Principal Designer Duties: CDM 2015 & Building Safety Act

The Principal Designer is one of the most consequential appointments on a construction project, and one of the most widely misunderstood. Part of the confusion is that there are now two separate Principal Designer roles in England — one under the Construction (Design and Management) Regulations 2015, and a newer one under the Building Regulations — each with its own duties and its own consequences for getting it wrong. This is a practical checklist of what the role requires under each regime, how the two differ, and the documentation that proves the duties were met if a regulator, insurer or building control body ever asks.

Two Roles, One Confusing Name

It helps to be precise about which role is being discussed, because the words "Principal Designer" now point at two distinct statutory duties. The first is the long-standing role created by CDM 2015, concerned with health and safety. The second was introduced on 1 October 2023 by the Building Regulations etc. (Amendment) (England) Regulations 2023, which inserted a new dutyholder regime into the Building Regulations, concerned with compliance rather than site safety. We cover the wider split between the design and construction dutyholders in our guide to the Principal Designer and Principal Contractor roles; this article stays with the Principal Designer and turns each regime into a working list of duties and the evidence that supports them.

The distinction matters because a firm can competently hold one role and be unqualified for the other: a safety-literate design manager may make an excellent CDM Principal Designer without the design authority to coordinate Building Regulations compliance, while a lead architect may suit the Building Regulations role but not construction-phase risk. Treating the two as a single job — a mistake we see regularly — is where accountability quietly falls through the gap between them.

The CDM 2015 Principal Designer: A Duty Checklist

Under CDM 2015, the client must appoint a Principal Designer in writing whenever it is reasonably foreseeable that more than one contractor will be involved — which covers the great majority of real projects, including many domestic ones. The role sits in the pre-construction phase and, in the words of the Health and Safety Executive, exists to plan, manage, monitor and coordinate health and safety while the project is still being designed. In practice, that resolves into a small number of concrete duties.

The first is to identify, eliminate or control foreseeable risks in the design — where a hazard can be designed out rather than managed later, it should be, the classic example being a roof detail maintained from inside rather than committing future workers to the roof edge. The second is to coordinate the design team so that one discipline's solution does not create a hazard for another. The third is to gather and pass on pre-construction information — surveys, existing hazards, site constraints — to those who will carry out the work, so the contractor is not discovering surprises mid-build. The fourth is to liaise with the Principal Contractor on anything relevant to running the construction phase safely. And the last, easiest to neglect, is to prepare the health and safety file: the record a future owner or maintenance team will rely on to work on the building safely.

Each of these leaves a documentary trace, and that trace is the point: an appointment in writing; a design risk register that shows hazards identified and resolved rather than merely noted; records of design coordination and the decisions taken; the pre-construction information issued to the contractor; and a health and safety file handed over at completion. If those exist and are coherent, the duty was discharged. If they do not, "we managed it informally" carries little weight with an inspector.

The Building Regulations Principal Designer: A Second Checklist

The second role runs in parallel and is easy to underestimate because it shares a name with the first. Set out in the Building Safety Regulator's guidance on meeting building requirements, the Building Regulations Principal Designer must be appointed by the client — again, in writing, where more than one designer or contractor is involved — and its duty is to plan, manage, monitor and coordinate matters related to the design work, so that the building work is designed to comply with all relevant requirements of the Building Regulations.

This is a compliance duty, not a health and safety one. It reaches across the Approved Documents — structure, fire safety, thermal performance, ventilation and the rest — and asks a single question of the design as a whole: if built as drawn, will it meet the Building Regulations? Because it applies to nearly all work needing building control approval, not only higher-risk buildings, it lands on a very wide range of projects.

The evidence for this role looks different from the CDM file: the written appointment; a record that the client checked the designer's competence before appointing; design coordination records showing compliance being actively managed rather than assumed; and the compliance information supporting the building control application. On higher-risk buildings the documentary burden steps up sharply, because the design must survive formal scrutiny before construction can begin.

Where the Two Regimes Diverge — and Where They Overlap

The overlap is real: both roles demand the same discipline of planning, managing and monitoring, and both are triggered by the same "more than one contractor" test. That tempts people to fold them into a single "Principal Designer" appointment — the trap, because the two duties are enforced by different bodies against different standards. A design can be entirely safe to build and still fail the Building Regulations; it can comply with them and still leave a latent maintenance hazard the health and safety file should have captured. One appointment letter cannot cover both unless it says so explicitly and the appointed party is competent in both.

This is also where the golden thread of building information becomes practical rather than abstract. On higher-risk buildings the design and safety information must be created, maintained and handed on as a reliable record across the building's life, and the Principal Designer — in both senses — is a main contributor to it. A golden thread is only as good as the coordination records feeding it, which is precisely what the two duties are meant to produce.

What People Overlook

The most common failure is not a dramatic breach but a quiet gap: the role is accepted verbally, or bundled into a design-and-build appointment, and never pinned to a named, competent party for each regime. The duties do not disappear — they become undocumented, which exposes client and designer alike, with no one able to show who was responsible for what.

Competence is the second blind spot. Both regimes require the client to satisfy itself, before appointing, that the Principal Designer has the skills, knowledge, experience and organisational capability for the job — and to record that it did. "We assumed they were competent because they are a large firm" is not a defence; competence must be assessed against the specific project, not inferred from reputation. The third is timing: a Principal Designer appointed after the design is essentially fixed cannot influence the decisions that matter, and the role collapses into a paperwork exercise. Its value is highest while design options are still genuinely open.

What Good Practice Looks Like

Projects that handle this cleanly tend to do the same handful of things. They name both roles explicitly in writing, stating which regime each appointment covers rather than relying on a single ambiguous title. They assess and record competence against the actual project before appointing. They appoint early, while design decisions can still be shaped. They keep live coordination records — design risk registers, compliance reviews, meeting decisions — as the project develops rather than reconstructing them at the end. And they treat the health and safety file and the compliance information as deliverables with owners and deadlines, not documents assembled in a rush at handover.

For developers and contractors carrying these duties across a portfolio, the sensible step is to make this repeatable: a standard appointment structure, a competence assessment template, and a defined home for the records. That is the substance of good project governance and documentation — turning statutory duties into a system that produces its own evidence, so compliance is demonstrable rather than merely claimed. Where the design touches higher-risk work, an independent compliance and building safety review before submission is often the difference between a design that clears scrutiny first time and one that stalls.

What to Consider Before You Appoint

Before making or accepting a Principal Designer appointment, answer three questions honestly. Which regime — or both — does this appointment cover, and does the letter say so? Is the appointed party genuinely competent for each duty, and is that recorded? And is there a defined home for the coordination records, the health and safety file and the compliance information? If any answer is vague, that vagueness is the risk — far cheaper to resolve before design than to explain after an incident, a stalled submission or a dispute.

It is also worth being realistic about capacity. Accepting a Principal Designer role — in either sense — commits a firm to active management, not passive presence, and taking it on without the time, authority or competence to discharge it is an exposure for both parties. This is one of the clearest cases where bringing in consultancy support for developers and contractors early costs far less than correcting a compliance problem discovered late.

The Takeaway

The Principal Designer role is not one duty but two, sharing a name and diverging in purpose: one keeps the design safe, the other keeps it compliant. Neither is satisfied by an appointment letter alone — both are satisfied by a demonstrable pattern of planning, managing and monitoring, evidenced in records a regulator, insurer or future owner can follow. The projects that stay out of trouble decide who holds each role, verify they are competent, appoint them early, and document the work as it happens. The uncertainty is the risk; the cure is a paper trail written while decisions are being made, not after someone asks.

Frequently Asked Questions

Is the CDM Principal Designer the same as the Building Regulations Principal Designer?

No. They share a name but are separate statutory roles. The CDM 2015 Principal Designer manages health and safety risk during the pre-construction phase; the Building Regulations Principal Designer, introduced on 1 October 2023, coordinates the design so the building work is designed to comply with the Building Regulations. One organisation can hold both, but only if competent in each and the appointment makes that clear. Treating them as a single role is a common source of compliance gaps.

Who has to appoint the Principal Designer?

The client. Under both regimes, where it is reasonably foreseeable that more than one contractor will be involved, the client must appoint a Principal Designer in writing. If the client does not make a valid appointment, the duties do not vanish — the client can end up carrying them, or they can pass to another party by default. Because that default is easy to trigger unintentionally, a clear written appointment is always the safer route. Understanding the wider dutyholder framework helps clients see where responsibility actually sits.

What documents prove the Principal Designer met its duties?

For the CDM role: the written appointment, a design risk register showing hazards identified and addressed, records of design coordination, the pre-construction information issued to the contractor, and the completed health and safety file. For the Building Regulations role: the written appointment, a recorded competence assessment, design compliance coordination records, and the information supporting the building control application. If the records do not exist, the duty is very hard to demonstrate after the fact.

This article is general guidance, not legal advice. Principal Designer appointments and compliance with CDM 2015, the Building Regulations and the Building Safety Act 2022 depend on the specifics of each project and should be confirmed with a competent professional. Tarj Construction's consulting team can help clients, developers and contractors structure these appointments and the supporting documentation correctly from the outset.