Do I Need Planning Permission for a House Extension in London?

Most house extensions in London don't need planning permission if they qualify for Permitted Development Rights. A single-storey rear extension can extend up to 3 metres from a terraced or semi-detached house (or 4 metres from a detached house) without planning permission. However, London has many conservation areas and Article 4 Directions that can remove these rights — so always check before you build.

What Are Permitted Development Rights?

Permitted Development (PD) Rights are a set of national planning rules in England that allow certain types of work to be carried out without a full planning application. They are set by the government through the Town and Country Planning (General Permitted Development) (England) Order 2015, and they apply to most residential properties in England.

PD rights exist because the government recognises that minor changes to homes — like modest extensions, loft conversions and outbuildings — should not require local councils to assess each one individually. The rules specify precise limits on size, height, position and materials to ensure that the most common domestic projects can proceed without bureaucratic delay.

For house extensions, PD rights allow homeowners to extend their properties within defined limits. Whether your extension qualifies for PD or requires a full planning application depends on several factors: the size and height of the proposed extension, the type of property, whether it faces a highway, and whether your property is subject to any restrictions that override the national rules.

Permitted Development Rules for Rear Extensions in London

Rear extensions are the most common type of home extension in London, and the permitted development rules for them are relatively straightforward — with some important nuances.

Under the standard PD rules for single-storey rear extensions:

• The extension must not extend beyond the rear wall of the original house by more than 3 metres for a terraced or semi-detached house, or 4 metres for a detached house.
• The maximum height of a single-storey rear extension is 4 metres.
• The extension must not be higher than the highest part of the existing roof.
• The extension must not occupy more than half the garden area of the original house.

House Type	Max Rear Projection (PD)	Max Height
Terraced house	3 metres	4 metres
Semi-detached house	3 metres	4 metres
Detached house	4 metres	4 metres

There is also a Prior Approval / Larger Home Extension scheme that allows single-storey rear extensions of up to 6 metres (terraced/semi) or 8 metres (detached) without full planning permission, provided neighbours are notified and do not object. This scheme requires a Prior Approval application to the local council, but is significantly quicker and cheaper than a full planning application.

At Alstruct, we often advise clients in London to use the Prior Approval route for larger rear extensions — particularly in areas without Article 4 Directions — as it can save several months of waiting time.

Permitted Development Rules for Side Extensions

Side extensions are more restricted under PD rules. A single-storey side extension is permitted development provided:

• The extension is no wider than half the width of the original house.
• The extension does not extend beyond the front wall of the original house.
• The extension is no higher than 4 metres.
• The extension does not face a highway (road, footpath or public right of way).

In practice, the restriction on side extensions facing a highway is significant in London. Many Victorian terraced houses have a side return that faces a side alley or passageway — but if that passageway is a public right of way, you may need planning permission. Always check your property's boundaries and the status of any adjacent paths before proceeding.

Side extensions on corner plots (where the side elevation faces a highway) are not permitted development and will always require planning permission.

Permitted Development Rules for Two-Storey Extensions

Two-storey (double-storey) extensions have stricter PD limits than single-storey extensions:

• The extension must not extend beyond the rear wall of the original house by more than 3 metres.
• The extension must be no higher than the highest part of the existing roof.
• The extension must be set back at least 7 metres from any boundary opposite the rear wall.
• The roof pitch of the extension should match the existing house as far as practicable.
• Any upper floor window in the side elevation must be obscure-glazed and non-opening below 1.7 metres from the floor.

In London, very few double-storey extensions fall within PD limits because the 7-metre setback requirement from the rear boundary is rarely achievable for properties with small gardens. Most double-storey extensions in London will require a full planning application. This is not a barrier — London boroughs grant the majority of compliant double-storey extension applications — but it does add 10–12 weeks to the programme.

When Do You Definitely Need Planning Permission?

Planning permission is always required for a house extension if any of the following apply:

• Your property is a listed building (you also need Listed Building Consent).
• The extension exceeds the PD size limits described above.
• Your property is in a conservation area and the extension would be visible from a highway.
• Your property is subject to an Article 4 Direction that removes PD rights (see below).
• The extension would cover more than half the garden of the original house.
• You are proposing a side extension on a corner plot with a highway-facing elevation.
• The conditions of your original planning permission or a Section 106 agreement have removed PD rights.
• The property is a flat or maisonette rather than a house.

If in doubt, the safest approach is to apply for a Lawful Development Certificate (LDC) — a formal confirmation from the council that your proposed works are lawful as permitted development. While not strictly required, an LDC provides legal certainty and is strongly recommended if you plan to sell the property in the future.

What Is an Article 4 Direction? (London-Specific)

An Article 4 Direction is a formal order made by a local planning authority that withdraws specified permitted development rights from an area or a class of buildings. Where an Article 4 Direction applies, you will need planning permission for works that would otherwise be permitted development — including extensions, roof alterations and changes to materials.

Article 4 Directions are particularly widespread in London, where councils have used them to protect the character of Victorian and Edwardian residential streets. The following London boroughs have extensive Article 4 Direction coverage that affects house extensions:

• Islington — Article 4 Directions cover large parts of the borough, including most Victorian terraced streets. Even modest rear extensions require planning permission in many areas.
• Hackney — Extensive coverage in conservation areas and many residential streets outside them.
• Camden — Article 4 Directions are widespread, reflecting the high density of listed and historically significant streets.
• Lambeth — Covers numerous Victorian conservation areas in Brixton, Clapham and Stockwell.
• Southwark — Strong Article 4 coverage in Dulwich, Bermondsey and Peckham conservation areas.

Other boroughs with significant Article 4 coverage include Lewisham, Wandsworth, Haringey and Hammersmith & Fulham. You can check whether your property is subject to an Article 4 Direction via your council's planning portal or by searching the Planning Portal at gov.uk.

What Is a Conservation Area and How Does It Affect Extensions?

A conservation area is a geographic area designated by a local planning authority as having special architectural or historic interest worth preserving or enhancing. London has hundreds of conservation areas — far more than any other part of England — covering Victorian terraces, Georgian squares, inter-war suburbs and even post-war housing estates.

Living in a conservation area does not prevent you from extending your home, but it does mean additional restrictions apply:

• Any extension visible from a highway or public place will need planning permission, regardless of size.
• Rear extensions that would otherwise be permitted development are restricted: the extension must not result in the total area of extensions exceeding 50% of the garden of the original house.
• External cladding of the house with stone, artificial stone, pebble dash, render, timber, plastic or tiles requires planning permission in a conservation area.
• Some councils have Supplementary Planning Documents (SPDs) for their conservation areas that set out specific design expectations for extensions — materials, windows, roof form and more.

When designing an extension in a conservation area, it pays to engage an architect who understands the local planning context. At Alstruct, our in-house architectural team has extensive experience preparing planning applications in London conservation areas, and we maintain good working relationships with planning officers across the main London boroughs.

How to Check If Your Property Has Permitted Development Rights

There are several reliable ways to determine whether your property has PD rights and whether any restrictions apply:

1. Planning Portal (gov.uk) — The government's interactive guide to permitted development is a useful starting point. It walks you through questions about your property and proposed works to indicate whether planning permission is likely to be needed.
2. Your council's planning portal — Search for your address to see any historic planning applications, conditions and Article 4 Directions affecting your property.
3. Pre-application advice — Most London boroughs offer a formal pre-application advice service (typically £100–£400 depending on the council) where a planning officer will give you written guidance on whether your proposed extension needs permission and what they are likely to require.
4. Apply for a Lawful Development Certificate — If you want legal certainty before starting work, apply for an LDC. This is a formal council determination confirming your works are permitted development. It costs £129 as of 2026 and takes up to 8 weeks.

At Alstruct, we carry out a planning check for every client before we design anything. We review the property, check for Article 4 Directions, conservation area designations and any historic planning conditions, and advise on the best route to consent. This service is included in our free initial consultation.

How to Apply for Householder Planning Permission

If your extension requires full planning permission, the process involves the following steps:

1. Commission architectural drawings. You will need a set of accurate scaled drawings showing the existing property and proposed extension, including floor plans, elevations and a site plan. Our architectural team prepares these as part of our service.
2. Submit the application. Householder planning applications are submitted via the Planning Portal (planningportal.co.uk). The current application fee is £258.
3. Validation. The council checks the application is complete and formally validates it, starting the determination clock.
4. Consultation. Neighbours are notified and have 21 days to submit comments. The planning officer may also consult other departments (highways, conservation, trees).
5. Decision. The planning officer issues a decision notice — approval or refusal — typically within 8 weeks of validation. Approvals are usually subject to conditions.
6. Discharge of conditions. Before starting work, you may need to discharge pre-commencement conditions by submitting information to the council (e.g., material samples, drainage details).

How Long Does Planning Permission Take in London?

The statutory determination period for a householder planning application is 8 weeks from validation. In practice, this is rarely achieved in London.

Most London boroughs take 10–12 weeks. Some — including Islington, Hackney and Southwark — regularly take 14–16 weeks or longer, particularly in conservation areas where the planning officer must consult the council's conservation team. Complex applications, or those where amendments are required, can take longer still.

You can reduce the risk of delays by:

• Submitting a complete application with all required documents on the first attempt.
• Using a pre-application advice service to understand what the council expects before you apply.
• Choosing a builder with experience in your specific borough, who can anticipate local planning officer preferences.
• Avoiding applications during the summer recess (July–August) when planning departments are typically understaffed.

How Alstruct Helps with Planning

At Alstruct, planning is not an afterthought — it is integral to our design and construction process. Our in-house architectural team handles every aspect of the planning journey, from the initial feasibility check through to construction on site.

We have submitted and managed successful planning applications across every major London borough, including in some of the most restricted conservation areas in the city. Our understanding of local planning policy, borough-specific design guidance and planning officer expectations means we consistently achieve planning approval for our clients' projects.

Our planning service includes:

• Initial planning feasibility assessment (free, included in first consultation).
• Architectural drawings prepared to planning specification.
• Planning application submission and fee management.
• Liaison with planning officers throughout the determination period.
• Responding to requests for information or amendments.
• Discharge of planning conditions prior to construction.

Explore our house extension services or view our completed extension projects for examples of our work across London.

Frequently Asked Questions