Do I need planning permission for a rear extension?

A single-storey rear extension doesn't usually need planning permission if it's no more than 3m deep on a semi-detached or terraced house (4m on a detached house) and no more than 4m tall. With prior approval you can go up to 6m or 8m. Flats, listed buildings and some protected areas have stricter rules.

What size rear extension can I build without planning permission?

• Single storey: up to 3m from the back of a semi-detached or terraced house, or 4m from a detached house, and no more than 4m tall.
• Bigger single storey: up to 6m (semi or terrace) or 8m (detached) through the larger home extension scheme, which needs prior approval from the council first.
• Two storeys: up to 3m deep, and at least 7m from the boundary at the back of the garden.
• Not allowed at all for flats and maisonettes, and much more limited for listed buildings, in conservation areas, National Landscapes and national parks, and where an Article 4 direction applies.

What are the permitted development rules for rear extensions?

To be permitted development, a rear extension must meet every one of these:

• An extension of more than one storey can extend no more than 3m beyond the rear wall of the original house. Schedule 2, Part 1, Class A, Class A.1(h)(i)
• An extension of more than one storey must be at least 7m from the boundary opposite the rear wall. Schedule 2, Part 1, Class A, Class A.1(h)(ii)
• A single-storey rear extension can be no more than 4m tall. Schedule 2, Part 1, Class A, Class A.1(f) and (g)
• A single-storey rear extension to a detached house can extend no more than 8m, even with prior approval. Schedule 2, Part 1, Class A, Class A.1(g)
• A single-storey rear extension to a semi-detached or terraced house can extend no more than 6m, even with prior approval. Schedule 2, Part 1, Class A, Class A.1(g)
• Within 2m of a boundary, the eaves can be no higher than 3m. Schedule 2, Part 1, Class A, Class A.1(i)
• No higher than the highest part of the existing roof, and eaves no higher than the existing eaves.
• Together with other extensions and outbuildings, it can cover no more than half the garden around the original house.
• No verandahs, balconies or raised platforms (decking more than 30cm high counts).
• Materials must look similar to the existing house (conservatories are exempt).
• Two-storey extensions: upper-floor side windows must be obscure-glazed and fixed shut below 1.7m, and the roof pitch should match the house.
• In a conservation area, National Landscape, national park or World Heritage Site, the house can't be clad in stone, render, timber, plastic or tiles.

Bigger projects can still be permitted development after prior approval:

• Between 4m and 8m is allowed for a detached house under the larger home extension scheme, but only after prior approval: you tell the council, it notifies your neighbours, and you can build if no neighbour objects or the council approves it. The council has 42 days to decide. Class A.1(g) and A.4
• Between 3m and 6m is allowed for a semi-detached or terraced house under the larger home extension scheme, but only after prior approval: you tell the council, it notifies your neighbours, and you can build if no neighbour objects or the council approves it. The council has 42 days to decide. Class A.1(g) and A.4

What counts as the original house?

All the depth limits are measured from the back wall of the original house: the house as it was first built, or as it stood on 1 July 1948 if it's older. If a previous owner added a conservatory or kitchen extension, that counts towards the limit. So if your semi already has a 2m extension, a new one joining onto it can only add another 1m under the standard limit.

Heights are measured from the ground next to the extension. On a sloping garden, use the highest ground level next to it.

Can I build a 6m or 8m extension without planning permission?

If you want to go beyond 3m (semi or terrace) or 4m (detached), you can apply for prior approval for a single-storey extension of up to 6m or 8m. It's a lighter process than a planning application:

1. You send the council a description of the extension, its depth, its height and eaves height, and a plan.
2. The council writes to the neighbours whose land adjoins yours, including at the back. They have 21 days to object.
3. If no neighbour objects, the council doesn't assess the effect on them, and the extension can go ahead as long as it meets the other limits. If a neighbour does object, the council decides whether the extension would harm their living conditions, such as their light, outlook or privacy.
4. The council has 42 days to decide. If it doesn't tell you in that time, you can go ahead.

The larger scheme isn't available in conservation areas, National Landscapes, national parks, World Heritage Sites or Sites of Special Scientific Interest.

Do two-storey extensions need planning permission?

A two-storey extension is permitted development if it extends no more than 3m beyond the original back wall and leaves at least 7m to the rear boundary. The roof pitch should match the house as far as practicable, and any upper-floor windows in the side walls must be obscure-glazed and fixed shut below 1.7m above the floor. Two-storey extensions aren't permitted development in conservation areas, National Landscapes, national parks or World Heritage Sites.

When does a rear extension need planning permission?

• The home is a flat or maisonette, or was created by converting another building under permitted development.
• The original planning permission for your home (common on newer estates) has a condition removing permitted development rights.
• An Article 4 direction covers your home and removes Part 1 Class A rights.
• The extension includes a balcony, roof terrace, or decking more than 30cm off the ground.

Where are the rules stricter?

• Rear extensions in a conservation area
• Rear extensions in a National Landscape or national park
• Listed buildings
• Article 4 directions
• Conservation areas and Article 4 directions by council
• Flats and maisonettes

Do I need building regulations approval?

Planning permission and building regulations are separate. Planning is about whether you can build it and how it looks; building regulations are about whether it is built safely (structure, fire safety, insulation, drainage). Permitted development only covers planning, so you may still need building regulations approval.

Rear extensions almost always need building regulations approval, covering foundations, structure, insulation, drainage and fire escape. Building over or near a public sewer also needs your water company's agreement.

How can I prove I don't need planning permission?

If you're confident your project is permitted development, you can apply to your council for a Lawful Development Certificate. It's a formal confirmation that the work is lawful without planning permission, it costs less than a planning application, and it's useful when you come to sell the house. If you're not sure, many councils offer pre-application advice.

Last reviewed 29 October 2026 Based on General Permitted Development Order 2015, Schedule 2, Part 1, Class A