Planning permission vs building regulations: what's the difference?

“Do I need planning permission?” is one of the first questions we get asked about extensions. It’s a good question, but it’s only half of the answer. There are two separate approvals, and they cover different things.

The short version

• Planning permission asks: should this be built here? It covers the size, height and look of a building, and how it affects the neighbours and the street.
• Building regulations ask: is it being built properly? They cover structure, foundations, insulation, ventilation, drainage, fire safety and electrics.

You might not need planning permission. You’ll almost always need building regulations approval for an extension.

When you might not need planning permission

Many single-storey rear extensions on houses fall under permitted development, which means you can build without a full planning application, as long as you stay within the limits. For a single-storey rear extension in England, these include:

• It can’t extend more than 3 metres beyond the original back wall of the house, or 4 metres for a detached house.
• It can’t be more than 4 metres high.
• If it’s within 2 metres of a boundary, the eaves can’t be higher than 3 metres.

There’s also a larger option. With prior approval from the council, you can go up to 6 metres, or 8 metres for a detached house. The council lets your neighbours comment before deciding.

A few things take permitted development off the table or shrink it. These include flats and maisonettes, listed buildings, and homes in conservation areas or other protected areas. Some newer estates also had permitted development rights removed when they were built. If you’re in any doubt, check.

Tip: even if you’re sure you don’t need planning permission, a Lawful Development Certificate from the council confirms it in writing. It’s not compulsory, but it can save awkward questions when you come to sell.

When you will need planning permission

If your extension goes beyond those limits, is at the side or front of the house, or your home is in one of the protected categories above, you’ll need to apply. In Somerset, applications go to Somerset Council, and you can search past applications in your street on its planning portal. That’s a useful way to see what’s been approved nearby.

Building regulations: the part people forget

Building regulations apply whether or not you need planning permission. For an extension, building control will check things like:

• foundations and structure, including steels and lintels
• insulation and energy efficiency
• drainage
• fire safety and escape routes
• ventilation

You can use the council’s building control team or a private registered building control approver. Either way, inspections happen at key stages during the build, and you get a completion certificate at the end. Keep it safe. Your buyer’s solicitor will ask for it when you sell.

What about smaller jobs?

A like-for-like kitchen or bathroom refit usually doesn’t need building regulations approval. Some of the work inside it might, though. For example, new electrical circuits, or electrical work close to a bath or shower, either has to be done by an electrician registered with a competent person scheme or signed off by building control. A registered electrician handles that paperwork for you.

Where to start

If you’re thinking about an extension, start with the question of size. Measure how far you’d like it to come out from the back of the house, and compare it with the limits above. That one number tells you a lot about which route you’re on.

For what to sort out beyond permissions, see our guide to planning a kitchen extension.

This is general guidance for homes in England, not legal advice. The rules have more detail than we can cover here, and the Planning Portal and Somerset Council are the official sources.