Written by Nikki O’Hagan, 4th July 2024

“Is it ancillary or incidental?”

This is a question we are frequently asked here at Planning Direct so we’ve put together this quick guide.

The terms “ancillary” and “incidental” refer to a use or physical feature within a site or building. They describe a use or physical feature that is both subordinate and connected – in some way – to the main use of the site or building.

In some circumstances, the terms are used interchangeably. We have also noticed that some local councils will refer to a specific use or feature – such as a car park – as incidental and other councils will refer to the same use or feature as ancillary. So you are quite right to be confused!

In most situations, it does not really matter whether something is described as “ancillary” or “incidental”. However, there is one very specific circumstance in which the difference is absolutely critical – householder permitted development outbuildings.

Householder permitted development rights

Householder permitted development rights are legal rights that enable most homeowners in England to make certain additions and alterations to their home and garden without any need to apply for planning permission.

Click the button below for more general information about householder permitted development rights.

One of these permitted development rights enables you to construct or alter outbuildings within the curtilage of your home. This is known as the “class E” permitted development right and outbuildings constructed in accordance with this right are commonly referred to as “class E outbuildings”.

Class E outbuildings

There are various rules and restrictions on class E outbuildings. These include size limits and locational restrictions. For example, the outbuilding:

  • Cannot be located in front of your home.
  • Cannot be physically attached to your home (refer to separate rules on extensions).
  • Is limited to a single storey in height.
  • Must not be within the curtilage of any listed building.

Incidental use restriction

One of the most important and contentious class E rules is that the outbuilding must be “for a purpose incidental to the enjoyment of the dwellinghouse“. Many unsuspecting homeowners have been caught out by this rule, not realising that various common uses of domestic outbuildings are actually “ancillary” and not “incidental”.

It is important to understand that your outbuilding must comply with every single “class E” rule and restriction, including the rule on incidental use. If it doesn’t, it is not permitted development. That means you will have to apply to your local council for householder planning permission and may only construct the outbuilding if permission is granted. If you have already constructed the outbuilding and permission is refused, you may face enforcement action and could ultimately be required to tear it down.

Click the buttons below to find out more about planning applications and dealing with enforcement action.

What is an incidental use of an outbuilding and what is not?

Government guidance

Although there is no definitive list, the government has issued guidance to tell us what uses are likely to be incidental and what uses will never be incidental. However, this does not cover every possible use of an outbuilding. The following table provides a straightforward summary of the government’s official guidance. Click the button below to access a copy of the government guidance for yourself.

Likely incidental usesNot incidental uses
Buildings and enclosures for the keeping of animals, including poultry, bees, pets and birds but only if the animals are solely kept for the domestic needs or personal enjoyment of occupants of the house.Primary living accommodation such as a bedroom, bathroom or kitchen.
Garden sheds and domestic storage.Self-contained residential accommodation such as “granny annexes”.
Garages, car ports and other car/cycle storage buildings.
Containers for domestic heating purposes (oil or gas tanks).
Garden decking (subject to a strict height limit).
Swimming pools.

Appeal decisions and court cases

Because of the lack of guidance on other common outbuilding uses, this matter is frequently debated in the Courts and in planning appeal decisions. We rely on these previous appeal decisions and court cases to determine whether a specific use is likely to be incidental or not. The following table is our informal list of likely incidental uses, based on a range of planning appeal decisions and court judgments. It is not definitive.

Likely incidental uses
Home office/study.
Home gym or fitness studio.
Home spa (sauna etc.).
Playroom or games room.
Summerhouse or garden room.
Hobby room or art studio.
Home workshop (but only for home/DIY purposes).
Home cinema.
Home bar.
Pool house or changing rooms.

The bathroom exception

Bathrooms, toilets and shower rooms count as primary living accommodation. According to government guidance, this means they are not incidental uses. However, there is an important exception to this rule. If the bathroom, toilet or shower room would serve a legitimate incidental use, it may be acceptable. For example, if the outbuilding is a home gym, spa or pool room, you may be able to include a small shower or bathroom. It may also be appropriate to include a small toilet within a home office or home bar.

In all cases, your local council will very carefully consider whether there is a legitimate reason for a separate bathroom facility to be provided within the outbuilding. Their main concern will be to ensure that the outbuilding will not be used as self-contained accommodation.

Will a so-called “likely” incidental use always be incidental?

It is impossible to say that a specific use will always be incidental as there are other factors at play. For example, home gyms are commonly agreed to be a type of incidental use. However, in at least one well-known appeal case, a home gym was found not to be incidental as it was bigger than the house itself. The Inspector in this case emphasised the fact that to be incidental, the use must be legitimately subordinate to the main use. In their opinion, the fact that the home gym was larger than the main dwelling meant it was not subordinate. In other cases, outbuildings that have exceeded the footprint of the main house have been found to be incidental. Whether a use is legitimately subordinate to another will always be open to interpretation and there are no definitive size limits.

If a decision-maker is not convinced that the outbuilding would be used for its stated purpose or for purposes strictly connected to the main house then this could also be grounds for refusal. For example, if an outbuilding is proposed as a garage but contains space for an excessive number of cars, it may not be agreed to be incidental. What counts as an “excessive” number of cars will always be open to interpretation.

How do I confirm whether the use of my outbuilding is ancillary or incidental?

As we’ve explained above, a use could be incidental in one circumstance but not in another. There are various factors at play, including the size of the outbuilding in relation to the main house.

If any of the following factors apply to your outbuilding then the risk that it is not incidental will increase:

  • It contains any form of primary living accommodation, including a toilet or shower room.
  • It is very large, especially in proportion to the main house or site area.
  • It includes space that is not accounted for (e.g. blank areas on the floor plan).
  • Its size is not well-related to its proposed use.
  • It is proposed for a use that is already met by another on-site building.
  • It has the appearance of self-contained accommodation (such as a bungalow or typical annexe).

Lawful Development Certificates

The only way to be certain that your proposed outbuilding is incidental is by applying to your local council for a Lawful Development Certificate. This is a relatively quick and inexpensive process. You will need to send drawings of the outbuilding and a description of its use to your local council. Your council will assess your outbuilding against all class E rules, including the rule on incidental use. If they are satisfied that all the rules are met, they will issue a Lawful Development Certificate. This certificate will act as formal confirmation that the outbuilding is forever lawful, provided you build and use it in accordance with the information you sent to the council. It will be a useful document to have should you decide to sell your home in future.

If your council doesn’t think your outbuilding complies with the rules, they will refuse to issue a certificate. Although a refusal is always disappointing, it is far better to find out an outbuilding is not permitted development before you build it! If your council refuses to issue a certificate, they must tell you which rule – or rules – are breached. If you are able to resolve the issues, you can make some changes to the proposal and re-apply.

Click the button below to find out more about applying for a Lawful Development Certificate.

If you require assistance with a domestic outbuilding, householder planning application or an application for a lawful development certificate, please get in touch. Our initial advice is always free of charge.

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