What Is a Principal Designer Under CDM 2015? Duties Explained

A practical guide for UK site managers, contractors and small builders.

The principal designer is the person the client puts in charge of managing health and safety during the design and planning stage of a construction project. Under CDM 2015 the role is about designing risk out of a job before anyone reaches for a tool, and it is required whenever more than one contractor is involved. It is easy to confuse with the principal contractor, but they sit at opposite ends of the same project. Here is what a principal designer is, when the role is required, what the duties actually are, and how it differs from the principal contractor in plain English.

What a principal designer actually is

A principal designer is a designer, an organisation or an individual, appointed by the client to take control of the pre-construction phase of a project. Pre-construction means everything up to the point work starts on site: the design work, the planning, and the decisions that lock in how a building will be built. The principal designer's job is to make sure health and safety is planned in from the start, not bolted on at the end. It is a coordinating role, so the principal designer does not have to draw every detail themselves, but they do have to pull the design side together so that foreseeable risks are spotted and dealt with early.

When a principal designer is required

The trigger is simple. On any project where there is, or is likely to be, more than one contractor, the client must appoint a principal designer in writing. That is the same trigger that requires a principal contractor, so on most jobs with two or more contractors you need both. If only one contractor is involved the roles are not required, though the health and safety duties themselves still apply. The appointment should be made early, because the whole value of the role is in shaping decisions before the design is fixed. If the client does not make the appointment, the client takes on the principal designer duties by default.

The main duties

The principal designer's duties all point at one thing, managing health and safety risk in the design and planning stage. In practice the role covers:

• Plan, manage and monitor the pre-construction phase so that the project is prepared with health and safety in mind.
• Help designers eliminate, reduce or control foreseeable risks through their design decisions, applying the general principles of prevention.
• Coordinate health and safety across the design so that different designers are not working against each other.
• Assist the client with pre-construction information, helping gather it and making sure it reaches every designer and contractor who needs it.
• Liaise with the principal contractor, sharing information relevant to the construction phase plan and any design that continues once work has started.
• Prepare the health and safety file where one is required, and hand it over at the end for whoever works on the structure next.

The thread running through all of it is foresight. The principal designer is the person best placed to remove a hazard by changing a design, rather than leaving the contractor to manage it on site.

Designing risk out at the front end

The reason the role exists is that the cheapest and safest place to deal with a hazard is on the drawing, not on the scaffold. A designer who specifies a different material, changes an access route, or moves a plant location can remove a risk entirely before it ever reaches site. The principal designer's coordinating job is to make sure that thinking happens across the whole design and gets recorded, so contractors inherit a project where the obvious dangers have already been designed out and the ones that remain are clearly flagged. Good pre-construction information out of this stage feeds straight into a sharper construction phase plan.

Who appoints the principal designer

Appointing the principal designer is a client duty under CDM 2015, and it must be done in writing. The client should appoint someone with the skills, knowledge, experience and, for an organisation, the organisational capability to carry out the role. On a domestic project the client duties generally pass to others, so the principal designer, principal contractor or contractor picks them up rather than the homeowner. On commercial work the client is squarely responsible for making the appointment, and for making it early enough to matter.

Principal designer versus principal contractor

The two roles are easy to mix up because the names are similar and both are triggered by having more than one contractor. The difference is timing and focus. The principal designer runs health and safety during the pre-construction phase, the design and planning stage. The principal contractor takes over for the construction phase, managing health and safety while work is actually happening on site. One designs the risks out, the other manages what is left as the building goes up. On many projects there is a handover point where the principal designer passes pre-construction information and, where relevant, the emerging health and safety file across to the principal contractor. They are two halves of the same duty, split across the life of the job.

Frequently asked questions

This article is general guidance for UK construction and is not legal advice. For requirements specific to your work, check current HSE guidance and your own duty holder obligations under CDM 2015.