Rear extension in Merton
Do you need planning permission for a rear extension in Merton?
Often under permitted development on the Victorian and interwar stock of Colliers Wood, South Wimbledon, Mitcham and Morden. Inside the Wimbledon conservation cluster or the planned Edwardian streets that carry old-style householder Article 4 directions, a full application is needed. Two houses a few streets apart can face entirely different consent routes.
Terraces in Colliers Wood, South Wimbledon and Mitcham extend under PD; the John Innes and Wimbledon conservation areas need a full application.
Merton's planning character is dominated by the Wimbledon set pieces at one end of the spectrum and ordinary terrace and interwar streets at the other. House prices and design scrutiny peak in the Wimbledon conservation areas; the planned Edwardian streets around Merton Park carry particularly wide-ranging Article 4 controls that pull most extensions into full applications. Elsewhere, side returns, rear extensions and lofts are common with a deep precedent base. The address-level check is decisive.
What actually applies in Merton
Conservation areas in Merton
Real · planning.data.gov.ukEvery designated conservation area in Merton from the official dataset — inside one, permitted development narrows and design scrutiny rises.
- Bathgate Road
- Bertram Cottages
- Copse Hill
- Dennis Park Crescent
- Drax Avenue
- Dunmore Road
- Durham Road
- John Innes (Merton Park)
- John Innes (Wilton Crescent)
- Kenilworth Avenue
- Lambton Road
- Leopold Road
- Merton Hall Road
- Mitcham Cricket Green
- Pelham Road
- South Park Gardens
- Upper Morden
- Vineyard Hill Road
- Wandle Valley
- Westcoombe Avenue
- Wimbeldon Broadway
- Wimbledon Chase
- Wimbledon Hill Road
- Wimbledon North
- Wimbledon Village
- Wimbledon West
- Wimbledon Windmill
- Wool Road
Source: planning.data.gov.uk · Open Government Licence. Boundaries are checked at address level by the area report.
Article 4 directions in Merton
Real · planning.data.gov.ukNo Article 4 geometry for Merton appears in the national planning.data.gov.uk dataset, but the borough operates significant householder directions: the John Innes conservation areas at Merton Park and Wilton Crescent carry old-style Article 4(2) directions (the Merton Park directions confirmed in 2007) that remove a wide range of permitted development rights, so most extensions there need planning permission. A separate direction controls office-to-residential conversion. Check the council's Article 4 pages and the John Innes Design Guide for the position at a specific address.
Source: planning.data.gov.uk · Open Government Licence. 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 Merton, 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 Merton?
| 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 Merton
Assuming Colliers Wood rules apply in Merton Park — or the reverse — is the classic mistake. The national dataset does not currently hold Merton's Article 4 geometry, so confirm those householder directions on the council's own pages as well as checking conservation-area status.
Postcode districts in Merton
SW19 spans Wimbledon Village, Wimbledon West and Wimbledon North — the borough's most tightly controlled conservation areas — and the John Innes estate at Merton Park, whose conservation areas carry old-style Article 4(2) directions removing most permitted development.
SW19 — Wimbledon & Merton Park →SW20 covers Raynes Park and West Wimbledon, including the Copse Hill and Westcoombe Avenue conservation areas.
SW20 — Raynes Park & West Wimbledon →CR4 is Mitcham — the Mitcham Cricket Green conservation area, one of the oldest cricket greens in the world, anchors the historic core.
CR4 — Mitcham →SM4 is Morden — the Upper Morden conservation area and the interwar St Helier estate fringe.
SM4 — Morden →Rear extension in Merton, asked straight
Do I need planning permission for a rear extension in Merton?
How much does a rear extension cost in Merton?
Which parts of Merton have householder Article 4 directions?
Can I extend under PD in Colliers Wood or Mitcham?
Do I need a party wall agreement?
What applies at your address?
Borough-level rules only narrow it down. Enter a Merton 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 Merton 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.