Understanding Ancillary vs. Incidental Use: A Guide to Residential Annexe Planning

Have you ever dreamed of creating more living space for loved ones on your property, but weren’t sure what was allowed?  The terms “ancillary” and “incidental” use can be confusing when planning an annexe.  This guide will break down the key differences and implications to help you navigate the process.

What’s the Difference Between Ancillary and Incidental Use?

In simple terms:

Ancillary use is linked the main residential use of the dwelling. An example would be a residential/Granny annex – Separate living quarters for elderly family members, yet with a link to the main property.  If fully self-contained, it could create a new planning unit.

Incidental use is a minor additional activity that does not impact on the primary use as a home.  Such as a shed, home office, greenhouse etc.

The distinction of use matters, here’s why…

Permitted Development Rights

Under Part 1, Class E of the Town and Country Planning (General Permitted Development) (England) Order 2015 (as amended) (the GPDO), certain building can be erected under “permitted development rights”, bypassing a full planning application.  On the basis of criteria including that the use of the building must be incidental to the enjoyment of a dwellinghouse (ancillary use does not qualify for this permitted development right – it’s important to take this into account).

Whilst we’re focusing on outbuildings should a proposed annex be attached to the existing dwellinghouse, the extension could be also permitted development if it is occupied by a family member and it meets the criteria and conditions outlined within Part 1, Class A of the GPDO.

Can an existing outbuilding be used as a Granny Annexe?

Converting an existing outbuilding like a garage or outbuilding into a granny annex may not require full planning permission, provided certain criteria are met:

  • A separate planning unit should not be formed. This means the annex occupants must still be dependent on the main house and not fully independent in how they function. Factors like access, facilities, and ownership will be considered.
  • The building’s location within the defined residential curtilage of the property is key. Being situated outside these established boundaries could trigger the need for permission.
  • Any existing conditions attached to the outbuilding must still be adhered to. For example, if it was approved only for vehicle parking or prohibited from window/door changes, diverging from any imposed condition could represent a breach.

Self-contained granny annex conversions of appropriately located outbuildings may fly under the radar as “not being development”. But planning authorities will scrutinise how separated the functions are from the main dwelling. Maintaining compliance with prior restrictions is also important to avoid issues.

To secure confirmation that your proposed annexe does not require planning permission a Certificate of Lawful Development for a Proposed Use or Development (CLPUD) or if you’ve already carried out the work to form an annexe a Certificate of Lawfulness for Existing Use or Development (CLEUD) could be sought.  Take a look at our Practical Guides on these issues. 

Let’s deep dive into this a little more…

Within the Town and Country Planning act 1990, there are circumstances where existing “incidental” outbuildings within residential curtilage such as the garage can be converted into “ancillary” living accommodation as this is not considered a “material change of use”.

S55(1) of the Act sets out that “development” means the carrying out of building, engineering, mining or other operations in, on, over or under land, or the making of any material change in the use of any buildings or other land.  S55(2) sets out that certain operations or uses of land shall not be taken for the purposes of the Act to involve development of the land, including (a) the carrying out for the maintenance, improvement or other alteration of any building of works which – (i) affect only the interior of the building, or (ii) do not materially affect the external appearance of the building.

So if the overall planning unit (the unit of occupation, until or unless some other unit is identified which is physically and/or functionally separate from it – ie a single residential property and its curtilage) would continue in occupation by the same family.  Even if the annexe would contain facilities for day-to-day living, as long as there would be links to the main dwelling there would be no material change of use.

For planning purposes, it is well established that the right to use land for some primary purpose includes the right to use it for any purpose which is ancillary to that dominant purpose.  The essential feature of an ancillary use is that there should be some functional relationship with the primary use of the planning unit.

There is a wealth of planning appeal cases to support this as it’s often an area of planning that town planners can be confused about.

What if I need planning permission for my Granny Annexe?

If you’re proposing a new building to accommodate a Granny Annexe planning permission will be required.  The good news is ancillary annexes are often supported by council policies when genuine need exists.  With thorough research and planning, you can navigate the process to enrich your family’s living situation for years to come. Always consult the experts early for the best chance of approval.

Related Content

More information for you is available in our series of eBooks and Practical Guides which cover everything from the very basics of town planning to application processes and what developers need to consider.

If you’re not sure if you need help from a Town Planner take a look at blog on When to Hire a Town Planner our download a Guide on How to Choose a Town Planner.

Ancillary vs. Incidental Use