Fire Safety in Modern Methods of Construction (MMC)

Modern Methods of Construction can deliver speed, repeatability and improved factory quality. However, fire safety cannot be treated as a collection of individual products. The building must be developed as a coordinated system, with the fire strategy, structural design, architecture, services and manufacturing details aligned from the outset.

Key principle: A change to a board, stud, fixing, joint, penetration or support condition may affect the evidence supporting the complete fire-resisting assembly. Product substitutions should therefore be reviewed before approval or installation.

Fire Safety in MMC is a system issue

In modular and off-site construction, fire performance depends on the interaction between materials, components and completed assemblies. Repetition can improve consistency, but it also means that an unresolved detail may be repeated across many units. The design should therefore address not only the nominal wall, floor or ceiling build-up, but also how that construction continues through module joints, connections, interfaces and service zones.

• Structural fire resistance, including the protection of columns, beams and other elements that contribute to stability.
• Compartment walls, floors, ceilings and cavity barriers, including continuity at junctions and concealed spaces.
• Module-to-module connections, bolt locations, board joints and local clashes that can interrupt protective linings.
• Penetrations for electrical and mechanical services, together with appropriate tested fire-stopping arrangements.
• External wall and façade interfaces, including the relationship between fire protection, weathering and structural support.
• Installation tolerances, sequencing, inspection access and the quality controls needed in the factory and on site.

Start with the project fire strategy

The applicable fire-resistance periods and other fire-safety measures depend on the building use, height, layout, compartmentation and regulatory route. In Ireland, the project-specific design should be developed against the current Building Regulations guidance, including Technical Guidance Document B, Fire Safety, together with the relevant Fire Safety Certificate, fire strategy and any project or client requirements.

For example, recent school projects reviewed by Boylan Consulting have required coordinated consideration of 60-minute structural fire resistance, fire-rated suspended ceilings, protected steel columns, compartment walls, fire doors, cavity barriers and the treatment of penetrations. These are project-specific outcomes rather than universal MMC rules, and the required performance must be established for each building.

Evidence must match the proposed construction

Fire test evidence is most useful when the proposed construction remains within the tested arrangement and field of application. The review should consider the complete build-up and installation, not simply the reaction-to-fire classification of an individual board or insulation product.

• Board type, thickness, number of layers, orientation and joint treatment.
• Stud, joist, track or framing type, dimensions, gauge and spacing.
• Fixing type, length and spacing, including screws or staples between adjoining boards where required by the tested system.
• Insulation type, thickness and density, and whether it is required for the claimed performance.
• Support conditions, spans, loading and the direction of fire exposure.
• Openings, services, access panels, doors, glazing and module interfaces.
• Fire-test reports, classification reports, assessments, product system references, declarations of performance and current manufacturer installation guidance.

Where a proposed detail differs from the available evidence, the departure should be identified and assessed by an appropriately competent fire professional. A visually similar detail should not automatically be assumed to provide equivalent performance.

The details that often decide performance

Fire protection to structural steel

Protective encasement must remain continuous around the steelwork for the required period. At modular connections, bolt heads, nuts and connection plates can interrupt the lining. Openings and make-good pieces should be detailed so that the connection bears correctly on the structure without leaving unprotected steel or relying on the fire-protection board to carry connection forces. The fixing arrangement should follow the tested system and the manufacturer’s current guidance.

Fire-Rated Ceilings and Protected Roof Beams

A fire-rated ceiling may form part of the protection strategy for columns, beams or the structure above. Its role should be established through the structural fire design and supporting system evidence. The ceiling build-up, hangers, perimeter details, service penetrations and interfaces with partitions must all be coordinated.

Cavity Barriers and Concealed Spaces

Concealed roof and wall voids need early attention because modular layouts can create long, interconnected cavities. Cavity barriers should be located and detailed in accordance with the project fire strategy and the applicable guidance. Their continuity at module lines, changes in level, services and inaccessible roof zones should be resolved before manufacture.

Services and Penetrations

Every penetration through fire-resisting construction must maintain the required performance of the element. The selected arrangement should be suitable for the wall or floor construction, the service type and size, the annular gap, movement and the required fire resistance. Recessed sockets, ducts, pipes, cable trays and mixed-service openings should be coordinated before panels are closed in the factory.

A practical design and assurance process

1. Define Performance : Confirm the fire strategy, required resistance periods, compartmentation, escape provisions and any Fire Safety Certificate or client requirements.

2. Map the Evidence : Create a schedule linking each wall, floor, ceiling, structural protection and penetration detail to its supporting test, classification, assessment or manufacturer system reference.

3. Resolve Interfaces : Develop details for module joints, connections, façades, roofs, foundations, service zones and changes between systems.

4. Control Substitutions : Review proposed changes against the evidence before procurement or installation. Record approvals and limitations.

5. Build Quality into Manufacture : Use approved drawings, installation instructions, checklists and photographic records. Identify hold points before linings conceal critical work.

6. Verify on Site : Inspect transport-related damage, module connections, fire stopping, cavity barriers, ceiling continuity and final interfaces. Close out non-conformances with traceable records.

How Boylan Consulting Supports MMC Projects

Boylan Consulting provides coordinated fire, structural and civil engineering input for MMC and modular projects. Our role can include:

• Fire strategy and Fire Safety Certificate design support.
• Review of fire-resisting walls, floors, ceilings, doors, glazing and cavity barriers.
• Structural fire engineering and coordination of protection to steelwork.
• Review of fire-test evidence, classification reports, technical assessments and manufacturer details.
• Development and review of module-interface, connection and penetration details.
• Fire-testing advice, test-specimen coordination and review of proposed systems.
• Factory and site inspections, technical queries and evidence-based close-out support.

The objective is not simply to specify fire-resistant products. It is to develop a clear, buildable and evidence-based solution that preserves fire performance from design through manufacture, assembly and completion.

Note: This article provides general information only. Fire-safety requirements and acceptable evidence are project-specific and should be confirmed by the appointed competent professionals and relevant approval authorities.