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Construction compliance guide

Principal Contractor vs Contractor: What’s the Difference?

CDM 2015 principal contractor duties explained in plain English. What the role means, how it differs from a regular contractor, and how to know when you are the PC.

CDM 2015 duty holders explained

The Construction (Design and Management) Regulations 2015 define five duty holder roles: client, principal designer, principal contractor, contractor, and worker. Each role carries its own set of legal duties, and understanding which role you hold on a given project is the first step to getting compliance right.

On any project with more than one contractor, the client must appoint both a principal designer and a principal contractor. The principal designer leads health and safety in the pre-construction phase; the principal contractor leads it during the construction phase.

On projects with only one contractor, there is no requirement to appoint a principal designer or principal contractor. Instead, the sole contractor picks up the relevant duties directly — including producing the Construction Phase Plan.

What does a principal contractor do?

The principal contractor (PC) is the contractor appointed by the client to plan, manage, monitor, and coordinate health and safety during the construction phase. Their core duties under CDM 2015 are:

Prepare and maintain the Construction Phase Plan

The PC must draw up the CPP before the construction phase begins and keep it up to date throughout the project. The plan must be proportionate to the risks and complexity of the work.

Coordinate health and safety between all contractors

Where multiple firms are working on site, the PC is responsible for making sure their activities do not create risks for each other. This means managing sequencing, shared access routes, and overlapping work areas.

Ensure all workers receive a suitable site induction

Every person who comes onto site must receive an induction covering the site rules, key risks, emergency procedures, and welfare arrangements. The PC must make sure this happens — even for subcontractors’ employees.

Manage and monitor health and safety on site

The PC must actively manage health and safety throughout the construction phase, not just write a plan and hope for the best. This includes carrying out regular checks, addressing issues promptly, and keeping records.

Liaise with the principal designer

The PC must work with the principal designer to share information about risks, design decisions that affect buildability, and any changes that emerge during construction.

Ensure welfare facilities are in place

Toilets, washing facilities, drinking water, rest areas, and somewhere to change and store clothing must all be provided before work starts and maintained throughout the project.

Display the F10 notification (if the project is notifiable)

If the project exceeds the notification thresholds — more than 30 working days with more than 20 workers, or more than 500 person-days — the PC must display a copy of the F10 in a visible location on site.

Contractor duties under CDM 2015

Every contractor on site — whether they are the PC or not — has their own set of duties under CDM 2015. These apply to sole traders, small firms, and large subcontractors alike:

  • Plan, manage, and monitor their own work to ensure it is carried out safely
  • Ensure workers under their control are competent and properly supervised
  • Provide relevant information to the principal contractor
  • Comply with the Construction Phase Plan and any site rules set by the PC
  • Report anything likely to endanger health and safety to the PC

The key difference is this: contractors are responsible for their own work; the principal contractor is responsible for coordinating everyone’s work. A subcontractor must make sure their team is working safely. The PC must make sure all the teams on site are working safely together.

Client duties

The client — the person or organisation paying for the work — also has duties under CDM 2015. They must:

  • Make suitable arrangements for managing the project, including adequate time and resources
  • Ensure adequate welfare facilities are provided from the start
  • Appoint a principal designer and principal contractor (if more than one contractor is involved)
  • Provide pre-construction information to designers and contractors
  • Ensure the Construction Phase Plan is in place before work starts on site

On domestic projects, these duties transfer automatically to the contractor or principal contractor. The homeowner does not have to do anything — but that means the builder picks up the responsibility. If you are working on a domestic job, you cannot say “that’s the homeowner’s problem.” It is yours.

When are you the principal contractor?

If there are two or more contractors on site, someone must be the principal contractor. This includes subcontractors — if you hire a plumber and an electrician, that is three contractors (including you), and the project needs a PC.

On commercial projects, the client appoints the PC in writing. It is usually the main contractor, but it can be any competent contractor involved in the project.

On domestic projects, the homeowner rarely makes a formal appointment. Instead, the client duties — including the duty to appoint a PC — transfer automatically to the contractor who is in charge of the construction phase. In practice, this means the builder running the job becomes the PC by default.

Many small builders end up being the principal contractor without realising it. If you are managing subcontractors on a domestic job — deciding when they come to site, telling them where to work, coordinating their activities — you are almost certainly the PC. The duties apply whether or not anyone has used the words “principal contractor.”

How The Site Book helps

The Site Book identifies your role based on your project setup and ensures your documentation matches your duties. You tell us about the project — how many contractors are involved, whether the client is domestic or commercial — and we work out whether you are the principal contractor, the only contractor, or a contractor under a PC.

If you are the PC, The Site Book creates a full Construction Phase Plan with coordination sections — covering how you will manage multiple contractors, site inductions, welfare facilities, and emergency procedures. It also creates site induction content, so every subcontractor who comes on site gets a proper briefing.

If you are a contractor working under a PC, The Site Book creates RAMS appropriate to your scope of work. You get site-specific Risk Assessments and Method Statements that you can hand to the PC as part of their coordination requirements.

Either way, you end up with the right documents for your role — no guesswork, no generic templates, and no paying a consultant to tell you what CDM already says in plain English.

Frequently asked questions

Common questions builders ask about principal contractor duties.

Can a sole trader be a principal contractor?

Yes. There is nothing in CDM 2015 that prevents a sole trader from being the principal contractor. The regulations do not require a specific company structure, turnover level, or number of employees. If you are the contractor managing and coordinating the construction phase on a project with more than one contractor, you are the principal contractor — regardless of whether you are a sole trader, a partnership, or a limited company. What matters is competence: you must have the skills, knowledge, experience, and organisational capability to carry out the role. For most domestic projects with a couple of subcontractors, a competent sole trader is perfectly capable of fulfilling principal contractor duties.

What’s the difference between principal contractor and main contractor?

‘Main contractor’ is a commercial term used in contracts to describe the firm that wins the job and manages the build. ‘Principal contractor’ is a legal term defined by CDM 2015 — it refers to the contractor appointed by the client to plan, manage, monitor, and coordinate health and safety during the construction phase when more than one contractor is involved. In practice, the main contractor and the principal contractor are usually the same company, but they do not have to be. The client can appoint any competent contractor as the PC, even if that contractor is not the main contractor commercially. The key distinction is that ‘principal contractor’ carries specific legal duties under CDM 2015, whereas ‘main contractor’ is simply a contractual role.

Do I need to be SSIP accredited to be a principal contractor?

No. There is no legal requirement under CDM 2015 to hold SSIP (Safety Schemes in Procurement) accreditation or any other third-party certification in order to act as the principal contractor. CDM 2015 requires that you are competent — that you have the skills, knowledge, experience, and organisational capability to fulfil the role — but it does not mandate a specific accreditation scheme. That said, many commercial clients and tier-one contractors will require SSIP accreditation (such as CHAS, SafeContractor, or Constructionline) as a pre-qualification requirement before they will appoint you. On domestic projects, accreditation is rarely requested. Whether or not you hold accreditation, the legal duties of the principal contractor are the same.

What happens if no one is appointed as principal contractor?

If a project has more than one contractor and the client fails to appoint a principal contractor, the client is in breach of CDM 2015. However, this does not let anyone else off the hook. On a commercial project, the client retains the duty to appoint and the HSE can take enforcement action against them. On a domestic project, the situation is different: because domestic client duties transfer automatically to the contractor or principal contractor, the contractor who is in control of the construction phase effectively inherits the PC role by default. In practice, if you are managing subcontractors on a domestic job and no one has been formally appointed as PC, you are almost certainly carrying out the role — and the duties apply to you whether or not anyone has used the words ‘principal contractor.’

Can the client be the principal contractor?

Yes, but only if the client is a contractor themselves — that is, they carry out, manage, or control construction work. A developer who employs their own site team and manages the build directly could, in theory, act as both the client and the principal contractor. However, a homeowner who is simply commissioning work is not a contractor and cannot be the principal contractor. On domestic projects, the client duties transfer automatically to the contractor or PC anyway, so the homeowner does not need to take on any CDM role. In practice, it is unusual for the client to act as PC because the role requires hands-on management of the construction phase, which most clients are not equipped to do.

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Related guides

CDM 2015 for Small Builders

Your duties under CDM 2015, explained without the jargon.

What is a Construction Phase Plan?

A plain-English guide to CPPs for UK builders.

F10 Notification Guide

When you need to notify the HSE and how to submit your F10.

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