Permitted development rear extensions — the complete 2026 guide
Everything architects need to know about Class A permitted development rights for rear extensions — size limits, height rules, the neighbour consultation scheme, and when prior approval is required.
Rear extensions are the most common residential planning project in England, and the permitted development rules that govern them are among the most frequently misapplied. This guide sets out the full Class A framework under the Town and Country Planning (General Permitted Development) (England) Order 2015, as it applies in 2026.
What is Class A permitted development?
Class A of Part 1 of Schedule 2 to the GPDO 2015 grants planning permission for the enlargement, improvement, or alteration of a dwellinghouse. This includes single and double storey rear extensions, side extensions, and loft conversions involving rear dormers. The permission is automatic — no application is required — provided the development complies with all the conditions and limitations set out in the Order.
It is important to note that permitted development rights apply only to dwellinghouses. Flats, maisonettes, and houses converted into flats do not benefit from Class A rights. Properties subject to an Article 4 Direction may also have their PD rights removed in full or in part.
Single storey rear extensions — size limits
The depth limits for single storey rear extensions depend on property type:
| Property type | Standard PD limit | Larger home extension limit* |
|---|---|---|
| Detached house | 4 metres | Up to 8 metres |
| Semi-detached or terraced | 3 metres | Up to 6 metres |
*The larger home extension limits are available under the Neighbour Consultation Scheme (prior approval) and are discussed in detail below.
In addition to depth, single storey rear extensions must not exceed 4 metres in height. The extension must not extend beyond the side elevation of the original dwellinghouse, and must not be forward of the principal elevation.
Two storey rear extensions
Two storey extensions at the rear are permitted development subject to stricter limits. The depth must not exceed 3 metres, and the extension must be no closer than 7 metres from the rear boundary. The roof pitch should, where practicable, match the existing house. Two storey extensions must also not result in any part of the dwellinghouse being closer than 7 metres to the rear boundary of the curtilage.
Height rules for all rear extensions
All extensions must comply with height restrictions. The eaves of an extension must not exceed the eaves of the existing dwellinghouse. The overall height of the extension must not exceed the height of the highest part of the roof of the existing house. For extensions within 2 metres of a boundary, the eaves height is further restricted to 3 metres.
The 50% curtilage rule
The total area of buildings, enclosures, and containers within the curtilage of the original dwellinghouse — excluding the original house footprint itself — must not exceed 50% of the total curtilage area. This includes all extensions, outbuildings, and other structures, whether existing or proposed. Architects must calculate this carefully, particularly on smaller plots.
The Neighbour Consultation Scheme — larger home extensions
Single storey rear extensions exceeding the standard PD depth limits (more than 4m for detached houses, more than 3m for other houses) can still proceed without a full planning application, but they require prior approval under the Neighbour Consultation Scheme (Article 2(12) of the GPDO 2015). This is sometimes called Class A prior approval or a larger home extension.
The procedure
- The developer must notify the LPA before work begins, providing the name and address of the developer, the address of the property, a description of the proposed works, and a plan showing the site and the proposed extension
- The LPA notifies adjoining owners and occupiers, who have 21 days to make representations
- The LPA may only consider the impact on the amenity of adjoining properties — it cannot refuse on design, policy, or other grounds
- The LPA must issue its decision within 42 days of receipt. If no decision is issued within 42 days, prior approval is deemed granted
- Work cannot begin until prior approval is granted or the 42-day period expires
Even where a rear extension is clearly permitted development, many clients benefit from a Lawful Development Certificate (LDC). An LDC provides legal certainty — particularly useful when selling a property, remortgaging, or where a dispute with neighbours is possible. Buildwise generates LDC supporting statements automatically from your permitted development assessment.
Designated areas and Article 4 Directions
Permitted development rights are more restricted in designated areas. In conservation areas, National Parks, AONBs, and the Broads, side extensions are not permitted development and rear extensions may face additional restrictions. Article 4 Directions can further remove or restrict PD rights in specific areas — always check whether an Article 4 is in force before advising a client that works are permitted development.
- Measuring from a rear extension rather than the original house — depth must be measured from the rear wall of the original dwellinghouse, not from any existing extension
- Forgetting that the 50% curtilage limit includes existing outbuildings
- Assuming PD rights apply to converted houses — flats do not benefit from Class A
- Proceeding without checking for an Article 4 Direction or planning conditions that remove PD rights
When a planning application is required
A full householder planning application is required where the proposed extension exceeds the PD limits, is located on designated land where PD rights are restricted, or where an Article 4 Direction or planning condition has removed the relevant rights. In these cases, a Design & Access Statement will typically be required — particularly where the property is in a conservation area or other designated area.
Our guide to Design & Access Statements explains exactly when one is required and what it must contain.
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