Guidance · Reviewed October 2026
Who the duty holders are, when a principal designer and principal contractor must be appointed, whether your project is notifiable, and the documents CDM actually requires.
The short answer
The Construction (Design and Management) Regulations 2015 set out how health and safety must be planned and managed on construction projects in Great Britain. CDM applies to every project, whatever its size and whoever the client is. What varies is which duties apply: appointments depend on whether more than one contractor is involved, and notification depends on size.
CDM 2015 came into force on 6 April 2015, replacing CDM 2007, which had itself replaced the original 1994 regulations. Northern Ireland has its own equivalent, CDM (NI) 2016, enforced by HSENI.
It is not a paperwork exercise. The emphasis is on getting the right people involved early, sharing information between them, and designing risk out before anyone arrives on site, rather than managing risk through documentation after the fact.
What changed in 2015
If you learned CDM under the 2007 regulations, four things are different:
- The CDM coordinator role was abolished and replaced by the principal designer, who sits inside the design team rather than alongside it.
- Domestic clients are now covered, though their duties normally pass to someone else on the project.
- The notification threshold changed, and notification no longer determines who must be appointed.
- The CDM 2007 Approved Code of Practice (L144) was withdrawn and replaced by HSE guidance on the regulations, L153.
Who CDM Applies To
The regulations create a framework of duties covering everyone involved in a project, from the organisation commissioning the work down to the operatives carrying it out. Each role is a duty holder with its own legally binding responsibilities, and breaching them is a criminal offence. One organisation or individual can hold more than one role; a firm may be both designer and contractor.
Commercial clients
Anyone having construction work done as part of a business. They make the appointments, provide pre-construction information, allow adequate time and resources, and must be satisfied the arrangements for managing health and safety are suitable.
Domestic clients
Individuals having work done on their own home. In practice their duties pass to the contractor, or to the principal contractor where there is more than one, unless there is a written agreement for the principal designer to take them on.
Principal designer
Plans, manages and monitors the pre-construction phase and coordinates the other designers. Required wherever there is more than one contractor, and there can only be one at a time. Covered in full below.
Designers
Architects, engineers, surveyors and technicians: anyone who prepares or modifies a design, or specifies materials or methods. They must eliminate foreseeable risks where possible and reduce or control what remains.
Principal contractor
Plans, manages and monitors the construction phase and coordinates the contractors. Required wherever there is more than one contractor. Draws up the construction phase plan and organises site induction, welfare and site security.
Contractors and workers
Contractors plan and manage their own work and coordinate with others. Workers must be consulted and must report anything they see that is likely to endanger people. As on any workplace, workers cannot be charged for the PPE they need.
The Appointment Test
This is the point most often misunderstood. The trigger for appointing a principal designer and a principal contractor is whether the project involves more than one contractor, not how long it lasts, how many people are on site, or whether it is notifiable to HSE. Both appointments must be made in writing by the client. If the client does not make them, the client must carry out those duties itself.
A one-day job with two contractors needs both appointments. A six-month job with a single contractor does not. Engage even one subcontractor, such as a groundworker, an electrician or a plasterer, and the test is met.
The Principal Designer Role
CDM 2015 abolished the CDM coordinator and created the principal designer in its place. The change was deliberate: the coordinator sat alongside the design team as an adviser, while the principal designer sits inside it, with control over the pre-construction phase. The aim was to put health and safety at the heart of the design process.
The principal designer must be a designer, appointed in writing by the client, on any project involving more than one contractor. There can only be one at a time. The role is often held by the lead architect or design consultant, although specialist CDM consultants also take it on, particularly for clients without in-house expertise.
The duties are to plan, manage and monitor the pre-construction phase; coordinate health and safety matters across the design team; identify and eliminate foreseeable risks, or reduce and control those that cannot be eliminated; make sure designers comply with their own duties; help the client provide the pre-construction information and pass it to every designer and contractor who needs it; prepare the health and safety file, reviewing and updating it as the project progresses; and liaise with the principal contractor throughout.
If you need a principal designer or CDM adviser for a project, our sister site, Raybee, helps you find consultants covering your area and contact them directly.
Two points often get overlooked. First, temporary works designers are designers too. The people designing falsework, propping and excavation support have the same regulation 9 duties as anyone else, and the principal designer must make sure they comply. See Temporary Works Coordinator and Temporary Works Supervisor training.
Second, where a design is prepared or modified outside Great Britain for use on a GB project, the person who commissions it (if based in Great Britain), or otherwise the client, must make sure the regulation 9 designer duties are met.
There are now two principal designers, and they are not the same role
This is a common source of confusion on projects. Since 1 October 2023, the Building Regulations etc. (Amendment) (England) Regulations 2023 have required a Principal Designer (Building Regulations) and a principal contractor on building work in England where there is, or is likely to be, more than one contractor. That includes domestic work such as extensions. The name mirrors the CDM role, but the duties are separate.
| Principal Designer (CDM 2015) | Principal Designer (Building Regulations) | |
|---|---|---|
| Made under | Health and Safety at Work etc. Act 1974 | Building Act 1984, as amended by the Building Safety Act 2022 |
| Focus | Health and safety risks during construction, and in later use, maintenance and demolition | That the design, if built, complies with the Building Regulations |
| Trigger | More than one contractor | Building work with more than one contractor |
| Extent | Great Britain | England (Wales has had its own equivalent since 1 July 2026) |
One organisation can hold both roles if it is competent for each, and the appointment should say which roles it covers. A client can confirm that its CDM principal designer and principal contractor also hold the Building Regulations roles. Assuming one appointment automatically covers both is a common compliance gap.
If a client, consultant or tender document refers to “the principal designer” without saying which, ask which role they mean before you agree to anything. See also building safety.
Is Your Project Notifiable? The F10
Separately from the appointment question, some projects must be notified to HSE before the construction phase begins, using form F10. Under regulation 6, a project is notifiable if the construction work is likely to either:
- last longer than 30 working days and have more than 20 workers working simultaneously at any point, or
- exceed 500 person days in total.
A person day is one person working for one day, so eleven workers for fifty days (550 person days) is over the threshold. Every day on which construction work is likely to be carried out counts, including weekends and holidays, even where the work that day is brief. The duty to notify sits with the client, though someone else can submit it on the client’s behalf. Where a project is notifiable, the notice must be clearly displayed on site and kept up to date.
Free F10 Notification Checker
Rather than working the thresholds out by hand, run the project through our free checker. It applies the regulation 6 test to your programme and worker numbers, tells you whether the project is notifiable and why, shows who must be appointed in writing, lists the documents your project needs, and sets out the details the F10 form asks for, with a printable record at the end. No signup.
Check whether your project is notifiable ↗ Free · on envicourse.com, our course marketplace · opens in a new tab
The Documents CDM Requires
| Document | What it is, and when it’s required |
|---|---|
| Pre-construction information | What the client knows, or could reasonably obtain, about the site and the project, provided to the designers and contractors who need it. Required on every project. |
| Construction phase plan | How health and safety will be managed during the build. Required on every project, including single-contractor domestic jobs, and it must be drawn up before the construction phase starts. Size affects the length, not whether you need one. |
| Health and safety file | Information anyone will need to manage risk during future work on the structure. Required only where there is more than one contractor. Prepared by the principal designer and handed to the client at the end. |
| Welfare facilities | Not a document, but required throughout the construction phase: toilets, washing, drinking water, rest and changing arrangements to the standard set out in Schedule 2. |
Frequently Asked Questions
Does CDM apply to my project?
Yes. CDM 2015 applies to every construction project in Great Britain, whatever its size, duration or client. What varies is which duties apply: the appointment of a principal designer and principal contractor depends on whether more than one contractor is involved, and notification depends on the size thresholds.
Is the CDM coordinator role still current?
No. CDM 2015 abolished it from 6 April 2015 and replaced it with the principal designer. If a tender document, contract or job advert still refers to a CDM coordinator, it is using out-of-date terminology. Clarify what they actually want, because the two roles sit differently in the project.
Do weekends and bank holidays count towards the 30 days?
Yes. HSE’s guidance is that every day on which construction work is likely to be carried out should be counted, including holidays and weekends, even where the work that day is of short duration.
Who has to submit the F10?
The client holds the duty to notify. In practice the client often asks someone else, such as the principal designer or principal contractor, to submit it on their behalf. That is permitted, but the duty stays with the client, so the client should check it has been done.
Do we need a construction phase plan on a small job?
Yes. A construction phase plan is required on every project, including single-contractor and domestic work, and it must be in place before construction starts. A short, specific plan covering site rules, welfare, emergency arrangements and the significant risks is proportionate for a small job. A generic template that hasn’t been adapted to the site is a common failing.
Does CDM apply to maintenance work?
Not to all of it. The definition of construction work did not change under CDM 2015, so some maintenance is construction work and some is not. It depends on the nature of the work rather than what it is called, which is why routine servicing and a refurbishment can fall on opposite sides of the line.
What happens if we don’t have a plan or haven’t notified?
Breaching CDM duties is a criminal offence under section 33 of the Health and Safety at Work etc. Act 1974, enforced by HSE. Beyond prosecution, where an inspector finds a material breach HSE can recover its costs under Fee for Intervention, so a site visit over a missing construction phase plan can carry a cost even where nothing further follows.
Does CDM apply in Northern Ireland and Scotland?
CDM 2015 covers Great Britain: England, Scotland and Wales. Northern Ireland has its own equivalent, CDM (NI) 2016, enforced by HSENI. The separate Building Regulations principal designer role applies in England, and Wales introduced its own equivalent from 1 July 2026.
On-Site Responsibilities and Training
Safe management should be designed into a project from the outset, so that the principal contractor is given something that can actually be built safely. Beyond that, everyone carrying out the work needs to understand the risks they face and create.
The principal contractor should establish a positive culture of safety on site: proper induction for visitors, contractors and subcontractors, workers who are competent for the roles they are given, and a genuine willingness to report hazards and get them dealt with rather than work around them.
CDM is not about generating paperwork. It is about creating safe working environments for workers, visitors and clients, with the minimum documentation needed to do that. A health and safety risk review will identify what your arrangements are missing before a client asks.
| If you need to… | Usual route |
|---|---|
| Understand CDM generally | CDM Awareness or CDM: An Overview. |
| Act as designer or principal designer | CDM for Designers and Principal Designers. |
| Act as contractor or principal contractor | CDM for Contractors and Principal Contractors. |
| Apply it on live projects | CDM 2015 in Practice, or Breaking Ground in Construction for duty holders. |
| Manage or supervise a site | SMSTS for site managers, SSSTS for supervisors. |
| Qualify formally | NEBOSH Construction Certificate, or browse all CDM training courses. |
Related Guidance
General guidance only, reviewed in October 2026 against CDM 2015, HSE guidance L153 and the Building Regulations 2010 Part 2A. Check current requirements with HSE. Envico is an independent training intermediary and is not affiliated with the HSE.