Do I Need Planning Permission for a Rear Extension?

"Do I need planning permission for my extension?" – I get asked this question at least twice a week. The short answer is: probably not, if you're building a single-storey rear extension within certain size limits. But the rules are more complicated than most people realise, especially in London where conservation areas and Article 4 directions affect large parts of many boroughs.

Permitted Development Rights: The Basics

Permitted Development (PD) is a national grant of planning permission for certain types of building work. For rear extensions, it means you can build without making a planning application – as long as you stay within the limits.

Here are the key limits for single-storey rear extensions:

There are other conditions too: the extension must be single storey, materials should be similar to the existing house, no verandas, balconies or raised platforms, and the extension can't be forward of the principal elevation facing a highway.

The Prior Approval Route: 4-6 Metres

If you want to build between 3-6 metres on a terrace (or 4-8 metres on a detached house), you can still avoid full planning permission by using the Prior Approval process – sometimes called the "neighbour consultation scheme."

Here's how it works:

• You submit a Prior Approval application to your council (£120 fee)
• The council writes to your immediate neighbours giving them 21 days to comment
• The council then has 42 days to decide
• If no objections, or objections are considered unreasonable, you get approval
• If there's no decision within 42 days, you can proceed anyway (deemed approval)

The council can only consider the impact on the amenity of adjoining properties – they can't refuse because they don't like the design. This makes it much harder to refuse than a full planning application.

Important note: the Prior Approval route was set to expire in 2024 but has been extended. However, it doesn't apply in conservation areas, so check before you rely on it.

When You Definitely Need Full Planning Permission

No matter how small your extension, you'll need to submit a full planning application if:

• You're in a conservation area: Much of inner London falls into conservation areas – large chunks of Islington, Hackney, Camden, Kensington, Westminster, and others. Side extensions and any extension that would be visible from the street typically need planning.
• Your property is listed: Listed buildings need Listed Building Consent for almost any alteration, internal or external. This is a separate application from planning permission.
• There's an Article 4 direction: Some councils have removed PD rights for specific areas. Common in London for things like window changes and front gardens.
• You're building a two-storey extension: Two-storey rear extensions always need planning permission, even if they're modest.
• You want to exceed PD limits: Going over 4m high, more than 50% garden coverage, or deeper than allowed.
• You're on a corner plot: Extensions visible from a side road often need planning.

Conservation Areas: What's Actually Different?

In a conservation area, your PD rights are restricted. You can still build under PD, but with tighter limits:

• No cladding of any kind
• No side extensions without planning
• Extensions that would be visible from a public highway need planning
• The Prior Approval larger extension route doesn't apply

The good news? Rear extensions that aren't visible from a public road or footpath can still proceed under PD, up to the normal 3m/4m limits. Most London terraces have their rear gardens screened by fences and other houses, so you can often still build without planning.

If you do need planning permission in a conservation area, expect more scrutiny. Conservation officers will want materials to match existing, appropriate window proportions, and a roof design that respects the character of the area. It's worth getting an architect who knows your borough.

Getting a Lawful Development Certificate

Even if your extension falls within PD, I strongly recommend getting a Lawful Development Certificate (LDC). This is an official document from the council confirming that your proposed work is lawful.

Why bother? Several reasons:

• Proof for buyers: When you sell, the buyer's solicitor will ask for evidence that extensions were built legally. An LDC is the gold standard.
• Certainty before you build: If you've misunderstood the rules, better to find out before you've spent £60,000.
• Council confirmation: The council formally confirms your interpretation of PD rights is correct.

An LDC application typically costs £103-258 depending on the council, and takes 6-8 weeks. You'll need drawings showing what you propose to build. It's a fraction of the cost of a full planning application and gives you peace of mind.

What If Neighbours Object?

This is a common worry, but it's important to understand: if you're building under Permitted Development (not Prior Approval), neighbours have no legal right to object. PD is a right granted by Parliament – your neighbours can't override it.

That said, you'll still need to comply with the Party Wall Act if you're building within 3 metres of a neighbour's wall, or up to/on the boundary. This means serving notice and potentially paying for a surveyor if they request one. It's a separate process from planning.

My advice? Even though you don't legally need to, it's worth talking to your neighbours before you start. Show them the plans, explain the timeline, reassure them about noise and disruption. A bottle of wine when work starts goes a long way. Most neighbour disputes I've seen come from lack of communication, not the actual building work.

Quick Decision Flowchart

Here's how I work out whether clients need planning permission:

• Is it a listed building? → Full planning + Listed Building Consent
• Is it in a conservation area and visible from the street? → Full planning
• Is there an Article 4 direction? → Check what it covers, probably full planning
• Is it a two-storey extension? → Full planning
• Is it 3m or less (attached) / 4m or less (detached) and within all other PD limits? → No planning needed (get LDC)
• Is it 3-6m (attached) / 4-8m (detached) and not in conservation area? → Prior Approval route
• Anything else → Probably needs full planning