Permitted Development Volume Calculator
Check whether a rear extension or loft conversion falls within permitted development volume and height limits, or needs full planning permission.
- Rear Extension
- 3–6 m
- Depth limit
- Loft Volume
- 40–50 m³
- Roof space
- Height Limit
- 4 m
- Single storey
Formula & Statutory Rule
Formula
volume = width × depth × height
Statutory Rule
rear_extension: 3 m terraced, 4 m semi, 6 m detached; loft: 40 m³ terraced, 50 m³ detachedRegional Benchmark Reference
| Jurisdiction / Tier | Rate or Limit | Statutory Note |
|---|---|---|
| Rear extension | 3–6 m | Depth |
| Loft volume | 40–50 m³ | Roof |
| Height | 4 m | Single storey |
Frequently Asked Questions
What is permitted development?
It allows certain extensions and alterations without a full planning application, within set limits.
How deep can a rear extension be?
A single-storey rear extension may extend 3 metres for a terraced house and up to 6 metres for a detached house under prior approval.
How much loft space can I add?
Loft conversions are typically limited to 40 cubic metres for terraced houses and 50 for detached.
Do I need prior approval?
Larger rear extensions require a prior approval application to the local authority.