A First Principles Guide to Permitted Development
Don't guess. Understand the official rules for your property type to see if your extension qualifies for permitted development, or if you need planning permission.
Permitted Development Rules by Property Type
Select your property type to see the specific Class A permitted development rules based on the official UK government technical guidance.
Single-Storey Rear Extension
- Depth: Max 4m (or 8m with prior approval)
- Height: Max 4m
Two-Storey Rear Extension
- Depth: Max 3m
- Rear Boundary: Must be >7m from boundary
Side Extension
- Storeys: Single storey only
- Height: Max 4m
- Width: Max 50% of original house width
Video Guide: Coming Soon
A detailed video guide for detached houses is on its way.
Single-Storey Rear Extension
- Depth: Max 3m (or 6m with prior approval)
- Height: Max 4m
Two-Storey Rear Extension
- Depth: Max 3m
- Rear Boundary: Must be >7m from boundary
Side Extension
- Storeys: Single storey only
- Height: Max 4m
- Width: Max 50% of original house width
Video Guide: Coming Soon
A detailed video guide for semi-detached houses is on its way.
Single-Storey Rear Extension
- Depth: Max 3m (or 6m with prior approval)
- Height: Max 4m
Two-Storey Rear Extension
- Depth: Max 3m
- Rear Boundary: Must be >7m from boundary
Side Extension
- Not applicable under PD
Single-Storey Rear Extension
- Depth: Max 4m (Detached) or 3m (Attached)
- Height: Max 4m
Roof Additions / Loft Conversion
- Generally requires planning permission as it changes the nature of the dwelling from a single-storey property.
Side Extension
- Storeys: Single storey only
- Height: Max 4m
- Width: Max 50% of original house width
Video Guide: Coming Soon
A detailed video guide for bungalows is on its way.
Essential Viewing: Do You Have PD Rights?
This video explains how to check for restrictions like Article 4 directions which can remove your permitted development rights.
General Conditions for All Extensions (Class A)
Location & Siting
- No extension forward of the principal elevation.
- No extension forward of a side elevation fronting a highway.
- Total extensions/buildings must not exceed 50% of curtilage.
Height & Eaves
- Extension height cannot exceed existing roof height.
- Extension eaves cannot exceed existing eaves height.
- Within 2m of a boundary, max eaves height is 3m.
Design & Materials
- Materials must be of similar appearance to the existing house.
- Side-facing upper-floor windows must be obscure-glazed.
- Two-storey extensions: roof pitch must match existing.
- Verandas, balconies, and raised platforms are not permitted.
This is a simplified summary based on the Town and Country Planning (General Permitted Development) (England) Order 2015. Always consult the official guidance or your local planning authority. Article 4 directions or other restrictions may apply.
Planning Permission vs Permitted Development
Direct comparison of the two routes to help you choose the right approach for your extension.
| Aspect | Permitted Development | Planning Permission | Advantage |
|---|---|---|---|
| Application Time | 6 weeks (Prior Approval) | 8+ weeks (often 12-16 weeks) | PD |
| Application Cost | £192 (Prior Approval fee) | £462 (Householder application) | PD |
| Design Flexibility | Highly restricted | Design freedom within policy | Planning |
| Size Limits | Strict maximum sizes | Case-by-case assessment | Planning |
| Neighbour Consultation | Automatic (21 days) | Formal consultation (21 days) | Equal |
| Success Rates | 85% (if conditions met) | 65% (London average) | PD |
Key Insight
While PD rights offer faster, cheaper approvals, most meaningful extensions exceed the size limits. Planning permission provides design freedom and often delivers better long-term value.