Can I Build an Extension Without Planning Permission?
Usually, yes — if your extension is within the permitted development limits set out in Class A of the GPDO 2015.
Most single-storey rear extensions up to 4 metres deep (detached houses) or 3 metres deep (semi-detached and terraced houses) can be built without planning permission. Two-storey rear extensions up to 3 metres deep are also permitted development on detached and semi-detached houses, with additional conditions.
Last updated: April 2026
The key limits
| Rule | Detached | Semi-detached | Terraced |
|---|---|---|---|
| Max depth (single-storey) | 4m | 3m | 3m |
| Max depth (two-storey) | 3m | 3m | Not PD |
| Max depth (prior approval) | 8m | 6m | 6m |
| Max eaves height | 3m | 3m | 3m |
| Max overall height (single-storey) | 4m | 4m | 4m |
| Side extension max width | Half original house | Half original house | Half original house |
| Total site coverage | 50% | 50% | 50% |
For deeper extensions, the Larger Home Extension scheme allows single-storey extensions up to 8m (detached) or 6m (semi/terrace) via prior approval, which costs £249.
For full details on every rule, read our rear extension PD guide and extension depth guide.
When you will need planning permission
You will need planning permission if:
- Your extension exceeds the depth, height, or width limits above
- Your property is a listed building (PD rights do not apply)
- An Article 4 direction removes Class A rights at your address
- You are on designated land (conservation area, AONB, National Park) and want a side extension or two-storey rear extension
- The extension would cover more than 50% of the curtilage (including existing outbuildings and previous extensions)
- The extension extends beyond the principal elevation of the original house
Do not forget
Even if your extension is permitted development and does not need planning permission, you will still need:
- Building regulations approval — always required for extensions. Covers structure, insulation, drainage, fire safety.
- Party wall notices — if you are building within 3–6 metres of a neighbouring structure
- A Lawful Development Certificate — not legally required, but strongly recommended. It costs £274 and proves your extension is lawful when you sell. Read why you need one.
Our PD Certificate Report (£39) gives you a full PD assessment and application checklist tailored to your property and project.
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