Most rear extensions in England can be built without a full planning application, thanks to permitted development rights. This guide walks through the exact size and height limits, the larger-home-extension prior approval route, and the situations where full planning permission is unavoidable.
You do not need planning permission for a rear extension if it stays within permitted development limits: a single-storey rear extension may project up to 3 metres beyond the original rear wall of an attached house, or 4 metres for a detached house, with a maximum height of 4 metres. Go further — up to 6 metres for attached houses or 8 metres for detached — and you can still avoid a full application by using the prior approval route for larger home extensions. Only projects outside those limits, or on properties where permitted development has been removed, need full planning permission.
Those rights come from the Town and Country Planning (General Permitted Development) (England) Order 2015, as amended — usually shortened to the GPDO. Class A of Part 1 grants every dwellinghouse in England a bundle of pre-approved extension rights, provided a long list of conditions is met. The rights attach to the house, not the owner, so previous extensions built since the house was first constructed count against your allowance.
The catch is in the detail. 'Original rear wall' means the rear wall as the house stood on 1 July 1948, or as it was first built if later — not the rear wall as it stands today. If a previous owner already added a rear projection, that depth is used up. Measuring from the wrong wall is one of the most common reasons homeowners build what they believe is a lawful extension and then run into trouble when they sell.
A rear extension needs planning permission when it exceeds permitted development limits: deeper than 3m (attached) or 4m (detached) without prior approval, taller than 4m, more than half the garden covered, or on a flat, maisonette or Article 4 property. Check every item below before assuming your project is permitted development:
The 6m and 8m rule is the GPDO's middle path between permitted development and a full application: the larger-home-extension provisions — originally a temporary scheme, made permanent in 2019 — allow single-storey rear extensions of up to 6 metres on terraced and semi-detached houses, and up to 8 metres on detached houses, subject to a prior approval process often called the neighbour consultation scheme. It is the route to use when the standard 3 or 4 metres is not enough.
Here is how it works. You notify your local planning authority before starting work, submitting a written description of the extension and a plan showing its depth, maximum height and eaves height. The council then writes to your adjoining neighbours, who have 21 days to object. If no neighbour objects, the council confirms that prior approval is not required and you may build. If a neighbour does object, the council assesses the impact on the amenity of adjoining properties — and only that. It cannot refuse on design taste, materials or garden size, which makes prior approval considerably more predictable than a full planning application.
The council has 42 days to make its decision. If it fails to respond within that period, approval is deemed granted and you may proceed. Two important limits: the extension must still meet all the other Class A conditions (height, eaves, materials), and the route is not available on Article 2(3) land — conservation areas, National Parks, Areas of Outstanding Natural Beauty and World Heritage Sites — where the standard 3m/4m limits apply.
Every rear extension in England follows one of three consent routes: permitted development, prior approval, or full planning permission. The right one depends on your dimensions, your property type and your street.
No application needed if every Class A condition is met. Strongly consider a lawful development certificate so you have formal proof for buyers, mortgage lenders and building control.
Notify the council, neighbours get 21 days to comment, and the council decides within 42 days on neighbour amenity alone. Ideal for deeper single-storey kitchen-diner extensions.
Required for two-storey rear extensions beyond PD limits, flats, conservation-area and Article 4 properties, and any design that breaks the height, coverage or materials rules. Decided against local policy within a target of 8 weeks.
Permitted development is measured to the centimetre — depth from the original rear wall, eaves height at the boundary, ridge lines against the existing roof. Accurate scaled drawings are what prove your extension complies, whether you build under PD, apply for prior approval or submit a full application.
Work through these four steps before committing to a design — they save weeks of wasted time and redrawing.
Compare your house today with how it stood in 1948 or as first built. Old plans, historic maps and your council's planning history search reveal previous extensions that eat into your allowance.
Search your address on the council's website for conservation areas, Article 4 directions and listed-building status. A quick call to the duty planner confirms anything unclear.
Test depth, height, eaves, boundary distances and total coverage against the limits above. If everything passes, you are in permitted development territory; if only depth fails, prior approval may rescue the scheme.
Commission existing and proposed drawings, then either apply for a lawful development certificate, submit the prior approval notification, or make a full householder application — whichever route your dimensions demand.
The same six-metre rule plays out very differently street by street. These are the neighbourhoods where we draw rear extensions most often — each with its own planning quirks.
Stucco-fronted terraces with narrow side returns dominate Fulham. Most rear extensions here combine a wraparound with the six-metre prior approval route — and party wall agreements with both neighbours are almost always needed.
Conservation areas cover most of Chelsea, so Article 4 directions often remove permitted development rights — expect a full householder application with heritage-sensitive drawings.
Clapham's Victorian terraces suit the classic full-width rear extension. Depth beyond three metres means prior approval — our drawings make the neighbour consultation painless.
Edwardian semis in Wimbledon usually keep their PD rights, so a well-measured single-storey rear extension can proceed under a lawful development certificate.
Hampstead's conservation areas and listed cottages demand full applications with careful heritage drawings — approval hinges on materials and roofline detail.
Tell us about your project and get a fixed, no-obligation quote back within one working day. If you don't need planning permission at all, we'll tell you that too — for free.
Under permitted development you can build a single-storey rear extension up to 3 metres beyond the original rear wall of a terraced or semi-detached house, or 4 metres on a detached house. With prior approval under the larger-home-extension scheme, those limits rise to 6 metres and 8 metres respectively.
Yes. Flats and maisonettes have no householder permitted development rights, so any rear extension to a flat needs full planning permission — and usually the freeholder's consent too. The 3m, 4m, 6m and 8m allowances discussed in this guide apply only to houses.
The 6 metre rule refers to the larger-home-extension prior approval scheme: attached houses may extend a single-storey rear extension up to 6 metres (8 metres if detached) if the council is notified first, neighbours are consulted for 21 days, and no unresolved amenity objection is upheld within 42 days.
Often, yes. In conservation areas the larger-home-extension route is unavailable, side extensions are excluded from permitted development, and many councils add Article 4 directions removing rear extension rights entirely. Check your council's conservation-area rules before designing — a modest 3m extension may still be permitted development.
It is strongly recommended. A lawful development certificate is formal council confirmation that your extension is lawful without planning permission. Solicitors and mortgage lenders routinely ask for one when you sell, and it protects you if a neighbour complains or the council questions the build years later.
The council can serve an enforcement notice requiring alteration or demolition, and you would have no lawful use of the space until resolved. You can apply for retrospective permission, but there is no guarantee of approval. Getting the consent route right before building is always cheaper and safer.
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