Residential conversion project is defined as an existing apartment house, apartment hotel, hotel, or multiple dwellings used exclusively for residential purposes, proposed for conversion to a condominium, stock cooperative, or community apartment project to be used exclusively for residential purposes through approval of a tract map or parcel map. For purposes of this definition, the term existing means that the building was constructed prior to 1945 or, where built after 1945, a Certificate of Occupancy has been issued for the building prior to the time of map application.