4th May, 2023

What Is A Principal Contractor?

In construction, clients are legally required to appoint a principal contractor under CDM. Most construction projects will need one, but what is a principal contractor? How are they different to a main contractor? And who can be one?

What Is A Principal Contractor? header image

The principal contractor is a role required under the Construction (Design & Management) Regulations - known as the CDM regulations. The CDM regulations apply to every construction project.

The principal contractor is the contractor in overall control of health and safety during the construction work, and the client has to appoint a principal contractor before work starts on their project.

But there are a couple of exceptions to the above rules. Not every construction project will need a principal contractor. And the principal contractor isn't always appointed by the client - in some specific circumstances.

So before we dive into the principal contractor role, let's take a closer look at when the principal contractor needs to be appointed.

When must a client appoint a principal contractor?

The client must appoint a principal contractor - in writing - on any project involving more than one contractor.

5.—(1) 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—

  1. a designer with control over the pre-construction phase as principal designer; and
  2. a contractor as principal contractor.

And this is most construction projects. Because even if the client only appoints a main contractor directly, the chances are that they will use subcontractors during the project.

Often contractors will use other contractors, like scaffolders, groundworkers, electricians, plumbers, gas engineers, plasterers etc. And when there is more than one contractor, you need a principal contractor.

Got a project with only one contractor? Read CDM 2015 For Only One Contractor for guidance on what you need to do.

On any project with more than one contractor, the client needs to appoint the principal contractor in writing - unless it's a domestic client. If the client is a domestic client under CDM, the principal contractor is appointed automatically.

And if the client fails to appoint a principal contractor, and they are not a domestic client, they become the principal contractor.

principal contractor appointment flowchart

What does a principal contractor do?

The principal contractor is responsible for health and safety during the construction phase of the project.

That means they have to:

Find out more in CDM 2015 Principal Contractor Duties Explained.

Who can be a principal contractor?

The principal contractor is:

While the regulations say that the client needs to appoint "a contractor" as the principal contractor, this shouldn't just be a random selection. The principal contractor should be on site (most of the time), and they have various principal contractor duties to complete throughout the project.

There can only be one principal contractor appointed on a project at any one time. And in most cases, the principal contractor won't change during the project.

contractors looking at design

A construction project might have a few contractors involved, but there is usually one contractor managing the work. This contractor might be the one who has been contracted directly by the client, and they will usually be the main contractor or the contractor in charge.

CDM 2015 defines the principal contractor as the contractor with control over the construction phase of the project.

So the person or business appointed as the principal contractor should be in control of the work and the other contractors on site. Usually, this will be the main contractor, but it could also be a project manager or another contractor who is:

In some cases, the client might be the principal contractor. For example, if the client is a developer, they might be the client and the main contractor. As they are managing the construction work on the site, it would make sense to take on the role (and responsibilities) of the principal contractor.

When making or accepting appointments under CDM, you should check for competence. Find out more in CDM competence.

What is the difference between a main contractor and a principal contractor?

Construction projects will often have a contractor who is responsible for the construction work on the project. They will usually be referred to as the main contractor, but could be called:

This contractor might be the only contractor appointed by the client, and they then hire other contractors (referred to as subcontractors) to carry out specialist areas of work (like gas and electric work).

contractors doing paperwork

The main contractor will often be appointed as the principal contractor. It makes sense, because they are the contractor responsible for the work, and they are managing the other contractors anyway. So they are the best (and possibly the only) contractor able to carry out the principal contractor duties on the project.

But not every project has a main contractor, and a main contractor isn't required by law. On some projects, the client might appoint multiple subcontractors, and manage the work themselves. In this case, they won't have a main contractor, but they still need to appoint a principal contractor. And this could be a project manager, for example.

Unlike a main contractor, which is a contractual appointment, the principal contractor is:

That's not to say that other contractors (and main contractors) don't have legal health and safety responsibilities - they do. Every contractor has CDM health and safety duties. But the principal contractor has additional duties because they take overall legal responsibility for health and safety during construction.


Find out more about principal contractor duties in our free CDM duty holder guide for principal contractors. And check your project CDM compliance with the free CDM checklist.

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This article was written by Emma at HASpod. Emma has over 10 years experience in health and safety and BSc (Hons) Construction Management. She is NEBOSH qualified and Tech IOSH.

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