Extending your London home does not always mean making a full planning application. In many cases, permitted development for extensions allows homeowners to add useful extra space without applying for planning permission, provided the work stays within specific limits.
This can make the route to a larger kitchen, dining area or family space more straightforward. However, London properties can be affected by conservation areas, Article 4 Directions and other local restrictions, so it is important to check what applies before finalising your plans.
Permitted development rights are national planning rights that allow certain home improvements to take place without a full planning application.
What is Permitted Development for an Extension?
Permitted development rights for extensions can cover rear extensions, side extensions and some two-storey additions. However, the rules include limits on size, height, position and design.
They generally apply to houses rather than flats or maisonettes, and rights may have been restricted for a particular property or area.
If your project falls outside permitted development, it does not necessarily mean you cannot build it. You may simply need to apply for planning permission instead.
Permitted Development Rules for Extensions
Some of the main permitted development rules for extensions include:
- Extensions and other buildings must not cover more than 50% of the land around the original house.
- An extension cannot normally project beyond the front of the original house.
- Height and eaves limits apply, particularly near boundaries.
- Previous extensions can reduce the amount of additional space you can build.
- Different restrictions apply to rear, side and multi-storey extensions.
The rules refer to the “original house”, meaning the property as it stood on 1 July 1948, or as first built if it was constructed after that date. Previous additions therefore need to be taken into account.
Permitted Development for Rear Extensions
Permitted development for rear extensions is particularly useful for London homeowners wanting to create larger kitchens and open-plan living areas.
Under the standard rules, a single-storey rear extension can generally extend up to:
- 4 metres beyond the original rear wall of a detached house
- 3 metres beyond the original rear wall of a semi-detached or terraced house
The extension must also be no more than 4 metres high.
Larger single-storey rear extensions may sometimes be possible. Subject to the relevant conditions, these can extend up to 8 metres for detached houses and 6 metres for other houses.
These larger extensions require the prior approval process, including neighbour consultation, so you must contact the local planning authority before starting work.
Permitted Development for Side Extensions
The permitted development rules for side extensions are more restrictive.
A qualifying side extension must generally:
- Be single-storey
- Be no more than 4 metres high
- Be no wider than half the width of the original house
These rules are especially relevant to London’s popular side-return extensions.
Combined side and rear extensions can be more complicated because both sets of restrictions may need to be considered. Side extensions are also not permitted development on certain protected land, including conservation areas.
Can You Build a Two-storey Extension Under Permitted Development?
In some cases, yes, although the rules are stricter.
A multi-storey rear extension may qualify where it extends no more than 3 metres beyond the original rear wall and remains at least 7 metres from the boundary opposite the rear wall. Other height, design and materials conditions also apply.
Multi-storey rear extensions do not benefit from the same permitted development rights on protected land such as conservation areas.
For many London properties, especially homes with smaller gardens or additional local restrictions, planning permission may therefore be required.
Permitted Development Extension Size Limits
The headline measurements are only part of the picture.
Permitted development extension size limits can also depend on the distance from neighbouring boundaries, previous extensions, the shape of the property and how much land around the original house has already been developed.
For example, where part of a single-storey extension is within 2 metres of a boundary, the maximum eaves height is generally 3 metres.
Checking these details early can help you understand what is realistically possible before design work progresses too far.
Permitted Development and London Planning Restrictions
Although permitted development rules are national, London properties can be affected by additional local controls.
Councils can use an Article 4 Direction to remove specific permitted development rights within particular areas. As a result, work that might be permitted development elsewhere could require planning permission.
Conservation areas also have additional restrictions. Side extensions and multi-storey rear extensions, for example, face tighter controls.
Individual planning permissions may also include conditions that remove permitted development rights from a property.
Do Permitted Development Rights Apply to Your London Property?
Before assuming your extension qualifies, check:
- Whether the property is a house rather than a flat or maisonette
- Whether it is in a conservation area
- Whether an Article 4 Direction applies
- Whether previous planning permissions restrict permitted development
- What extensions have already been added
- Whether the proposed size and design meet the relevant rules
Two similar-looking London homes can have very different planning requirements, so checking the individual property is essential.
Permitted Development vs Planning Permission
Permitted development and planning permission are two different routes.
With permitted development, the project must meet a defined set of national rules and conditions.
With planning permission, the local authority considers the individual proposal against local and national planning policies.
If your extension falls outside permitted development, a planning application may actually offer greater flexibility over its size, layout or design.
Lawful Development Certificate for an Extension
Even if your project falls within permitted development, applying for a Lawful Development Certificate can be useful.
A Lawful Development Certificate provides formal confirmation from the council that the proposed work is lawful for planning purposes.
Although it is not normally compulsory for permitted development, it can provide valuable evidence of the extension’s planning status, particularly when selling your home in the future.
Do You Still Need Building Regulations Approval?
Yes. Permitted development and building regulations are separate.
An extension may not require planning permission but can still need to comply with rules covering structural safety, insulation, ventilation, drainage, fire safety and electrical work.
You can find out more in the Plus Rooms guide to building regulations.
Other requirements, including the Party Wall etc. Act 1996, may also apply depending on the project.
What Happens if Your Extension Doesn’t Qualify for Permitted Development?
If your project falls outside permitted development, you can usually consider a householder planning application.
This does not mean the extension cannot go ahead. It simply means the council will assess the proposal through the normal planning process.
Establishing the correct route early helps avoid delays or planning problems once building work has begun.
Common Permitted Development Mistakes
Common mistakes include:
- Measuring from an existing extension instead of the original house
- Assuming all London properties have the same permitted development rights
- Overlooking conservation areas or Article 4 Directions
- Forgetting to include previous extensions
- Assuming every side-return extension qualifies
- Starting a larger rear extension before prior approval
- Confusing permitted development with building regulations approval
Planning Your London Extension with Confidence
If you are considering an extension, Plus Rooms can help you take the project from the first ideas through to completion. Our Extension Design and Build service brings design, planning and construction together in one coordinated process, with an experienced team helping to manage each stage of the project.
Whether you are exploring permitted development, preparing a planning application or simply working out the best way to make more of your existing space, Plus Rooms can help you understand the options available and create an extension designed around your home and the way you live.
Contact Plus Rooms to find out more about our Extension Design and Build services and discuss what could be possible for your property.
Frequently Asked Questions
Do I need planning permission for a 3 metre rear extension?
For many terraced and semi-detached houses, a 3 metre single-storey rear extension may be permitted development if all other conditions are met. Detached houses can generally extend up to 4 metres under the standard rules.
Can I extend further than 3 metres without full planning permission?
Potentially. The larger home extension process can allow qualifying rear extensions of up to 6 metres for terraced and semi-detached houses and 8 metres for detached houses. Prior approval is required.
Can I build a side-return extension under permitted development?
Sometimes. The extension must normally be single storey, no more than 4 metres high and no wider than half the width of the original house. Conservation area and combined-extension restrictions may also apply.
Does permitted development apply in London conservation areas?
Some rights still apply, but there are extra restrictions. Side extensions and multi-storey rear extensions, for example, do not benefit from the normal Class A permitted development rights in conservation areas.
