It depends on the size, position, and type of extension. Many single-storey rear extensions fall under permitted development and don't need planning permission. However, if your extension exceeds certain size limits, is on the front of your property, or you live in a conservation area or listed building, you'll likely need to apply. The rules vary by property type and location.

Permitted development (PD) rights allow you to make certain changes to your property without applying for planning permission. These rights cover many common projects like rear extensions, loft conversions, and outbuildings, but only if they meet specific size and design criteria. Some properties have had their PD rights removed, so you should always check before assuming your project qualifies.

Start by checking whether your property is in a conservation area, an Area of Outstanding Natural Beauty, or is a listed building. These designations often restrict PD rights. You can also check if your local council has issued an Article 4 direction removing specific rights. Your property deeds or a call to your local planning department can confirm your status.

For single-storey rear extensions, you can typically extend 3 metres from the rear wall on an attached house or 4 metres on a detached house under permitted development. Under the Larger Home Extension scheme (with neighbour consultation), this increases to 6 metres and 8 metres respectively. Side extensions are limited to half the width of the original house and must be single storey with a maximum height of 4 metres.

Most loft conversions fall under permitted development if they stay within volume limits (40 cubic metres for terraced houses, 50 cubic metres for detached and semi-detached). However, you'll need planning permission if you extend beyond the existing roof slope facing a highway, raise the roof height, or live in a conservation area or listed building. Dormer windows to the front typically require permission.

If you build without the required permission, your council can issue an enforcement notice requiring you to undo the work or apply retrospectively. Enforcement action can be taken up to 4 years after completion for building works, or 10 years for change of use. When you sell your property, buyers and their solicitors will check for planning compliance, which can delay or collapse sales.

A householder planning application in England currently costs £258. This is a fixed fee set by the government. If your application is refused and you want to appeal, there's no fee for the appeal itself, but resubmitting an amended application is free within 12 months of the original decision. Additional costs may include architectural drawings and supporting documents.

Most householder applications are decided within 8 weeks. More complex applications can take 13 weeks or longer. Your council will validate your application first, which can take 1 to 2 weeks, then consult neighbours and assess the proposal. You can check the progress through your council's planning portal. Delays often occur when additional information is requested.

Neighbours can object to your application, but objections alone don't guarantee refusal. Planning officers assess applications against local planning policies, not popularity. However, valid concerns about overlooking, loss of light, or overbearing impact carry weight. If multiple neighbours raise the same material planning concern, officers will consider this carefully in their assessment.

A Lawful Development Certificate (LDC) confirms that your project falls under permitted development and doesn't need planning permission. It costs £129 and provides legal proof that your work is lawful. While not mandatory, an LDC protects you if rules change and makes selling your property easier, since buyers will have documented proof that the work was compliant.