11 minutes

Building a Single Storey Rear Extension

Single-storey rear extensions are a great way to optimise space in your property and can help increase the value of your home.

Whether you are looking to construct your perfect open plan living/kitchen and dining space or to add extra bedrooms in your property, a rear extension can be used to facilitate any additional space you may need!

Not sure where to start? Have a read through our guide below and our handy tips, which will help you to plan out a clear strategy for your ideal single-storey addition.

So, what is a Single-Storey Rear Extension and how big can it be on my property?

Without sounding too obvious, a single-storey rear extension adds additional space to the back of your property and consists of only one floor. People usually opt for these if there is surplus garden space and if they are looking to add a little more value to their homes.

The size of your rear extension depends on several factors including:

  • The size of your home and how much garden space you have/want to use
  • What the addition will be consisting of and how big you want these spaces to be
  • What you can get consent for from your local authority
  • Your budget

Depending on what type of house you have and the size of the extension, there are different types of applications and guidelines that you will need to follow for your rear extension. In short think of it in this way:

Small Extensions can fall under permitted development rights


Larger Extensions will need prior approval or a householder planning application.

What is permitted development?

Certain types of work on your property do not need a planning application and fall under “permitted development rights.” Certain single-storey rear extensions depending on their size can fall under Permitted Development.

The rules of Permitted development are split up into a series of parts and classes in Schedule 2 of the Order.

Rear extensions fall under “Class A” which covers “The enlargement, improvement or other alteration of a dwellinghouse” including rear or side extensions. Class A also includes a “neighbour consultation scheme” which through submitting a prior approval application can allow you to build a larger extension.

If your rear extension satisfies the requirements in Class A, you do not need to apply for planning permission which will evidently be quicker and avoids the backwards and forwards with the Council. However, it is highly advised to obtain a “Certificate of Lawfulness” for the works to confirm that the proposal is lawful.

If your proposal falls within Permitted Development or not does rely on several factors including the design and size alongside if the property is in a conservation area or is listed.

What if the extension doesn’t fall under Permitted Development?

In this case, you could submit a “Prior Approval Application” under the neighbour consultation scheme. This would mean that the Council would ask your neighbours about your proposal first and consider their opinion on what you are seeking to add.


You can submit a householder planning application if it is bigger than is allowed under Permitted Development.

With this in mind,

How much space you can add to your property and the type of application you would need can be summarised as per the below:

On a semi-detached house:

· Up to 3 meters, this will usually fall under Class A of permitted development rights (subject to meeting the requirements)

· Up to 6 meters – this will need to meet the requirements of Class A of permitted development rights and will require you to submit prior approval.

On a detached house:

· Up to 4 meters, this will usually fall under Class A of permitted development rights (subject to meeting the requirements)

· Up to 8 meters – this will need to meet the requirements of Class A of permitted development rights and will require you to submit prior approval.

On a terraced house:

· Up to 3 meters, this will usually fall under Class A of permitted development rights (subject to meeting the requirements)

· Up to 6 meters – this will need to meet the requirements of Class A of permitted development rights and will require you to submit prior approval.

If you want to go bigger and your home doesn’t fall under permitted development (i.e) it could be listed or situated within a conservation area, you will need to submit a householder planning application.

When would I need to apply for planning permission?

Alongside if your property is listed or within a conservation area or if it is larger than the limits mentioned above, there are several other scenarios when you will need to apply for householder planning permission for a rear extension.

To summarise a few:

  • If your rear extension comes within two meters of the boundary of your property and is higher than three meters.
  • If the extension is more than half the width or more of its host property
  • If the roof or eaves of the addition is higher than the highest point of the existing roof or eaves (a single-storey rear extension cannot be taller than 4 meters)
  • If your rear extension includes a veranda/patio, raised decking, masts, flues, SVPs or a balcony.
  • Your rear extension will massively be different to the host building (it should match!) and the proposal seeks to change the roof of the host property.

Please note, if you are using an architectural designer, they should be able to talk you through your options and what they believe, based on past experience, should be allowed.

And yes, you WILL need approval from building regulations for your rear extension, regardless of its size and which application you have applied for.

You will need to submit a separate detailed set of drawings that indicate structure, ventilation, drainage, electrics, insulation, fire safety (etc.)

Can I add a single-storey rear extension if my property is listed?

In short, potentially – although it will require a lot of work and patience!

There are such strict rules when it comes to working on listed buildings, as the Council wants to protect the buildings original features/character as much as possible.

If you are looking to add a single-storey rear extension, this will require a lot of time and research into the existing building. You may be required to put together a report showing the original plans and detailed analysis about the materials used on the existing property and how your proposal intends to be in keeping with the original features.

You can then apply for a listed building consent where the Council will decide whether the proposal will harm the original character of the property. It is often the case that the Council will ask you to change the design or withdraw the idea.

However, there are situations where the proposal may pass:

  • If you can prove that it will be exactly in keeping with the rest of the property
  • If you can show that due to the location of the rear extension, it will be completely hidden creating little impact on the rest of the building.
  • If you can prove that the building did have a rear extension in the past and that your proposal will be more in keeping with its original design
  • If you can prove that your proposal will protect and preserve the structure of the original property and needs to be added as a necessity.

What if my property is situated in a conservation area?

As we have mentioned in this article, if your property is situated within a conservation area, you will need to apply for planning permission.

A lot more needs to be considered when dealing with the design of a rear extension on a property in a conservation area. This will include careful conservation of the conservation area policies which your Council will have on their website. They give an idea of what will/will not be acceptable and in which style would be considered “in keeping” with the tone of the local area.

The impact on neighbouring properties and the overall conservation area will also be a determining factor if you will receive permission or not.

Am I better off building a conservatory?

In the UK, homeowners sometimes opt for the addition of a conservatory over a rear extension, as they are both cheaper construct and less time consuming to build. They do however have many downfalls in comparison to a rear extension. From a financial perspective, they do not add as much value to a property and they are quite one-dimensional in the sense that they can’t really be used for a multitude of purposes like a rear extension. They can also be quite cold in the winter months and warm during the summer, making them not the ideal space to want to be in for prolonged periods of time.

How complicated is it to add a single-storey rear extension?

If your property is a detached house, the process will be fairly straightforward – that’s if the property isn’t listed or in a conservation area. The process will also be less tricky when it comes to your neighbours’ opinions and will be generally easier when applying for Planning Permission or under Permitted Development rights.

If your property is semi-detached, there is more flexibility when it comes to adding a rear extension on the side that isn’t attached or potentially at the front of the property if there is scope.

If your property is a terraced house, there could be a few challenges along the way as you are more restricted in terms of space so the rear is really the only space you have to add an addition. But, a lot of terraced houses in London choose to add rear extensions without compromising too much garden space and this should be an exciting opportunity for a good designer!

How much will a single-storey rear extension cost me on average?

This is very dependent on a number of factors including the design and scale of the extension. However, in London you could be looking at paying between £1,500-£3,000 per square metre which includes materials, planning permission and materials. We always recommend paying that little bit extra when it comes to your extension, as you want something that will achieve a high-quality finish while being durable and adding value to your property.

Now with the legislation bit out of the way…

How can we help in terms of design?

If you have an idea or want a bit of extra advice on how adding a rear extension could transform your property, please feel free to get in touch.

But, as some general advice, we have put together the following, which includes our top tips, and some design ideas for your rear addition:


Make a list of the spaces that it needs to facilitate and decide on what kind of aesthetic you are after including an idea of materials – this will help lead a conversation if you are using an architect or designer. You could even put together a Pinterest board or file of images that you like or maybe even roughly sketch out some plans.

Think of what you are trying to achieve

A rear extension could be used in several ways. Perhaps you could create a bigger version of an existing room (i.e) a larger lounge space or a downstairs bedroom. Or, perhaps you could consider using the rear extension combined with the existing spaces to create a more open-plan layout. A very popular option that may opt for is an open plan living/dining and kitchen space, which can add a more social aspect to your property for entertaining guests.

How do you want it to look from the outside?

There are many different ways you could approach the external materials. (Subject to the property not being listed or the extension being added under permitted development) Perhaps you may want to look into an interesting cladding that could contrast the existing property. Let’s say if the property is brick, using zinc cladding could create a more contemporary feel. If bringing more light into the space is a priority, you could explore different ways to use glazing to maximise the amount of sunlight the space gets. This could be through the addition of Crittall doors or rooflights including wrap-around glazing and lantern rooflights.

What type of roof do you want the addition to have?

Many people opt for a flat roof for a single-storey extension, which is both cheaper and more time-efficient to construct. There is also the option to create a pitched roof which if this is a feature of the existing property, you could mirror on the extension. These are more expensive to construct but could prove to be more cost-effective in the long run as they have a longer life span in comparison to flat roofs.

What style of external doors would you go for?

We mentioned above the addition of Crittall Doors but consider what type of doors you would add. For example, bi-fold doors can be used to open up and connect the indoor and outdoor space – great for hosting summer garden parties alongside bringing fresh air and sunlight into the space. Alternatively, you could opt for sliding or French doors to create a similar effect. Sliding doors could be a more space-saving method as the doors double up in comparison to bi-folds, which require space for the doors to be pushed into.

If you’d like us to help plan, design and build your single-storey rear extension please get in touch using the form below. We’re happy to help!

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