Rear extension in Brent
Do you need planning permission for a rear extension in Brent?
Outside the conservation areas, much of Brent's terrace and semi-detached stock keeps permitted development rights for a single-storey rear extension within the limits, or larger via prior approval, judged against the Residential Extensions and Alterations SPD. Inside a residential conservation area — all of which carry householder Article 4 directions — even small external changes need a full application. The borough-wide small-HMO conversion direction does not itself remove ordinary rear-extension rights.
Terraces in Willesden, Harlesden and Kilburn extend under PD; all of Brent's residential conservation areas carry Article 4 directions, so those need a full application.
Brent runs from Victorian terraces and villas in the south through Willesden, Kilburn and Harlesden to Wembley and the Metro-land suburbs of Sudbury, Kingsbury and Kenton. Conservation-area design control is tight because every residential conservation area has Article 4 coverage, but outside those pockets rear extensions remain everyday projects. Employment-land Article 4 parcels in the national dataset are not householder restrictions — do not read them as a ban on home extensions.
What actually applies in Brent
Conservation areas in Brent
Real · planning.data.gov.ukEvery designated conservation area in Brent from the official dataset — inside one, permitted development narrows and design scrutiny rises.
- Barn Hill
- Brondesbury
- Buck Lane
- Harlesden
- Homestead Park
- Kensal Green
- Kensal Rise
- Kilburn
- Lawns Court
- Mapesbury
- Mount Stewart
- Neasden Village
- North Kilburn
- Northwick Circle
- Paddington Cemetery
- Queens Park
- Roe Green Village
- South Kilburn
- St Andrews
- Sudbury Cottages
- Sudbury Court
- Wembley High Street
- Willesden Green
Source: planning.data.gov.uk · Open Government Licence. Boundaries are checked at address level by the area report.
Article 4 directions in Brent
Real · planning.data.gov.ukBrent's Article 4 directions, recorded as around 80 named parcels in the national dataset, fall into three groups: a borough-wide HMO direction (in force since 1 November 2022) removing the right to convert a house to a small HMO; design control across all of the borough's residential conservation areas; and protections on strategic industrial land and site allocations (employment-land, not householder). The Residential Extensions and Alterations SPD sets householder design expectations. 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 · 80 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 Brent, 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 Brent?
| 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 Brent
Assuming every Brent address sits under a householder Article 4 is wrong; assuming none do is equally wrong. The address check separates conservation-area full applications from permitted-development terraces. Daylight and party wall issues remain the routine hold-ups.
Postcode districts in Brent
NW2 takes in the Mapesbury and Willesden Green conservation areas — handsome late-Victorian villa streets where, as across Brent, conservation areas carry Article 4 directions removing permitted development.
NW2 — Cricklewood & Mapesbury →NW10 spans the Harlesden, Kensal Green and Kensal Rise conservation areas and the terraces of Willesden.
NW10 — Harlesden, Willesden & Kensal Green →NW9 includes the Roe Green Village conservation area — a planned garden village — and Buck Lane, alongside the Colindale regeneration.
NW9 — Kingsbury & Colindale →HA9 is Wembley Park and the Barn Hill conservation area on the slopes above the stadium — a Tudor Walters–era estate of mature gardens.
HA9 — Wembley Park & Barn Hill →HA0 covers Wembley Central, Alperton and Sudbury — the Sudbury Court and Sudbury Cottages conservation areas among the protected pockets.
HA0 — Wembley & Alperton →Rear extension in Brent, asked straight
Do I need planning permission for a rear extension in Brent?
How much does a rear extension cost in Brent?
Does the small-HMO conversion direction affect rear extensions?
Do all conservation areas need a full application?
Do I need a party wall agreement?
What applies at your address?
Borough-level rules only narrow it down. Enter a Brent 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 Brent 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.