Planning Consultant - Chris Scott
Hi, I’m Chris,
I hold an MA in Planning and work as a Planning Consultant

I’m going to guess that you have found this page by researching the permitted development rights for outbuildings. You may have learnt there are various restrictions on outbuildings. Such as how tall outbuildings can be, and that development must not exceed the 50% rule of the properties curtilage. However, there is a specific rule associated with the use of outbuildings, they must be incidental and not ancillary to the host dwelling. Therefore, before you carry out the construction of any outbuildings you need to be confident it falls under an incidental use. Otherwise, you may get a visit from the local planning enforcement officer.

First, what are the Definitions of Incidental and Ancillary?

The Oxford Dictionary definition of incidental is “happening as a minor accompaniment to something else“. The definition of ancillary is “in addition to something else, but not as important“. From reading the above definitions its easy to understand why incidental and ancillary uses would appear very similar. However, when it comes to planning and the General Permitted Development Order 2015 there is a big difference.

The 2015 General Permitted Development Order states the following:

(a) any building or enclosure, swimming or other pool required for a purpose incidental to the enjoyment of the dwellinghouse as such, or the maintenance, improvement or other alteration of such a building or enclosure.

The Governments technical guidance on the GDPO also states the following:

“A purpose incidental to a house would not, however, 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.”

Residential Annexes are Not an Incidental Use

Therefore residential or ‘granny’ annexes are not a use permitted for outbuildings under the GDPO. To receive approval for such a use you would be required to submit a planning application. This is something I have personal experience of. My own dwelling is an ancillary residential annexe of my parent’s dwelling. Both properties are located within the same curtilage. My home is located within the Green Belt. Therefore, I volunteered a planning condition to restrict the use of the building as a ‘family annexe’ to secure approval.

Ancillary Residential Annex
I secured permission for my own dwelling as an ‘Ancillary residential annexe’.

Something that is worth noting. An ancillary residential annexe comes under a full planning application and not a householder planning application. It would appear to come under a householder application, as the building will be located within the same curtilage as the main dwelling.

‘Reasonably’ Required for an Incidental Use

An incidental use for outbuildings allowed for under GDPO can typically include garden sheds and greenhouses. However, as noted above it can even include a swimming pool. Lawful development certificates (LDC) for proposed development are submitted for various outbuilding uses. However, upon appeal, not all of these uses are deemed to be incidental as they are not ‘reasonably’ required. Let’s look at some examples.

Example 1: Swimming Pools and Social Rooms

This example is an appeal decision on a LDC in April 2019 ( APP/K3605/X/18/3209784). The appeal concerned a quite significant outbuilding of 225m2 for use as a swimming pool, steam room, sauna and social room. Both the council and Planning Inspector agreed that the outbuilding complied with the GDPO in terms of the size of the curtilage and the size of the building.

The Inspector stated that the incidental use of the outbuilding must be reasonably required, and “not rest on the unrestrained whim of a householder”. Furthermore, the use of the outbuilding is used for subordinate activities to the host dwelling. Both the council and Inspector found that the swimming pool, steam room and sauna were an incidental use.

However, the issue was around the size of the social room (which also contained a bar). The Inspector concluded that the size of the social area and the potential number of people using that space at one time would not make it incidental to the main dwelling and dismissed the appeal.

Swimming Pool Incidental Use
While a swimming pool may be interpreted as an incidental use for an outbuilding, associated social rooms may not be.

Example 2: Too much Garage Space?

In December 2018 an appeal decision(APP/H2265/X/18/3198695) was determined on a LDC for a four-car garage of 99m2. The appeal was set to fail as the structure did not comply with GDPO rules around for the size of the building. Furthermore, the Class E rights for outbuildings were removed from the dwelling in the year 2000. However, for this example were are more interested in the Inspectors comments on if the development was incidental. The Inspector stated the following:

“I note that the proposed garage would provide spaces for four cars, while the present Ahremee building already provides garaging for four cars. A total of 8 garage spaces for a two bedroom flat suggests the likelihood of a vehicle use not incidental to use of the dwellinghouse.”

Garage Incidental Use
Don’t presume a new garage is incidental use under the GDPO.

Conclusions on the Difference between Ancillary and Incidental Uses

So as a general rule, ancillary uses will require some form of planning permission. Incidental uses can be permitted development. As seen with the two examples above, whether a use is incidental is open to interpretation. Therefore with certain outbuildings is a good practice to apply for a Lawful Development Certificate. Remember, it is the responsibility of the applicant/appellant or their agent to adequately demonstrate that the use of the outbuilding will be incidental. If you need planning advice or support please get in touch. 🙂