Do I Need Planning Permission for a Rear Extension?

Many single-storey rear extensions can be built without a full planning application, under what are called permitted development rights. Others need planning permission. Knowing which category your project falls into is the first step, and it can save you months of delay.

Permitted development versus planning permission

Permitted development rights let you carry out certain works without a full planning application, as long as you stay within set limits and conditions. If your extension goes beyond those limits, or if permitted development does not apply to your property, you will need to apply for planning permission from your local council.

Standard permitted development limits

For a single-storey rear extension, the current standard limits are:

• Up to 3 metres beyond the original rear wall for a terraced or semi-detached house, or up to 4 metres for a detached house.
• A maximum height of 4 metres.
• Where the extension is within 2 metres of a boundary, the eaves height must not exceed 3 metres.

The word original matters here. It means the house as it was first built, or as it stood on 1 July 1948 if it is older. If a previous owner already extended, that may have used up some or all of the allowance.

The Larger Home Extension Scheme

You can build deeper under a route called prior approval. This allows a single-storey rear extension of up to 6 metres for a terraced or semi-detached house, or up to 8 metres for a detached house. You must apply to the council first, and your neighbours are consulted for 21 days. If they raise no valid objections, the work can proceed. It is not automatic, so it should be confirmed before you build.

Other conditions that must be met

Even within the depth limits, your extension only counts as permitted development if it also satisfies every other condition. The main ones include:

• The extension, together with other buildings, must not cover more than half the land around the original house.
• It must not extend beyond the front, or the principal elevation facing a road.
• Materials should be similar in appearance to the existing house.
• Verandas, balconies and raised platforms are not covered.

Fail any single condition and the extension is no longer permitted development, regardless of how deep it is.

When permitted development does not apply

Permitted development rights are restricted or removed in a number of situations that are common across North West London:

• Conservation areas, which cover much of Hampstead, Highgate and Belsize Park, where tighter rules apply.
• Listed buildings, which need listed building consent for most changes.
• Properties affected by an Article 4 direction, which removes specific permitted development rights. Areas near Hampstead Garden Suburb in Barnet are a well known example.
• Flats and maisonettes, which do not have these rights at all.

Do not forget Building Regulations

Planning and Building Regulations are separate things. Even an extension that is permitted development must still comply with Building Regulations, covering structure, insulation, drainage, fire safety and more. If your work affects a shared wall, the Party Wall Act may also apply and require notice to your neighbours.

The safest approach

Because the rules depend on your exact property and location, it is always worth confirming your position with the local planning authority, whether that is Camden, Barnet, Haringey or another borough, before work begins. Many homeowners also apply for a Lawful Development Certificate, which gives you formal proof that your extension is permitted development. It is useful for peace of mind and when you come to sell.

This article is general guidance only and reflects the permitted development rules for single-storey rear extensions in England as of 2026. Rules change over time and depend on your specific property and location. Always confirm your position with your local planning authority before starting work.