PPS 7 (Addendum): Residential Extensions and Alterations
2.8 There may be occasions when people wish to provide ancillary accommodation to provide additional living space for elderly relatives or to meet a variety of other personal and domestic circumstances.
2.9 To be ancillary, accommodation must be subordinate to the main dwelling and its function supplementary to the use of the existing residence. Such additional accommodation should normally be attached to the existing property and be internally accessible from it, although a separate doorway access will also be acceptable.
2.10 Where an extension to the existing house is not practicable and it is proposed to convert and extend an existing outbuilding, planning permission will normally depend on the development providing a modest scale of accommodation. The purpose of this is to ensure the use of the building as part of the main dwelling. The construction of a separate building, as self contained accommodation, within the curtilage of an existing dwelling house will not be acceptable, unless a separate dwelling would be granted permission in its own right. Other proposals for ancillary residential use which are clearly incidental to the enjoyment of the property, such as a garden room or a gazebo, will be treated on their merits within the terms of the policy.
2.11 In all cases the Department will need to be satisfied that the proposed accommodation will remain ancillary to the main residential property and careful consideration will be given to the impact of proposals on neighbouring dwellings. Where permission is granted it will be subject to a condition that the extension will only be used for ancillary residential purposes in connection with the main dwelling, and not as a separate unit of accommodation.