The CDM 2015 principal designer
Under regulation 5 of CDM 2015, a client must appoint a principal designer and a principal contractor in writing when there is, or is likely to be, more than one contractor on a project. The principal designer plans, manages and coordinates health and safety in the pre-construction phase. Their duties (regulation 11) include:
- identifying, eliminating or controlling foreseeable risks through design;
- making sure designers comply with their duties;
- helping the client provide pre-construction information;
- passing information to the principal contractor for the construction phase plan;
- preparing the health and safety file.
Domestic projects
A domestic client often won't appoint anyone. If they don't:
- the designer in control of the pre-construction phase becomes the principal designer, and
- the contractor in control of the construction phase becomes the principal contractor.
A domestic client can also agree in writing for the designer to take on the client's duties. For builders, that means on many extensions and refurbishments you are the principal contractor whether you planned to be or not.
The Building Regulations principal designer
From 1 October 2023, the Building Regulations etc. (Amendment) (England) Regulations 2023 introduced a separate set of dutyholders, including a principal designer and principal contractor responsible for planning, managing and monitoring compliance with the Building Regulations. The same firm can hold both the CDM and Building Regulations roles, and on small jobs it often does, but they are different duties.
| CDM 2015 principal designer | Building Regulations principal designer | |
|---|---|---|
| Focus | Health and safety risks of building and using the structure | Compliance of the design with the Building Regulations |
| When needed | More than one contractor | More than one contractor |
| Applies to | Great Britain | England (Wales has similar rules) |
How much does a principal designer cost?
Fees vary with the size and complexity of the project. On small domestic projects, the architect or designer often takes on the CDM principal designer role as part of their fee. On commercial projects it is commonly a separate appointment. Ask for the fee and the scope in writing, and check the appointment covers both roles if you need both.
Frequently asked questions
Do I need a principal designer for a single contractor job?
Under CDM 2015, no. A principal designer is required when there is, or is likely to be, more than one contractor.
Can a builder be the principal designer?
A builder who does design work and controls the pre-construction phase can be, if they have the skills, knowledge and experience to carry out the role.
Who pays for the principal designer?
The client appoints and pays for the role. On domestic jobs it's usually included in the architect's or design-and-build contractor's fee.
Sources
This guide is written from the legislation and HSE guidance below. Last checked 23 October 2026.