Summary
- There are two distinct Principal Designer roles with the same name: the CDM 2015 PD manages health and safety risk in the pre-construction phase; the BSA 2022 PD coordinates design compliance with Building Regulations (Parts A–T).
- Both are triggered when a project has more than one contractor. On domestic projects, the architect risks holding the principal designer role without agreeing to it — under BSA 2022 via regulation 11C(2) (multi-contractor) or regulation 11D(6)–(7) (single-contractor), and under CDM 2015 via regulation 7(2) where the domestic client fails to appoint. In both regimes, the client's own duties pass to the contractor or principal contractor — not to the designer.
- One practice can — and usually should — hold both roles on a small project, but they need separate appointment terms, separate competence evidence (PAS 8671 for BSA) and separate deliverables.
Why the confusion exists
When the Building Safety Act's dutyholder regime commenced on 1 October 2023, it reused the title 'Principal Designer' from the Construction (Design and Management) Regulations 2015 while giving it an entirely different job. Search engines and clients struggle with the distinction for the same reason architects do: two legal roles, one name, overlapping projects.
The CDM 2015 Principal Designer plans, manages, monitors and coordinates health and safety in the pre-construction phase — buildability, foreseeable construction risks, the pre-construction information and the health and safety file. The BSA 2022 Principal Designer plans, manages, monitors and coordinates the design work so that, if built in accordance with it, the building would comply with all relevant requirements of the Building Regulations. One is about people being hurt; the other is about the building being non-compliant.
On a typical non-HRB domestic project, the architect frequently ends up holding both — sometimes deliberately, sometimes by the domestic-client default. The professional risk is holding them without distinguishing them: quoting one fee, issuing one appointment letter, and keeping one undifferentiated file.
The comparison table
BSA 2022 vs CDM 2015 Principal Designer at a glance
| Aspect | Principal Designer (BSA 2022) | Principal Designer (CDM 2015) |
|---|---|---|
| Legal basis | Building Safety Act 2022 / Building Regulations 2010 Part 2A (as amended 2023) | Construction (Design and Management) Regulations 2015 |
| Core purpose | Design compliance with Building Regulations (Parts A–T) | Health and safety in the pre-construction phase |
| Regulator | Building control bodies; Building Safety Regulator oversight | Health and Safety Executive (HSE) |
| Trigger | More than one contractor on work subject to Building Regulations | More than one contractor on a construction project |
| Domestic client position | PD role: designer in control of design phase if no written appointment on multi-contractor projects (reg 11C(2)); designer(s) address PD duties on single-contractor projects (reg 11D(6)–(7)). Client's own duties pass to contractor or PC (reg 11C(1)) | Client duties pass to contractor or PC (reg 7(1)). Where a domestic client fails to appoint (reg 5), the designer in control of the pre-construction phase is the principal designer and the contractor in control of the construction phase is the principal contractor (reg 7(2)) |
| Competence benchmark | PAS 8671 (framework for PD competence); organisational capability | Skills, knowledge, experience; PAS 8672 covers Principal Contractor |
| Key deliverables | Compliance coordination records, design compliance statements, handover of building information | Pre-construction information, H&S risk coordination, health and safety file |
| Typical start point (RIBA) | Stage 0–1, before design work begins | Formally when >1 contractor is known — often confirmed by Stage 4 |
| Ends | Completion of the design work / building control completion | End of pre-construction phase (handover of H&S file) |
How the two roles map to RIBA Stages 2–4 on a domestic job
- Stage 2 (Concept): BSA PD — confirm the design team's competence, open the Parts A–T relevant-requirements tracker, record fire/structure/energy strategies. CDM PD — start the designer's risk reviews (working at height, demolition sequence, buried services) feeding pre-construction information.
- Stage 3 (Spatial Coordination): BSA PD — coordinate compliance interfaces between designers (structure vs fire-stopping, thermal vs ventilation). CDM PD — coordinate elimination/reduction of construction risks in the maturing design and update the PCI.
- Stage 4 (Technical Design): BSA PD — close out the evidence trail per Part: specifications, calculations, certified products. CDM PD — finalise pre-construction information for tender; on many domestic jobs this is when the second contractor appears and the CDM appointments are formalised (they should have been earlier).
Appointment letters: one practice, two hats, two records
If your practice takes both roles, say so in writing — separately. The BSA appointment should reference the Building Regulations Part 2A duties and your PAS 8671-aligned competence statement; the CDM appointment should reference Regulation 5 of CDM 2015. If you are declining one role (commonly CDM PD where a project manager or the contractor's designer takes it), decline it in writing before start on site, or the domestic default rules may hand it to you anyway.
The same logic applies at the end: the CDM role concludes with the health and safety file; the BSA role concludes with compliance handover. Two closing letters, two evidence bundles — the file structure is the defence.
Common pitfalls that catch out sole practitioners
- Quoting a 'PD fee' without saying which role — the client thinks they bought both; you priced one.
- Assuming CDM competence evidence covers the BSA role; PAS 8671 sets a different bar aimed at Building Regulations compliance capability.
- Believing the BSA PD role only exists on HRBs — it applies to all multi-contractor work subject to Building Regulations.
- Letting the domestic position assign you the role silently: on a multi-contractor project, if you are the designer in control of the design phase and no written PD appointment has been made, the principal designer role is already yours under regulation 11C(2) — without a fee and without an explicit agreement. On a single-contractor project, the designer must address the principal designer duties under regulation 11D(6)–(7). In neither case do the client's own duties come to you — those pass to the contractor or principal contractor.
Frequently asked questions
Can the same person be Principal Designer under both BSA 2022 and CDM 2015?
Yes, and on small projects it is common and usually efficient. But they are separate legal roles with separate duties, competence expectations and deliverables — appoint, evidence and conclude them separately.
Which Principal Designer role applies to a single-contractor domestic project?
The CDM 2015 principal designer appointment (under Regulation 5) is only required on projects with more than one contractor — so the CDM PD appointment is not triggered on a single-contractor project. Under the Building Safety Act, however, the position is different: for a single-contractor domestic project, the contractor is treated as principal contractor (regulation 11D(6)), but the principal designer duties must still be addressed — by the sole designer if there is only one, or by whichever designer the others have agreed in writing if there are more than one (regulation 11D(7)). Adding a second contractor immediately triggers formal CDM PD appointment obligations as well.
What happens if a domestic client never appoints a Principal Designer?
The two regimes work differently but reach the same outcome for the architect. Under the Building Regulations (Part 2A): where a domestic client on a multi-contractor project has not made a written appointment, regulation 11C(2) provides that the designer in control of the design phase is the principal designer — the role falls on them without a fee or explicit agreement. The client's own Building Regulations duties pass to the contractor or principal contractor under regulation 11C(1), not to the designer. Under CDM 2015: regulation 7(1) provides that the client's own CDM duties pass to the contractor (single-contractor) or principal contractor (multi-contractor) — not to the designer. Separately, regulation 7(2) contains an explicit deemed-PD provision: where a domestic client fails to make the appointments required by regulation 5, the designer in control of the pre-construction phase is the principal designer (regulation 7(2)(a)) and the contractor in control of the construction phase is the principal contractor (regulation 7(2)(b)). In both regimes the professional risk is the same: the architect holds the role, without the fee, unless the appointment — or the declination — is in writing.
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