Do I need planning? A quick guide to exempted development and what it means for you...

Do I need planning?

I'm going to be coming back to this subject (with some pictures), but for now, here are some of the main things you need to know about what kind of house extension does not need planning permission...

1- Size: the overall amount of area you can build is 40 sq.m. This can be all on ground floor, half on ground and half on 1st (only if the house is detached), or 28 sq.m. on ground floor and 12 sq.m. on 1st for a terraced or semi-d house. The thing that will catch you out here is that you have to include any previous extension built after 1964 in your totals - so if you already have an extension its size needs to be factored in.

2- Location: exempt extensions have to be at the back of the house. That means all parts of it behind the rear wall. For detached country houses this can sometimes be a funny one as the back of the house may be very visible. Garage conversions are the exception here, as they are exempt if they are attached to the house at the rear but also (and more usually) at the side.

3- Party boundary distances: if you are building an exempt 1st floor extension, then no part of the extension above the first floor can be closer than 2m from the party wall / boundary line. This does not mean you can't build a tall single storey extension - as long as it doesn't have a first floor it can be built up to or on the party boundary line, even if it is taller than the first floor in the existing house.

4- Height: the heights of the walls of the extension can be as high as the walls of the house, not including any gable wall of the original house. Basically the gutters for the new extension can be as high as the gutters for the original. And the roof of the extension can't go higher than the roof of the original house. If the extension is flat roofed then that flat roof can't go highter than the existing eaves or parapet, if there is one.

5- Garden Space: the extension must leave at least 25 sq.m. of private open space to the rear of the house. This is a show-stopper - it overrules the 40 sq.m. allowance and often means that the amount of exempt extension is reduced to preserve the 25 sq.m. garden. In tight urban sites this is the rule often leads to planning applications for very small extensions.

6- Windows: the windows at ground floor can't be any closer than 1metre from the boundaries they face. The windows at first floor can't be any closer than 11metres from the boundaries they face. This is another case where small sites lead to applications for extensions that would be exempt on a bigger plot. The good news is that rooflights for a ground floor extension don't count as first floor and don't need 11metre separation, although there have been a few fights about this one in the past...

7- Balconies: lastly, you can't use the roof of your exempt extension as a roof garden or a balcony. There are lots of good examples of 1st floor outdoor spaces around, but one thing they all have in common is that they needed planning permission (and it is often very tricky to get).

8- Protected Structures: a big exception to all the above is if your house is a protected structure (or a proposed protected structure). In that case you are going to have to deal with the planning authority for anything more invasive than polishing the letterbox...

9- Demolitions: a further exception is where you are demolishing a building or part of a building that abuts a party wall, and where there is a building on the other side of that wall. In that case you would need permission for the demolition job, even if the subsequent extension is exempt under all the rules above.

10- One more thing (until I find out more) to be aware of... If your house is in an estate there is often a planning condition for the original application that says that any extensions need planning permission and this overrules exempted development law. So if the house is relatively recent and part of an estate this is one thing you should check out - before a neighbour with a grudge checks it out for themselves and lands you in it.

As can be seen from the above, the smaller the site you have to work with, the more likely you are to need to get planning permission.

In more typical situations it is often the case that a well worked out design can be exempt from planning permission, especially if it is ground floor only.

And there are a couple of areas where you could be caught out. Exempted development is really useful, but proceed with caution!

Any questions?

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small spaces is a one-man architectural practice dedicated to helping people find the best way to add space to their home, or to make the most of what they’ve got. You can find out more here.