Extension Rules: What's Allowed?

Glass Extension - Photo Paul Massey. Extension Rules have changed

When you're extending your home or converting the loft, you often won't need planning permission, as the permitted development rights give you the green light. But how big an extension or loft conversion can you create under the rules?

By Sarah Warwick

Extension - Photo Richard Bryant. Extension Rules have ch

Back in 2008, the government changed the planning regulations to allow many more household projects to go ahead without the need to apply for planning permission. Then Housing and Planning Minister Caroline Flint said, 'The new rules will cut out planning permission for about 80,000 households a year...saving as much as £1,000 in some cases.'

Crucially, though, the rules don't mean that you can just go ahead and extend with impunity. It's important to follow the guidelines on size, position and design if you don't want the hassle and expense of applying for planning permission.

Remember, too, that if you live in a listed building, or World Heritage Site, Conservation Area, National Park, Area of Outstanding Natural Beauty or the Norfolk or Suffolk Broads then your rights are different, so you'll need to check with your local authority when you're extending in one of those areas.

When Can You Extend Without Planning Permission?

The rules apply to houses, so if you live in a flat or maisonette, check out government advice on the government's planning portal.


You can extend without an application for planning permission so long as you don't cover more than half the area of land around the original house. For planning purposes 'original house' means as it was first built, or as it stood at 1 July 1948 if it's older than that. Don't forget, too, that any existing extension by the house's previous owner(s) counts towards the total allowance.

Your extension shouldn't be forward of the principal elevation of the house, ie the front, but also shouldn't be forward of the side of the house if this is what fronts the road.

Terraced Houses

A single-storey or more than one storey rear extension can go a maximum of 3m beyond the rear wall of the original house. The maximum height of a single storey extension is 4m.

Loft conversions can have a maximum volume of 40 cubic metres (and any additions by the previous owners count towards this).

Semi-Detached Houses

A single-storey or more than one storey rear extension can go a maximum of 3m beyond the rear wall of the original house. The maximum height of a single storey extension is 4m.

Loft conversions can have a maximum volume of 50 cubic metres (and any additions by the previous owners count towards this).

Detached Houses

A single-storey rear extension can extend go a maximum of 4m beyond the rear wall of the original house; if it's more than one storey, the maximum is 3m. The maximum height of a single storey extension is 4m.
Loft conversions can have a maximum volume of 50 cubic metres (and any additions by the previous owners count towards this).

Need Expert Help?

Find a trusted extension specialist in your area using MyBuilder.com

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