Do you need planning permission for an extension?
28 Aug 2026
Not every extension needs full planning permission. A lot of common single-storey rear extensions fall under permitted development rights in England, which let you build without a full planning application - but the limits are specific, and it's easy to assume you're covered when you're not.
Do you need planning permission for a single storey extension?
Often not, provided it stays within permitted development limits. As a rough guide (rules differ for flats, listed buildings, and conservation areas, and have changed over time, so always verify current rules for your property):
- A single-storey rear extension is commonly allowed up to 3m beyond the rear wall for a terraced or semi-detached house, or 4m for a detached house, without needing planning permission.
- Under the "larger home extension" prior approval scheme, those limits extend to 6m (terraced/semi-detached) or 8m (detached) - but this route requires notifying your neighbours via the council and waiting out an objection period before building, rather than a full planning application.
- Height limits typically apply too - commonly around 4m maximum for a single-storey rear extension, and no higher than 4m within 2m of a boundary.
- Materials are generally expected to be similar in appearance to the existing house.
- Side extensions and two-storey extensions have their own, generally stricter, limits.
When do you need full planning permission for an extension?
- You're in a conservation area, an Area of Outstanding Natural Beauty, or your building is listed.
- The extension exceeds permitted development size or height limits above.
- Your property is a flat or maisonette - permitted development rights for extensions generally don't apply.
- A previous extension has already used up your permitted development allowance.
Get it confirmed, don't assume it
Even where permitted development likely applies, it's strongly worth getting a Lawful Development Certificate from your local council - a formal, low-cost confirmation that protects you if a neighbour complains or you come to sell the house later. An experienced local builder or architect will usually have a good instinct for whether your plans are within permitted development limits, but the council's confirmation is the only thing that removes doubt entirely.
Once you know roughly what you're planning, our extension cost calculator gives a ballpark estimate, and you can post the job free to hear from builders who work in your area.
Frequently asked questions
Do I need planning permission for a single storey rear extension?
Usually not if it stays within the 3m/4m permitted development limits (or 6m/8m under the larger home extension scheme) - but always check for conservation area, listed building, or flat/maisonette restrictions first.
When do you need planning permission for an extension?
As soon as your plans exceed permitted development size, height, or boundary limits, or your property type or location (flats, listed buildings, conservation areas) removes permitted development rights entirely.
Is a Lawful Development Certificate the same as planning permission?
No - it's formal confirmation that a project doesn't need planning permission because it falls within permitted development. It's optional but strongly recommended, since it removes any doubt if a neighbour complains or you sell the house later.
Ready to get started?