Construction compliance guide
Principal contractor duties under CDM 2015 — the plain-English guide
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.
TL;DR
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.
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Who is the principal contractor under CDM 2015?
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
Where there is more than one contractor, 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
On a project with more than one contractor, the PC must ensure every site worker receives a suitable induction. HSE guidance also recommends proportionate inductions for occasional and once-only visitors, with less detail for escorted visitors.
Manage and monitor health and safety on site
The PC must actively manage health and safety throughout the construction phase, not just fill in the paperwork 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.
Check who must display the F10 (if the project is notifiable)
For a notifiable commercial project, the client must ensure an up-to-date F10 is displayed in the site office where workers can read it. A PC may display it on the client's behalf while the client remains responsible. On a domestic project with more than one contractor, the PC holds the F10 display duty by default unless a principal designer agrees in writing to fulfil it.
A practical coordination sequence for a small site
The legal duties above become a site routine. If you are coordinating a two-storey extension, refit or small commercial job, use this sequence before each work stage. Keep it proportionate to the risks and the people doing the work.
Before the first trade starts
- Confirm the appointment and the people involved. Record who the client is, who the principal designer is where one is appointed, which firms are contractors, and who is supervising each work area. For a domestic client, check the domestic-client duty arrangements explained above. Do not assume that an informal “I’m running the job” conversation answers the appointment and duty route.
- Read the information that affects the work. Gather the pre-construction information, drawings, surveys, service information, design decisions, access limits, occupied areas, neighbour constraints and temporary-works requirements. Pass each relevant item to the contractor who needs it. Keep the current drawing or instruction identifiable so an old version is not used by mistake.
- Put the CPP arrangements in place before site setup. Record record work fronts, access and delivery routes, restricted areas, welfare, emergencies, inductions and who can stop work when conditions change. Review the CPP when the job, design or sequence changes.
- Sequence the work and agree handovers. Write down what must be complete before the next trade starts. Mark shared routes, lifting areas, overhead work, live services and places where one trade can affect another. For example, agree when an electrician can follow plastering, who protects a finished surface, and when a groundworker hands back an excavation or route.
- Check competence and resources. Ask each contractor how the work will be supervised, what plant and access are needed, and what information or specialist training is required. Checking a certificate can form part of this, but a document alone does not prove that the proposed people, time, equipment and controls are enough for the actual job.
- Brief and induct the workers. Make sure the site-specific induction covers rules, current hazards, emergency arrangements, access and welfare. Re-brief people when the work stage or site conditions make the old briefing incomplete. Keep the signed record with the project paperwork.
A subcontractor’s RAMS is one input. Check how its method fits the CPP, work area and other trades, then record any action needed. A document check does not by itself prove the work is safe.
When the work or trade changes
Treat a new trade, late delivery, design revision, changed access or altered method as a coordination trigger. Ask what has changed, who could be affected, and what must be controlled before work continues. Tell the affected contractors. Update the relevant CPP arrangement, drawing, RAMS interface, site rule or emergency information. Brief the workers who need the change and record the decision, owner and follow-up date.
If the change creates a risk that is not controlled, stop that part of the work until a competent person has agreed the arrangement. Do not rely on a revised file sitting in an office. The people on site need the current instruction and a route to raise a problem.
Daily and weekly checks
At the start of a work stage, check who is on site, which areas are active, which routes are shared and what each trade is handing over. A short walkaround or supervisor check should look for blocked access, missing controls, changing ground conditions, unsuitable welfare, clashes between work fronts and actions that have not been closed.
Use these questions weekly:
- Which contractors are working this week, and what does each one need from another?
- Have the work fronts, deliveries, access routes or welfare arrangements changed?
- Does the current drawing, CPP and RAMS interface match what is being done?
- Have workers received the induction or update for this stage?
- Which inspection, near miss or corrective action is open, and who owns it?
- What must be ready before the next trade starts?
Record the finding, immediate control, named owner and follow-up. Close an action after checking the work or evidence, not simply because its due date has passed. Statutory inspections still need the competent person, timing and report arrangements that apply to that activity.
Handover and close-out
Before the job finishes, review the work with the client and principal designer where appointed. Gather the health and safety information that may be needed for later work, maintenance, cleaning, alteration or demolition. Pass the health and safety file information through the agreed route and record what was handed over.
Keep the final CPP, relevant RAMS, induction evidence, inspection and action records, change decisions and handover record together. The record shows what was planned, changed and checked. It does not cure a weak arrangement after the event.
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 away from the client — by default to the contractor if there is only one contractor or to the principal contractor if there is more than one contractor, or, where there is more than one contractor, instead to a principal designer if the domestic client agrees in writing that the principal designer will take them on. Either way, the competence check moves with the duties: regulation 8(3) requires whoever appoints a designer or contractor to take reasonable steps to satisfy themselves that they have the skills, knowledge and experience for the role, and regulation 8(7) places that duty, so far as it would otherwise fall on a domestic client, on whoever holds the client duties under regulation 7(1) — you as the only contractor, the principal contractor where there is more than one contractor, or, where there is more than one contractor, the principal designer under that written agreement. Where there is more than one contractor, the written-agreement route does still need the principal designer to agree to it in writing. A homeowner is sensibly advised to pick a capable builder, and the HSE encourages them to ask about a firm’s health and safety track record, but CDM 2015 places no such duty on them. Neither route touches your own duties: the only contractor prepares the Construction Phase Plan on a single-contractor project, while the principal contractor prepares it where there is more than one contractor. If you are working on a domestic job, you cannot say “that’s the homeowner’s problem.” The day-to-day site responsibility is always 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, where there is more than one contractor, 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. That does not leave the role empty: where there is more than one contractor and no principal contractor has been appointed, regulation 7(2) deems the contractor in control of the construction phase to be the principal contractor. In practice, this means the builder running a multi-contractor domestic job is the PC by default. The client’s own duties are a separate matter — on a domestic project with more than one contractor, regulation 7(1) transfers them to that principal contractor by default, or, where there is more than one contractor, to a principal designer under a written agreement.
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
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 with more than one contractor, the situation is different: if no principal contractor is appointed, regulation 7(2) deems the contractor in control of the construction phase to be the principal contractor — there is no PC role to deem on a single-contractor job. On a domestic project with more than one contractor, the client's own duties are a separate question: by default they transfer to that principal contractor under regulation 7(1)(b). Where the client has instead made a written agreement with a principal designer under regulation 7(1)(c) — available only where there is more than one contractor — those client duties stay with the principal designer; the deemed PC still holds the PC role and its own duties. In practice, if you are managing subcontractors on a domestic job (which means more than one contractor) 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 away from the client — by default to the contractor if there is only one contractor or to the PC if there is more than one contractor, or, where there is more than one contractor, instead to a principal designer under a written agreement — so the homeowner does not need to take on any CDM role either way. 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.
What should I do when a new trade arrives halfway through the job?
Check the firm’s role, competence, scope, access, RAMS and supervision arrangements. Review how its work affects the CPP and other contractors. Update the sequence and site information, brief the people affected, and record who owns any follow-up. A new trade can change the coordination arrangements even if the number of people on site has not changed.
Principal Contractor role — rewards and exposures
Pros
- The PC is the single point of accountability — that makes coordination efficient on multi-contractor jobs.
- PC fees price in compliance overhead — you are not absorbing HSE risk for free.
- Where there is more than one contractor, owning the CPP lets the PC set the site rules and drive a proper safety culture from day one.
- Being the PC on reputable jobs is a strong portfolio signal for future work bids.
Cons
- The PC carries the enforcement risk on site — subcontractor breaches usually land on the PC's desk first.
- On a multi-contractor commercial job, appointment in writing makes you PC; on a multi-contractor domestic job without a principal contractor appointment, reg 7(2) deems the controlling contractor PC.
- Running the CPP as a live document (not a write-once file) is a real time cost on medium projects.
- If a PC fails to coordinate design risk with the PD, improvements notices and prosecutions follow quickly.
| Phase | PC duty | Regulation |
|---|---|---|
| Pre-construction | Accept PC appointment in writing from client (more than one contractor) | Reg 5(1) |
| Pre-construction | Domestic job with more than one contractor, no written appointment: the contractor in control of the construction phase is deemed the PC automatically | Reg 7(2) |
| Pre-construction | Draw up the Construction Phase Plan before setting up site (PD supplies relevant information) | Reg 12(1)+(3) |
| Construction | Keep the Construction Phase Plan reviewed, updated and revised as work progresses | Reg 12(4) |
| Construction | Give the Principal Designer information for the H&S File as it arises (the PD prepares and maintains the file itself) | Reg 12(7) |
| Construction | Ensure welfare facilities are provided | Reg 13(4)(c) |
| Construction | Coordinate work of all contractors on site | Reg 13(3) |
| Construction | Ensure site-specific induction + briefing for every worker | Reg 13(4)(a) |
| Construction | If the PD's appointment ends early, keep the H&S File reviewed, updated and revised until handover | Reg 12(9) |
| Handover | Take over the H&S File if the PD's appointment ends early, then pass it to the client | Reg 12(8)+(10) |
“The principal contractor must plan, manage and monitor the construction phase in liaison with the principal designer.”
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Sources
- CDM 2015 — Principal contractor duties — HSE · Accessed 17 April 2026
- CDM 2015, Regulations 5, 12 and 13 — legislation.gov.uk · Accessed 4 September 2026