CDM vs Building Regulations principal designer

What is the difference between the two principal designers?

The CDM principal designer manages health and safety risks in the pre-construction phase under the Construction (Design and Management) Regulations 2015. The Building Regulations principal designer manages design work so the building complies with the Building Regulations, under Part 2A of the Building Regulations 2010.

They share a name and often sit with the same firm, but they are two separate legal roles with different duties, different regulators and different things to sign off. Since 1 October 2023, when Part 2A came into force in England, a project with more than one contractor needs both roles filled. The same firm can hold both, but only if the client appoints it to both in writing.

Both are needed where more than one contractor is, or is reasonably foreseen to be, involved. On single-contractor projects, the CDM duties fall to the designer or client in control, and under the Building Regulations a sole designer carries the principal designer duties.

Same title, different law. One manages risk to people; the other manages compliance of the building.

What the CDM principal designer does

CDM 2015 (SI 2015/51) is health and safety legislation enforced by the Health and Safety Executive. Its core output is a design that can be built, maintained and used safely, recorded in a designer's risk register and the health and safety file.

Regulation 5 requires the client to appoint a principal designer in writing where more than one contractor will work on the project, as soon as practicable and in any event before the construction phase begins. Under regulation 11, the CDM principal designer must:

• plan, manage and monitor the pre-construction phase so that, as far as reasonably practicable, the project is carried out without risks to health or safety;
• identify and eliminate or control foreseeable risks to anyone building, maintaining, cleaning or using the structure as a workplace;
• ensure designers comply with their duties under regulation 9;
• ensure everyone in the pre-construction phase cooperates;
• help the client provide pre-construction information and pass it to designers and contractors; and
• liaise with the principal contractor.

Under regulation 12, the CDM principal designer also prepares and maintains the health and safety file and passes it to the client at the end of the project. The designer's risk register is where most of the day-to-day work is recorded.

What the Building Regulations principal designer does

Part 2A was inserted into the Building Regulations 2010 by SI 2023/911 under the Building Safety Act 2022. Its core output is a design that meets Schedule 1 (Parts A to T) and the other relevant requirements, and a record showing how that was managed.

Part 2A applies to almost all building work in England and is enforced through building control: the local authority or a registered building control approver, or the Building Safety Regulator on higher-risk buildings.

Regulation 11D requires the client to appoint a principal designer in writing where more than one contractor is involved. For higher-risk building work, the appointment must be made before the building control approval application is submitted; otherwise, before the construction phase begins. Under regulation 11M, the Building Regulations principal designer must:

• plan, manage and monitor the design work during the design phase;
• coordinate the design so that, if built, the work would comply with all relevant requirements;
• take reasonable steps to ensure designers cooperate, coordinate and comply with their duties;
• liaise and share information with the principal contractor; and
• within 28 days of the appointment ending, give the client a document setting out the arrangements it made.

At completion, the principal designer signs a statement confirming it fulfilled its Part 2A duties: in the completion notice under regulation 16(4A), or as a compliance declaration with the Gateway 3 application on a higher-risk building. We cover the duties in more depth in our principal designer duties guide.

The two roles side by side

The roles differ on almost every axis: legislation, purpose, phase, regulator, competence test and outputs. Only the appointment trigger, more than one contractor, is shared.

Can the same firm be both principal designers?

Yes. Regulation 11D(2) of the Building Regulations allows the client to certify in writing that the CDM principal designer is to be treated as appointed as principal designer for Building Regulations purposes.

Government guidance confirms the same people can fill both roles if the client confirms this in writing, and that where different people hold them they must work together and share information.

Dual appointment check

• ✓
  The appointment is explicit. The wording mentions Part 2A, or the client has certified under regulation 11D(2).
• ✓
  Competence covers both roles. A firm competent to manage construction health and safety risk is not automatically competent to coordinate Building Regulations compliance across all designers, and vice versa. Regulation 11G is a separate test, and the client must take reasonable steps under regulation 11E to check it.
• ✓
  Fees and resources reflect both. The Building Regulations role continues for as long as design work does, often well into construction on design and build. A fee sized for CDM pre-construction duties may not cover it.

Should architects take on both roles?

Architects are often well placed to be the Building Regulations principal designer, because the role sits close to the lead designer's coordination function. Taking on the CDM role as well is a resourcing and insurance decision as much as a legal one.

Practices should check with their professional indemnity insurer before accepting either appointment, and make sure the appointment documents describe the scope of each role separately. Where the roles are split between firms, a clear interface helps:

Design responsibility matrix

Shared between both principal designers, so each knows which designer owns which element.

Reporting routes

Agreed routes for raising compliance concerns and safety concerns, and for passing them between the two roles.

Single design record

One record of design decisions that both parties can rely on, rather than two partial versions.

Where Avoice fits

Both roles depend on a reliable record: one of hazards and design responses, the other of requirements and evidence. Keeping them in separate places is how gaps between the two appear.

The Avoice Compliance module keeps both sides of the job in one place. The CDM Designer's Risk Register records hazards, design responses and residual risks, and the Building Regs Tracker links design elements to requirements and evidence. Principal designer tooling for Building Regulations duties is coming, built on the same project record.

Software can record, link and flag. The principal designers, the client and the regulator still decide what is adequate.