It’s the first question almost everyone asks us, and the honest answer is: it depends on your house, your plot and what you want to build. This guide explains the main routes, so you know what to ask and what to check.
This is general guidance for houses in England. Rules differ in Wales, Scotland and Northern Ireland, and for flats, maisonettes, listed buildings and homes in conservation areas. The official source is the Planning Portal, and your local council has the final say.
Route 1: Permitted development
Many houses have permitted development rights, which let you build certain extensions without a full planning application. For a single storey rear extension, the broad limits are:
- It can extend up to 3 metres beyond the original rear wall of a semi-detached or terraced house, or 4 metres for a detached house.
- It can be no more than 4 metres high, and lower if it is within 2 metres of a boundary.
- Together with other extensions and outbuildings, it can cover no more than half the land around the original house.
- The materials should be similar in appearance to the existing house.
“Original” means the house as it was first built, or as it stood on 1 July 1948. Earlier extensions count against your allowance.
Some homes have had permitted development rights removed by a planning condition or an Article 4 direction. Check before you assume they apply.
Route 2: Larger home extensions (prior approval)
You can go further, up to 6 metres for semi-detached and terraced houses or 8 metres for detached houses, using the prior approval process. You notify the council, your neighbours are consulted, and the council decides whether the impact on them is acceptable. It is quicker and simpler than full planning, but you must have approval before you start work.
Route 3: Householder planning permission
If your extension is larger, two storeys, at the side or front of the house, or in a protected area, you will usually need a householder planning application. Councils aim to decide these within 8 weeks. Good drawings and an early chat with the neighbours make a real difference.
Lawful Development Certificate: worth it even when you don’t need planning
If you build under permitted development, consider applying for a Lawful Development Certificate. It is official confirmation that the extension was lawful, and buyers’ solicitors often ask for one when you sell.
Building regulations: always needed
Planning permission is about what you build and how it looks. Building regulations are about how it’s built: structure, fire safety, insulation, drainage, ventilation and electrics. Almost every extension needs building regulations approval, whichever planning route you take. You’ll receive a completion certificate at the end. Keep it safe.
The Party Wall Act
If you’re building on or near a shared boundary, or digging foundations close to a neighbour’s, the Party Wall etc. Act 1996 may require you to give your neighbours formal notice. Sort this out early, because it can delay your start date.
How we help
We’ll look at your house, tell you which route is likely to apply, and work with your architect (or introduce one) to get the right approvals in place before a spade goes in the ground. Get in touch for a free site visit.