Permitted Development vs Planning Permission
Understand when you can build under permitted development rights and when you need full planning permission for your London extension.
Quick Facts
London extension statistics
🎯 Most extensions exceed PD limits due to size requirements
Your 30-Minute Decision Process
Follow these four steps to determine whether your extension can use permitted development rights.
Measure Your Extension Plans
Calculate the exact size and height of your proposed extension
Action:
Measure extension footprint, height, and distance from boundaries using your architect's plans.
⚠️ Accurate measurements are crucial - even 1cm over the limits means planning permission is required
Check PD Size Limits
Compare your measurements against permitted development thresholds
Action:
Use our PD calculator below to check if your extension falls within permitted development limits.
⚠️ Terraced house limits are stricter (6m) than detached/semi-detached (8m)
Verify All PD Conditions
Ensure your extension meets ALL permitted development requirements
Action:
Check every condition in our comprehensive checklist - missing one invalidates PD rights.
⚠️ Common failures: height limits, boundary distances, roof pitch restrictions
Choose Your Application Route
Decide between PD, Prior Approval, or full Planning Permission
Action:
If all PD conditions met, proceed with Prior Approval. If not, prepare Planning Permission application.
⚠️ Prior Approval takes 6 weeks vs 8+ weeks for Planning Permission
Permitted Development Size Limits
Maximum extension sizes allowed under Class A permitted development rights by house type.
Terraced House
Single Storey:
6m from original rear wall
Two Storey:
3m from original rear wall
Height:
Max 4m high (single storey), 6m (two storey)
Width:
Cannot extend beyond side walls
📝 Most restrictive category - often requires planning permission
Semi-Detached House
Single Storey:
8m from original rear wall
Two Storey:
6m from original rear wall
Height:
Max 4m high (single storey), 6m (two storey)
Width:
Cannot extend beyond side walls
📝 More generous limits than terraced properties
Detached House
Single Storey:
8m from original rear wall
Two Storey:
6m from original rear wall
Height:
Max 4m high (single storey), 6m (two storey)
Width:
More flexibility on side extensions
📝 Best chance for permitted development compliance
Complete PD Conditions Checklist
Your extension must meet ALL conditions to qualify for permitted development rights. Missing one means planning permission is required.
Size & Height Limits
- Single storey: max 4m high, 6m/8m depth (terraced/other)
- Two storey: max 6m high, 3m/6m depth (terraced/other)
- Side extension: max 4m high, 50% of original house width
- Cannot extend beyond front wall of original house
⚠️ Common failure: 65% of extensions exceed size limits
Boundary & Neighbour Rules
- Min 2m from any boundary (or build on boundary)
- Cannot overlook neighbours within 21m
- Side windows must be obscure glazed below 1.7m
- Roof terraces/balconies not permitted under PD
⚠️ Common failure: 40% fail on boundary distances
Design & Materials
- Materials must match or be sympathetic to existing house
- Roof pitch must match existing (if applicable)
- No front extensions under Class A PD
- Cannot create separate dwelling
⚠️ Common failure: 25% fail on design requirements
Location Restrictions
- Article 4 directions may remove PD rights
- Conservation areas have additional restrictions
- National parks and AONBs have stricter rules
- Listed buildings cannot use PD rights
⚠️ Common failure: 30% in London affected by Article 4 directions
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.
Why Most Extensions Need Planning Permission
Understanding why 65% of London extensions require planning permission helps set realistic expectations.
Size Exceeds PD Limits
65%Most meaningful extensions go beyond permitted development size thresholds
Reality: Kitchen-diners typically need 6-8m depth, but terraced houses limited to 6m max
Design Ambitions
45%Architectural features and contemporary design require planning permission
Reality: Roof lights, bi-fold doors, modern materials often fall outside PD scope
Two-Storey Extensions
80%Two-storey extensions rarely comply with strict PD depth limits
Reality: PD allows only 3m depth for terraced, 6m for others - usually insufficient
Conservation Areas
30%Conservation areas and Article 4 directions restrict PD rights
Reality: Many London boroughs have Article 4 directions removing PD rights
The Bottom Line
While permitted development rights can work for simple, small extensions, most homeowners need the design freedom and size flexibility that only planning permission provides.