Do you need planning permission for a rear extension?

By James Reilly, Swanbourne Construction Ltd · Published 15 October 2026 · Checked against the permitted development order as in force October 2026

A single-storey rear extension usually does not need planning permission in England if it extends no more than 3m beyond the original back wall of an attached house (semi or terrace) or 4m on a detached house, is no more than 4m high, keeps its eaves to 3m or less within 2m of a boundary, uses materials similar to the house, and — with other extensions and outbuildings — covers no more than half the land around the original house. Through the "larger home extension" prior approval route you can go to 6m or 8m, after the council consults your neighbours. Outside those limits, or in a conservation area, the South Downs National Park or a flat, you need a householder application, which costs £548 from 1 April 2026.

Nothing in these rules has changed since 2021. You may read about "new 2026 extension rules"; the government consulted in 2024 on bigger extensions, but no change has been made. What follows is the law as it stands in October 2026.

Single-storey rear extensions

Source: GPDO 2015, Schedule 2, Part 1, Class A, as in force October 2026.

"Original" is the word that catches people

The depth is measured from the rear wall of the original house — as first built, or as it stood on 1 July 1948 if older — not from the back of the house as it is now. If a previous owner built a 2m extension in the 1990s, a 3m allowance on a semi has only 1m left in it, and the earlier extension also counts towards the half-the-garden rule. Older bungalows around Bognor Regis and Felpham often have a lean-to or a sun room that has quietly used up part of the allowance.

The 3m eaves rule near the boundary

If any part of the extension is within 2m of a boundary, its eaves must be no higher than 3m. On a typical semi, where the extension runs along the shared fence, that shapes the roof: a flat roof with a parapet, or a lean-to that falls towards the boundary, usually works; a tall pitched roof with high eaves at the fence does not.

The larger home extension: 6m and 8m

Between the standard depths and a full planning application sits the prior approval route. It lets you build a single-storey rear extension up to 6m deep on an attached house or 8m on a detached one, still no more than 4m high. It works like this:

1. Before starting, you send the council a description with the depth, height and eaves height, a site plan, your neighbours' addresses and the fee — £249 from 1 April 2026.
2. The council notifies the adjoining neighbours, who have at least 21 days to comment.
3. If anyone objects, the council judges the effect on the amenity of all the adjoining properties — mainly light and outlook.
4. You can start once the council says prior approval is not required or is given, or after 42 days with no decision.
5. You must build exactly what you submitted.

It is not available in conservation areas, the National Park or other designated land. Without objections it is usually straightforward; with them, it becomes a judgement about the neighbours' amenity, so it is worth talking to them before the letter arrives.

Two-storey rear extensions

A two-storey rear extension can be permitted development, but the limits rule most out:

• no more than 3m beyond the original rear wall;
• at least 7m from the boundary opposite the rear wall — the back fence;
• roof pitch matching the house as far as practicable;
• upper-floor side windows obscure-glazed and fixed below 1.7m;
• never permitted development in a conservation area or the National Park.

On the shorter gardens common in Bognor Regis and Littlehampton, the 7m rule is usually the one that bites, and a two-storey extension becomes a planning application. More on choosing between the two in single or double-storey extension.

Side extensions and wrap-arounds

A side extension is permitted development only if it is single storey, no more than 4m high, and no wider than half the width of the original house. It must not go forward of the front elevation, or of a side elevation facing a road — which matters on corner plots. A wrap-around extension, combining rear and side, is treated as one enlargement and usually needs planning permission. Side extensions are never permitted development in a conservation area.

When you do need planning permission

• Outside the size, height or boundary limits above.
• Flats and maisonettes — they have no Class A rights at all.
• Conservation areas, the South Downs National Park, the Chichester Harbour National Landscape — side extensions, rear extensions of more than one storey, the larger home extension route and external cladding are all switched off.
• An Article 4 direction removes the rights. In Arun the only conservation-area directions are at Craigweil House in Aldwick; Chichester has directions in several conservation areas, including the city.
• A planning condition on the house's original permission removing permitted development rights — common on newer estates.
• A listed building, which also needs listed building consent.
• Houses created through certain permitted development changes of use, which have no Class A rights.

Arun and Chichester

Arun District Council decides planning for Bognor Regis, Felpham, Aldwick, Pagham, Middleton-on-Sea, Littlehampton, Rustington and Arundel town. On ordinary householder extensions it is a pragmatic authority. It applies a 45-degree test to neighbours' windows and looks at overlooking, especially from bungalow conversions. Private estates — Felpham's Summerley Estate, Aldwick Bay — run their own covenants and design approval alongside the council's process, and both have to be cleared. Near the beach at Pagham, flood risk can be part of the application; see building near the coast.

Chichester District Council adopted its Local Plan 2021–2039 in August 2025. Inside the city's conservation area and Article 4 ring, scrutiny of materials and detail is close and timescales stretch; outside it, in Parklands, Summersdale and Whyke, permitted development works as normal. Arundel's planning position depends on exactly where the house sits relative to the National Park — see extending in a conservation area.

Lawful Development Certificates

If your extension is permitted development, you do not have to apply for anything. But a Lawful Development Certificate — the council confirming in writing that it is lawful — is worth having. A buyer's solicitor will ask for it, and if the measurements are close it removes the doubt before you build. The fee for a proposed-use certificate is half the householder fee: £274.

Fees and timescales

Source: MHCLG, planning fees from 1 April 2026. Draft regulations laid before Parliament in July 2026 would increase the householder fee to £575 and prior approval to £310 for applications made from 8 December 2026 if approved. Check the current fee before applying.

A planning permission normally lasts three years. If an application is refused, you generally have 12 weeks to appeal a householder decision.

What permitted development does not cover

Permitted development is planning only. An extension also needs:

• Building Regulations approval, always — foundations, structure, insulation, glazing, drainage, fire safety.
• A party wall notice, if you build on the boundary, work on a shared wall or dig close to next door's foundations. See party wall agreements explained.
• A Southern Water build-over agreement, if you build within 3m of a public sewer. See extension costs.
• Any estate covenant or freeholder consent.

Questions people ask about extension planning permission

Where these facts come from

• GPDO 2015, Schedule 2, Part 1, Class A.
• Planning Portal: extensions and planning permission.
• MHCLG: permitted development rights for householders, technical guidance.
• MHCLG: planning fees from 1 April 2026.
• GOV.UK: 2024 consultation on permitted development rights (no outcome published).