Rear extension in Lewisham
Do you need planning permission for a rear extension in Lewisham?
Outside the conservation-area householder Article 4 streets, much of Lewisham's Victorian and Edwardian terrace stock keeps permitted development rights for a single-storey rear extension within the limits, or larger via prior approval, to the Alterations and Extensions SPD (2019). Inside an Article 4 conservation area, a full application is needed. The borough-wide small-HMO conversion regime does not itself remove ordinary rear-extension rights.
Brockley, Ladywell and Forest Hill terraces are deep PD-precedent territory; the Article 4 conservation areas need a full application.
Lewisham runs from Blackheath and Telegraph Hill through Brockley, Ladywell, Forest Hill and Sydenham to Deptford. The terrace belts are deep permitted-development-precedent territory outside the tighter Article 4 conservation streets. Two layers of Article 4 control matter: borough-wide small-HMO conversion directions (southern wards since March 2020, the rest since January 2024) and separate conservation-area directions that pull householder external works into planning.
What actually applies in Lewisham
Conservation areas in Lewisham
Real · planning.data.gov.ukEvery designated conservation area in Lewisham from the official dataset — inside one, permitted development narrows and design scrutiny rises.
- Beckenham Place
- Belmont
- Blackheath
- Brockley
- Brookmill Road
- Cobbs Corner
- Culverley Green
- Deptford Creekside
- Deptford High Street & St Pauls Church
- Deptford Town Hall
- Forest Hill
- Halifax
- Hatcham
- Jews Walk
- Ladywell
- Lee Manor
- Lewisham Park
- Mercia Grove
- Perry Vale and Christmas Estate
- Perryfields
- Somerset Gardens
- St Johns
- St Marys
- St Stephens
- Stanstead Grove
- Sydenham Park
- Sydenham Thorpes
- Sydnenham Hill
- Telegraph Hill
…plus 1 further designated areas.
Source: planning.data.gov.uk · Open Government Licence. Boundaries are checked at address level by the area report.
Article 4 directions in Lewisham
Real · planning.data.gov.ukLewisham's Article 4 directions, recorded as around 89 named parcels in the national dataset, fall into two main groups for homeowners: a borough-wide HMO regime (two directions removing the right to convert a house to a small HMO — the southern wards since March 2020, the rest of the borough since January 2024) and conservation-area directions in areas such as Brockley, Brookmill Road, Deptford High Street and Forest Hill that remove householder permitted development. Others cover town centres and employment land. The Alterations and Extensions SPD sets householder design expectations. Use the area report, or the council's Article 4 pages, for the direction that applies at a given address.
Source: planning.data.gov.uk · Open Government Licence · 89 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 Lewisham, 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 Lewisham?
| 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 Lewisham
Do not confuse the HMO regime with a blanket ban on householder permitted development — they are different controls. Daylight, materials and party wall issues remain the routine hold-ups on unconstrained terraces.
Postcode districts in Lewisham
SE4 is the Brockley conservation area — one of London's largest Victorian conservation areas, with an Article 4 direction removing permitted development, so windows, doors and roof changes need consent.
SE4 — Brockley & Crofton Park →SE13 covers central Lewisham and the Ladywell, Lewisham Park and Lee Manor conservation areas.
SE13 — Lewisham & Ladywell →SE23 is Forest Hill — the Forest Hill conservation area (with Article 4 directions) and Jews Walk, near the Horniman.
SE23 — Forest Hill →SE8 is Deptford — the Deptford High Street and St Paul's and Brookmill Road conservation areas, both with Article 4 directions, plus Deptford Town Hall.
SE8 — Deptford →SE14 covers New Cross and the Telegraph Hill and Hatcham conservation areas — steep Victorian streets above the Thames basin.
SE14 — New Cross & Telegraph Hill →SE6 is Catford and Bellingham — Victorian and interwar terraces with deep side-return and loft precedent in Lewisham.
SE6 — Catford & Bellingham →SE12 covers Lee and Grove Park, spanning Lewisham with Bromley and Greenwich edges.
SE12 — Lee & Grove Park →SE26 is Sydenham and Lower Sydenham — Victorian terraces and larger houses with strong loft conversion activity, spanning Lewisham, Bromley and Southwark edges.
SE26 — Sydenham & Lower Sydenham →Rear extension in Lewisham, asked straight
Do I need planning permission for a rear extension in Lewisham?
How much does a rear extension cost in Lewisham?
Does the small-HMO conversion regime affect rear extensions?
Which streets need a full application for external works?
Do I need a party wall agreement?
What applies at your address?
Borough-level rules only narrow it down. Enter a Lewisham 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 Lewisham 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.