Principal Designers and the Building Safety Act: Retaining Your Architect Through Construction

Principal designers role under the Building Safety Act are one of the most important and least-understood changes to affect building projects in England in a generation. Since the Act’s key provisions came into force, the client on almost every building project carries a legal duty to appoint a principal designer, and in fact two distinct principal designer roles under two separate pieces of legislation. For residential, commercial and developer clients, understanding these duties is not optional. They carry legal weight and getting them wrong exposes the client to real risk.

This article explains what a principal contractor is and when they should be appointed, what a principal designer is and why the appointment must happen at the very start of a project, the crucial difference between the principal designer role under the CDM Regulations and the principal designer role under the Building Regulations, and what has changed in building control with the replacement of approved inspectors by registered building control approvers. It also explains, plainly, why a client who does not retain their architect through construction is taking a risk they may not be aware of.

What Is a Principal Contractor and When Should They Be Appointed?

A principal contractor is the contractor with control over the construction phase of a project. Where a project involves more than one contractor, which in practice means almost every project of any scale, the client has a legal duty to appoint a principal contractor to plan, manage, monitor and coordinate health and safety during the construction phase.

The principal contractor’s responsibilities are focused on the site itself: ensuring the construction phase is properly planned from a health and safety perspective, coordinating the work of the various contractors and subcontractors on site, managing site risks and ensuring that everyone working on the project is properly informed and, where necessary, inducted. The role sits under the Construction (Design and Management) Regulations 2015, usually referred to as CDM 2015.

The principal contractor should be appointed before the construction phase begins. In practice, the appointment is often made once the contractor is selected through the tender process, but the legal duty is clear that the appointment must be in place before construction work starts. Where a client fails to appoint a principal contractor on a project involving more than one contractor, the client assumes the duties of the role by default, which is rarely a position any client wishes to be in.

What Is a Principal Designer and When Should They Be Appointed?

A principal designer is the designer with control over the design phase of a project. Like the principal contractor, the role exists where a project involves more than one contractor, and the client carries the legal duty to make the appointment. The critical point about the principal designer, and the one that clients most frequently get wrong, is the timing of the appointment.

The principal designer must be appointed at the very start of the project, before any design work commences. This is not a matter of best practice or preference. It is a legal requirement, and there is a compelling practical reason behind it. The decisions that have the greatest influence on health and safety, and on regulatory compliance, are made in the earliest design stages. A principal designer appointed after the design has been developed inherits decisions they had no opportunity to shape, which defeats the purpose of the role entirely.

The client’s duty to appoint a principal designer applies wherever it is foreseeable that more than one contractor will carry out construction work on the project. This includes subcontractors, so a project involving, for example, a plumbing and heating engineer, an electrician, a roofing contractor and a window installer triggers the duty even if there is only one main contractor. This covers the overwhelming majority of building projects. Our guide to the RIBA stages explains where the principal designer appointment sits within the project sequence, at Stage 1, before design work begins. [PENDING: update link to /riba-stages-explained/ once live]

Two Principal Designers: CDM vs Building Regulations

Here is the point that surprises almost every client, and that a great many people in the construction industry itself have not fully grasped. There are two separate principal designer roles, under two different pieces of legislation, with two different legal purposes. They are distinct statutory duty-holder roles, and the client has a duty to appoint a competent principal designer for each.

The principal designer under CDM 2015.
This role focuses on health and safety risk during the design phase. Its purpose is to identify, eliminate or reduce foreseeable construction health and safety risks through design, to coordinate the health and safety duties of the other designers, to liaise with the principal contractor on design-related health and safety risks and to prepare, maintain and hand over the health and safety file at the end of the project. It has no responsibility for day-to-day site safety, which sits with the principal contractor. Enforcement of the CDM principal designer duties is by the Health and Safety Executive.

The principal designer under the Building Regulations.
This is a separate statutory duty-holder role, introduced through the Building Safety Act 2022 and given effect by the Building Regulations 2010 as amended by the Building Regulations etc. (Amendment) (England) Regulations 2023. Its focus is not health and safety risk but compliance with the Building Regulations. It includes planning, managing and monitoring design compliance, coordinating designers and specialist consultants including fire, structural and building services, managing and coordinating design changes that may affect regulatory compliance, and liaising with building control and, where applicable, the Building Safety Regulator.

The same organisation can hold both roles, and frequently does, but they are legally distinct and must both be appointed. A client who appoints a principal designer under CDM but overlooks the principal designer under the Building Regulations has not discharged their full legal duty. Both appointments should be made in writing, at project inception, before any design work commences.

Why You Must Retain Your Architect Through Construction

This is where the two principal designer duties translate into a practical decision that clients frequently get wrong, at real cost to themselves.

The principal designer duties, under both CDM and the Building Regulations, do not end when the design is complete. They continue through the construction phase. The principal designer under the Building Regulations is responsible for coordinating design compliance throughout construction, reviewing and coordinating any design changes that affect building regulations compliance, controlling the issue and revision of regulated drawings and responding to compliance-related queries as they arise on site. These are live, ongoing duties that run for the duration of the build.

The problem arises when a client, having engaged an architect to prepare the design and submit the building regulations application, does not retain that architect through construction. The design changes that inevitably occur on site, the substitutions, the value engineering, the decisions made by the contractor, all happen without the principal designer’s involvement. Then, at completion, the architect may be asked to sign a document confirming to the building control approver that the building has been constructed in accordance with the building regulations.

This is an untenable position. An architect who has not been retained through construction has no knowledge of how the building was actually built, what was changed and whether those changes comply. Being asked to certify compliance for work they did not oversee is a request no responsible practice can properly meet. The honest answer, in that situation, is that the architect cannot confirm what they did not see.

This is why retaining the architect through construction is not an optional extra but a necessary continuation of the principal designer duties the client is legally required to discharge. Where an architect is not retained during construction, their appointment as principal designer ceases at the end of the design stage, and the client must appoint a replacement competent principal designer to carry the statutory duties through the construction phase. The duties do not disappear because the architect has left. They transfer, and if the client makes no replacement appointment, they transfer to the client. Our guide to what property developers need from an architect covers why continuity of professional involvement through construction protects the client’s position.

Building Control Approvers vs the Old Approved Inspectors

The Building Safety Act 2022 also overhauled the building control profession, and the terminology has changed in a way that is worth understanding.

Under the old system, building control oversight could be provided either by the local authority or by a private-sector approved inspector. From 6th April 2024, the approved inspector role was abolished and replaced by the registered building control approver, usually abbreviated to RBCA. All approved inspectors were required to register in the new role by that date, and those who did not register were no longer able to carry out building control work.

For most projects, which is to say non-higher-risk buildings, the client retains a choice between local authority building control and a private-sector registered building control approver. The change is not simply one of name. Registered building control approvers, and the registered building inspectors who work within them, are subject to a more rigorous competence and registration regime overseen by the Building Safety Regulator, reflecting the broader tightening of building control standards that the Building Safety Act set out to achieve.

For higher-risk buildings, defined broadly as those at least 18 metres in height or with at least seven storeys and containing at least two residential units, the position is different again. These buildings are now overseen directly by the Building Safety Regulator through a more stringent gateway process, rather than by a local authority or a private-sector approver. For the developers and clients whose projects fall into this category, the regulatory burden and the importance of properly discharged dutyholder appointments are greater still.

What Clients Should Do

The practical implications of all this are straightforward, and acting on them protects the client from significant legal and practical risk.

Appoint both principal designers in writing at project inception.
The principal designer under CDM and the principal designer under the Building Regulations must both be appointed, in writing, before any design work commences. A verbal understanding or an assumption that the architect is fulfilling the role is not sufficient.

Appoint a principal contractor before construction begins.
Where more than one contractor will work on the project, the principal contractor appointment must be in place before the construction phase starts.

Retain your architect through construction.
If your architect holds the principal designer role, retaining them through the construction phase allows them to continue discharging the ongoing duties and to be in a position to confirm compliance at completion. If you do not retain them, you must appoint a replacement competent principal designer to carry the duties forward.

Confirm your building control route early.
Decide whether your project will use local authority building control or a registered building control approver, and confirm the appointment early in the process.

Talk to Discover Architecture

At Discover Architecture, we take on the principal designer role under both the CDM Regulations and the Building Regulations where we are appointed to do so, and we are clear from the outset about the duties involved and why continuity through construction matters. We help clients understand their legal responsibilities under the Building Safety Act and ensure the right appointments are in place at the right time. If you are planning a project and want to understand your dutyholder obligations, we are ready to have that conversation. Explore our full services or get in touch directly.

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