Extensions
Extensions without planning permission: what's actually allowed
The permitted development limits that let many extensions proceed without a full application.
Many single-storey rear and side extensions can be built without a full planning application, under permitted development, provided they stay within set depth, height and width limits - up to 4m deep for a detached house or 3m for other types as standard, or further under the Larger Home Extension route with prior approval.
Last updated 2 August 2026
·By Richard Anslow
Key points
- Standard single-storey rear extension limits: up to 4m for a detached house, 3m for semi-detached/terraced, within a 4m height cap.
- The Larger Home Extension route goes further (8m/6m) but needs neighbour notification and council prior approval first - and isn't available on designated land.
- Flats, listed buildings, an Article 4 direction, or a previously used-up permitted development allowance can all still trigger the need for a full application.
The standard limits
A single-storey rear extension can generally project up to 4m beyond the original rear wall for a detached house, or 3m for a semi-detached or terraced house, without needing a full planning application - subject to an overall height limit of 4m, and a lower eaves height limit if the extension comes within 2m of a boundary.
Side extensions are more restricted: single storey only, a maximum height of 4m, and no wider than half the width of the original house.
Going further with the Larger Home Extension route
If you want to go beyond the standard depth limit - up to 8m for a detached house or 6m for other types - the Larger Home Extension scheme allows this without a full planning application, but it requires notifying your neighbours and getting prior approval from the council first, rather than simply proceeding.
This route isn't available on designated land (conservation areas, National Parks, Areas of Outstanding Natural Beauty and similar), where a full application is needed for anything beyond the standard limit.
What can still tip you into needing an application
Being a flat, being listed, an Article 4 direction on your street, or having already used up your permitted development allowance on a previous extension can all mean planning permission is needed even for a project that would otherwise qualify.
FAQs
How do I know if my planned extension fits within permitted development?
Use our permitted development checker for a first steer against your specific dimensions, then we'll confirm the position for your property before design work begins - permitted development history on the property, not just the general rule, is what ultimately decides it.
Take this further
Have a question about your own project?