The short answer: many single-storey rear extensions in England do not need planning permission, because they fall under permitted development. Plenty do need it, and the rules are more specific than most homeowners expect.
This page is the quick version. For the full, up-to-date walkthrough — including the larger home extension route, conservation areas, loft conversions and what happens if you build without permission — read our complete guide: do I need planning permission for an extension?
When you probably do not need planning permission
In England, a single-storey rear extension is usually permitted development if it stays inside these limits:
- No more than 3m beyond the rear wall of the original house for a terraced or semi-detached home, or 4m for a detached home.
- No more than 4m in height.
- Eaves no higher than 3m where the extension comes within 2m of a boundary.
- No more than half the land around the original house covered by extensions and other buildings.
- Materials of a similar appearance to those on the existing house.
The word “original” matters. It means the house as it was originally built, so an extension a previous owner added still counts against your allowance even if you have never touched the place.
Going deeper: the larger home extension route
You can go beyond the standard limits without a full planning application, using the prior approval process: over 3m and up to 6m for a terraced or semi-detached house, and over 4m and up to 8m for a detached one.
It is not automatic. You apply to the council, the council writes to your adjoining neighbours, and they get at least 21 days to object on amenity grounds. The council then has 42 days to decide. If no one objects and you meet the criteria, you can build. So 6m and 8m are not straight permitted development — they need prior approval first.
What permitted development will not cover
- Verandas, balconies or raised platforms.
- A chimney, flue, or soil and vent pipe.
- Side extensions that are more than one storey, over 4m high, or wider than half the original house.
- Two-storey rear extensions more than 3m beyond the original rear wall, or within 7m of the boundary opposite that wall.
On designated land — conservation areas, National Parks, Areas of Outstanding Natural Beauty, World Heritage Sites and the Broads — permitted development is tighter again: cladding is not allowed, and side extensions and extensions of more than one storey are restricted. Rights can also have been removed from your particular property, so always check with your local planning authority before you commit.
Wales has its own rules
Everything above is the England position. Permitted development in Wales is set separately and the limits differ, so do not assume an English rule of thumb applies to a Welsh property. We work with homeowners across England and Wales and check your specific project either way.
Get it confirmed in writing
Where a project is permitted development, it is still worth applying for a Lawful Development Certificate. The council formally confirms the work is lawful, which protects you when you come to sell.
That matters more than it used to. In England, for building work substantially completed on or after 25 April 2024, the council has 10 years to take enforcement action, up from 4 years for work completed before that date.
The next step
If you want the detail, the full guide covers all of it: do I need planning permission for an extension?
If you would rather someone simply sorted it, that is us. We have completed 2,000+ home projects across England & Wales with a 94% planning approval rate, and we measure, draw, submit and chase the council for one fixed price. See planning permission drawings, or book an intro call.