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Can I build a Granny Annexe in my garden?

Planning Permission

Like so many families out there, perhaps you have an elderly relative whom you would like to spend as much time with as possible. If you don’t have lots of spare space in your house, a new ‘Granny Annexe’ might be the perfect solution.

Our planning team receive one or two enquires each week from homeowners asking, ‘Do you need planning permission for a granny annexe’?

It can be challenging to understand the rules, as there is a lot of conflicting information online. Google doesn’t always have the answer, or at least a clear one. This seems like an excellent opportunity for us to prepare a succinct guide regarding planning permission and granny annexes.

1. Permitted Development Outbuildings

You may have heard of the term ‘Permitted Development’. Part of this guidance allows homeowners to construct an outbuilding in their back garden, providing it meets the following requirements:

  • It does not take up more than 50% of the garden’s area
  • It is no taller than 2.5 metres at eaves height
  • Max height of 4m with a dual pitch roof (3m for any other roof)
  • Max height of 2.5m if within 2m of the boundary

For a comprehensive guide on outbuildings, feel free to click on the Planning Portal link here.

3D model of a Granny Annexe

2. Can I sleep in a Granny Annexe?

In terms of use, planning permission is not required for an outbuilding providing it is “incidental to the enjoyment of the main dwelling house” and its design falls within the definition of ‘Permitted Development’ described above.

Trying to find a clear and concise definition of the term ‘incidental use’ online is challenging.

Generally, ‘incidental’ covers uses which cannot exist without the main house. Such uses would include storage, swimming, bowling, a gym, an art studio, or something that can be classed as a hobby.

The Permitted Development for Householders – Technical Guidance (p.41) makes it clear that:

A purpose incidental to a dwelling house would not cover normal residential uses, such as separate self-contained accommodation, nor the use of an outbuilding for primary living accommodation such as a bedroom, bathroom, or kitchen.”

Bearing this in mind, if you intend to construct an outbuilding or granny annexe to sleep in, you would require planning permission.

In our experience, planning authorities vary in their approach to outbuildings, and many factors come into play when assessing your application. The factors used by local authorities include the size of the outbuilding, who will be using it, what it might be used for, how close it is to the main house, and how it is accessed.

Typically, if the local authority does grant planning permission, they will attach a planning condition to restrict occupation to members, guests or dependents of the household. They will also prevent the separate sale of this part of the property.  If you want to sell it, you will only be able to do so when you put the entire property up for sale.


A granny annexe can be a wonderful addition to the home.  Also, with the right design, such an annexe can significantly add to the value of your property. If we can help you realise your dreams for a little extra space at the end of your garden, feel free to call one of our planning experts anytime.

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