Dutyholders as defined in Regulation 2 of the Building Regulations 2010 (as amended):
Client: Any person for whom a project is carried out (usually the building owner or occupier).
Principal (or sole) Contractor: Any person who, in the course of a business carries out, manages, or controls any building work. Where there are several firms working on different aspects of the project, a domestic client should appoint a Principal Designer to be in control of design work and a Principal Contractor to be in control of the building work.
Principal (or sole) Designer: Any Person who, in the course of a business, carries out any design work or instructs another person to do so, (including a client, contractor or any other person such as a structural/fire engineer etc.). Where there are several firms working on different aspects of the project, a domestic client should appoint a Principal Designer to be in control of design work and a Principal Contractor to be in control of the building work.