The short answer
Usually not. In England a single-storey rear kitchen extension is permitted development if it reaches no more than 3 m beyond the original back wall of a terraced or semi-detached house, or 4 m on a detached house, and is no more than 4 m high. Flats, listed buildings, conservation areas and Scotland follow different rules, and building regulations approval is needed in every case.
The permitted development limits
Permitted development is planning permission that Parliament has already granted for common, modest building work. If your extension fits inside every limit below, you do not apply to the council at all.
For a single-storey rear extension to a house in England:
- Depth: no more than 3 m beyond the original rear wall if the house is terraced or semi-detached, or 4 m if it is detached.
- Height: no more than 4 m overall. If any part is within 2 m of a boundary, the eaves must be no higher than 3 m.
- Coverage: extensions and outbuildings together must not cover more than half the land around the original house.
- Materials: the outside must be of similar appearance to the existing house.
- Position: nothing forward of the front wall, and no balconies or raised platforms.
“Original” means the house as first built, or as it stood on 1 July 1948 if it is older. A previous owner’s extension counts against your allowance.
Going deeper: prior approval
There is a middle route. A single-storey rear extension may reach 6 m on a terraced or semi-detached house, and 8 m on a detached one, if you first apply to the council for prior approval. The council writes to your adjoining neighbours. If nobody objects, it must let the extension go ahead; if someone does, it judges the effect on their home. It has 42 days, and the fee is lower than for a full application.
This route is closed in conservation areas, national parks and areas of outstanding natural beauty.
Side returns and wraparounds
A side extension has its own test: single storey, no more than 4 m high, and no wider than half the width of the original house. A typical side return passes. But side extensions are not permitted development at all in a conservation area, and a great many Victorian terraces sit in one.
A wraparound, which joins a side return to a rear extension in one L-shaped room, is measured as a single extension. It is nearly always wider than half the house, so it needs a planning application.
When you will need to apply
You need a householder planning application if any of these is true:
- The extension breaks one of the limits above.
- The property is a flat or maisonette. They have no permitted development rights for extensions.
- The council has removed permitted development rights, either through an Article 4 direction covering the street or through a condition on the original planning permission for the estate. This is common on houses built since the 1990s.
- You want cladding or a roof that looks nothing like the house, such as zinc or charred timber on a brick semi.
A listed building needs listed building consent for any extension, whether or not planning permission is required as well.
An application is decided in about eight weeks. Refusals can be appealed, though a revised design agreed with the planning officer is usually quicker.
Get it in writing
Permitted development is self-certified, which means nobody checks unless a neighbour complains or you come to sell. A lawful development certificate fixes that. You send the council drawings, pay half the planning fee, and it confirms in writing that the extension is lawful. A buyer’s solicitor may well ask for one. For the sake of a modest fee against a kitchen extension cost of tens of thousands of pounds, it is worth having before the foundations go in.
Scotland, Wales and Northern Ireland
Each nation writes its own rules. Scotland’s permitted development limits for rear extensions are set out separately and differ in detail, and every extension in Scotland needs a building warrant from the council before work starts, with a completion certificate at the end. Wales and Northern Ireland each have their own version of the limits. Check with your own council before relying on anything written for England.
Planning is not building regulations
They are separate systems, and passing one says nothing about the other. Planning asks whether the extension should be there. Building regulations ask whether it will stand up, keep heat in, drain properly and let people out in a fire. Every kitchen extension needs building regulations approval, permitted development or not, and the completion certificate at the end is the document a future buyer’s solicitor will want to see.