Principal Contractor Duties Under CDM 2015: What You're Actually Responsible For

On smaller projects — the kind most of my readers work on — the main contractor often ends up as the principal contractor almost by default. The client's agent writes it into the pre-construction information, the main contractor signs the contract, and suddenly you've got a legal duty that carries personal criminal liability.

I've met plenty of site managers and directors who hold the PC role without fully understanding what it means. They know it has something to do with health and safety. They know there's a construction phase plan involved. Beyond that, the detail gets fuzzy.

That fuzziness is dangerous. CDM 2015 places specific, enforceable duties on the principal contractor. Getting it wrong doesn't result in a contractual dispute — it results in an enforcement notice, a prosecution, or a visit from the HSE after someone gets hurt.

The Core Duty

Regulation 13 of CDM 2015 sets out the principal contractor's duties. The overarching requirement is to plan, manage, and monitor the construction phase so it's carried out without risks to health and safety, so far as is reasonably practicable.

That phrase — "so far as is reasonably practicable" — is important. It doesn't mean eliminating all risk. It means doing what a competent contractor would reasonably do, given the nature of the work, the level of risk, and the cost of preventive measures. It's a proportionate standard.

But the specific duties underneath that overarching requirement are where the practical obligations sit.

The Construction Phase Plan

This is duty number one. Before the construction phase begins, the principal contractor must draw up (or arrange for) a construction phase plan. Under Schedule 3, the plan must include:

• A description of the project and the management arrangements
• Arrangements for controlling significant risks, including site access, emergency procedures, and welfare
• The health and safety file arrangements

The construction phase plan doesn't need to be a 200-page document. For a straightforward fit-out project, it might be 15 to 20 pages. What matters is that it addresses the actual risks on the actual project — not generic risks from a template.

I've reviewed construction phase plans that contained detailed sections on demolition, piling, and steel erection on a project that was a simple office refurbishment. That's not compliance — that's copying a template without thinking about it.

The plan should be a living document. Update it when conditions change, when new trades arrive on site, or when risks emerge that weren't anticipated at the start.

Cooperation and Coordination

The principal contractor must ensure cooperation between all persons working on the project. In practice, this means:

Inductions. Every worker on site must receive a site-specific induction before starting work. Not a generic health and safety video — a briefing that covers the specific risks, rules, and emergency procedures for this project, this site.

Communication. The PC must ensure that contractors (including subcontractors) are given appropriate directions and information. This means sharing the construction phase plan, communicating changes, and making sure everyone knows who's doing what, where, and when.

Coordination of work activities. When two trades are working in the same area, or when one trade's work creates risks for another, the PC must coordinate. Wet trades below dry trades. Hot works near combustible materials. Overhead work above occupied areas. These interfaces need managing, and that management sits with the PC.

Site Rules and Enforcement

The principal contractor must establish site rules that are appropriate for the project. These might cover PPE requirements, working hours, permit-to-work systems, housekeeping standards, or exclusion zones.

Having rules isn't enough — you need to enforce them. An HSE inspector asking about your site rules will follow up with "and how do you ensure compliance?" If the answer is "we told everyone at induction," that's not enforcement. Regular site inspections, toolbox talks, and a clear process for dealing with non-compliance are what demonstrates active management.

This is where the small contractor PC often falls short. The site manager is running the project, managing subcontractors, dealing with the client, and trying to do the health and safety coordination on top of everything else. It's too much for one person on a busy project. If you're taking on the PC role, you need to resource it properly — either with a dedicated person or by giving the site manager enough support that they can actually do the job.

The Health and Safety File

The PC must prepare, review, revise, and update the health and safety file as the project progresses, and hand it to the client at practical completion. The file should contain information about the completed works that's relevant to future maintenance, repair, or demolition.

For a fit-out project, this typically includes: as-built drawings showing the location of services, structural alterations, and hidden features; information about hazardous materials; details of any specialist installations; and operating and maintenance manuals for installed equipment.

The health and safety file is often the forgotten obligation. Everyone remembers the construction phase plan because it's needed at the start. The H&S file, due at the end, gets assembled in a rush at practical completion — or worse, never gets completed at all.

Subcontractor Management

One of the most important practical aspects of the PC role is ensuring that subcontractors are competent and adequately resourced. Under CDM 2015, the duty sits with whoever appoints a contractor (which includes subcontractors). As the main contractor appointing subbies, you need to satisfy yourself that each firm has the skills, knowledge, and resources to carry out their work safely.

This doesn't mean demanding folders of health and safety qualifications and CHAS certificates (though those have their place). It means asking practical questions: have they done this type of work before? Do they have the right equipment? Do they have enough people? Are their RAMS specific to this project?

When a subcontractor's work on site doesn't match their method statement, that's your problem as PC. You need to stop the work, discuss it, and resolve it before it continues.

What Catches People Out

Thinking the RAMS are enough. Having a drawer full of subcontractor RAMS isn't the same as managing health and safety. The PC's duty is active management — monitoring what's actually happening on site, not just filing paperwork.

Not updating the construction phase plan. The plan written before the project started reflects conditions at that time. Three months in, with two new subcontractors, a design change that introduces hot works, and scaffolding that wasn't in the original plan — the construction phase plan needs updating.

No record of inspections. If the HSE visits, one of the first things they'll ask for is evidence of regular inspections and monitoring. If you can't show a record of site safety inspections, you're not demonstrating active management.

Ignoring the welfare obligation. CDM 2015 requires the PC to ensure adequate welfare facilities. Toilets, washing facilities, rest areas, drinking water. On a refurbishment project in an occupied building, this sometimes falls through the cracks — "the client's toilets are available." That might work, or it might not meet the requirements. Check.

Being Practical About It

The PC role is serious but manageable. The key is systems: a structured induction process, a regular inspection regime, a documented approach to coordinating trades, and a method for updating the construction phase plan.

In Construction AI, the site management module handles inspections, site diary records, and safety documentation — construction health and safety software designed around how PCs actually work. Combined with project management tools for tracking RAMS and method statements, it gives you a framework for demonstrating active management. But the systems only work if someone's using them daily — not catching up on Friday afternoon.

If you're a small contractor taking on the PC role, resource it properly. Understand the duties. And take them seriously — not because the HSE might visit, but because the people on your site deserve to go home safely.