Permitted development for extensions in London: do you need planning permission?

Permitted development is a right, not a permission

Permitted development rights let you carry out certain building work without applying for planning permission. They come from national legislation, Schedule 2, Part 1, Class A of the General Permitted Development Order 2015, rather than from your council, which is why the rules are the same in Camden as in Croydon and why the exceptions matter so much, because those are local. You are not asking permission; you are relying on a right that either applies to your house or does not. If it does not and you build anyway, the council can require you to undo the work.

Permitted development for extensions: the limits

These are the Class A limits as the Order stands in September 2026, in the Planning Portal's summary and the Government's technical guidance. They apply to the total enlargement, so an extension a previous owner built counts against them, and the original house means the house as first built or as it stood on 1 July 1948.

Depth is measured from the base of the original rear wall to the outer face of the extension wall. Where the original rear wall is stepped, each step is a rear wall and the limit applies to whichever one you extend beyond. An extension that wraps a side and the rear has to satisfy both the side-extension rules and the rear-depth rule at once, which is the usual reason a London wraparound needs a planning application.

The larger home extension: prior approval

A single-storey rear extension deeper than 3 metres and up to 6, or deeper than 4 and up to 8 on a detached house, is still permitted development outside article 2(3) land (which includes conservation areas) and sites of special scientific interest, but only through the neighbour consultation scheme in paragraph A.4 of Class A, which the Planning Portal calls prior approval. Before starting you give the council a written description of the extension with its depth, its maximum height and its eaves height, a plan, the addresses of the adjoining premises and your contact details, plus the fee. The council notifies the adjoining owners and occupiers and gives them at least 21 days to object.

If nobody objects, or the council writes to say prior approval is not required, you can start; if a neighbour objects, the council decides whether the effect on the amenity of all adjoining premises is acceptable and can approve, approve with conditions or refuse. You cannot begin until you have the council's written notice or until 42 days have passed from the date it received your information without a decision, and the extension must then be built as described. It is quicker and cheaper than a planning application, but it is not a formality: a six-metre extension on a terrace overshadows a neighbour's garden, and that is precisely what the scheme exists to test.

When permitted development does not apply at all

• Flats and maisonettes: householder permitted development rights apply to houses only, and there is no version of Class A that covers a flat.
• Listed buildings: any external alteration needs listed building consent, which is a separate consent from planning permission.
• Conservation areas and other article 2(3) land: rear extensions are limited to 3 or 4 metres with no prior approval route, and side extensions, two-storey rear extensions and cladding are outside permitted development.
• Article 4 directions: a council can withdraw specified permitted development rights across a defined area, most often in conservation areas but sometimes street by street.
• Houses whose rights were removed by a condition on a planning permission, which is common on newer estates.
• Houses created under permitted development from a non-residential building, or built as new dwellings under permitted development, which cannot use Class A afterwards.

Planning permission and Building Regulations are different things

This is the point that causes the most confusion. Planning permission is about whether you may build something and what it looks like. Building Regulations are about whether it is structurally sound, insulated, ventilated, drained and safe in a fire. An extension can be permitted development and still need full Building Regulations approval, and it almost always does: the Planning Portal says most extensions require approval, with foundations, floors, walls, structural openings, ventilation and energy efficiency all controlled. The four London boroughs that publish a clear schedule charge £859–£1,288 including VAT for a single-storey extension of up to 60 square metres (2025/26 and 2026/27 schedules).

Get a lawful development certificate anyway

If your extension is permitted development, you can apply for a lawful development certificate confirming it. It is not compulsory. It is also the document a buyer's solicitor will ask for in five years' time, and without it the sale can stall while everyone tries to establish whether the work was lawful. A certificate for proposed works costs half the householder application fee, £274 in England from April 2026, against £548 for a certificate covering works already built (the householder fee in the Planning Portal's fee guidance), plus the Portal's online service charge, usually £99 including VAT (its Band 1; some application types carry no charge). The council has eight weeks to decide. Apply before you start, because a certificate for proposed development holds unless something material changes before the work begins, and a later Article 4 direction is exactly that.

The Party Wall etc. Act is a third, separate obligation

If you are building up to or astride a boundary, excavating within three metres of a neighbouring building to below their foundations, or cutting into a shared wall, you have duties under the Party Wall etc. Act 1996 regardless of planning or Building Regulations. Notice periods run to two months for work to a party wall and one month for a new wall on the boundary or for excavation, so this belongs at the start of a programme rather than the end. Published London figures put an agreed surveyor at £700–£1,800 per neighbour. Our guide to party wall agreements in London covers the notices, the surveyors and what happens if a neighbour dissents.

If you do need to apply

A householder planning application in England costs £548 from 1 April 2026, the figure in the Planning Portal's fee guidance; draft regulations laid before Parliament on 16 July 2026 would raise it to £575 from 8 December 2026, so check the fee before you apply. On top comes the Portal's online service charge, usually £99 including VAT (its Band 1; some application types carry no charge). The statutory period for a decision is eight weeks, though validation delays and requests for an extension of time are common in busy boroughs, so plan on three months from submission to decision. The application needs scaled existing and proposed drawings, a location plan and a block plan; in a conservation area a short design statement explaining the materials and how the extension sits behind the house is worth its cost. Our house extension cost guide sets the fee against the build prices.