You've decided to extend out the back. Maybe it's a new kitchen-diner. Maybe it's a bigger living space that opens onto the garden. Whatever the plan, there's a question hanging over the whole project: will the council say yes?
We can't guarantee the outcome of any individual application. But we can tell you what the data says — and the data is extensive.
PlanningLens has analysed over 2,500,000+ planning decisions from 226 UK councils. Here's what we found about rear extensions specifically.
The National Success Rate
Rear extensions are among the most commonly approved project types in UK planning. The vast majority of applications that go to a decision are approved.
That's partly because rear extensions have less impact on the street scene than front or side extensions. They're also one of the most well-understood project types — planning officers deal with them constantly, and there's usually strong local precedent.
But the national figure is an average. And averages can mislead.
Council-Level Variation Is Significant
When we break the data down by council, the picture gets more interesting. Some councils approve rear extensions at rates above 95%. At these councils, refusal is genuinely rare — you'd need to propose something significantly problematic to get a no.
Other councils sit below 80% — even for rear extensions. That means one in five applications is refused. If you're in one of these areas, preparation matters far more.
The gap between the most permissive and most restrictive councils for rear extensions is over 20 percentage points. That's not noise — it's a fundamentally different planning environment.
See the full breakdown: Rear Extension Approval Rates by Council
What Separates Approved From Refused
When a rear extension gets refused, the reasons tend to cluster around a few themes.
Depth. Going too far back into the garden — particularly on terraced or semi-detached houses where neighbours are close — is the most common trigger for refusal. Planning officers apply the "45-degree rule" or similar tests to check whether your extension would unacceptably overshadow a neighbour's windows.
Height. Two-storey rear extensions face considerably more scrutiny than single storey ones. The additional height creates more overlooking, more shadow, and more visual impact. Our data shows two-storey rear extensions have a noticeably lower approval rate than single storey equivalents.
Design. A flat-roofed extension on a Victorian terrace. Render on a brick street. These design mismatches crop up regularly in refusal reasons. Planning officers want extensions to look like they belong.
Cumulative impact. If your property has already been extended — or if you're proposing a rear extension alongside other changes — the combined impact is assessed. A modest rear extension might be fine on its own, but if you're also doing a loft conversion and a side extension, the cumulative effect could push you over the line.
The Ward Effect
Within any given council, rear extension approval rates can vary significantly between wards. Conservation areas typically have lower approval rates. Wards near Green Belt boundaries can be tougher. And some wards simply have a pattern of stricter decision-making, for reasons that aren't always obvious from the outside.
Your council's overall rear extension approval rate is a starting point. But the rate in your specific ward is what actually affects you.
What's the rear extension approval rate in your area?
PlanningLens shows you approval rates broken down by council, ward, and extension type — based on real decisions, not estimates.
Check Your Postcode →How to Use This Data
Knowing the approval rate for rear extensions in your area doesn't guarantee anything about your specific application. But it does something arguably more valuable: it calibrates your expectations and informs your approach.
If your council approves 95% of rear extensions, you can be fairly confident that a well-designed proposal will succeed. Brief your architect accordingly — the pattern is strongly in your favour.
If your council approves 78% of rear extensions, you need to be more careful. Look at what's been refused nearby. Understand the pressure points. Consider going slightly smaller or more conservative than your ideal — because a first-time approval saves you months and thousands of pounds compared to a refusal and redesign.
The smart money isn't on hoping for the best. It's on knowing the landscape before you commit.
Check the approval rate in your council →
The Bottom Line
Rear extensions have strong approval rates nationally. The odds are in your favour. But "the odds are in your favour" and "your application will definitely be approved" are two very different statements.
The difference between homeowners who sail through planning and those who don't usually comes down to preparation. Understanding what your council approves, what it refuses, and where the boundaries are.
That's what PlanningLens is for. Over two million decisions. 226 councils. Broken down by extension type, ward, and refusal pattern. All starting from a postcode.
Free Postcode Check
See rear extension approval rates, comparable decisions, and refusal patterns near your property. Takes 10 seconds.
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