Rear extension in Westminster
Assume you need a full householder application — that's the safe default in Westminster. Most homes here are flats or maisonettes, which have no permitted development rights at all, and even on a whole house, Westminster's conservation areas — which cover most of the borough — combined with dense Article 4 coverage mean permitted development does very little of the work it might do elsewhere in London. A single-storey rear extension can still be designed and approved, but expect it to go through a full application judged on massing, materials and neighbour daylight rather than proceed as of right.
Mostly flats and listed stock — assume a full application and check for listed building consent.
Rear extension is a minority project in Westminster simply because so much of the borough's stock is flats without a garden or a rear elevation of their own to extend — the project mainly applies to the whole houses that survive in places like St John's Wood, Pimlico and pockets of Marylebone and Maida Vale. Where a house does qualify, officers expect a design that defers to the host building rather than competing with it — modest scale, materials pulled from the existing house, and nothing showy at roof level. In Mayfair and Belgravia, an estate management scheme sits on top of planning control, so even a consented design may still need separate estate sign-off before work starts.
What actually applies in Westminster
Conservation areas in Westminster
Real · planning.data.gov.ukEvery designated conservation area in Westminster from the official dataset — inside one, permitted development narrows and design scrutiny rises.
- Adelphi
- Albert Gate
- Aldridge Road Villas And Leamington Road Villas
- Bayswater
- Belgravia
- Birdcage Walk
- Broadway And Christchurch Gardens
- Charlotte Street, West
- Chinatown
- Churchill Gardens
- Cleveland Street
- Covent Garden
- Dolphin Square
- Dorset Square
- East Marylebone
- Fisherton Street Estate
- Grosvenor Gardens
- Hallfield Estate
- Hanway Street
- Harley Street
- Haymarket
- Knightsbridge
- Knightsbridge Green
- Leicester Square
- Lillington Gardens
- Lisson Grove
- Maida Vale
- Mayfair
- Medway Street
- Millbank
- Molyneux Street
- Paddington Green
- Page Street
- Peabody Avenue
- Peabody Estates: South Westminster
- Pimlico
- Portman Estate
- Queens Park Estate
- Queensway
- Regency Street
- Regent Street
- Regent's Park
- Royal Parks
- Savoy
- Smith Square
- Soho
- St James's
- St John's Wood
- Strand
- Stratford Place
- Trafalgar Square
- Vincent Square
- Westbourne
- Westminster Abbey And Parliament Square
- Westminster Cathedral
- Whitehall
Source: planning.data.gov.uk · Open Government Licence. Boundaries are checked at address level by the area report.
Article 4 directions in Westminster
Real · planning.data.gov.ukArticle 4 directions in Westminster remove specific permitted development rights street by street — the single most common reason a "no permission needed" project turns out to need one.
- 1-27 Bridstow Place, W2
- 1-37 Bristol Gardens, W9
- 1-47 And 2-56 Abbey Gardens, NW8
- 1, 4, 8, 11, 12, 13 Relton Mews, SW7
- 168-208 Sussex Gardens, W2
- 6-10 Moncorvo Close, SW7
- Article 4 Basement Development Permitted Rights Removed
- Article 4 Direction Class E To C3 In Central Activities Zone
- Article 4 Direction Class E To C3 Out Central Activity Zone
- Queens Park Estate
Source: planning.data.gov.uk · Open Government Licence. Boundaries are checked at address level by the area report.
Prices: HM Land Registry UK House Price Index, November 2025 · Open Government Licence.
The planning route — PD or permission?
Permitted development (GPDO Class A) covers single-storey rear extensions up to 3m beyond the original rear wall on attached houses and 4m on detached, with a maximum height of 4m. The 'larger home extension' route extends this to 6m/8m through prior approval with neighbour consultation — but that larger route is not available in conservation areas.
In conservation areas, the basic 3m/4m single-storey rear PD allowance usually survives — what conservation-area status removes is side extensions and two-storey rear extensions. An Article 4 direction can remove more, but Camden's directions in Hampstead and Belsize target front-and-side appearance (solar panels, window changes, boundary treatments), not the single-storey rear allowance. Flats have no PD rights at all. Two-storey rear extensions in conservation areas always need full permission.
Practical rule across London: check the address first. If a conservation area or Article 4 direction applies, budget for a full householder application decided on design, neighbour daylight (the 45-degree test) and materials.
What it really costs
| Cost per m² (low — straightforward site) | £3,000 |
| Cost per m² (expected) | £3,800 |
| Cost per m² (high — conservation spec, hard access) | £4,600+ |
| Typical build cost (12–18m² single storey) | £36,000 – £83,000 |
| Professional fees, surveys, party wall (add) | 10–18% of build |
Indicative London ranges calibrated from real project data. Conservation-area specifications (matching stock brick, lime mortar, bespoke glazing) and restricted rear access are the two biggest cost drivers. VAT not included.
Realistic timeline
| Design and drawings | 4–8 weeks |
| Planning decision (full application) | 8–12 weeks (8-week statutory target) |
| Prior approval route, where available | 42 days |
| Party wall agreements | 4–10 weeks (parallel) |
| Build | 3–5 months |
What catches people out in Westminster
The biggest risk is assuming the standard single-storey PD allowance applies without checking — Westminster's Article 4 coverage is dense enough that it may have been removed at your specific address, and finding that out after drawings are done is the expensive way to learn it. Even inside a full application, Westminster's conservation officers scrutinise brick bond, render finish and window proportions closely enough that a scheme drafted to a generic London brief will stall.
Westminster planning, area by area
Usually a full application — and on a mansion-block flat, often not available at all.
Do I need permission? →Usually a full application on a house, and typically not possible on a mansion-block flat.
Do I need permission? →Yes — a full planning application under Westminster's basement policy, and on the area's many listed villas, excavation is usually ruled out.
Do I need permission? →St John's Wood is heavily listed, so there's a real chance your property is — and if it is, listed building consent is required for works affecting its character inside and out, on top of planning permission.
Do I need permission? →For most of Maida Vale, an external extension isn't really the question — the area is dominated by purpose-built mansion blocks, which are flats with no permitted-development rights, so works are internal and governed by your lease as much as by planning.
Do I need permission? →In most of Maida Vale, a loft conversion isn't available to you — the mansion blocks are flats whose roofs are common parts owned by the freeholder.
Do I need permission? →On Maida Vale's mansion blocks, a private basement generally isn't available — the structure is shared and the ground belongs to the freeholder.
Do I need permission? →Parts of Maida Vale are listed — including some of the mansion blocks and stucco terraces — and if your building is, listed building consent is required for works affecting its character inside and out, on top of planning permission and (on a flat) a freeholder licence to alter.
Do I need permission? →Almost certainly not as permitted development — and on the Nash terraces, an external extension is usually off the table entirely.
Do I need permission? →On the Nash terraces, effectively no — roof alterations to a Grade I-listed composition are not the kind of change that gets consent.
Do I need permission? →On the Grade I-listed Nash terraces, excavation is protected against almost absolutely — a basement is generally not available.
Do I need permission? →Most of Regent's Park's residential terraces are Grade I-listed Nash architecture, so listed building consent is the governing permission — required for works affecting the building's special character inside and out, in addition to planning permission.
Do I need permission? →Rear extension in Westminster, district by district
First check: Whether it's permitted development or needs a planning application
Service guide →First check: Whether it's permitted development or needs a planning application
Service guide →First check: Whether it's permitted development or needs a planning application
Service guide →First check: Whether it's permitted development or needs a planning application
Service guide →First check: Whether it's permitted development or needs a planning application
Service guide →Rear extension in Westminster, asked straight
Can I add a rear extension to my Westminster flat?
Do I need listed building consent for a rear extension in Westminster?
Will a single-storey rear extension always need planning permission in Westminster?
Does a Westminster rear extension need a party wall agreement?
Does a Westminster rear extension cost more than elsewhere in London?
What applies at your address?
Borough-level rules only narrow it down. Enter a Westminster postcode for the live constraint check — conservation area, Article 4 and sold-price comparables, cited to source.
Planning Permission Checker provides planning and cost intelligence for early feasibility only. It is not legal, planning, valuation, architectural, structural, or surveying advice. All estimates are indicative and must be verified by qualified professionals before purchase, design, planning submission, or construction.
Cost estimates are indicative only — not a quotation. Final price depends on survey, specification, structure, access, party wall matters, VAT, professional fees, and contractor availability.
Planning outcomes are not guaranteed. Local planning authorities make final decisions.