Factory-fitted services in MMC create unique fire-stopping challenges at building interfaces. This guide details best-practice solutions for sealing penetrations between modules and into concrete cores.. The Rise of MMC and the Fire Stopping Imperative Modern Methods of Construction (MMC), particularly volumetric modular building, offer significant advantages in terms of speed, efficiency, and quality control. However, the inherent nature of fabricating modules off site and then assembling them on site introduces unique complexities, especially concerning passive fire protection. A critical area where these complexities manifest is in the fire stopping of service penetrations at the interfaces between individual modules and where modules connect to traditional building elements, such as concrete cores. The Building Safety Act 2022 (BSA 2022) places clear responsibilities on Accountable Persons to manage fire safety risks in higher risk buildings, with adequate fire compartmentalisation being paramount. This necessitates a meticulous approach to sealing voids and penetrations to maintain the integrity of fire resisting elements, preventing the spread of fire and smoke as mandated by the Regulatory Reform (Fire Safety) Order 2005 (RRO 2005). Understanding the Challenge: Inter Module and Core Penetrations Volumetric MMC often involves extensive factory pre fitting of services, including electrical conduits, pipework, and ventilation ducts, within each module. When these modules are interconnected on site, these services inevitably pass through the fire resisting walls and floors that separate modules. Similarly, where modules abut a central concrete core — which typically houses risers, stairwells, and lifts — services will penetrate the interface. These interfaces represent critical junctures where breaches in fire resistance can occur if not appropriately sealed. The challenge lies in achieving robust, tested fire stopping solutions that can accommodate potential movement between modules, installation tolerances, and the diverse range of service types and sizes. BS 9991:2015, Fire safety in the design, management and use of residential buildings – Code of practice , and BS 9999:2017, Fire safety in the design, management and use of commercial buildings – Code of practice , both emphasise the importance of maintaining fire compartmentation through effective sealing of penetrations. Statutory Framework and Approved Guidance The legal and regulatory framework underpinning fire safety in the UK is robust. The BSA 2022, amplified by the RRO 2005, places stringent duties on those responsible for building safety. Specifically, Approved Document B (ADB) of the Building Regulations 2010 provides practical guidance on how to satisfy the functional requirements for fire safety, including the need for fire resisting construction and the sealing of penetrations. ADB requires that penetrations through fire resisting elements are fire stopped to the same performance as the element itself. Furthermore, the Fire Safety (England) Regulations 2022 (FS(E)R 2022) introduce specific duties for Responsible Persons in multi occupied residential buildings, including providing residents with information on fire safety matters. This underscores the need for demonstrable compliance and robust assurance regarding fire stopping, particularly in innovative construction methods like MMC where traditional inspection points may be less accessible post completion. Best Practice for Design and Specification Effective fire stopping in MMC begins at the design stage. Fire engineers and designers must collaborate closely with MMC manufacturers to integrate fire stopping solutions into the modular design. Key considerations include: Early engagement: Fire engineers should be involved from concept design to ensure fire stopping strategies are inherent, not an afterthought. Standardised details: Develop and test standardised fire stopping details for common service penetrations at module interfaces and core connections. Movement accommodation: Specify products and systems that can accommodate differential movement between modules – a critical factor in performance. Expansion joints and compressible fire stopping materials are often necessary. Accessibility for inspection: Design for inspectability. While off site fabrication offers quality control benefits, the ability to inspect critical areas post assembly must be factored in. This may involve designated inspection hatches or photographic records of hidden works. Material compatibility: Ensure all components of the fire stopping system are compatible and tested together, in accordance with relevant British Standards. Installation and Workmanship: The Critical Link Even the best designed fire stopping system is only as effective as its installation. Workmanship is paramount, especially given the complexities of MMC. Training and competency of installers are crucial. All personnel involved in fire s