Permitted Development Rules for Extensions in London (2026 Guide)

What is permitted development?

Permitted development (PD) is a set of national rules, defined by the Town and Country Planning (General Permitted Development) Order 2015 (as amended), that allow certain building works to go ahead without needing planning permission from your local council.

Think of it as a pre-approved right to extend your home — provided you stay within specific size, height, and position limits. The rules were designed to let homeowners make reasonable improvements to their properties without the cost and delay of a full planning application.

Key point: permitted development only applies to houses (detached, semi-detached, terraced). Flats, maisonettes, and commercial properties do not have PD rights for extensions.

Single-storey rear extension rules

This is the most common type of extension in London, and the one that most often qualifies for permitted development. Here are the key limits:

• Maximum depth from the original rear wall: 3 metres for semi-detached and terraced houses, 4 metres for detached houses.
• Maximum height: 4 metres overall. If within 2 metres of a boundary, the eaves height must not exceed 3 metres.
• Maximum coverage: the extension (plus any other buildings in the garden) must not cover more than 50% of the garden area.
• Materials: must be similar in appearance to the existing house.
• No balconies, verandas, or raised platforms over 300 mm above ground level.

The larger home extension scheme (prior approval)

The larger home extension scheme doubles the permitted depth for single-storey rear extensions: up to 6 metres for semi-detached/terraced houses and 8 metres for detached houses. This is not “planning permission” — it uses a simpler process called prior approval.

How prior approval works

1. You submit a prior approval application to your council (£120 fee).
2. The council notifies your immediate neighbours by letter.
3. Neighbours have 21 days to comment.
4. The council has 42 days from the application date to decide.
5. If no objections are raised, or the council determines the impact is acceptable, you receive prior approval.
6. If the council does not respond within 42 days, approval is deemed granted by default.

This scheme is popular in London because many terraced houses need more than 3 metres to create a meaningful open-plan living space. In our experience, prior approval applications succeed roughly 75–80% of the time in London boroughs.

Two-storey rear extension rules

Two-storey rear extensions can be built under PD, but the rules are stricter:

• Maximum depth: 3 metres from the original rear wall (no larger-home extension scheme for two-storey).
• Must be at least 7 metres from the rear boundary.
• Maximum eaves and ridge height must not exceed the existing house.
• Roof pitch must match the existing house as closely as practicable.
• No balconies or windows in the side elevation overlooking neighbours (or they must be obscure-glazed and non-opening below 1.7 m).

In practice, the 7-metre rule from the rear boundary makes two-storey rear PD extensions difficult on small London plots. Many London gardens are only 8–12 metres deep, leaving almost no room after the 7-metre setback. This is why most two-storey extensions in London require full planning permission.

Side extension rules

Side extensions (often used to extend a kitchen along a side-return alley) are allowed under PD with these conditions:

• Single storey only.
• Maximum width: no more than half the width of the original house.
• Maximum height: 4 metres.
• Must not extend forward of the principal elevation (front of the house) facing a highway.
• If in a conservation area or other designated land, side extensions are not permitted under PD.

Loft conversion permitted development rules

Loft conversions are a separate category of permitted development. The rules are based on volume added, not floor area:

• Terraced houses: up to 40 m³ of additional roof space.
• Detached and semi-detached houses: up to 50 m³.
• Dormers must not be higher than the existing ridge.
• Side-facing windows must be obscure-glazed and non-opening below 1.7 m.
• Dormer windows on the front (street-facing) elevation are not permitted under PD.
• Materials must be similar in appearance to the existing house.

Most standard dormer loft conversions in London fall within these limits. Hip-to-gable conversions on semi-detached houses are also usually permitted, as they add volume efficiently.

Conservation areas and Article 4 directions

London has hundreds of conservation areas, and if your property is in one, your permitted development rights are significantly reduced:

• No side extensions under PD.
• No two-storey rear extensions under PD.
• No rear dormers visible from a highway.
• No cladding of the exterior.
• Single-storey rear extensions are usually still permitted under PD, unless an Article 4 direction has removed those rights.

An Article 4 direction is a specific order made by the council that removes certain PD rights in a defined area. Some London boroughs (particularly Kensington & Chelsea, Westminster, and Camden) use Article 4 directions extensively. If an Article 4 is in place, you need planning permission for almost everything.

Building regulations: a separate requirement

This is the single most misunderstood point in home extensions: permitted development does NOT mean you can skip building regulations. They are two completely separate legal requirements.

• Planning permission — governs what you can build (size, position, appearance). PD exempts you from this.
• Building regulations — govern how you build it (structural safety, fire escape, insulation, drainage, electrics). You always need building regulations approval, whether or not you need planning permission.

You can apply for building regulations approval through your local council's building control team, or through a private Approved Inspector. At Delta, we typically use Approved Inspectors as they offer faster turnaround and more flexible site inspection schedules.

Lawful development certificates: why you should get one

A lawful development certificate (LDC) is a document from your council confirming that your extension is lawful under permitted development. It costs £117 and takes approximately 8 weeks to obtain.

Technically it's optional — but we strongly recommend getting one for every PD extension. Here's why:

• Property sale protection — when you sell your home, the buyer's solicitor will ask for proof that all extensions were built lawfully. Without an LDC, you may face delays or be asked to buy indemnity insurance.
• Mortgage lender requirements — many lenders now require evidence that extensions comply with planning law.
• Certainty before you start — an LDC confirms the council agrees your plans fall within PD before you spend money on construction.

Party wall agreements

If your extension involves work on or near a shared boundary wall, you'll need to comply with the Party Wall etc. Act 1996. This applies regardless of whether you need planning permission.

You must serve a party wall notice on your neighbours at least two months before starting work that involves:

• Building on the boundary line
• Cutting into a party wall (e.g. inserting a beam)
• Excavating within 3 metres of a neighbour's structure (or 6 metres if the excavation goes deeper than their foundations)

If your neighbour agrees in writing (a “consent”), no surveyor is needed and there's no cost. If they dissent or don't respond within 14 days, both parties appoint surveyors to prepare a Party Wall Award. Budget £1,000–£3,000 per neighbour — you (the building owner) pay for both surveyors.

Your pre-build checklist

1. Check if you're in a conservation area — search your borough's planning map.
2. Check for Article 4 directions — some areas have PD rights removed entirely.
3. Measure from the original rear wall — not the current one if the house was already extended.
4. Apply for a lawful development certificate (£117) — optional but strongly recommended.
5. Consider prior approval if you need more than 3 m depth (semi/terrace) or 4 m (detached).
6. Submit building regulations application — this is mandatory regardless of planning status.
7. Serve party wall notices — at least 2 months before starting if the work affects shared boundaries.
8. Check for public sewers — Thames Water build-over agreements may be needed.
9. Get quotes from builders — see our guide to extension costs in London for realistic figures.