Yes, building regulation consent is required if you intend to install a new bathroom, WC or shower room in a room which was not previously used for that purpose. Consideration will need to be given to the various issues including whether the existing structure is adequate if a bath is being installed and ensuring suitable extract ventilation is provided, etc. In some cases, the company undertaking these works may be registered with a competent scheme, such as APHC, Benchmark, BESCA, Certsure, HETAS, NAPIT or Stroma. If this is the case, the installer will register the works with their scheme provider and the local authority will receive notification that these works have been undertaken. You are advised to check that the installer is registered and can self-certify the works under the provisions of the building regulations, since if these works are undertaken without suitable certification, the works would be considered unauthorised. If you intend to replace existing fittings within an existing bathroom, building regulation consent is not required.