayes UB4, we are ideally positioned for the whole of West London. Contact us to confirm coverage for your specific postcode.
Do you manage the planning application on my behalf?
Yes. Signature Build Properties manages the complete planning process in-house — from the initial feasibility assessment, through architectural drawings and planning submission, to tracking the application and receiving the decision. Furthermore, there is no separate charge for this service when you build with us.
Book a free site survey with Signature Build Properties. We visit your property, confirm your planning position and advise on the best extension design for your home — completely free, no obligation.
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