Do You Need Planning Permission for an Extension?

Do You Need Planning Permission? A Homeowner’s Guide to Extensions and Renovations

Almost every extension conversation we have with a homeowner starts the same way: “Do we actually need planning permission for this?” It’s a fair question, and it’s usually the first thing standing between an idea sketched on the back of an envelope and a builder on site.

The honest answer is: it depends, and it depends on more than most people expect. So let’s walk through it properly.

The short version

Some extensions can be built under what’s called “permitted development” — a set of national rules that let you build without applying for planning permission, provided you stay within specific limits on size, height and position. Go past those limits, or your property or area has extra restrictions, and you’ll need full planning permission from your local council.

Neither route is better or worse. Permitted development is faster and cheaper to get moving on. Full planning permission takes longer and costs more upfront, but it opens the door to bigger, more ambitious projects. Which one applies to you depends entirely on what you’re building and where.

What counts as permitted development?

For a single storey rear extension in England, the current (as of August 2026) permitted development limits are:

Detached houses: up to 4 metres deep or up to 8 metres deep using the Larger Home Extension Scheme (more on that below)
Semi-detached and terraced houses: up to 3metres deep without prior approval or up to 6 metres with it.
Maximum height; 4 metres overall, dropping to a 3 metre eaves height f the extension sits within 2 metres of a boundary

Side extensions are more tightly limited — generally no wider than half the width of the original house, and capped at the same 4 metre height.

If your extension fits inside those numbers, you may not need planning permission at all. That’s genuinely useful to know before you start sketching, because it changes both your timeline and your budget for professional fees.

The Larger Home Extension Scheme

This is the bit that catches people out. If your single storey rear extension goes beyond the basic permitted development limits (say, 6 metres deep on a detached house) but stays within the larger limits (up to 8 metres), you don’t need full planning permission — but you do need to notify your council, who then give your neighbours 21 days to raise any objections about the impact on their light or privacy. If no one objects, or the council decides the objections don’t hold up, you can proceed.

It’s a genuinely useful middle ground. We’d always rather a client understood this route existed before assuming they either needed nothing or needed full planning — it’s neither, and it can save real time.

When you’ll need full planning permission:

A few things push a project out of permitted development territory altogether, regardless of size:

Two storey extensions have their own, much tighter rules (generally no more than 3 metres deep, and set back at least 7 metres from the rear boundary).
Listed buildings where almost any external change needs listed building consent, separate from planning permission, and this applies even to works that would otherwise be permitted development.
Conservation areas mean permitted development rights are often reduced or removed entirely, particularly for side extensions and anything affecting the front of the property.
Flats and maisonettes permitted development rights for extensions generally don’t apply at all; flats almost always need planning permission.
Article 4 directions— some councils remove specific permitted development rights in particular streets or conservation areas. It’s worth checking with your local planning authority before assuming the standard rules apply.

Building regulations still apply either way!

This trips people up constantly: permitted development permission (or the lack of a need for it) has nothing to do with building regulations. Building regs cover the technical side — structural safety, insulation, fire safety, drainage — and they apply to almost all extension work regardless of whether planning permission was needed. We cover this properly in our building regulations guide, but the short version is: getting the planning question right is only step one.

What happens if you build without checking first?

Every so often we meet a homeowner who’s already started work, or bought a property with an extension that was never properly consented, and wants to know how much of a problem that actually is. It varies, but it’s worth understanding the risk rather than hoping it won’t come up.

If work goes ahead without planning permission when it was needed, the council can serve an enforcement notice requiring the work to be altered or removed — and in England, they generally have up to four years to act on operational development (like an extension) and ten years for a change of use, though this varies by circumstance. Retrospective planning applications are possible, and often successful if the work would have been approved anyway, but they cost time and money, and there’s no guarantee of a favourable outcome. On a listed building, unauthorised works are a more serious matter — listed building consent breaches can be a criminal offence, not just a planning enforcement issue.

If you’re buying a property and something looks like it might not have proper consent — an extension that seems larger than permitted development limits, for instance — it’s worth raising with your solicitor before you complete, not after. Indemnity insurance exists for exactly this situation, but it’s a far better position to know what you’re buying into than to discover it later.

Why pre-applications are your friend:

Before you fall in love with a design, it’s worth getting a straight answer on which route your project sits in. A pre-application enquiry with your local planning authority is inexpensive and gives you a genuine steer, especially for anything borderline. For listed buildings or conservation areas, we’d always get that confirmed before spending money on detailed drawings — redesigning after refusal costs far more than checking first.

This is exactly why meticulous planning sits at the front of how we run every project under our Built Right Method. We’d rather spend an extra week confirming what’s actually achievable than watch a client fall for a design that was never going to get consent.

Your planning permission checklist:

Confirm whether your extension fits within permitted development limits for your property type
Check whether you’re in a conservation area, on a listed building, or subject to an Article 4 direction
If you’re near the permitted development limits, consider the Larger Home Extension Scheme route
Don’t assume building regulations sign-off is automatic just because planning permission wasn’t needed
Get written confirmation from your council for anything borderline — verbal advice isn’t something you can rely on later