The limits
| House type | Without applying | With prior approval |
|---|---|---|
| Detached | 4 m | 8 m |
| Semi-detached | 3 m | 6 m |
| Terraced | 3 m | 6 m |
| Flat or maisonette | Not permitted | Not permitted |
How deep is 3 m?
Single-storey rear extension limits: 3 m on a semi-detached or terraced house, 4 m on a detached house, or 6 m and 8 m with prior approval.
Other conditions
- Single storey, no higher than 4 m.
- Eaves no higher than 3 m if within 2 m of a boundary.
- Eaves and ridge no higher than those of the existing house.
- Materials similar in appearance to the existing house.
- No verandas, balconies or raised platforms over 0.3 m.
- Together with other buildings, no more than half the garden covered.
When you can’t use permitted development
Flats & maisonettes
No householder permitted development rights at all.
Listed buildings
Listed building consent is needed for almost any change.
Conservation areas
Same 4 m / 3 m depths, but the larger home extension scheme is not available. No cladding in stone, render, timber, plastic or tiles.
Article 4 directions
Your council may have removed this right on your street.
Planning conditions
An old permission may have removed permitted development rights. Not published anywhere.
New builds
Often have permitted development removed by condition. Check your deeds.
Your exact limits
House type, plot size, Article 4 and trees — worked out for your address.
£14.99one-off
Get my reportGoing to 6 m or 8 m: prior approval
The larger home extension scheme lets you double the depth — 6 m on a semi or terrace, 8 m on a detached house — as long as you tell the council first. It is still permitted development, not a planning application, and the fee is far lower.
The council writes to your neighbours. If nobody objects, the council can't refuse. If a neighbour does object, the council judges only the effect on their light, outlook and privacy. It has 42 days to decide; if it doesn't, you can build.
The scheme isn't available in conservation areas, National Parks, National Landscapes (AONBs), the Broads or World Heritage Sites, and it doesn't apply to two-storey extensions.
Measuring from the original house
Depth is measured from the rear wall of the house as it stood on 1 July 1948 — or as first built, if later. If a previous owner already extended, that extension counts towards your allowance: a 2 m kitchen extension from the 1980s leaves 1 m on a semi.
The 50% garden rule works the same way: it counts every extension and outbuilding added since the original house, not just the one you're planning.
Rear extension rules by council
Some councils have Article 4 directions that change these limits. Pick yours to see what applies locally.
Common questions
- Can I build a 4 m rear extension on a semi-detached house?
- Not without applying. Without prior approval the limit on a semi is 3 m. Through the larger home extension scheme you can go up to 6 m, provided the council doesn't object after consulting your neighbours.
- Do I need building regulations approval?
- Yes. Permitted development only answers the planning question. Almost every extension needs building regulations approval, through your council's building control or an approved inspector.
- Can I build a rear extension in a conservation area?
- Yes — single-storey rear extensions keep the 3 m and 4 m limits in a conservation area, but you can't use prior approval to go further, and you can't clad it in stone, render, timber, plastic or tiles.
- Does a conservatory count as an extension?
- Yes. A conservatory is a single-storey rear extension under Class A and follows exactly the same depth, height and garden-coverage limits.