Two recently published reports provide details of possible fire safety risks and means of mitigation relating to volumetric modular construction
As reported by Construction News, the fire safety performance of volumetric modular construction has been the focus of recent work commissioned by the government and by the Health and Safety Executive (HSE).
The initial research, carried out by Harlow Consulting and Edinburgh Napier University, was tasked with investigating potential risks to safety and performance posed by offsite-manufactured volumetric modular construction (VMC). It also looked to identify potential options for mitigating those risks to help support greater use of modern methods of construction (MMC).
The report, finalised in July 2022 but released on 26 November 2024, covers many aspects of VMC and looks specifically at fire safety, stating that: “While there is insufficient evidence to suggest whether a fire is more or less likely in a modular building compared with a traditionally constructed building, the event of a serious fire may result in more serious consequences in a modular building if the choice has been made to use combustible elements in the voids and cavities through which fire and smoke can travel quickly – unless these risks are mitigated within the design, manufacture, and installation.”
The researchers also explained that there was broad agreement amongst the respondents surveyed that “there are gaps in the regulatory framework in relation to volumetric construction” but also noted that “Approved Document B is currently under review”.
It highlights concerns regarding the testing of single units, rather than units operating together as a system, notably in high-rise buildings, and concludes that standard fire testing is not fit for purpose in volumetric construction: “Further research is critical to have a clearer understanding of how materials (and combinations of materials/components) behave in modular buildings in the event of a fire.”
In response to the VMC research report, the government commissioned the HSE to undertake further research to identify evidence of fire or structural safety defects which were linked to the building safety of Permanent Volumetric Modular Construction (PVMC) as well as their likely frequency. The report of this additional research, RR1203: The impact of Permanent Volumetric Modular Construction (PVMC) on building safety, was published by the BSR in early December 2024.
In it, the researchers found evidence of the following fire safety issues:
- Missing or incorrectly installed cavity barriers
- Defects found in fire doors and door frames
- Penetrations through compartment walls that are not correctly fire stopped
- Fire safety barriers e.g. compartmentation compromised during modifications
- Hidden voids e.g. in walls, ceilings, and floors
- Lack of fire performance certificate
- Lack of clarification over structural fire design, e.g. for cross-laminated timber and lightweight steel in VMC.
In proposing a way forward, the report’s authors suggest the fire and structural testing of VMC modules could be done “in a way that represents the typical contexts of these modules e.g. stacked or part of a hybrid structure. This would help identify the consequences of any building safety issues in comparison to traditional (non-PVMC) builds.”
It also suggests that any testing should include timber VMC “to determine the nature of potential risks of VMC overlapping with the potential building safety risks of timber structures”, and notes that such tests might have implications for existing buildings and may inform any urgent concerns about VMC.
The publication of the two reports was accompanied by a statement from the government saying that “both reports are a reminder of the potential risks if developers do not fulfil their responsibilities in meeting building regulations, which is the case for any method of construction.”