Principal designer
When is a CDM principal designer required?
Short answer
A CDM principal designer must be appointed whenever a project involves, or it is reasonably foreseeable that it will involve, more than one contractor at any time. That is the whole test. It does not depend on the value of the work, the length of the programme, whether the project is notifiable, or whether the client is a homeowner or a business. The appointment must be in writing and must be made as soon as is practicable, and in any event before the construction phase begins.
The rule
Regulation 5(1) and 5(2): where there is more than one contractor, or if it is reasonably foreseeable that more than one contractor will be working on a project at any time, the client must appoint in writing a designer with control over the pre-construction phase as principal designer, and a contractor as principal contractor. The appointments must be made as soon as is practicable, and in any event before the construction phase begins.
What is not part of the test
| Often assumed to matter | Actually |
|---|---|
| The value of the works | Irrelevant. A £30,000 extension with a builder and an electrician needs one; a £300,000 single contractor job may not |
| Whether it is a house or a commercial building | Irrelevant to the trigger. CDM applies to domestic projects, though regulation 7 changes who carries the client duties |
| Whether the project is notifiable | A separate test with separate thresholds. Most domestic projects need a principal designer and are not notifiable |
| How many designers are involved | Not part of the test at all. The trigger counts contractors, not designers |
| Whether planning permission is needed | Nothing to do with it |
How this works in practice
Take an ordinary single storey rear extension. One builder is appointed. So far, one contractor. Then the builder brings in a groundworker for the foundations, an electrician to move the consumer unit, and a plasterer at the end. That is four contractors, and the project crossed the line the moment it was reasonably foreseeable that it would.
That last phrase does most of the work. You do not wait until the second contractor turns up. If at the point of designing the job it is obvious that specialist trades will be needed, it is reasonably foreseeable, and the appointment is required from then.
The genuinely single contractor project exists, but it is rarer than people think: a builder who does everything themselves, with nobody subcontracted in. If that is the position, no principal designer appointment is required, although CDM still applies and the contractor must draw up a construction phase plan under regulation 15(5).
When it has to be in place
As soon as is practicable, and before the construction phase begins. In practice that means during design, because the role is about the pre-construction phase: an appointment made the week before the builder starts has already missed most of what it exists to do.
Appointing late is better than not appointing, but the sensible point is when the design is taking shape and the drawings are starting to fix how the work will actually be built.
What this means for you
Clients: assume you need one unless you are genuinely certain a single contractor will do every part of the work. If in doubt, the free checker walks the test in six questions.
Designers: if the client has not made the appointment on a domestic project, the regulation does not simply wait. See whether it lands on you.
Sources
- CDM 2015, regulation 5: appointment of the principal designer and the principal contractor legislation.gov.uk
- CDM 2015, regulation 7: application to domestic clients legislation.gov.uk
- CDM 2015, regulation 15: duties of contractors legislation.gov.uk
- HSE: principal designers, roles and responsibilities hse.gov.uk
- Managing health and safety in construction, L153 HSE guidance on the Regulations
Find out where your project stands
The free checker asks six questions and tells you whether the appointment is required, and why.
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