Rear extension in London
A rear extension pushes the ground floor (occasionally two storeys) into the rear garden, almost always to create a larger kitchen-dining space opening onto the garden. On London's terraced and semi-detached stock it is the single most common domestic project — and the one with the deepest planning precedent record on nearly every street.
Value comes from added floor area and from reconfiguring the dark middle of a Victorian plan into one usable space. Typical London schemes add 12–20m² with full-width glazing; the build interacts with drainage, party walls on both sides, and — in conservation areas — close scrutiny of brick, bond and roofline.
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.
Do you need planning permission for a 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. Conservation areas, Article 4 directions and listed status change the route — check your own address before relying on them.
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
- Article 4 directions silently removing the PD route — always verified at address level, never assumed from the borough.
- The 45-degree daylight test trimming depth on tight terraced gardens.
- Party wall awards on both flanks adding cost and programme before a brick is laid.
- Drainage build-over agreements where the extension crosses a shared sewer.
- Conservation-area material conditions (brick match, roof finish) discovered after pricing rather than before.
Rear extensions, borough by borough
Precedent-driven: hold to your street's established projection depth and match the stock brick.
Rear extension in Camden →Mostly flats and listed stock — assume a full application and check for listed building consent.
Rear extension in Westminster →The 45-degree daylight test shapes rear extensions here more than any design policy.
Rear extension in Islington →London's most active rear-extension market; contemporary design with good brickwork is mainstream.
Rear extension in Hackney →PD carries many schemes in the east; Muswell Hill and Highgate need full applications.
Rear extension in Haringey →Conservation coverage and Article 4 directions make a full householder application the default; matching stock brick and lime mortar are expected.
Rear extension in Kensington and Chelsea →Outside the conservation areas many terraces keep PD rights; inside them, match the established depth and materials.
Rear extension in Hammersmith and Fulham →Camberwell, Peckham and Dulwich terraces extend constantly; outside the conservation areas PD or prior approval often carries it.
Rear extension in Southwark →Clapham, Brixton and Streatham terraces are deep PD-precedent territory; conservation and the targeted Article 4 areas need a full application.
Rear extension in Lambeth →Houses outside the conservation areas can extend under PD; the Spitalfields and Wapping listed stock needs consent.
Rear extension in Tower Hamlets →The 'between the commons' terraces extend routinely; scale against the neighbour's daylight to clear the 45-degree test.
Rear extension in Wandsworth →Single-storey rear extensions are unaffected by the basement Article 4, but conservation coverage is extensive — check whether the address sits in a designated area.
Rear extension in Richmond upon Thames →Generous interwar plots make rear and wrap-around extensions feasible; the Article 4 conservation areas (HGS, Mill Hill, Totteridge) need a full application.
Rear extension in Barnet →Long Victorian and Edwardian terraces in Hanwell, West Ealing and Acton extend routinely; conservation areas need a full application to SPD 4.
Rear extension in Ealing →Terraces in Colliers Wood, South Wimbledon and Mitcham extend under PD; the John Innes and Wimbledon conservation areas need a full application.
Rear extension in Merton →Surbiton, New Malden and Old Malden terraces extend under PD; the town-centre, riverside and Coombe conservation areas need a full application.
Rear extension in Kingston upon Thames →Interwar semis in Bromley, Beckenham and Orpington extend routinely under PD; conservation areas and the Green Belt's disproportionate-addition limits are the exceptions.
Rear extension in Bromley →Interwar semis in Pinner, Stanmore and Kenton extend routinely under PD; the Harrow on the Hill and Pinner conservation areas need a full application.
Rear extension in Harrow →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.
Rear extension in Brent →Charlton, Eltham and Plumstead terraces extend under PD; the Greenwich, Blackheath and Westcombe Park conservation areas need a full application.
Rear extension in Greenwich →Brockley, Ladywell and Forest Hill terraces are deep PD-precedent territory; the Article 4 conservation areas need a full application.
Rear extension in Lewisham →Edmonton, Palmers Green and Southgate stock extends under PD; the Enfield Town, Bush Hill Park and Winchmore Hill conservation areas need a full application.
Rear extension in Enfield →Leyton and Leytonstone terraces are among north-east London's most extended; Walthamstow Village and the other conservation areas need a full application.
Rear extension in Waltham Forest →Generous suburban plots in Sutton, Cheam and Carshalton extend under PD; the Sutton Garden Suburb and village conservation areas need a full application.
Rear extension in Sutton →Suburban Croydon stock extends under PD; the Waldrons, Webb Estate and other Article 4 conservation areas need a full application.
Rear extension in Croydon →Bexleyheath, Sidcup and Erith semis extend routinely under PD; Old Bexley and the conservation areas need a full application.
Rear extension in Bexley →Chiswick and Isleworth terraces extend under PD outside the conservation areas; Bedford Park and the heritage areas need a full application.
Rear extension in Hounslow →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.
Rear extension in Hillingdon →Ilford and Gants Hill semis extend under PD; the Wanstead, Snaresbrook and Woodford Green conservation areas need a full application.
Rear extension in Redbridge →Hornchurch, Upminster and Romford semis extend under PD; Gidea Park, the village conservation areas and Green Belt need a full application.
Rear extension in Havering →Forest Gate, East Ham and Plaistow terraces extend under PD outside the conservation areas; the Woodgrange Estate and town-centre areas need a full application.
Rear extension in Newham →Becontree and Dagenham semis extend under PD; the Barking Abbey and Dagenham Village conservation areas need a full application.
Rear extension in Barking and Dagenham →Barely applies — the City's homes are listed Barbican and Golden Lane flats with no PD rights, where listed building consent governs any change.
Rear extension in City of London →Rear extension planning, area by area
Almost certainly yes — assume a full householder application.
Do I need permission? →Usually a full householder application — and your tenure is the first question.
Do I need permission? →Usually a full householder application, and the constraint is as much the neighbours as the conservation area.
Do I need permission? →Usually a full application — and on a mansion-block flat, often not available at all.
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? →Almost certainly not as permitted development — and on the Nash terraces, an external extension is usually off the table entirely.
Do I need permission? →Rear extensions, asked straight
How much does a rear extension cost in London?
Do I need planning permission for a rear extension?
How long does the whole process take?
What adds the most value?
Do I need a party wall agreement?
Related reading
Almost every London extension, loft and basement engages this Act. Here's how it actually works.
Read the guide →The size limits, the exceptions, and the postcode-level traps.
Read the guide →Real ranges from real projects — not brochure numbers.
Read the guide →Bigger single-storey rear extensions without a full planning application — but it's a notification process, not a free pass.
Read the guide →Could you build one at your address?
The rules above bend at address level — conservation areas and Article 4 directions change the route entirely. Run the live constraint check before you spend on drawings.
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.