The principal designer will lead during the pre-construction phase but will continue through the construction phase as design changes are likely to continue to occur as the building work occurs this often means that different individuals play this role during the course of a project.

CDM Part 1 is mainly relevant to the pre-construction phase and involves checking whether or not CDM is applicable.

Once the build tender has been let, the principal contractor, appointed by the client, has overall control of the construction phase and is responsible for managing all contractors and their workers.

CDM Part 2, led by the client, is about ensuring that the right duty holders are engaged. It then requires that appropriate designs are drawn up, and the pre-construction information supporting the implementation of a safe project is gathered.

CDM Part 3 of the regulations becomes relevant during the construction phase and stipulates safety precautions to be in place to ensure that the building work is planned and carried out safely.