Belfast·SPG004 Residential Extensions and Alterations·Page 30·4.1.31-4.1.32
Ancillary accommodation and use conditions
Extensions creating separate dwelling units within the curtilage of existing properties will not be acceptable unless they would qualify as separate dwellings in their own right. Any permission granted must include a condition restricting use to ancillary residential purposes only.
In all other cases the Council will need to be satisfied that the proposed accommodation will remain ancillary to the main residential property. 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.
Source — /Users/richardhill/Documents/planning-arch-project/data/documents/belfast/SPG004 Residential Extensions and Alterations.pdf