Permitted development rights come from the General Permitted Development Order, and the classes most relevant to homeowners are Class A for extensions, Class AA for larger single-storey rear extensions with prior approval, and Class E for outbuildings. Each has its own size, height and positioning limits, and they interact with each other rather than sitting in isolation. This guide sets out the main limits in table form and flags the situations where the rights simply do not apply, so you know when to stop assuming and start checking properly.
Class A: extensions to a house
Class A covers single and two-storey extensions, subject to limits on depth, height and how close they sit to a boundary. The limits differ depending on whether the house is detached or attached (semi-detached or terraced), with detached houses generally getting slightly more generous depth allowances.
| House type | Standard PD depth | Extended PD depth (prior approval) | Max height | Max eaves height near boundary |
|---|---|---|---|---|
| Detached | 4m | 8m | 4m | 3m within 2m of boundary |
| Semi-detached / terraced | 3m | 6m | 4m | 3m within 2m of boundary |
Indicative summary of typical GPDO Class A limits; exact wording and exceptions should be checked against the current order or with the local planning authority before relying on it.
Class A: two-storey extensions
Two-storey rear extensions can fall under permitted development but the limits are much tighter: typically a maximum depth of 3 metres, a requirement to stay a set distance from the rear boundary, and materials that match the existing house. In practice a large number of two-storey rear extensions end up needing a full application because the depth limit is easily exceeded.
Class AA: the larger extension prior approval route
Class AA allows single-storey rear extensions beyond the standard Class A limits, up to 8 metres for a detached house or 6 metres for an attached one, but only through a prior approval process rather than as an automatic right. The council notifies adjoining neighbours, and if a neighbour raises an objection about the impact on their amenity, the council can refuse prior approval even though the same-sized extension might otherwise be permitted development.
- Application submitted to the council with a description and plans
- Adjoining neighbours notified and given 21 days to object
- If no objection, the extension proceeds without further planning input
- If objection is raised, the council assesses impact on neighbouring amenity only, not general planning merits
Class E: outbuildings
Class E covers detached garden rooms, garages and outbuildings incidental to the enjoyment of the house. They must not be forward of the principal elevation, are limited in height depending on roof type and proximity to boundaries, and cannot together with other outbuildings cover more than half the garden. A garden room used as self-contained living accommodation, rather than incidental use like a home office or gym, falls outside this class.
Article 4 directions
An Article 4 direction removes some or all permitted development rights across a defined area, usually to protect the character of a conservation area or estate. Where one applies, works that would normally be permitted development need a full planning application instead. Article 4 directions are set by the local authority and are checked via the council's planning pages or a direct enquiry, not by looking at the house itself.
Conservation areas and listed buildings
Conservation area status does not remove all permitted development rights automatically, but it does reduce some allowances, particularly for side extensions, cladding materials and roof alterations, and it often triggers additional consent requirements such as conservation area consent for demolition. Listed buildings are a separate and stricter regime again, where almost any alteration, internal or external, needs listed building consent regardless of size.
Getting certainty
Because permitted development rights are self-assessed until challenged, the only way to have a legally reliable answer is a lawful development certificate from the council, confirming the specific proposal is lawful. It is not compulsory, but it protects you if a neighbour queries the works or if a buyer's solicitor asks for evidence later.
Getting it wrong: what enforcement looks like
If you build under an assumed permitted development right that turns out not to apply, the council can serve an enforcement notice requiring the work to be altered or removed, and in the meantime the extension is unauthorised development. Enforcement action generally has to be taken within four years for operational development, but that is not a reason to take the risk deliberately; a wrongly built extension is disruptive and costly to correct, and mortgage lenders and buyers' solicitors will ask questions if the paper trail does not stack up.
Selling a house with permitted development work
When you come to sell, a conveyancing solicitor will typically ask for evidence that any extension or outbuilding was either granted planning permission or genuinely fell within permitted development at the time it was built. Without a lawful development certificate, that evidence can be difficult to reconstruct years later, particularly if the rules have since changed. Keeping dated photographs, measurements and a copy of the relevant GPDO class from the time of build is a cheap form of insurance against a stalled sale down the line.