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  • Writer's pictureJulie Bliss

What you need to know about planning permission for Annexes

Updated: Aug 4, 2023

Planning departments and architects all over the land are seeing a marked increase in applications for annexes and conversion or creation of outbuildings and garden rooms at the moment - all of which has been a direct result of the pandemic and the race for space.


In these cost-conscious times, this is also a sensible and more economical way to gain additional accommodation than selling up and moving house, so lucky property owners are making the most of their extra space to build ancillary accommodation, including garden offices, guest suites, gyms, games rooms, grandparent accommodation and teenager retreats.

If you’re in the market for an annexe, here’s a few things you should know.

Photo Credit: Welsh Oak Frame

What is an annexe?

"a building joined to or associated with a main building, providing additional space or accommodation"

An annexe is a self-contained living space, normally attached to or very close to a larger property, and often achieved by converting a garage or outbuilding. An annexe will have the necessary amenities for someone to live independently, ie. a kitchen, a bathroom and at least one bedroom, but must be ancillary to the main dwelling (you cannot have separate utilities connections etc, for example).

Annexes are a great way to increase the accommodation and value of your property.

They are generally ruled as ancillary accommodation, meaning they are additional to the main house, for use by you and your family, and cannot be used as a separate dwelling.

You should also check for any conditions on your property that could stipulate that an existing or proposed annexe may not become separate accommodation, to ensure that properties (particularly those within rural areas or conservation areas) do not get their own status and therefore permitted development rights to further expand.

FYI: An annexe cannot be used to create a new dwelling, independent of the main house. You cannot rent out or sell the annexe without obtaining planning permission.

Building under Permitted Development Rights

If your annexe or garden room simply provides additional accommodation for you and your family, you can build it under Permitted Development Rights (unless you’re in a Conservation Area) and is known as an 'incidental outbuilding’.

It must not be larger than 50% of your garden size, built past the front of your house and its eaves and roof height must not exceed height regulations (3.m), especially if built within 2m of a boundary. It must also be a single-storey structure.

If it's attached to your house, it may not extend beyond the rear wall of the original house (ie your house before any previous extensions) by more than 4m if a detached house; or more than 3m for any other house (ie semi-detached or terraced house).

Photo Credit: Homes & Gardens from their article "How to Build an Annexe" - see below

When does an existing or new annexe or garden room/cabin need planning permission?

In principle, you do not need planning permission simply to let out a room or rooms, provided the property remains primarily your home.

However, if you make alterations in order to subdivide the property or you create a separate dwelling from an annexe, then it is likely that planning permission will be required, whether it is for the purpose of renting or selling.

The situation becomes more complicated if the changes are to accommodate family members, providing them with a degree of independence. Here, there is a judgement as to whether the property as a whole remains in ‘single family occupation’. If you intend to use your annexe or garden room as an independent living space for non-family members or as rental or AirBNB etc, you will need to apply for planning permission.

The same applies to Shepherd's Huts and other so-called portable accommodation. If your shepherd hut is for your own use, it doesn't generally need permission. If, however, you change its use to rental or AirBNB or you give it more permanent facilities (e.g. connection to a septic tank or water supply), it may well need planning permission.

It can be complicated and there are a lot of judgements that have to be made. So as always, it is best to check with your local planning authority before embarking on any building works.

Julie Bliss has created some fabulous annexes for clients over the years, so please don't hesitate to call if you're in the market for increasing your space with the addition of an annexe or outbuilding.

If you need advice on annexes or any other planning, building, renovation or interior design matter, email

Further reading:

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