Aipedia: Principal designers and building safety

AI templates for PDs on domestic projects

Aipedia, by the Apex broking team · Last reviewed 2026-10-27

Small practices acting as principal designer on home projects can end up carrying the homeowner's duties as well as their own. AI-generated templates can assume a commercial client and miss that point.

Part of: AI in principal design and building safety

In short

On domestic projects with more than one contractor, a principal designer is needed under CDM 2015 and Part 2A. The homeowner's duties pass to the contractor or principal contractor, or to the PD if they agree in writing (CDM 2015 reg 7, Part 2A reg 11C). Under Part 2A, if the homeowner fails to appoint, the designer in control of the design phase becomes the PD. AI templates can assume a commercial client, list generic hazards and say nothing about client duties. Decide and record who holds those duties, and tailor documents to the home.

Why small practices end up as PD on home projects

Small architectural and design practices can act as principal designer on extensions, loft conversions and refurbishments for homeowners, sometimes without realising it. Both CDM 2015 and Part 2A of the Building Regulations apply to domestic work, with special rules for domestic clients. Where there is more than one contractor, a PD is needed under both regimes.

Small practices may also be drawn to AI templates, because the paperwork can feel out of proportion to a kitchen extension. The AI for principal designers overview covers the wider picture.

The duties that apply

CDM 2015 reg 7: a domestic client's CDM duties under regs 4(1) to (7) and 6 are carried out by the contractor (one contractor), the principal contractor (more than one), or the principal designer where there is a written agreement that it will fulfil them.
Part 2A reg 11C: a domestic client's duties under regs 11A(1) to (3) and 11E(2) to (5), including competence checks, are carried out by the contractor, the principal contractor, or the PD if the client and PD agree in writing. If a domestic client fails to appoint, the designer in control of the design phase becomes the PD.
CDM 2015 regs 11 and 12: PD duties on pre-construction information and the health and safety file still apply, scaled to the project.

So a practice can find itself carrying the client's duties as well as its own, either by agreement or by default. Apex's guide to whether CDM principal designers need PI explains the cover position.

Where AI templates do not fit

AI tools generate CDM documents, Part 2A appointment letters and health and safety file contents in seconds. On domestic work the problems are usually about fit:

commercial-project templates that assume a client with its own CDM knowledge and processes;
pre-construction information that lists generic site hazards but not the ones in an occupied home, such as family members living on site, shared party walls or old wiring;
an appointment letter that does not state whether the PD has agreed to take on the client's duties;
a health and safety file so long the homeowner cannot find what a future builder needs.

Illustrative scenario. A two-person practice designs a rear extension and side return. An AI-generated letter describes the practice as PD but says nothing about client duties. With several trades on site, the practice is later treated as having agreed to carry out client duties, including competence checks it never made. A dispute with the homeowner follows after a subcontractor's poor work.

How PI usually responds

There is no statutory PI requirement for PDs, but many practices doing this work hold PI through their profession: ARB sets a minimum of £250,000 each and every claim in its PII guidance. Whether the PD role and any client duties taken on are covered depends on how the practice's activities are described to insurers. A claim from a homeowner would usually be handled as professional negligence, subject to the wording. Check that the policy includes PD work.

Practical controls

Decide at the outset whether you will take on the client's duties, and say so in writing.
Use templates written for domestic projects, and edit out anything that does not apply.
Write the PCI from a site visit, not from the brief alone (see AI-drafted pre-construction information).
If you carry the client's competence duties, record the checks (see AI tools for checking competence).
Keep design risk records proportionate but specific (see AI design risk registers).
Keep the health and safety file short and specific for the homeowner.
Explain to the homeowner, in plain words, what CDM and Part 2A mean for them.

For more on the CDM role, see Apex's guide to CDM principal designer PI.

How Apex helps

Apex arranges PI for small practices that act as principal designer on domestic projects. A broker can check your policy covers PD work and any client duties you agree to take on.

Sources

Frequently asked

Does CDM apply to home extensions?

Yes. CDM 2015 applies to domestic projects, with reg 7 setting out who carries out the domestic client's duties. Where there is more than one contractor, a principal designer and principal contractor are needed.

Can a PD end up with the homeowner's duties?

Yes, if there is a written agreement that the PD will carry them out, under CDM 2015 reg 7 or Part 2A reg 11C. Otherwise they generally pass to the contractor or principal contractor.

Are AI-generated CDM templates acceptable?

They can be a starting point. Documents must be appropriate to the project, so edit out commercial assumptions, add site-specific hazards from a visit, and state clearly who holds the client's duties.

Check your PI covers how you use AI

Tell us about your firm and the work you do. A broker will review how your current PI treats AI-assisted work, or arrange new cover. No fee for a quote. Or call 0117 325 0027.

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Apex Insurance Brokers Limited is authorised and regulated by the Financial Conduct Authority. Registered in England and Wales, company number 07014570. This page is general information about how AI is used in the profession and how insurance may respond. It is not legal, regulatory or insurance advice on your circumstances, and it does not guarantee that cover will be available or on what terms.