The short answer
A principal contractor is the contractor appointed in writing by the client to plan, manage, monitor and coordinate health and safety during the construction phase of a project where more than one contractor will work. Their duties include the construction phase plan, site induction, welfare facilities and cooperation between trades. If the client does not appoint one when needed, the client must carry out the role.
On this page
“Principal contractor” is a legal role under the Construction (Design and Management) Regulations 2015, not a job title. On most commercial refurbishments it is held by the main fit-out or refurbishment contractor, but it brings specific duties that the client needs to understand.
When one must be appointed
The client must appoint a principal contractor in writing where more than one contractor will work on the project, at any point. On commercial refurbishment that is almost always the case: strip-out, partitions, mechanical and electrical trades, flooring and decoration are rarely all done by one firm’s own staff.
The appointment should be made as early as possible, and before the construction phase starts. If the client does not appoint a principal contractor where one is needed, the Regulations place the principal contractor’s duties on the client.
What the principal contractor does
| Duty | In practice |
|---|---|
| Plan, manage and monitor the construction phase | Programme, sequencing and supervision with safety in mind |
| Construction phase plan | Written before work starts, proportionate to the risks |
| Coordinate contractors | Share information, manage interfaces between trades |
| Site induction and information | Every worker inducted, site rules explained |
| Welfare facilities | Toilets, washing, drinking water, rest area from day one |
| Secure the site | Prevent unauthorised access, especially in occupied buildings |
| Liaise with the principal designer | Share information that affects design and the health and safety file |
| Consult workers | Give workers a way to raise safety concerns |
Principal contractor and main contractor
The two often describe the same firm, but they are different things. “Main contractor” is a commercial term for the firm that holds the building contract with the client. “Principal contractor” is the CDM role. On a design and build fit-out, the main contractor may also be appointed as principal designer. On a project with several direct contracts (for example an M&E contractor and a fit-out contractor both appointed by the client), the client must decide which one is principal contractor and appoint them in writing.
What the client should check
- The appointment is in writing and names the role.
- The firm has the skills, knowledge and experience for a project of this size and type; ask for similar recent work and how they managed it.
- A construction phase plan exists before work starts, and it reflects the building as it is (occupied, live services, asbestos).
- Welfare is in place from the first day.
- At the end, the principal contractor passes information for the health and safety file to the principal designer.
Competence: what to ask
CDM requires the client to make sure those it appoints have the skills, knowledge, experience and, for organisations, the organisational capability to do the job safely. For a principal contractor on a commercial refurbishment, useful questions include:
- Show us two or three recent projects of similar size, sector and occupancy, and how the site was separated from people using the building.
- Who will be the site manager, and what is their experience of occupied buildings?
- How will you manage asbestos, live services and fire safety during the works?
- What is your process for inducting and supervising subcontractors?
Third-party assessment schemes can help, but they do not replace a conversation about this particular project.
Small projects
On a small job with only one contractor, there is no principal contractor; the single contractor still has its own duties, including a construction phase plan proportionate to the work. Once a second contractor is involved, even briefly (an electrician brought in for a day, for example), the appointment is needed.
Building regulations dutyholders
Since October 2023, the Building Regulations in England also use the terms principal designer and principal contractor, for responsibility for building regulations compliance. Often the same firms hold both roles, but they are separate duties. Ask your contractor to confirm how both are covered.
At handover
At the end of the construction phase, the principal contractor passes the information needed for the health and safety file to the principal designer, who compiles it and gives it to the client. On a refurbishment this typically includes as-built drawings, details of any asbestos left in place, locations of concealed services and maintenance access arrangements. Keep the file with the building.
Where it fits
The principal contractor works alongside the client’s other duties set out on our CDM 2015 client duties page, using the pre-construction information the client provides. For services-led projects, see M&E contractors; for an overview across sectors, see commercial refurbishment contractors.
If you need a contractor able to act as principal contractor, the form below sends them a short brief.