Do I need planning permission for a single storey extension?

Not if it fits within permitted development: up to 3 m deep on a semi or terrace and 4 m on a detached house, no higher than 4 m, and covering no more than half the garden with other buildings. Beyond that, up to 6 m or 8 m, you need prior approval rather than full planning permission. Flats, listed buildings and some Article 4 areas need permission for any extension.

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.

Single storey extension permitted development — 3 m, 4 m, 6 m and 8 m rules

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?

Plan view, to scale. Depth is measured from the original rear wall — not from an earlier extension.

Garden →

House

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

Every project for your house type, with Article 4, listing and trees checked at your address.

£17.99one-off

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Going 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.

Buckinghamshire Cornwall Wiltshire Birmingham Leeds Manchester Bristol Barnet Camden Westminster Brighton and Hove York All 308 councils →

Common questions

Do I need planning permission for a single storey extension?: Not if it fits within permitted development: up to 3 m deep on a semi or terrace and 4 m on a detached house, no higher than 4 m, and covering no more than half the garden with other buildings. Beyond that, up to 6 m or 8 m, you need prior approval rather than full planning permission. Flats, listed buildings and some Article 4 areas need permission for any extension.
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.