If you’re thinking about adding a conservatory, garden room, or a small extension, the first question is whether you need to apply for planning permission. In most cases, the answer is no – thanks to the UK’s permitted development rights. These rules let you build certain sizes and types of extensions without a full planning application, as long as you stay within set limits.
But don’t assume every project is automatically covered. The rules vary by location, house type, and what you’re actually adding. Getting it wrong can cause headaches, fines, or even a forced removal of the new structure. Below we break down the basics, so you can check your project against the rules before you hire a builder.
Permitted development mainly covers three common projects: single‑storey rear extensions, loft conversions, and outbuildings like sheds or summerhouses. For a typical detached or semi‑detached house, a rear extension can be up to 3 metres deep (or 4 metres if the house was built after 1 July 1948) without needing permission. The total height of the new structure must not exceed 4 metres for a single‑storey build.
Garden rooms and conservatories fall under the same umbrella, but they have extra limits. The floor area of the addition can’t be more than half the original house’s floor area (or 40% for flats). Also, the new roof can’t rise more than 2.5 metres above the existing roof level.
If you live in a conservation area or a listed building, the rules tighten up considerably. In those cases, you’ll usually need full planning permission, even for modest projects.
Start by measuring the existing house footprint. Compare it to the intended size of your extension or conservatory. If the new floor area stays within the 50% limit, you’re probably okay. Next, look at the height restrictions: a single‑storey extension can’t be taller than 4 metres at the highest point, and the eaves can’t go above the existing roof line unless you’re adding a dormer.
Don’t forget the side and rear wall setbacks. The new structure must be set back at least 2 metres from any side boundary that adjoins a highway, and at least 5 metres from the rear boundary if the house is on a corner plot.
When in doubt, use the online permitted development calculator on the Planning Portal. It asks for simple inputs – house type, year built, and proposed dimensions – and tells you instantly if you’re within the limits.
If the calculator flags a breach, you have two options: modify the design to fit the rules, or submit a Full Planning Application. The latter involves drawings, a fee, and a waiting period, but it also gives you the freedom to go bigger.
Finally, check any local covenant or Article 4 Direction that might strip away permitted development rights. These are usually posted on your local council’s website. Ignoring them can lead to enforcement notices down the line.
By doing this quick check before you commit, you’ll save time, money, and avoid nasty legal surprises. Happy building!
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