Loft conversion in Hillingdon
Do you need planning permission for a loft conversion in Hillingdon?
Strong on the Ruislip and Eastcote semis under permitted development outside conservation areas, Green Belt and extension Article 4 parcels. Inside village conservation areas, dormer design is scrutinised through a full application. Building regulations always apply.
Strong on the Ruislip and Eastcote semis under PD; the village conservation areas scrutinise dormer design.
Rear dormers and hip-to-gable conversions suit much of the suburban roof stock where headroom allows. On protected streets, rear-facing, well set-back dormers have a better record than box forms or front alterations. Check whether an extension Article 4 parcel affects roof works at the address.
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 B) allows roof enlargements up to 40m³ on terraced houses and 50m³ on semis and detached — enough for a substantial rear dormer — provided nothing projects beyond the roof plane of the principal elevation, materials are similar, and dormers sit back from the eaves. Class B is excluded in conservation areas.
In conservation areas the route is a full application, and roof form decides it: rear mansards with traditional slate and proportioned dormers have a strong record on Victorian terraces; box dormers and front-facing alterations are the classic refusals. Article 4 directions (Muswell Hill is the local example) pull roof works into planning control even where conservation policy alone might not.
Whatever the route, building regulations approval is always required — fire escape, stair geometry and floor structure — and a Lawful Development Certificate is cheap insurance on PD schemes.
Permitted development limits — loft conversion
| Roof volume added — terraced house | Up to 40m³ |
| Roof volume added — semi-detached or detached | Up to 50m³ |
| Principal (street-facing) roof plane | No extension beyond it |
| Dormers | Set back from the eaves; materials similar |
| Conservation areas | Class B excluded — full permission |
| Flats | Always need permission |
| Building regulations | Always required, whatever the planning route |
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 loft conversion cost in Hillingdon?
| Cost per m² (low — rooflight conversion) | £3,000 |
| Cost per m² (expected — rear dormer) | £3,700 |
| Cost per m² (high — mansard, conservation spec) | £4,500+ |
| Typical project (20–28m² with bathroom) | £86,000 – £180,000 |
| Professional fees, surveys, party wall (add) | 8–15% of build |
Mansards in conservation areas sit at the top of the range — natural slate, lead detailing and officer negotiation all cost. Ranges calibrated from real project data; VAT excluded.
Realistic timeline
| Design and drawings | 4–6 weeks |
| PD route (Lawful Development Certificate) | 4–8 weeks |
| Full application (conservation areas) | 8–12 weeks (8-week statutory target) |
| Party wall award | 4–8 weeks (parallel) |
| Build | 10–14 weeks |
What catches people out in Hillingdon
Headroom and stair position still filter schemes early. Oversized box dormers and principal-elevation changes are classic refusals on protected streets.
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 →Loft conversion in Hillingdon, asked straight
Do I need planning permission for a loft conversion in Hillingdon?
How much does a loft conversion cost?
What designs get approved in conservation areas?
Is building regulations approval required?
Does the small-HMO conversion direction affect lofts?
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.