Permitted Development vs Full Planning Permission for a London Rear Extension

A rear extension can transform a London home, but choosing the right planning route matters as much as choosing the layout. Some projects qualify as permitted development; others need a planning application. The difference depends on the property, its planning history and the proposed design.

At Simplicity Designs UK Limited, we help homeowners establish what is possible before detailed design work begins. Here are the main checks we recommend.

What does permitted development mean?

Permitted development rights grant planning permission for certain works without a conventional planning application, provided every relevant condition is met. For house extensions in England, the rules sit within the General Permitted Development Order.

These rights generally apply to houses, not flats or maisonettes. If you own a ground-floor flat with a private garden, you should not assume that house extension rights apply.

Rights can also be restricted by an Article 4 direction or removed through a planning condition. Conservation areas have additional restrictions, while listed buildings require separate consideration, including whether listed building consent is needed.

How large can a rear extension be?

For a typical single-storey rear extension, the standard permitted development depth limit is three metres for an attached house and four metres for a detached house. Depth is measured from the rear wall of the original house, not necessarily the house as it stands today.

The Planning Portal explains that “original house” means the house as first built, or as it stood on 1 July 1948 if built before then. Previous extensions therefore matter, even if a former owner built them.

Other limits include a maximum overall height of four metres and, where the extension is within two metres of a boundary, a maximum eaves height of three metres. Materials must be similar in appearance to the existing house. There are also limits on how much surrounding land can be covered by buildings, alongside further restrictions for particular layouts.

These measurements are starting points, not a complete eligibility checklist. Wraparound extensions, stepped rear walls and earlier additions need careful assessment.

Where does prior approval fit in?

The larger home extension route can allow single-storey rear extensions up to six metres deep for attached houses and eight metres for detached houses, subject to eligibility and all other applicable conditions.

This is still permitted development, but it involves a prior approval process with the council before work starts. The council notifies adjoining neighbours and, where objections are received, assesses the impact on their amenity.

This route is not available everywhere, including conservation areas. We check the site's status and explain the applicable procedure before recommending it. A neighbour's objection does not automatically mean refusal, but neither should approval be assumed.

When is a planning application the better route?

For an extension to an existing house, the application is usually a householder planning application rather than a full planning application. Extensions to flats generally require full planning permission.

An application may be necessary where permitted development rights are unavailable or the design exceeds their limits. It can also offer greater design flexibility: permitted development is not always the best fit for your home.

The council will consider local planning policies, design, neighbouring outlook, daylight, privacy and other relevant matters. We assess these issues early, particularly on tightly packed London terraces where boundary relationships are important.

What should you secure before building?

For a permitted development scheme, we normally recommend obtaining a lawful development certificate to confirm its planning status. Prior approval, where required, is a separate process and should not be replaced by a certificate application.

Planning permission does not replace building regulations approval. Structural design, drainage and obligations under the Party Wall etc. Act may also need attention, along with leasehold or other private consents.

If you are considering a rear extension in London, call our team on 0203 026 2883 or send your property details and ideas to info@simplicity-designs.co.uk. We can help identify the appropriate planning route and next steps.