Builder Says I Don't Need Planning Permission - Can I Trust That?

Your builder has just told you not to worry about planning permission. "You don't need it for this," they say. "It's all covered under permitted development."

Maybe they're right. Plenty of extensions genuinely don't need planning permission. But here's the thing that should keep you up at night: if they're wrong, it's your problem, not theirs.

You own the property. You're responsible for what's built on it. If the council decides the extension is unlawful, they can issue an enforcement notice - and that means modifying the work or, in the worst case, demolishing it. At your expense.

So let's work out whether your builder actually knows what they're talking about.

What is permitted development?

Permitted development - PD for short - is your automatic right to make certain changes to your property without applying for planning permission. Think of it as a pre-approved set of rules. If your project fits within the limits, you can build without filling in a planning application.

For most single-storey rear extensions, PD covers quite a lot. That's why your builder probably isn't lying. They've built dozens of extensions that didn't need planning permission, and yours might well be the same.

But PD has conditions. Miss one and you're outside the rules.

The permitted development limits (in plain English)

For a single-storey rear extension in England, here are the key limits:

How far it sticks out. No more than 3 metres from the original rear wall if your house is attached (terraced or semi-detached). No more than 4 metres if it's detached. "Original" means the house as it was first built - or as it stood on 1 July 1948. If a previous owner already extended, their extension counts against your allowance.

How tall it is. Maximum 4 metres to the ridge. If any part of the extension is within 2 metres of a boundary (the edge of your property), the eaves (the bottom edge of the roof) can't exceed 3 metres.

How much of the garden it covers. The extension, plus any sheds, outbuildings, and other additions, can't cover more than half your garden. That's half of the total area around the original house, not half of what's left.

What it looks like. Materials must be similar in appearance to the existing house. You can't stick a glass-and-steel box on the back of a Victorian terrace under PD. Well - you can, but it needs planning permission.

No balconies, verandas, or raised platforms. If you want a balcony or raised decking over 30cm above ground level, that needs a planning application.

For a deeper dive into all the rules, our planning permission guide covers everything including two-storey extensions, loft conversions, and outbuildings.

When your builder is probably right

If your project is a straightforward single-storey rear extension on a standard house - semi-detached, not in a conservation area, no listed building complications, within the depth and height limits - then yes, they're almost certainly right. This is bread-and-butter work for most builders. They've done it before and PD covered it.

Common projects that usually fall under PD:

• Single-storey rear extension up to 3m (attached) or 4m (detached)
• Loft conversion with a rear dormer (up to 40m³ for terraced, 50m³ for detached/semi)
• Garage conversion (no external changes)
• Replacing windows and doors (like for like, same openings)
• Internal structural changes (knocking through rooms)
• Garden rooms and outbuildings (single storey, certain size limits)

If your project is one of these and your builder is experienced, they're probably right.

When your builder might be wrong

Here's where it gets tricky. There are situations where PD doesn't apply - and not all builders know about every one of them.

Conservation areas

A conservation area is a zone the council has designated as having special architectural or historic character. The rules are stricter. Side extensions, cladding changes, chimneys, and any alteration visible from a public highway usually need planning permission.

Your builder might not know whether you're in a conservation area. Many homeowners don't either. Check your council's website - most have an interactive map.

Listed buildings

If your property is listed (Grade I, II*, or II), virtually any external or internal change needs listed building consent. This is separate from planning permission and carries criminal penalties if you get it wrong. Your builder might know the house is old. They might not know it's listed.

Article 4 directions

Some councils have issued Article 4 directions - rules that remove your PD rights for specific types of work in specific areas. Your builder almost certainly doesn't know about these. Even some planning consultants miss them. Check with your local planning department directly.

Flats and maisonettes

PD rights for extensions apply to houses, not flats. If you live in a flat or maisonette, you have almost no PD rights for external work. Your builder might not realise this applies to you, especially if the property looks like a house from the outside.

Previous extensions

If a previous owner already extended under PD, their extension eats into your allowance. Your builder might not know the history of the property. If the house has already been extended at the rear by 2 metres, you've only got 1 metre of PD allowance left (for an attached house).

Terraced houses with side returns

Side return extensions (filling in the narrow alley down the side of a terraced house) technically extend towards the side boundary. Some councils treat these differently under PD rules. Your builder might assume it's fine. It might not be.

How to check for yourself

Don't take your builder's word for it. Don't take anyone's word for it. Check.

Option 1: The Planning Portal

Go to planningportal.co.uk and use their interactive tool. It asks you a series of questions about your property and project and tells you whether PD applies. It takes about ten minutes and it's free.

Option 2: Call your council

Ring the planning department at your local council. Explain what you're building and ask whether it falls under permitted development. Most planning officers will give you informal guidance over the phone. It's free and usually straightforward.

Some councils offer a pre-application advice service for a fee (typically £50–£200). This gives you a written response from a planning officer. It's not legally binding, but it's a strong indicator.

Option 3: Get a Lawful Development Certificate

This is the gold standard. A Lawful Development Certificate - an LDC - is an official document from your council confirming that your proposed work is lawful under PD. It costs £103 for a householder application and takes 6–8 weeks.

Why bother? Because when you sell the property, your buyer's solicitor will ask for evidence that extensions were built lawfully. If you've got an LDC, that's the conversation over. If you haven't, they'll dig deeper - and if they find problems, it can delay or derail the sale.

An LDC costs about £103 and protects a project worth tens of thousands. It's worth every penny.

What about building regulations?

Here's the bit your builder definitely should have mentioned. Even if you don't need planning permission, you almost certainly need building regulations approval.

Building regs (sometimes called building control) are the technical standards that make sure your extension is structurally sound, properly insulated, safely wired, and adequately drained. They cover foundations, walls, roof, electrics, plumbing, ventilation, and fire safety.

Planning permission is about whether you can build. Building regulations are about how you build. They're separate processes and you usually need both.

If your builder has told you that you don't need planning permission and also hasn't mentioned building regs, that's a concern. Check that building control fees are included in your quote. If they're missing from the quote altogether, push back and ask why.

Red flags in what your builder tells you

"You don't need any permissions at all." Wrong. You might not need planning permission, but you'll almost certainly need building regulations approval. A builder who conflates the two doesn't understand the system.

"I've done loads of these, never needed permission." Past projects might have been within PD limits. Yours might not be. Each property is different. Each council is different. "I've done it before" isn't a legal argument.

"The council won't check." They might not. Or they might. Councils can - and do - investigate unauthorised work, often years after completion, often triggered by neighbour complaints or when you try to sell. The risk isn't worth it.

"We'll sort it if there's a problem." You'll sort it. It's your property. The builder will be long gone.

What to do right now

If your builder says you don't need planning permission, here's your checklist:

1. Ask them to explain why. Which PD limits does your project fall under? What's the depth? What's the height? If they can't answer specifically, they're guessing.

2. Check the Planning Portal yourself. Ten minutes. Free. No excuse not to.

3. Consider an LDC. £103 and 6–8 weeks. Do it early in the process so it doesn't delay the build.

4. Confirm building regs are covered. Make sure your quote includes building control fees and that the builder plans to notify the council or an approved inspector. A proper quote covers this - here's what to look for.

5. Get your cost estimate from MyBuildAlly to make sure the builder's overall pricing stacks up. If the quote is already missing something as fundamental as planning considerations, there might be other gaps too.

The bottom line

Your builder might be absolutely right. Most rear extensions don't need planning permission and your builder has probably built plenty of them.

But "probably" isn't "definitely." And the consequences of getting it wrong - enforcement action, demolition orders, problems when you sell - are severe enough that spending ten minutes on the Planning Portal or £103 on an LDC is an obvious investment.

Trust your builder's experience. Verify their advice independently. Protect yourself in writing.

Create your free MyBuildAlly account to check that your builder's quote covers everything it should - including the bits they might have forgotten to mention.