The CDM 2015 regulations put a duty on the Principal Designer to:

• “Plan, manage and monitor the pre-construction phase and coordinate matters relating to health and safety during the pre-construction phase to ensure that, so far as is reasonably practicable, the project is carried out without risks to health or safety.”
• Help and advise the client in compiling the pre-construction information and ensuring it gets circulated throughout the project teams as required.
• Work with the designers to eliminate any foreseeable risks. If it is not possible to eliminate them reduce them to the lowest practicable risk.
• Ensure cooperation and effective communication between all parties involved in the pre-construction phase.
• Liaise with the Principal Contractor to ensure they are kept aware of any risks pertaining to the construction phase.

On domestic projects, if the client does not appoint a principal designer the role defaults to the designer in control of the pre-construction phase.