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Do I Need Planning Permission for an Extension? UK 2026 Guide

Bhavesh Ramburn

Do you need planning permission for an extension?

Short answer: It depends. Most extensions are Permitted Development under the Town and Country Planning (General Permitted Development) (England) Order 2015 (the GPDO), meaning planning permission is not required. But several common scenarios push a project outside Permitted Development, requiring a full planning application to your Local Planning Authority.

Whether you need planning permission depends on four factors:

  1. The location of the extension (rear, side, front, or wraparound).
  2. The size of the extension (volume, footprint, height, ridge height).
  3. The relationship to the principal elevation of the original house.
  4. Local restrictions (Conservation Area, Area of Outstanding Natural Beauty / National Landscape, Article 4 Direction, listed building, the original house’s Permitted Development “original dwelling” status).

For the broader context, see our Permitted Development Rights in 2026 guide and our householder planning permission guide.

Rear extensions under Permitted Development

A single-storey rear extension is the most common extension type and is Permitted Development under Class A, Part 1, Schedule 2 of the GPDO 2015, subject to the following limits:

  • The extension must not extend more than 4 metres beyond the rear wall of the original dwelling if it is a detached house.
  • The extension must not extend more than 3 metres beyond the rear wall if it is a terraced or semi-detached house.
  • The extension must not exceed 4 metres in height (or 3 metres if within 2 metres of a boundary).
  • The extension must not exceed 50% of the curtilage of the original dwelling (taking the extension together with any other outbuildings).
  • The extension must be built in materials of similar appearance to those of the original dwelling.

Where any of these limits is exceeded, planning permission is required.

For neighbour consultation under the Neighbour Consultation Scheme (introduced in 2024), the LPA must notify adjoining neighbours of a proposed larger rear extension under the 8-metre / 6-metre prior approval procedure.

Side extensions under Permitted Development

A side extension is Permitted Development under Class A of the GPDO 2015, subject to the following limits:

  • The extension must not extend more than half the width of the original dwelling.
  • The extension must not be forward of the principal elevation of any neighbouring house.
  • The extension must not exceed 4 metres in height (or higher if hipped).
  • The materials must match the original dwelling.

The single-storey 4-metre limit that applies to rear extensions does not apply to side extensions. A side extension can be 2-storey or even 3-storey, subject to the height limits and the 50% curtilage test.

For a side extension that exceeds the width or height limits, planning permission is required.

Front extensions under Permitted Development

A front extension is rarely Permitted Development. Under Class A, Part 1 of the GPDO 2015, an extension is Permitted Development only if it does not extend forward of the principal elevation of the original dwelling. This means that a true front extension (extending forward of the existing front wall) almost always requires planning permission.

The “principal elevation” is the elevation of the original dwelling that faces the road. Where the road is at the front of the house, the principal elevation is the front. Where the road is at the side or rear (a common arrangement on corner plots), the principal elevation is the road-facing side.

For a front porch, a narrow exemption applies under Class D of the GPDO 2015:

  • The porch must be single-storey.
  • The porch must have a floor area not exceeding 3 m².
  • The porch must be at least 2 metres from any boundary with a road.

Where a porch satisfies all three criteria, no planning permission is required. Most porches are Permitted Development. A larger porch (more than 3 m²) requires planning permission.

For more on porches and front extensions, see our householder planning permission guide.

Wraparound extensions under Permitted Development

A wraparound extension combines a rear extension and a side extension into a single L-shaped structure. Whether it is Permitted Development depends on which Class the extension falls under:

  • Single-storey wraparound extensions can fall within Class A, but the test is more nuanced because the extension extends beyond both the rear wall and the side wall. The 4-metre / 3-metre rear extension limit applies to the rear part; the half-width limit applies to the side part. Both must be satisfied.
  • Two-storey wraparound extensions are rarely Permitted Development because the Class A height limit (4 metres) is breached.

Most two-storey wraparound extensions require planning permission. A planning consultant or architect can advise on the specific dimensional limits.

Conservation Areas and Permitted Development rights

In a Conservation Area, Permitted Development rights are more restricted under Class A, Part 1 of the GPDO 2015:

  • An extension of any size to a single-storey property is permitted, but the volume limit (115 m³ for terraced/semi, 70 m³ for detached) applies.
  • An extension to a two-or-more-storey property must not exceed the volume of the original dwelling.
  • The materials must match the original dwelling.
  • The extension must not extend forward of the principal elevation.

For a substantial enlargement of a dwelling in a Conservation Area, prior approval of the LPA is required under Class A. The LPA must consider the impact on the Conservation Area.

Many LPAs have removed Permitted Development rights for extensions in Conservation Areas via Article 4 Directions. Where an Article 4 Direction is in force, planning permission is required for any extension.

For more on Conservation Areas, see our Permitted Development Rights in 2026 guide and our householder planning permission guide.

National Landscapes (formerly AONBs) and Permitted Development rights

In an Area of Outstanding Natural Beauty (AONB) — renamed National Landscape in England by the Levelling Up and Regeneration Act 2023 — the same Permitted Development limits apply, but the LPA is required to give greater weight to the conservation of landscape beauty. This can effectively limit the size and design of any extension in a National Landscape.

In a National Park (e.g. the Lake District, Peak District, Snowdonia / Eryri, Dartmoor, Exmoor, the Yorkshire Dales, the North York Moors), planning permission is always required for extensions because the National Park Authority is the LPA and applies its own planning policies.

For more on the National Landscape and National Park regimes, see our Permitted Development Rights in 2026 guide.

Article 4 Directions and Permitted Development rights

An Article 4 Direction is a planning instrument issued by the LPA that removes specific Permitted Development rights from a defined area. Article 4 Directions are commonly used in Conservation Areas, in town centres, in areas of special architectural or historic interest, and in areas where the character is at risk of being eroded by incremental development.

Where an Article 4 Direction is in force that affects extensions, planning permission is required for any extension. The LPA must serve notice on the affected owners and the Direction must be confirmed by the Secretary of State (now the Secretary of State for Levelling Up, Housing and Communities) before it takes effect.

Article 4 Directions must be made in line with the 2015 GPDO and the Town and Country Planning (Compensation for the Withdrawal of Permitted Development Rights) Regulations 2015, which provide compensation rights to owners where Permitted Development rights are withdrawn.

For more on Article 4 Directions, see our Permitted Development Rights in 2026 guide.

Listed Buildings and Permitted Development rights

A listed building is a building of special architectural or historic interest that is included on the statutory list maintained by Historic England (or by the equivalent authority in Wales — Cadw — Scotland — Historic Environment Scotland — and Northern Ireland — the Department for Communities).

For a listed building, Permitted Development rights do not apply. Planning permission and Listed Building Consent are both required for any extension, even a small one. The Listed Building Consent application is decided separately from the planning application and is concerned with the impact on the special interest of the building.

For more on listed building consent, see our Permitted Development Rights in 2026 guide.

What if planning permission IS required?

Where an extension is outside Permitted Development, planning permission is required. The process is:

  1. Pre-application advice (optional). Most LPAs offer a paid pre-application advice service, where you submit your proposal in confidence and receive written feedback.
  2. Application submission. Submit the planning application via the Planning Portal, with the required drawings, the application form, and the application fee.
  3. Validation. The LPA validates the application, ensuring it is complete.
  4. Public consultation. The LPA advertises the application by site notice and neighbour letter. The public has 21 days to comment.
  5. Determination. The planning officer (or, for major applications, the planning committee) determines the application. The statutory determination period is 8 weeks for householder applications.
  6. Decision. The LPA issues a decision notice (approval, approval with conditions, or refusal).
  7. Appeal. If refused, an appeal can be made to the Planning Inspectorate in Bristol.

For the broader planning-permission process, see our householder planning permission guide and our UK Planning Appeals guide.

Common scenarios and whether planning permission is required

Scenario Planning permission required?
4 m single-storey rear extension, semi-detached house Generally no — Permitted Development under Class A
3 m two-storey rear extension Generally no — Permitted Development under Class A
5 m rear extension, detached house Yes — exceeds the 4 m limit
Wraparound extension that breaches the 50% curtilage rule Yes — exceeds the curtilage limit
Front extension Yes — front extensions are not Permitted Development
Side extension extending more than half the width Yes — exceeds the half-width limit
Side extension within half the width and 4 m height Generally no — Permitted Development under Class A
Any extension in a Conservation Area with an Article 4 Direction Yes — Article 4 removes PD rights
Any extension to a listed building Yes — Listed Building Consent and Planning Permission required
Any extension in a National Park Yes — National Park Authority is the LPA
Front porch under 3 m² and over 2 m from road No — Permitted Development under Class D
Front porch over 3 m² Yes
Two-storey side extension over 4 m height Yes

For more on the specific PD tests, see our Permitted Development Rights in 2026 guide.

How to check if your extension is Permitted Development

There are several ways to check whether your extension is Permitted Development:

  • DIY PD check. Walk through the Class A test in the GPDO 2015 and the Schedule 2 limits. Most extensions can be checked by hand.
  • Planning Portal PD checker. The Planning Portal hosts an interactive Permitted Development checker that walks through the test step by step.
  • Pre-application enquiry to your LPA. Most LPAs offer a paid pre-application advice service.
  • Independent planning consultant. A chartered planning consultant registered with the RTPI can review the proposal and confirm whether planning permission is required.
  • Certificate of Lawfulness application. Submit a Lawful Development Certificate (LDC) application to your LPA. The LPA will issue a certificate confirming whether the extension is Permitted Development. The fee is typically half the full planning application fee.

The LDC route is the most secure option where the position is unclear, and is often used by homeowners to confirm the position before starting work.

For more on Lawful Development Certificates, see our Permitted Development Rights in 2026 guide.

Next steps and resources

Editorial note. This article is for guidance only and does not constitute regulated advice. The GPDO 2015 is the primary source of Permitted Development rights for extensions and is regularly updated. Always check the current version of the GPDO before relying on a Permitted Development position, and consider obtaining a Lawful Development Certificate to confirm the position. For project-specific questions, consult a chartered planning professional registered with the Royal Town Planning Institute (RTPI).