CDM 2015 for HV designers: your duties before anyone digs

TL;DR. CDM 2015 puts duties on designers from the first drawing, not only on the site team. Designers must eliminate foreseeable risk so far as reasonably practicable, reduce or control what remains, and pass the information on. Where more than one contractor will work on a project, the client must appoint a principal designer and a principal contractor in writing before construction starts. Some projects must also be notified to HSE.

What is CDM 2015?

It is the Construction (Design and Management) Regulations 2015, Statutory Instrument 2015 No. 51. They set out how health and safety is managed across a construction project. HSE lists the duty holders as commercial clients, domestic clients, designers, principal designers, principal contractors, contractors and construction workers.

What must a designer do?

Regulation 9 sets the designer’s duties. In summary:

• Before starting, a designer must be satisfied that the client is aware of the client’s duties under the Regulations.
• When preparing or modifying a design, a designer must take into account the general principles of prevention and any pre-construction information, to eliminate so far as is reasonably practicable foreseeable risks to people carrying out or affected by construction work, people maintaining or cleaning the structure, and people using a structure designed as a workplace.
• If a risk cannot be eliminated, the designer must take steps to reduce it or, if that is not possible, control it through the rest of the design. The designer must also give information about those risks to the principal designer and make sure appropriate information goes in the health and safety file.
• With the design, a designer must take all reasonable steps to provide enough information about the design, construction or maintenance of the structure to help the client, other designers and contractors comply with their own duties.

For a substation design, the practical reading is that the people who will build it, maintain it and work in it are all in scope, so design decisions need their safety consequences recorded where the project team can find them.

When does a project need a principal designer?

Where there is more than one contractor, or it is reasonably foreseeable that more than one will work on the project at any time, the client must appoint in writing a designer with control over the pre-construction phase as principal designer, and a contractor as principal contractor. The appointments must be made as soon as practicable and in any event before the construction phase begins.

If the client fails to appoint a principal designer, the client must fulfil the principal designer’s duties. If no principal contractor is appointed, the client must fulfil that role’s duties. This is worth saying to a client early, because many clients assume the duty belongs to somebody else.

What does the principal designer do?

HSE describes the role as a designer, an organisation or, on smaller projects, an individual, appointed by the client where a project involves more than one contractor. The principal designer must plan, manage, monitor and coordinate health and safety in the pre-construction phase. That includes working with other designers to eliminate foreseeable risks, helping the client gather pre-construction information and passing it to designers and contractors, and keeping the principal contractor informed of risks that must be controlled during construction. The regulations also require the principal designer to ensure all designers comply with their own duties.

Does the project have to be notified to HSE?

Only if it is 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, or to exceed 500 person days. The client must notify HSE in writing, as soon as practicable before the construction phase begins, using the F10 form. The notice has to be displayed in the site office where workers can read it.

Notification is separate from the appointments above. Appointing a principal designer and principal contractor is not conditional on the project being notifiable.

What should a design team keep?

• The client’s awareness. A note that the client was told of their duties before you started.
• A design risk record. What you eliminated, what you reduced, what remains, and who was told.
• What went to the principal designer. Dated, so the trail shows the information moved.
• What went into the health and safety file. The information the file needs about the structure, for the people who will use and maintain it later.

None of this turns a template into a risk assessment. Whether a risk has been eliminated or controlled so far as is reasonably practicable is a judgement for the responsible designer.

Sources

Accessed 14 October 2026.

• The Construction (Design and Management) Regulations 2015, regulation 5, legislation.gov.uk.
• Regulation 6, notification, legislation.gov.uk.
• Regulation 9, duties of designers, legislation.gov.uk.
• Regulation 11, principal designer, legislation.gov.uk.
• CDM 2015, commercial clients, Health and Safety Executive.
• CDM 2015, principal designers, Health and Safety Executive.
• CDM 2015 overview, Health and Safety Executive.