Rear Extension Permitted Development: Quick Guide
Most single-storey rear extensions can be built without planning permission under Class A of the GPDO 2015. This quick-reference guide covers the key limits at a glance. For a comprehensive deep-dive into every rule, read our full rear extension guide.
Last updated: April 2026
At-a-glance limits
| Rule | Detached | Semi / End-Terrace | Mid-Terrace |
|---|---|---|---|
| Max depth (single-storey) | 4m | 3m | 3m |
| Max depth (prior approval) | 8m | 6m | 6m |
| Max depth (two-storey) | 3m | 3m | Not PD |
| Max eaves height | 3m | 3m | 3m |
| Max overall height (single-storey) | 4m | 4m | 4m |
| Max overall height (two-storey) | Eaves of original house | Eaves of original house | N/A |
| Side extension max width | Half original house width | Half original house width | Half original house width |
| Total site coverage | 50% | 50% | 50% |
Single-storey vs two-storey
Single-storey rear extensions are the most common type and have the most generous PD limits. At 4m (detached) or 3m (semi/terrace), most kitchen-diners and open-plan living spaces can be built without planning permission.
Two-storey rear extensions have tighter rules. The maximum depth is 3m for all house types. The extension must be at least 7m from the rear boundary, cannot be within 2m of a side boundary, and must use matching materials. Terraced houses cannot build two-storey rear extensions under PD.
For larger single-storey projects, the Larger Home Extension scheme allows depths up to 8m (detached) or 6m (semi/terrace) via a prior approval application costing £249.
When you need planning permission instead
You will need planning permission for a rear extension if:
- The depth exceeds the PD limits (including prior approval limits)
- The height exceeds the eaves or ridge limits
- Total extensions and outbuildings cover more than 50% of the curtilage
- Your property is a listed building (PD rights do not apply)
- An Article 4 direction removes Class A rights in your area
- The extension is forward of the principal elevation
- You are building on the side and the extension is more than half the width of the original house
Use our extension depth calculator for an instant check of whether your planned depth is within limits.
Prior approval for larger extensions
The Larger Home Extension scheme allows single-storey rear extensions beyond the standard PD limits via prior approval:
- Detached houses: up to 8m depth
- Semi-detached and terraced: up to 6m depth
Prior approval costs £249 and your council has 42 days to decide. They will notify adjoining neighbours, who have 21 days to comment. The council can only consider the impact on the amenity of adjoining properties — not design, appearance, or planning policy.
If your council does not respond within 42 days, prior approval is deemed to have been granted.
Common mistakes
- Forgetting the "original house" rule — previous extensions by former owners count against your PD allowances. The original house is defined as the house as it was first built, or as it stood on 1 July 1948
- Ignoring the 50% rule — extensions, outbuildings, and any other buildings all count towards the 50% curtilage coverage limit
- Not checking designated land status — if your property is in a conservation area, AONB, or National Park, additional restrictions apply and side extensions are not PD
- Misunderstanding eaves height — the eaves of your extension cannot be higher than the eaves of the original house, even if the ground slopes
- Not serving party wall notices — if your extension is within 3–6 metres of a neighbour’s building, you may need to serve party wall notices under the Party Wall Act
Get planning updates by email
Related guides, tool tips, and planning news — no spam, unsubscribe any time.
Frequently asked questions
Get personalised recommendations for your property
Enter your address to see planning rules specific to your council, any conservation area restrictions, and what you can build without planning permission.
Free check — no account required