Rear extension in Hillingdon
Do you need planning permission for a rear extension in Hillingdon?
Outside the conservation areas, Green Belt and any extension Article 4 area, much of Hillingdon's suburban stock keeps permitted development rights for a single-storey rear extension within the limits, or larger via prior approval. The borough's Article 4 directions are unusually wide-ranging — including a direction removing residential-extension permitted development in defined areas — so the address-level check matters more than in most boroughs. The borough-wide small-HMO conversion direction is a separate control.
Ruislip, Eastcote and Uxbridge stock extends under PD; the village conservation areas, Green Belt and the borough's extension Article 4 can need a full application.
Hillingdon is London's second-largest borough by area: Metro-land suburbs of Ruislip, Eastcote and Northwood, through Uxbridge and Hayes, to Heathrow and extensive Green Belt in the west. Village conservation cores and Green Belt policy sit alongside several Article 4 layers. Do not assume permitted development from the borough name alone.
What actually applies in Hillingdon
Conservation areas in Hillingdon
Real · planning.data.gov.ukEvery designated conservation area in Hillingdon from the official dataset — inside one, permitted development narrows and design scrutiny rises.
- Black Jacks Lock
- Botwell: Nestles
- Botwell: Thorn EMI
- Bulls Bridge
- Copper Mill Lock
- Coppermill Lock
- Cowley Church (St. Laurence)
- Cowley Lock
- Denham Lock
- Eastcote (Morford Way)
- Eastcote Park Estate
- Eastcote Village
- Harefield Village
- Harlington Village
- Harmondsworth Village
- Hayes Village
- Hillingdon Village
- Ickenham Village
- Longford Village
- Northwood Town Centre, Green Lane
- Northwood, Frithwood
- Old Uxbridge / Windsor Street
- Rockingham Bridge, Uxbridge
- Ruislip Village
- Ruislip, Manor Way
- Springwell Lock
- The Glen, Northwood
- The Greenway
- Uxbridge Moor
- West Drayton Green
- Widewater Lock
Source: planning.data.gov.uk · Open Government Licence. Boundaries are checked at address level by the area report.
Article 4 directions in Hillingdon
Real · planning.data.gov.ukHillingdon's Article 4 directions are recorded in the national dataset and are unusually wide-ranging: a borough-wide HMO direction (planning permission to convert a house to a small HMO), a direction removing permitted development for residential extensions in defined areas, and directions controlling commercial-to-residential conversion and the demolition-and-rebuild of commercial buildings. Green Belt covers much of the borough's west. Use the area report, or the council's Article 4 register, for the direction that applies at a given address.
Source: planning.data.gov.uk · Open Government Licence · 4 directions recorded. Checked at address level by the area report.
Prices: HM Land Registry UK House Price Index, December 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.
Permitted development limits — rear extension
| Single-storey rear depth — attached house | 3m beyond the original rear wall |
| Single-storey rear depth — detached house | 4m beyond the original rear wall |
| Larger extension via prior approval | 6m attached / 8m detached — not in conservation areas |
| Maximum height (single storey) | 4m |
| Two-storey rear in a conservation area | Full planning permission required |
| Flats | No permitted development rights |
Limits summarise the General Permitted Development Order (Schedule 2, Part 1) as it applies in London. In Hillingdon, a conservation area, Article 4 direction or listed status changes the route — the panels above show what is designated, and the address check confirms what applies at your property.
How much does a rear extension cost in Hillingdon?
| 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 Hillingdon
Missing an extension Article 4 parcel or Green Belt designation at the address is the classic false start. Confirm against the area report and the council's register.
Postcode districts in Hillingdon
UB10 covers Hillingdon village and eastern Uxbridge — the Hillingdon Village conservation area among them.
UB10 — Hillingdon & Uxbridge →UB8 is Uxbridge — the Old Uxbridge / Windsor Street and Uxbridge Moor conservation areas and the Grand Union Canal.
UB8 — Uxbridge →HA4 covers Ruislip and Eastcote — the Ruislip Village, Eastcote Village and Eastcote Park Estate conservation areas, with Ruislip Woods beyond.
HA4 — Ruislip & Eastcote →HA6 is Northwood — the Frithwood and Green Lane conservation areas and the wooded, higher-value streets on the borough's northern edge.
HA6 — Northwood →UB7 covers West Drayton and Harmondsworth — the West Drayton Green and Harmondsworth Village conservation areas (the latter with its medieval tithe barn), near Heathrow and the Colne Valley Green Belt.
UB7 — West Drayton & Harmondsworth →UB3 is Hayes in Hillingdon — industrial-edge and suburban streets with regeneration pockets.
UB3 — Hayes →UB4 covers Yeading and the Hayes end of Hillingdon — suburban plots with more side access than inner terraces.
UB4 — Yeading & Hayes end →UB9 straddles the London boundary: Harefield and South Harefield sit in Hillingdon, while Denham and the Colne-side fringe lie outside it, in Buckinghamshire and Hertfordshire — so the deciding authority changes with the address, not the postcode.
UB9 — Harefield & Denham →Rear extension in Hillingdon, asked straight
Do I need planning permission for a rear extension in Hillingdon?
How much does a rear extension cost in Hillingdon?
Could an Article 4 remove my rear-extension rights?
Is Green Belt a problem for rear extensions?
Do I need a party wall agreement?
What applies at your address?
Borough-level rules only narrow it down. Enter a Hillingdon postcode for the live constraint check — conservation area, Article 4 and sold-price comparables, cited to source.
Need it in writing for one address? A planning permission report for a Hillingdon property — from £59, or surveyor-reviewed from £295.
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.