How Big Can I Build An Extension Without Planning Permission?


There are many reasons why you might want to build an extension on your home. Often, you will be keen to try and increase the value of the property, and this is certainly one of the best ways of doing so. It might also be a practical concern, for instance because you have less space than you need, and you are keen to make sure that you can fit all of your family into the home comfortable and have space to move around. Whatever your underlying reason, there are many things that you are going to have to consider when planning such an extension. One of the main ones, of course, is the size of the house extension.

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Here we run into a number of difficulties which you need to consider, in particular the matter of how big you can build an extension if you don’t have specific planning permission to do so. And the answer to that is not quite as straightforward as you might hope. In this article, we’ll take a look at some of the concerns that go into answering this specific issue. You might be surprised at some of the things you need to consider here.


The Type Of Property

Something that has an effect on this is what kind of property you are living in. That’s because there are many different kinds of rules for different types of property, so you will have to make sure that you are following the rules for your specific property type. In particular, you will need to think about whether you are in a flat or maisonette. That’s because these properties do not have any permitted development rights, meaning that you can’t build anything at all. This can also be true of a property that has been converted in the past, but the rules there are a little more up in the air and you will need to check with your specific situation. However, the type of property is nonetheless always something you are going to need to consider.

Previous Extensions

Something else that will be taken into consideration here is whether or not the house in question has had any previous extensions. If you or anyone else who has lived in the property has extended the house at all since 1948, then you will find that the allowance for building extensions has been used up, meaning that you won’t be allowed to do so again. This can be surprising if you were not even aware that your previous owners had done so, which is a common situation that many people find themselves in.

Listed Properties

It should go without saying that listed properties have their own rules, and if your property is listed, you will need to make sure that you are aware of whatever restrictions there might be on it. You might not be allowed to do anything at all, or in some cases it might simply be that you are not allowed to carry out specific types of extensions. Generally, these would be side extensions or those with a cladded exterior, or those with more than one storey. However, you need to check, as you might live somewhere where your permitted development rights have been removed, perhaps because you live on a World Heritage Site.

Extension Rules

There are a number of specific rules which you need to follow if you want to make sure that you are building an extension right, and that you are not going to encounter any issues for doing so. In particular, you may not be able to have any balconies, platforms or raised verandas, and the extension cannot be taller than the existing building.

Finally, the extension should not take up more than half of whatever garden or outdoor space there is in the home, and a single storey extension can’t be more than four metres high, or three metres high if the extension is within two metres of the property’s boundary.

No front extension is allowed under normal rules, so if you are planning that then you will need to seek specific planning permission – which is not necessarily likely to be granted, but it all depends on the situation at hand.

There are also some specific rules for side extensions. For instance, it cannot front onto the road at all, it can only be single storey, and it must be a maximum of three metres out from the original house. It also can’t be more than half the width of the original house.

If you are planning a single-storey rear extension – which is the most common type there is – then you will need to follow the same rules. However, there is also a relaxed rule surrounding this, which means that you can extend up to eight metres for a detached house or six metres for any other type of property. However, for these larger extensions you will have to give notification of their existence to the local area, and if you get any objections you might be blocked from building the extension in question.

If you are planning a double-storey rear extension, the rules are tighter, for obvious reasons. These can extend only three metres from the original house, and can’t be closer than seven metres to the property’s rear boundary. The roof must also match the existing house as closely as possible, and any upper floor, side facing windows have to be obscure glazed, with any opening being 1.7 metres above the floor.

As you can see, there are plenty of rules you need to consider if you are planning an extension. However, as long as you bear all this in mind, you should be able to plan the extension you are hoping for and dreaming of, and make your home exactly the way you want it to be.

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