What Size Extension Under Permitted Development?
Quick Answer
Detached: 8m • Semi/terrace: 6m (single storey rear)
Two-storey: detached 6m, semi/terrace 3m. Subject to prior notification and other conditions
Single-Storey Rear Extension Limits (England)
- Detached house: Up to 8m projection (prior notification required over 4m)
- Semi-detached/terrace: Up to 6m projection (prior notification required over 3m)
- Maximum height: 4m (or eaves height of existing house, whichever is lower)
- Eaves height: Must not exceed 3m if within 2m of a boundary
Two-Storey Rear Extension Limits
- Detached: Up to 6m projection
- Semi-detached/terrace: Up to 3m projection
- Must be at least 7m from the rear boundary
- Ridge height must not exceed existing roof
- Eaves must match existing eaves height
Other Key PD Rules
- Total additions must not exceed 50% of the curtilage (garden) area
- No extension forward of the principal elevation facing a highway
- Materials must be similar in appearance to the existing house
- No balconies, verandas, or raised platforms
- Upper-floor side windows must be obscure-glazed and non-opening (below 1.7m)
When PD Does NOT Apply
- Listed buildings: Listed building consent always required
- Conservation areas: Side extensions and two-storey rear extensions removed
- Article 4 directions: Local authority may remove specific PD rights
- Flats and maisonettes: No PD rights for extensions
- AONB, National Parks, Broads: Reduced limits apply
Always verify with your local planning authority before proceeding. Rules differ in Scotland, Wales, and Northern Ireland.
Last updated: April 2026