Do I Need Planning Permission for My Extension in London? (2026)
The fastest way to find out: use our free AI chat. Here's what determines whether your extension needs planning permission - and how to check in under 2 minutes.
TL;DR - The Quick Answer
Whether your extension needs planning permission depends on three things: (1) what type of extension it is, (2) the size and position, and (3) your specific address. Most single-storey rear extensions qualify as permitted development - no planning needed. But in conservation areas and Article 4 direction zones (which affect Hackney, Islington, Camden, and large parts of inner London), planning permission is required regardless of size. The only way to know for certain is to check your specific postcode.
Does My Extension Need Planning Permission?
| Extension Type | Usually Needs Planning? | Exception |
|---|---|---|
| Single-storey rear (under 3m/4m deep) | No - usually PD | Conservation areas, Article 4 zones |
| Single-storey rear (over 3m/4m deep) | No - Prior Approval | Neighbour objections can block |
| Two-storey rear extension | Yes - almost always | Rarely within PD limits |
| Side extension | Sometimes | Article 4 removes PD in inner London |
| Loft conversion (dormer/Velux) | No - usually PD | Mansards, conservation areas |
| Mansard loft conversion | Yes - always | No permitted development route |
| Basement extension | Yes - always | No permitted development route |
| Outbuilding / garden room | No - usually PD | Over 50% garden covered |
| Porch | No - usually PD | Over 3m² footprint, within 2m of highway |
The most common case - a single-storey rear extension in a standard residential street outside a conservation area - doesn't need planning permission. Most of the complexity comes from London's density of conservation areas and Article 4 directions.
Conservation Areas and Article 4 Directions: London's Key Variable
London has over 1,000 conservation areas - more than any other city in the UK. In these areas, permitted development rights are removed or restricted, meaning planning permission is required for extensions that would otherwise be automatic.
Article 4 directions go further: they remove PD rights on specific streets or areas, even outside conservation areas. Hackney's Stoke Newington and Dalston, Islington, and parts of Camden all have Article 4 directions that require planning permission for rear extensions, loft conversions, and side extensions.
If you're in a conservation area or Article 4 direction zone: you still need to apply for planning permission, but extensions are regularly approved when designed appropriately. It's a process, not a barrier.
How to Check if Your Extension Needs Planning Permission
- Mayfair Studio's free AI chat - enter your address, instantly checks conservation area status, Article 4 directions, listed building status, and TPOs. Takes under 2 minutes. No contact details required.
- Your local council's planning map - search your postcode on the council website to see conservation area boundaries. Doesn't show Article 4 directions clearly.
- Planning Portal's My Property information - some guidance available but not comprehensive for London-specific Article 4 directions.
Mayfair Studio's AI is the fastest and most comprehensive option for London properties - it cross-references multiple planning datasets including conservation areas, Article 4 directions, listed buildings, TPOs, and flood risk zones for your specific address.
What Happens if You Need Planning Permission?
Getting planning permission for a home extension is a routine process - it's not a barrier, just a step. The key facts:
- Householder planning application fee: £258 (standard) or £578 (full planning)
- Determination period: 8 weeks from valid application
- Approval rate: 70–80% in outer London boroughs, 55–65% in conservation area-heavy boroughs
- Well-designed applications with appropriate materials are routinely approved in conservation areas
- Mayfair Studio handles the full planning application as part of its £1,295 fixed fee
Building Without Planning Permission: The Prior Approval Scheme
Even if your extension is too large for standard permitted development, the Prior Approval scheme allows larger rear extensions without full planning permission:
- Terraced and semi-detached houses: up to 6m deep rear extension
- Detached houses: up to 8m deep rear extension
- Single-storey only, maximum 4m high
- Requires neighbour notification period (42 days)
- £120 application fee
- Not available in conservation areas
Most single-storey rear extensions under 3m deep (terraced/semi-detached) or 4m deep (detached) don't need planning permission in London - they qualify as permitted development. But conservation areas and Article 4 directions affect over 40% of London properties and remove these rights. Two-storey extensions and mansard lofts almost always need planning permission. The fastest way to check your specific address is Mayfair Studio's free AI chat - results in under 2 minutes.
Frequently Asked Questions
Do I need planning permission for my extension in London?
It depends on your extension type, size, and location. Single-storey rear extensions under 3m deep (terraced/semi-detached) or 4m deep (detached) typically qualify as permitted development - no planning needed. Two-storey extensions almost always require planning permission. In conservation areas and Article 4 direction zones (affecting 40%+ of London properties), planning permission is required for most extensions regardless of size. Check your specific postcode with Mayfair Studio's free AI tool.
How do I check if my extension needs planning permission in London?
The fastest way: use Mayfair Studio's free AI chat - enter your address and it instantly checks conservation area status, Article 4 directions, listed building status, and your permitted development limits. Takes under 2 minutes, no contact details required. Alternatively: check your local council's planning map for conservation area boundaries, or contact your council's planning department for pre-application advice.
Can I build a home extension without planning permission in London?
Yes - single-storey rear extensions under 3m deep (terraced/semi) or 4m deep (detached) typically qualify as permitted development and need no planning permission. The Prior Approval scheme extends this to 6m or 8m with neighbour notification. However, conservation areas, Article 4 directions, listed buildings, and two-storey extensions require planning permission. Approximately 60% of standard London rear extension projects proceed under permitted development.
What extensions don't need planning permission in London?
Extensions that typically don't need planning permission in London: single-storey rear extensions under 3m deep (terraced/semi) or 4m deep (detached); loft conversions under 40m³ (terraced) or 50m³ volume; outbuildings under 50% garden coverage; porches under 3m². Exceptions: conservation areas, Article 4 directions, and listed buildings remove these rights. Two-storey extensions, mansard lofts, and basements always need planning permission.
What is the penalty for building an extension without planning permission in London?
Building without planning permission when it's required is a planning breach. The council can issue an enforcement notice requiring you to remove or alter the extension within a set period. There is no fine, but you bear the cost of removal or alteration (potentially thousands of pounds). Most enforcement cases arise from neighbour complaints. The 4-year rule means enforcement action cannot be taken more than 4 years after completion - but this doesn't legalise the extension for mortgage or sale purposes.