UK construction compliance guide
CDM 2015 explained: dutyholders, duties and when it applies
The Construction (Design and Management) Regulations 2015 (“CDM 2015”) are the main health and safety rules for construction projects in Great Britain. They set out five dutyholders - client, principal designer, designer, principal contractor and contractor - and what each must do to plan, manage and coordinate the work. They apply to every construction project, however small, and a construction phase plan is always required.
Written by Thomas Featherstone, NEBOSH IGC-qualified and IOSH Managing Safely trained · Reviewed July 2026
When do the CDM regulations apply?
CDM 2015 applies to all construction work in Great Britain - building, civil engineering, alteration, fitting out, maintenance, decommissioning and demolition. There is no minimum project size. A homeowner having an extension built and a national contractor on a large site are both covered, though the duties are shared out differently depending on how many contractors are involved and whether the client is commercial or domestic.
The two questions that shape most projects are: is there more than one contractor? (which decides whether a principal designer and principal contractor must be appointed and whether a health and safety file is needed) and is the project notifiable? (which decides whether the client must send an F10 to the HSE).
The CDM dutyholders and what each must do
| Dutyholder | Who it is | Main duties |
|---|---|---|
| Client | Anyone the construction work is carried out for | Makes suitable arrangements for managing the project, provides pre-construction information, ensures other dutyholders are appointed and that welfare is provided. On projects with more than one contractor, appoints the principal designer and principal contractor in writing. |
| Principal designer | A designer appointed by the client on projects with more than one contractor | Plans, manages and monitors the pre-construction phase and coordinates health and safety in design. Helps compile pre-construction information and prepares the health and safety file. |
| Designer | Anyone who prepares or modifies a design, or arranges for it | When preparing or modifying designs, eliminates, reduces or controls foreseeable risks that may arise during construction and the maintenance and use of a building once built. |
| Principal contractor | A contractor appointed by the client on projects with more than one contractor | Plans, manages and monitors the construction phase, coordinates the work, draws up the construction phase plan, secures the site and ensures workers are inducted and consulted. |
| Contractor | Anyone who carries out or manages construction work | Plans, manages and monitors their own work and that of their workers, complies with directions from the principal designer or principal contractor, and (on single-contractor projects) prepares the construction phase plan. |
| Worker | Anyone working for or under the control of a contractor on site | Follows the site rules, reports anything that might endanger themselves or others, and cooperates with the employer and other dutyholders. |
The documents CDM 2015 expects
| Document | When needed | What it is |
|---|---|---|
| Pre-construction information | Every project | Information the client already has or can reasonably obtain about the site and project, given to designers and contractors so they can plan the work safely. |
| Construction phase plan | Every project, including single-contractor and domestic work | Sets out the health and safety arrangements, site rules and specific measures for the construction phase. Must be drawn up before the site is set up. |
| Health and safety file | Only where there is more than one contractor | A record of information useful for anyone carrying out future construction or maintenance work on the building. Prepared by the principal designer and handed to the client at the end. |
The construction phase plan is the one every project needs. Our guide to the construction phase plan explains what to put in it, including the Schedule 3 particular risks.
When is a project notifiable (F10)?
A project is notifiable when the construction work is scheduled to meet either threshold below. Where it is, the client must notify the HSE using form F10 before the construction phase begins. Notifying does not add to or reduce anyone’s duties - a non-notifiable project still has to be planned, managed and documented in the same way.
| Scheduled scale of work | Result |
|---|---|
| Longer than 30 working days AND more than 20 workers at the same time | The project is notifiable to the HSE. |
| More than 500 person-days of construction work | The project is notifiable to the HSE. |
| Below both thresholds | Not notifiable - but every other CDM duty, including the construction phase plan, still applies. |
A common misunderstanding
Many small builders assume CDM only bites on large or notifiable jobs. It does not. The dutyholder roles and the construction phase plan apply to a single-contractor kitchen extension just as they do to a multi-contractor site - the paperwork should simply be proportionate to the size and risk of the work. Notification is an extra step for larger projects, not the trigger for CDM itself.
CDM 2015 FAQs
Common questions
What does CDM stand for?
CDM stands for the Construction (Design and Management) Regulations 2015. They set out how health and safety should be planned and managed across the whole life of a construction project, from concept and design through to construction and future maintenance.
Do the CDM regulations apply to small or domestic projects?
Yes. CDM 2015 applies to all construction work in Great Britain, including small commercial jobs and domestic projects. For domestic clients the client duties usually pass to the contractor, the principal contractor, or the principal designer where there is a written agreement.
When do I need a principal designer and principal contractor?
Whenever there is, or it is reasonably foreseeable that there will be, more than one contractor working on the project. The client must appoint both in writing. On a single-contractor project the contractor takes on the relevant duties instead.
What makes a project notifiable?
A project is notifiable if the construction work is scheduled to last longer than 30 working days and have more than 20 workers working at the same time at any point, or to exceed 500 person-days. The client notifies the HSE using form F10. Notifying does not change anyone's legal duties.
Is a construction phase plan always required?
Yes. A construction phase plan is required for every construction project, even a single-contractor domestic job. It must be drawn up before the construction phase begins.
Does using CDM software make my project compliant?
No. Software can organise the records and coordination CDM expects, but the legal duties stay with the dutyholders and the decisions remain human. Featherstone Safety Hub supports your CDM record keeping; it does not transfer the duties.
Official sources
- HSE - Managing health and safety in construction (CDM 2015)
- HSE L153 - Managing health and safety in construction (guidance)
- CDM 2015 (legislation.gov.uk)
This is a plain-English summary for UK SMEs, not legal advice, and does not replace the current HSE guidance or professional judgement on a specific project. Always check the latest guidance on hse.gov.uk and take advice where you are unsure.
Organise CDM by project
Keep your CDM records together, project by project
Featherstone Safety Hub gives every project its own workspace: dutyholders, F10 details, construction phase plan, RAMS, inspections, inductions, permits and the health and safety file information, with an audit trail as you go. It supports your record keeping; the CDM duties stay with the dutyholders. 14-day free trial, no card required.