Thousands of UK homeowners build extensions, outbuildings, and conversions every year without ever applying for planning permission. Some of them are perfectly within the law. Others are unknowingly exposed to enforcement action — and they have no idea.
The problem is that most homeowners can't tell which camp they're in. The rules around what counts as permitted development are complex, and whether your build qualifies depends on factors that aren't always obvious. That's exactly why WhatCanIBuild exists — to give you a clear, property-specific answer instead of a guess.
The short version
- Building without permission isn't automatically illegal — but whether you're protected depends on your specific property and build
- Enforcement risk doesn't disappear on its own — time limits exist, but they're not as simple as most people think
- Doing nothing and hoping for the best is a risk that can affect your ability to sell
"It's Probably Permitted Development" Is Not Good Enough
Permitted development rights allow certain types of work without a planning application. Many homeowners assume their build falls within these rights — but assumption is not the same as confirmation.
Whether your work qualifies depends on your property type, its location, what's already been built, and a range of conditions that most homeowners never check. A build that would be fine on one street might be a breach on the next. Most homeowners don't realise how many variables are in play until it's too late.
If a neighbour complains, or the council investigates, "I thought it was fine" offers no protection.
The Enforcement Clock Is More Complicated Than You Think
You may have heard of the "4-year rule" — the idea that after four years, the council can no longer take action against your build. It's real, but the picture has changed.
Under the Town and Country Planning Act 1990, the time limits for enforcement action depend heavily on when the work was substantially completed. For operational development completed before 25 April 2024, a 4-year limit applies. For work completed on or after that date, the limit is 10 years. And for certain other breaches, a 10-year limit has always applied.
So the question isn't just "how long ago did I build it?" — it's which rules apply to your specific situation, and whether you can actually demonstrate when the work was completed. That's a much harder question than most people expect.
Don't assume the clock has run
Even if several years have passed, enforcement immunity depends on specific legal thresholds and what type of breach is involved. It's not automatic, and it's not always straightforward to prove.
It Can Affect Your Sale — Sometimes Years Later
Many homeowners only discover the problem when they try to sell. Solicitors routinely ask about planning compliance during conveyancing, and an unauthorised build that hasn't been regularised can delay or collapse a sale. Buyers' solicitors are not going to take your word for it that everything is fine.
If you've built something without permission and you're not certain it was permitted development, the time to find out is before someone else forces the issue.
The Best Way to Know Where You Stand
WhatCanIBuild is a free tool built specifically for this situation. It checks whether your work was likely to be permitted development, assesses your enforcement risk based on when the work was done, and explains what the 4-year (or 10-year) immunity rules mean for your property.
It won't replace a solicitor or planning consultant for complex cases — but it will tell you whether you need to worry, and why. That's a much better starting point than hoping nothing comes of it.
If you've already built something and you're not 100% certain it was lawful, WhatCanIBuild is the best way to get a clear picture of where you stand.
These rules vary by property
Conservation areas, Article 4 directions, and other constraints can change everything. Check what actually applies to your address.
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