Planning Permission UK Extensions: What You Need to Know

When you want to add an extension to your home in the UK, you’re dealing with planning permission UK, the legal system that controls how land and buildings are used and modified. Also known as development control, it’s not just paperwork—it’s a gatekeeper that can save you thousands in fines or forced removals. Many people assume that if it’s just a small addition, they don’t need approval. That’s a dangerous myth. Even a modest rear extension can cross the line if it’s too tall, too close to a boundary, or covers more than half your garden.

Permitted development, a set of automatic rights allowing certain small changes without formal planning approval is where most homeowners get confused. For example, a single-storey rear extension can often be built without permission—if it doesn’t extend more than 6 metres for a detached house or 4 metres for semi-detached, and stays under 4 metres in height. But if you live in a conservation area, a listed building, or an Area of Outstanding Natural Beauty, those rules vanish. And don’t forget UK building regulations, the technical standards for safety, energy efficiency, and structural soundness. You can have planning permission but still fail building control if your insulation is wrong or your foundation isn’t deep enough.

What most people don’t realize is that planning permission isn’t just about size. It’s about impact. Does your extension block a neighbor’s light? Does it change the character of the street? Are you adding a second floor where others have single-storey homes? These aren’t just opinions—they’re official criteria councils use to decide. And if your neighbor complains, the council will investigate, even if you thought you were fine.

There’s no one-size-fits-all answer. A 2023 survey by the Royal Institution of Chartered Surveyors found that over 40% of homeowners who skipped planning permission ended up paying to fix it later—either by applying retrospectively, paying fines, or even removing the structure. The cheapest route isn’t always the fastest. Getting advice upfront from your local council’s planning department can save you months and thousands.

That’s why the articles below cover everything from real-world extension designs that slipped through the cracks, to how to read your local council’s rules, to what materials and heights actually trigger a full application. You’ll find guides on how to avoid common mistakes, what inspectors look for, and how to talk to neighbors before you even submit a form. Whether you’re adding a kitchen extension, converting a garage, or building a two-storey side annex, the rules are tight—but they’re not impossible. Just don’t guess. Know them first.