In line with BG6, the responsibilities are clearly outlined. It follows a Design Responsibility Matrix instead of allocating design duties to a single team. The workflow initiates with the submission of technical designs by the architects, structural engineers, and building services consultants. Later on, coordination takes place to resolve critical clashes. Once their designs are finalised, the installation-specific design begins with contractors and specialist designers. In short, Stage 4 is all about collective efforts rather than one party being accountable, as established by the BG6 guidelines.

Common Misconceptions About Stage 4 Design Responsibility

From our experience, the emergence of two misconceptions is very likely on MEP projects. One of them assumes that, before handover, the consultant should model every element, including manufacturer-specific details. The other is that the contractor should take ownership of coordination once appointed, utilising only the model provided by the design team at Stage 4 as a starting point.

Both misread what BG6/2018 actually specifies. The Design Responsibility Matrix is followed at Stage 4, the RIBA Technical Design stage. Each design activity, in compliance with it, is divided into Lead, Support, and Review roles among consultants, contractors, and specialist designers. The core objective is to assign modelling responsibilities while ensuring everyone clearly understands them. If they are undefined, the above two misconceptions start surfacing, ultimately leading to duplicate modelling, missing information, and clashes left unresolved in some areas that could only be identified during on-site installation.

What BG6 Really Assigns During Stage 4

BG6's Proforma 4 gradually takes the building services technical design through three phases instead of treating it as a single deliverable:

1. Feasible-Generic Design

Generic components are used to represent services rather than specify equipment, just to make sure everything fits spatially in the initial phase.

2. Coordinated-Generic Design

In this second phase, the specification is still unconfirmed; however, the generic components are coordinated with interdisciplinary models for clash identification and resolution.

3. Coordinated-Specific Design

Upon the appointment of specialist contractors, where applicable, or the selection of specific equipment, the process concludes with this final phase, where generic components are replaced with project-specific ones, and coordination is reviewed to ensure the systems fit and function properly.

The adoption sequence of these three phases depends on the procurement route. It can go in two ways:

• Early involvement of the specialist contractor means the exclusion of the second phase, i.e., Coordinated-Generic Design, and a direct shift from the first phase to the third phase.
• Late involvement of the specialist contractor typically means that all three phases are carried out as described above, as per BG6 Proforma 4.

Case Study: MEP Coordination on a Major UK UndergroundInfrastructure Project

Recently, on a major UK underground infrastructure project, we had the opportunity to deliver BIM modelling and coordination services for the MEP disciplines. The confined underground environment was one of the key constraints, as we had to accommodate all building services within a limited space. Consequently, this created the utmost need for early clash detection and resolution, as addressing clashes later on site could be costly and time-intensive.

Within our scope of work, the coordination of the federated BIM model among all disciplines was one of the core responsibilities, alongside other tasks such as arranging regular coordination meetings, issuing construction drawings only upon coordination approval, and producing walkthrough models so that the client and contractor could gain insight into the design prior to installation.

How the Project Applied BG6’s Stage 4 Sequence

As a matter of fact, this project wasn't undertaken in accordance with the BG6 guidelines as a checklist; however, our workflow throughout resembled the approach prescribed by BG6, and it was quite an effective way of dealing with MEP system coordination in such an intricate underground environment.

We initiated the project with generic layouts to ensure everything fit spatially within the confined space, which BG6 refers to as Feasible-Generic Design.

This was followed by coordinating the generic layouts to resolve critical clashes prior to construction, which is exactly what the Coordinated-Generic Design phase entails.

As the project progressed, we reached the final phase, i.e., Coordinated-Specific Design, which marks the finalisation of Stage 4. We replaced the generic components with project-specific information after the selection of equipment, including ducts, pipes, cable trays, and associated services.

This way, we stayed closely aligned with the recommendations provided by the BG6 guidelines, coordinated the MEP systems, and then issued the construction drawings, ultimately leading to seamless installation with a budget-friendly delivery.

Who Models What at Stage 4

On this project, and on most MEP-focused Stage 4 projects, each team is responsible for modelling a specific part of the building:

• Architect: Building layout, rooms, ceilings, and access requirements.
• Structural Engineer: Structural frame, openings, penetrations, and structural coordination.
• Mechanical Engineer: HVAC systems, pipework, ventilation systems, and plant rooms.
• Electrical Engineer: Cable containment, power distribution, lighting, and electrical equipment.
• Public Health Engineer: Drainage and water services.
• BIM Coordinator: Federated model, clash detection, coordination reviews, issue tracking, and model quality checks.
• Specialist Contractors: Installation-specific designs, specialist systems, and manufacturer-specific equipment where required.

No single party models the entire project. Each discipline is responsible for its own part of the model, while the BIM Coordinator ensures that all models fit together and function as one coordinated, clash-free, and buildable design.

Client Story

While the project was being coordinated, potential issues emerged, such as interdisciplinary services competing for the same limited space for installation. To prevent these conflicts, the design team thoroughly identified them during federated model reviews, revised and finalised service reroutings, and promptly updated the coordinated BIM model before issuing construction drawings rather than overlooking them. Doing so substantially minimised costly rework, reduced installation risks, enhanced buildability, and ensured that the design team and the site team were working from the same up-to-date information and stayed on the same page.

Why Stage 4 Coordination Matters

The aim at Stage 4 goes beyond increasing the level of detail within an uncoordinated model. The objective, consistent with BG6, is to deliver a coordinated model that is practical, with defined roles and resolved clashes before a single brick is laid on site.

If responsibilities are unclear, the outcomes are RFIs, site rework, and costly delays. Otherwise, clearly allocated roles and coordination can help avoid these challenges.

Conclusion

• Teams should be aware of their responsibilities for project success.
• During the pre-construction phases, coordination conflicts should be resolved as the utmost priority.
• Ensure the delivery of a well-coordinated and clash-free model to the site team to enable confident construction.
• Project success is interconnected with collaboration, clear ownership, and seamless communication, supported by the framework provided by BG6.

FAQs

1. What is BG6 in BIM?

BG6/2018 (A Design Framework for Building Services) is a BSRIA guide that provides insight into the roles and responsibilities at each RIBA Plan of Work stage for different building services design tasks. Not only that, but it also specifies who will lead, support, and review each design activity.

2. Who is responsible for design coordination at RIBA Stage 4?

Responsibilities are shared rather than being handled by one party alone.

• Consultants develop their technical designs.
• The lead designer reviews and coordinates them.
• Where applicable, specialist contractors finalise their own designs from the design team's well-coordinated model.

3. What happens if design responsibilities are unclear at Stage 4?

If design responsibilities are not clearly defined at Stage 4, it can create confusion among project teams. This may lead to duplicate modelling, missing information, unresolved clashes, and delays during construction. Clear responsibility allocation helps each party understand their role and ensures that the design is properly coordinated before on-site execution.

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