On a design and build contract, the contractor that develops or changes the design is a designer under CDM 2015 and carries the designer duties in Regulation 9. The client keeps its own duties, including making sure a principal designer is in place for as long as the role is needed. Design work does not stop at contract award, so the principal designer role should not stop there either.
The common assumption is simple: the contractor takes the design, so the contractor takes the duty. Part of that is true. The rest is where gaps open.
Who is a designer
Regulation 2 defines a designer as anyone who, in the course of a business, prepares or modifies a design, or arranges for or instructs someone under their control to do so. That expressly includes a client or a contractor. "Design" includes drawings, design details, specifications and bills of quantities, and calculations.
So on design and build:
the contractor is a designer for every part of the design it develops or changes, and for design done by its subcontractors and suppliers under its control;
specialist subcontractors who design their own packages, such as steel connections, cladding fixings or mechanical systems, are designers too;
the client can be a designer too, for example by specifying particular products, since a specification counts as design.
What every designer must do
Regulation 9 applies to all of them. A designer must:
not start work unless satisfied the client is aware of its duties;
take account of the general principles of prevention and the pre-construction information to eliminate foreseeable risks, so far as reasonably practicable;
where risks cannot be eliminated, reduce or control them, tell the principal designer about them, and make sure appropriate information goes into the health and safety file;
provide enough information with the design to help the client, other designers and contractors meet their duties.
The principal designer at contract award
Design and build projects often start with a concept architect or project manager, and the design and build contractor or a novated designer takes over later. HSE's guidance (L153) recognises this: it may be appropriate to end the first principal designer appointment and appoint a new principal designer. What it does not support is no principal designer at all once the contractor takes over.
L153 says the principal designer should be in place for as long as there is a need for the role, taking account of design work that continues into the construction phase. On design and build there is almost always such work. If the appointment lapses at contract award, the coordination of design risk lapses with it, and changes made by the contractor and its supply chain are checked by nobody with an overview.
What the client should do
Decide before tender who will be principal designer after contract award, and make the new appointment in writing at the handover.
Make sure the outgoing principal designer passes on the pre-construction information, the design risk information and the health and safety file.
Check that the incoming principal designer has control over the design work that remains, and the competence to do the role (Regulation 8).
If the principal designer's appointment ends before the project does, make sure the file passes to the principal contractor (Regulation 12(8)), and that the principal contractor is fully briefed on design matters relevant to the remaining work.
Common questions
Can the design and build contractor be both principal designer and principal contractor?
Yes, if it has control over the design and the construction and the competence for both roles. The appointments should still be made in writing, as two roles.
Does a change made on site count as design?
Yes. Changing a detail on site is modifying a design. See changing a detail on site? You may now be the designer.
Who keeps the health and safety file up to date during construction?
The principal designer, or the principal contractor if the principal designer's appointment has ended. See the health and safety file under CDM 2015.
Related: when to appoint a principal designer, the designer: duties start before anything reaches a drawing and our free design review checklist.
This article is general information, not legal advice.