Introduction
One of the most common questions homeowners ask before starting an extension project is: do I need planning permission? The answer depends on the size and type of extension, the type of property, and whether any restrictions apply to your specific address. This guide gives a plain-English overview of when planning permission is and isn't required for a house extension in England.
What Are Permitted Development Rights?
Permitted Development (PD) rights allow certain types of building work to be carried out without needing to apply for planning permission. They're set out in the Town and Country Planning (General Permitted Development) Order and apply across England — though they can be restricted or removed in certain areas. Most single-storey rear extensions can be built under PD rights, subject to size limits. Double-storey extensions, first-floor extensions, and most side extensions require planning permission.
Single-Storey Rear Extensions
Under Permitted Development, you can add a single-storey rear extension without planning permission if it meets all of the following: it doesn't exceed 3 metres in depth from the original rear wall for terrace or semi-detached houses (or 4 metres for detached houses); it doesn't exceed 4 metres in height; its roof pitch and materials are similar to the existing house; it's not forward of the principal elevation; and the total area of all extensions doesn't exceed 50% of the original garden area. Extensions up to 6 metres (terrace/semi) or 8 metres (detached) in depth can be built under a prior approval process — you notify the council, they consult neighbours, and issue or refuse prior approval. This is not full planning permission but is a formal process with a fee.
Double-Storey Extensions
Double-storey rear extensions nearly always require planning permission. PD rights for double-storey extensions require that they are not within 7 metres of the rear boundary, don't exceed the height of the existing roof, are not within 2 metres of the side boundary, and have a pitch that matches the main house. In most London back garden situations, the 7-metre setback from the rear boundary rules out double-storey rear extensions under PD — these almost always need a planning application.
Side Extensions
Side extensions require planning permission in most cases. PD rights for side extensions exist but are limited: the extension must not exceed half the width of the original house, must not be forward of the principal elevation, and must have no first floor element above the side. In practice, most side extensions in London require a planning application.
When PD Rights Are Removed
PD rights can be removed or restricted in several circumstances. In conservation areas, PD rights are restricted and side extensions always require planning permission. Where a local council has issued an Article 4 Direction, it removes some or all PD rights — many London boroughs have Article 4 Directions covering parts of their residential areas. Listed buildings have no PD rights at all. And a condition on a previous planning permission may have removed PD rights for a specific property.
How to Check for Your Property
Before assuming PD rights apply: check whether your postcode is in a conservation area (your council's planning portal will show this); check whether an Article 4 Direction applies to your area; check previous planning permissions on your property for conditions that restrict PD; and consider applying for a Lawful Development Certificate — a formal confirmation from the council that your proposed works are lawful under PD rights, providing documentary evidence useful when you sell. RCB Design & Build advises on planning position as part of our pre-construction process. Contact us to discuss your extension project.