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Does a house extension need planning permission or is it permitted development?

Last checked 24-10-2026. A plain guide, not legal advice: check the official guidance below for your job.

In England, many rear and side extensions to a house can be built under permitted development without a planning application, but only if every limit is met. Flats, designated land, Article 4 areas and planning conditions can remove those rights, so confirm with the client and the council before you start.

The limits that apply to every extension

This is the Planning Portal summary of Class A of the General Permitted Development Order 2015. It applies to houses, and counts the new work together with earlier extensions. "Original house" means the house as first built, or as it stood on 1 July 1948 if older.

  • Buildings other than the original house, including extensions and outbuildings, can cover no more than 50% of the curtilage once the original house area is excluded.
  • No higher than the highest part of the existing roof, and no higher at the eaves than the existing eaves.
  • Eaves no more than 3 m high if the extension is within 2 m of a boundary.
  • Not forward of the principal elevation, or of a side elevation that fronts a highway.
  • No verandas, balconies or raised platforms (the government guidance counts a platform as raised above 0.3 m), no microwave antenna, no chimney, flue or soil and vent pipe, and no alteration to the existing roof.
  • Materials of a similar appearance to the existing house.

Rear extensions

  • Single storey: no more than 4 m beyond the rear wall of the original house if detached, or 3 m for any other house, and no more than 4 m high.
  • More than one storey: no more than 3 m beyond the rear wall, and not within 7 m of the boundary opposite the rear wall. The roof pitch should match the house as far as practicable.
  • Any upper-floor window in a side elevation must be obscure-glazed, and non-opening unless the opening part is over 1.7 m above the floor.

Larger home extension prior approval

Away from designated land and sites of special scientific interest, a single-storey rear extension can go to 8 m if the house is detached, or 6 m for any other house, still up to 4 m high. You must first tell the council. The developer supplies a written description with the depth, maximum height and eaves height, a plan, the neighbours' addresses and any fee.

The council notifies the adjoining owners and gives them at least 21 days to comment. If a neighbour objects, the council decides on prior approval, looking at the effect on neighbours' amenity. You cannot start until the council says approval is not needed, gives approval, or 42 days pass without a decision.

Side extensions and designated land

An extension that goes beyond a side wall of the original house must be single storey, no more than 4 m high and no more than half the width of the original house.

On Article 2(3) designated land (conservation areas, National Parks, the Broads, areas of outstanding natural beauty and World Heritage Sites, among others) there are no side extensions, no rear extensions of more than one storey, no cladding in stone, artificial stone, pebble dash, render, timber, plastic or tiles, and no larger 8 m or 6 m scheme.

When permitted development does not apply, or is not enough

  • Flats and maisonettes. The Planning Portal says the rights that apply to many house projects do not apply to them.
  • Houses made by change of use under some Part 3 classes, and new dwellings built under Part 20.
  • Article 4 directions, which a council can use to remove some or all permitted development rights, and planning conditions on the original permission.
  • Listed buildings. Class A does not exclude them, but permitted development only gives planning permission. Most extensions to a listed house also need listed building consent, and it is a criminal offence to do work that needs it without it.

Check first

A lawful development certificate from the council confirms in writing that a proposed extension is lawful. The Planning Portal says the council should decide within 8 weeks of validating it.

Permitted development does not remove the need for Building Regulations approval or Party Wall Act requirements. Before you price or start, check the planning position with the client and the council, including Article 4 and any conditions on the house.

Sources

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