Granny Annex Planning Explained

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Having spent 5 days at Grand Designs Live with IHUS earlier this month we were still amazed at the amount of what can only be described as “mis-information” out there when it comes to Granny Annex planning.

Up until this year we have always applied for planning permission for any of our granny annexes directly to the relevant Local Planning Authority and have a 98% success rate in doing so.

In most cases we have used the Householder Planning Application process but this is not necessarily consistent with every Local Planning Authority.

Some have policies relating to granny annex building and some do not.

In all cases your Local Planning Authority will look at your planning application on it’s own merit and you will not find a consistent approach to the process throughout the country.

The latest recommended route (which is one used by many granny annex companies in the UK) is to apply for a “Certificate of Lawfulness” using what is known as the Caravan Act.

Here’s more about it and why you need to be careful when people tell you that granny annexes do not need planning permission.

Feature Article: Granny Annex Planning Explained 

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Granny Annex planning starts with understanding what can and cannot be done with regards to your Local Planning Authority. Even if you choose to apply for a Certificate of Lawfulness rather than head down the normal planning permission route, ultimately the decision still rests with your Local Planning Authority.

This year in particular we have seen them start to refuse more applications that do not meet the stricter criteria of what they deem to be an annex and for clarity we decided to put this “mini-guide together” to clear up some of the “mis-information” out there with regards to granny annex planning.

Permitted Development

This is very rarely used for granny annexes as it is really for a garden outbuilding such as a home office, gym or summer house. As soon as you add a kitchen and bathroom, the building will fall outside of the scope covered by permitted development. It also has severe restrictions of external eaves heights which would make the ceiling heiht of your annexe very low.

A Certificate of Lawfulness must be issued by the LPA prior to the build taking place.

Planning Permission

There are 2 types of planning applications, full applications and home owner applications. Full applications are for a new dwelling or dwellings and is generally a more involved application and is potentially more difficult to obtain and will have “planning conditions” that must be met.

Secondly, the home owner application has a lower threshold and is the type we will always try to use in getting planning permission for your annexe. However in some cases the LPA will insist on a full application.

There are also a number of surveys that the LPA may require in deciding on a planning application which may include:-

  • Arboricultural Survey – this is a tree survey and must be completed in accordance with BS5837
  • Ecological Survey – this is for animals and the protection of their habitat.
  • Flood Risk Assessment – where the property is in a known flood risk area.
  • Heritage Report – where the host property is a listed building.
  • Topological Survey – this is to record the varying ground levels at the site. 
  • Archaeological Survey – where the property is on a known site of historical interest.

If the main property is in a conservation area, National Park, Green-belt, Area of Special or Specific Scientific Interest or Outstanding Natural Beauty, the LPA Conservation Officer will be consulted and can have a bearing on what can be built and how it will look.

**Every LPA have their own Adopted Policies and Conditions which mean that no 2 applications are the same; what one LPA will accept, another may refuse.

The Caravan Act

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Whereas Planning Permission is classed as development if a site, this act allows for a “structure” to be placed on a site; providing it meets 3 specific tests and is defined in the Caravan Sites & Control of Development Act 1960 / Caravans Sites Act 1968. The annexe in this case is defined under the act as:-

“Any structure designed or adapted for human habitation which is capable of being moved from one place to another (whether being towed, or by being transported on a motor vehicle or trailer.)

The definition of a “caravan / structure” was amended in 2006, the 3 specific tests that it has to meet to comply with the act are:-

  1. Dimensions
  • The maximum dimensions allowed under the act are:-
  • Depth – External  6.8metres (22 feet 3 3/4 inches)
  • Length – External 20 metres (65 feet 7 1/2 inches)
  • Ceiling Height – Internal 3.05 metres ( 10 feet 0 inches)

2. Construction

  • It must not be composed of more than two halves separately constructed and joined together on site by means of bolts, clamps and other devises; each half can be constructed of many parts.

       3. Movability

  • The structure when constructed “Is, when assembled, physically capable of being moved by road from one place to another (whether being towed, or transported on a motor vehicle or trailer.
  • The act further states that the structure “shall not be treated as not being (or have been) a caravan whithin means of Part 1 of the Caravan Sites Control of Development Act 1960 by reason that it cannot be lawfully moved on a highway when assembled.”
  • Utilising the Caravan Act has allowed us to build the self-same annexe that we have had a planning application for refused by the LPA as it by-passes all of the LPA adopted policies and rules. We can comply with all 3 tests for which the LPA issues a certificate of Lawfulness as they would under a permitted development application.

All Applied For On Your Behalf As Part Of The Service

Within our Free On Site Consultation service we will visit your proposed site and advise you on the best route for your particular granny annex.

In most cases we either choose the Householder Planning Application option or the Caravan Act and in some cases both.

The fee for preparing a Caravan Act Application and submitting it to your LPA is currently £1,640.00 including VAT (terms and conditions apply).

The process of preparing all the drawings, carrying out a site survey and gaining either planning permission of a Certificate of Lawfulness can take loner than actually manufacturing and building your granny annex.

It’s best to allow between 10 and 12 weeks for the whole process and as you may be aware Local Planning Authorities are extremely busy at the moment dealing with all the new home construction going on throughout the UK.

Our best advice is to plan ahead in good time if you are thinking about building a granny annex in your back garden as planning permission may take longer than you think to come through.


  1. There are 3 main routes to obtaining permission to build a granny annex in your back garden.
  2. The first is Permitted Development but that is hardly likely to ever apply to a granny annex.
  3. The second is by submitting a Householder Planning Application.   
  4. The third and increasingly popular way to obtain permission is by obtaining a Certificate of Lawfulness.
  5. In every case your Local Planning Authority needs to be involved, if you fail to obtain the relevant permission or certification you will have problems selling your home in the future.

As always we look forward to your thoughts and comments below or join in the conversation on our Facebook Page !

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About The Author

Diane Cossie

Diane Cossie is a blogger and social media enthusiast who is the face behind our popular Facebook page, creator of our website and one of our annexe and specialists.

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