CA92500 | Structures and buildings allowance (SBA): use: residential use
From HM Revenue & Customs · Capital Allowances Manual
A building is in residential use, and therefore excluded from SBA, if it is used as, or for purposes ancillary to use as:
A building is treated as being in residential use if it is ancillary to a residential building, or situated on land intended to be occupied or enjoyed with a building in residential use. For example, swimming pools located in the grounds of a dwelling and facilities, gyms, cinemas and car parks provided as facilities for dwelling houses such as a block of flats would be ancillary and therefore excluded from SBA.