Building an Annexe in the Garden

In the UK, building an annexe in the garden is quite common and if you own a big enough property, you will most likely be able to raise it. These types of constructions are sometimes, even encouraged by the UK government. However, the legal procedures required to build a garden annexe are sometimes confusing and contradictory. The reason behind it is simple: there are different types of buildings that can be used as a garden annexe, and each one of them has different requirements.

Type of annexe building Does it need planning permission?
Traditionally built Granny Annex Yes
Prefab Cabin as a Granny Annex Yes
Prefab on wheels as a Granny Annex No, though it needs to be approved.
Garden Shed, Storage or Garage No

Understanding the planning requirements for each type of building can be of great help when choosing an annexe. Still, the selection of the type of building shouldn’t be based solely on the planning permission requirements.

What is a garden annexe?

A garden annexe is an additional space to your original house generally built as a small construction that is placed on your property and can be attached or separated from your main house. This type of house addition originated as a solution to provide independent living for elderly family members which granted this construction the popular name of the granny annexe. Despite their accepted label, garden annexes are highly versatile and can be used for multiple purposes.

Do you need planning permission to build a garden annexe?

There is a lot of confusion regarding the need for planning permission to build a garden annexe, and while in most cases you do, the answer can vary depending on the type of building chosen and the purpose of the space.

Traditionally built garden annexe

Traditionally built granny annexes can be of different materials, dimensions and layouts. Yet, this construction is always built on-site and has the main purpose of providing additional residential space. Therefore, it usually includes a bedroom, a bathroom and a kitchen; as well as necessary elements such as doors and at least one window.

Also, it often includes all the necessary equipment to maintain a comfortable environment such as electricity, water and heating systems. Still, these offerings can vary from one project to another depending on your needs. However, regardless of the design choices, to raise a traditionally built granny annexe, planning permission is always required.

Prefab Cabin as a garden annexe

Prefab cabins are small dwellings with one bedroom or a loft layout, usually including a bathroom and kitchen, which perfectly defines the common granny annexe layout. Just like traditionally built annexes, prefab cabins offer all the required elements to create a comfortable indoor living space.

They are built in a factory-like environment, delivered to the property and installed on foundations; defining a structure that is as solid as if traditionally built. Being prefabricated highly accelerates their construction though they still have to adhere to most of the regulations required for traditional houses and need a planning permit to be installed as an annexe.

Prefab on wheels as a garden annexe

Prefabs on wheels usually referred to as tiny homes, are generally exempted from planning permission. Prefabs on wheels can often skip the requirement for planning permission as they might comply with the caravan act. Still, while this option might look very attractive, the decision of choosing a tiny home as an annexe shouldn’t be based solely on the possibility of avoiding planning permits but on the offerings this type of building grants us. Keep in mind that to build an annexe under the caravan act, approval from the planning authorities is still required and it could be refused.

Garden Shed, Storage or Garage

In the UK, it is possible to perform some renovations and extension works under what is known as the permitted development rights. These exclude you from the need for planning permission but garden annexes rarely qualify for it. That is unless this annexe is not meant to be lived in and instead used as a storage unit, a garage, or a garden shed [1]. If the purpose of the garden annexe isn’t domestic or residential, you might not require to obtain a planning application.

What is the cost of building an annexe?

A traditionally built one-bedroom (including a kitchen and a bathroom) garden annexe price usually can range from £80,000 to £100,000 [2]. However, this price can be highly reduced by choosing a prefab cabin instead since the construction cost of a prefab cabin begins at £13,000 [3][4]. Still, despite the initial building price, the total cost of building a garden annexe should take into consideration the different taxes that might be required to pay.

Do you pay Council tax on an annexe in the UK?

When building a garden annexe you should consider the extra cost of the Council tax. Every construction built as domestic property is expected to pay this tax, and an annexe is no exception for it. However, there are some circumstances where discounts or even exemptions are possible.

You will pay the full amount of Council tax on your annexe unless:

  • The purpose of the annexe is family elderly care.
  • It is occupied by disabled relatives.
  • The relatives living in the annexe are mentally impaired.
  • If the only people living in the annexe are under 18.

Some of these discounts are encouraged by the UK government which offers discounts on Council tax bills of up to 50%. The main purpose of these discounts is to offer support services to both younger and older citizens by encouraging the construction of their own space inside the boundaries of their family property [5].

What type of annexe should you choose?

Building an Annexe in the Garden
The Nordic Prefab cabin model makes a beautiful 30sqm garden annexe

Choosing a type of annexe that doesn’t require building permits might sound attractive. However, if like most, you are looking for a permanent small construction that despite its size offers all the necessary features to be used as a high-quality self-contained accommodation, you might not be able to choose a planning permit-free annexe.

Still, don’t get discouraged, because there is a simple way. By choosing a prefab cabin, you will obtain all the benefits of traditional granny annexes, without the headaches of a complicated process and at a lower cost. Given that cabins are a type of prefab that is likely to be bought as a garden annexe, prefab manufacturers are very familiarised with it. As a result, the architect of the company designs them to comply with the necessary building regulation requirements and often the same manufacturer takes care of the planning permit procedure, saving you time and stress.

Frequently Asked Questions

Can I rent out an annexe while on holiday?

Renting this additional living accommodation is a good way to get some of the initial investment back. Given that garden annexes are independent units with their own entrance, renting them out is quite safe and allows you to keep your personal space private.

Do you pay stamp duty on an annexe?

Stamp duty does not apply to building a garden annexe. This tax is a one-off payment associated with the purchase of new property and since there is no property transfer while building an annexe, this tax doesn’t apply.

Does an annexe qualify for multiple dwelling relief?

Given that multiple dwelling relief is a discount applied to the Stamp Duty tax and the construction of a garden annexe is exempt from this tax, there is no need to qualify for it.

[1](2019, September) Permitted development rights for householders (Technical Guidance) Ministry of Housing, Communities & Local Government
[2]Emma M. (2022, August 31) Cost of Granny Annexe HomeHow
[3]Living Box Cabin
[4]Nidus Dove Cabin
[5]Hopkins, K. & the Ministry of Housing, Communities & Local Government (2015, March 25) Thousands of granny flats benefiting from Council Tax cut Government UK

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