Who Is Responsible for Specialist Design Compliance Under a Principal Contractor? 🚧

This week we’re going to discuss a deceptively simple question with big consequences: under the Building Safety Act and the new Building Regulations dutyholder regime, when the Principal Contractor is in place, who is actually responsible for specialist design compliance?

The Building Safety Act has reshaped the way we think about design responsibility. It introduces new statutory dutyholders, the Principal Designer and Principal Contractor under the Building Regulations, alongside more familiar contractual roles such as lead designer, design-and-build contractor, and specialist subcontractors.

So in today we look at a very focused question:

Under the Principal Contractor, who is responsible for specialist design compliance?

In other words, once the main contractor is on board and specialist packages kick in, such as cladding, MEP, fire systems, lifts, and so on, who carries the responsibility for ensuring that design work complies with the Building Regulations?

The Dutyholder Framework: Who Does What?

Under the Building Regulations as amended by the Building Safety Act, the key statutory dutyholders are:

• The Client

• The Principal Designer

• Designers

• The Principal Contractor

• Contractors

The Client must appoint a Principal Designer and Principal Contractor in writing for almost all projects. If they fail to do so, they effectively take on those duties themselves (with domestic clients treated differently).

The Principal Designer’s statutory role is to plan, manage and monitor the design work, and coordinate design so that, so far as reasonably practicable, if the building is constructed in accordance with that design, it will comply with the Building Regulations. This includes compliance with Schedule 1 requirements and Regulation 7 on materials and workmanship.

However, individual Designers remain responsible for the compliance of their own design work. This includes:

• Structural engineers

• Fire engineers

• Specialist subcontractors providing design services

The Principal Contractor, in a parallel role, must plan, manage and monitor the building work so that construction complies with the Building Regulations. They must also coordinate contractors on site to achieve this.

A crucial point to understand here is this:

The Principal Designer does not “take over” design compliance from other designers.

Instead, they coordinate and manage the process so that everyone’s design work collectively results in a compliant building.

This distinction becomes particularly important when we start looking at specialist design under a Principal Contractor.

When the Principal Contractor Takes Control of Specialist Design

This scenario is especially common in design and build procurement.

Under this route, the contractor appoints subcontractors responsible for specialist packages such as:

• Cladding and façade systems

• MEP services

• Fire systems

• Lifts and specialist equipment

Each of these subcontractors often carries design responsibility within their own package. Here’s the key point:

Specialist subcontractors are Designers under the Building Regulations in their own right.

This means they each have a direct duty to ensure their design complies with the Building Regulations. Meanwhile:

• The Principal Designer must coordinate these design activities to ensure that the overall design could produce a compliant building.

• The Principal Contractor must ensure that the building work carried out on site complies with the regulations.

When the Contractor Becomes the “Designer in Control”

On many design-and-build projects, once the design team is novated to the contractor, the contractor effectively becomes the party controlling the design process.

This is the pivot point.

If the contractor is now controlling and directing specialist design, they may need to be appointed both Principal Contractor and Principal Designer, provided they are competent to carry out that role.

The professional risk question for architects and consultants then becomes:

If the Principal Contractor is the designer in control, who carries responsibility for specialist design compliance and how far does that extend up the chain?

The Typical Design-and-Build Transition

The process usually unfolds like this:

1. Initial design team appointed by the clientThe architect and consultants may act as lead designer, and sometimes Principal Designer during early stages.

2. Contract awardThe design team is novated to the contractor, who becomes responsible for completing the design.

3. Contractor manages specialist design packagesThese include façade, MEP, fire systems, and other specialist elements.

At this stage, the contractor should typically be appointed by the client as both Principal Designer and Principal Contractor, because they have become the designer in control of the design process.

An important legal detail:

The Principal Designer role cannot be novated.

The appointment must come directly from the client, because the Building Regulations require the client to make that appointment formally. So a contractor cannot simply assume the Principal Designer role because the design team has been novated to them. A fresh appointment is required.

Specialist Design Responsibility: Who Is Actually Liable?

1. Individual Specialist Designers

Each specialist subcontractor or consultant that carries out design work is a Designer under the regulations.

They must:

• Ensure their design complies with the Building Regulations

• Cooperate with the Principal Designer and Principal Contractor

• Share relevant design information

• Follow coordinated design decisions

For example:

• The façade contractor is responsible for façade design compliance

• The MEP contractor is responsible for services design compliance

Their liability is direct and cannot be absorbed by the Principal Designer or Principal Contractor.

2. The Principal Designer’s Coordinating Duty

The Principal Designer must:

• Plan, manage and monitor the design work

• Coordinate all designers

• Ensure that reasonable steps are taken so the overall design could lead to regulatory compliance

However:

The Principal Designer does not sign off compliance for every design element.

That responsibility remains with the individual designers. Instead, the Principal Designer ensures:

• Effective design coordination

• Clear information exchange

• Conflicts or gaps are resolved early

The goal is to ensure the design process itself is robust enough to produce a compliant building.

3. The Principal Contractor’s Construction Responsibility

The Principal Contractor must:

• Plan, manage and monitor construction work

• Coordinate contractors on site

• Ensure that built work complies with Building Regulations

On Higher-Risk Buildings, they must also ensure appropriate inspection of construction work for safety occurrencesunder the Higher-Risk Buildings Procedures Regulations.

Even when work is subcontracted, the Principal Contractor retains overarching legal responsibility.

When the Contractor Holds Both Roles

If the contractor becomes the designer in control, they should typically be appointed as both Principal Designer and Principal Contractor.

In that combined role, the contractor must:

• Coordinate specialist design work

• Ensure the design could achieve compliance

• Ensure the constructed building actually complies

However:

The statutory Principal Designer liability cannot be delegated to consultants or subcontractors.

The responsibility stays with whoever the client appoints as Principal Designer.

Higher-Risk Buildings and Inspection Duties

For Higher-Risk Buildings, the regulatory framework becomes stricter.

The Building (Higher-Risk Buildings Procedures) (England) Regulations 2023 introduce additional duties.

The Principal Designer must ensure:

• An appropriate frequency of inspections of design work for safety occurrences throughout construction

The Principal Contractor must ensure:

• An adequate frequency of inspections of construction work for safety occurrences

Importantly, these inspections focus on process and safety oversight, not traditional architectural site inspection duties.

A Principal Designer completion statement confirms compliance with Part 2A duties, not that the building is compliant in every respect.

Practical Guidance for Architects and Consultants

If you are considering taking on the Principal Designer role, you should only do so where you have the:

• Skills

• Knowledge

• Experience

• Behaviours

necessary for that specific project.

Some key practice points:

• The lead designer is often well placed to act as Principal Designer

• Architects should refuse appointments that exceed their competence

• Where the contractor is Principal Designer, the architect may act in an advisory role, if PI insurance allows, without taking on the statutory duty

Conclusion

Under the Building Regulations dutyholder regime:

• Specialist designers remain directly responsible for the compliance of their own design work.

• The Principal Designer must plan, manage and monitor the design process, coordinating designers so the design as a whole could produce a compliant building.

• The Principal Contractor must plan, manage and monitor construction, ensuring that the building work carried out complies with the Building Regulations.

On design-and-build projects, where the contractor becomes the designer in control, they should normally be appointed as both Principal Designer and Principal Contractor, subject to competence.

However:

The Principal Designer role cannot be novated or delegated, and the legal responsibility remains with whoever the client appoints directly.

For Higher-Risk Buildings, additional duties apply, including inspection regimes for both design work and construction work.

The Short Answer

So to answer the original question as clearly as possible:

Under a Principal Contractor controlling specialist design:

• Specialist designers are responsible for the compliance of their own designs.

• The Principal Designer (often the contractor in this scenario) is responsible for coordinating the design so that compliance is achievable.

• The Principal Contractor is responsible for ensuring the building work carried out in reliance on that design complies with the Building Regulations.