Modular building standards

F&RM talks to BSI for an update on their work producing a national standard for modular construction.

The housebuilding sector in the UK is currently wrestling with how to resolve the dual challenges of a shortage of affordable housing and the demands of hitting sustainability targets. One of the proposed solutions to help deal with both of these challenges is the use of modular, or off-site, construction products and techniques.

This style of building involves manufacturing entire building sections (or modules) off-site in a factory. The final modules are transported to the site where they are then installed. According to Dr Seyed Ghaffar, Associate Professor in Civil Engineering and Senior Lecturer in the Department of Civil Engineering at Brunel University, in a piece written for BSI, “the terms ‘prefabrication’, ‘modular housing’, or ‘volumetric construction’ are generally used more for in one-piece products, including manufacturing of structural volumetric spaces (e.g., enclosed modules or entire houses), non-structural volumetric spaces (e.g., bathroom pods), and wall panels”.

Whilst the terminology may differ, the opportunity this style of building provides has been seized upon, with Dr Ghaffar concluding, “Offsite housing construction has been promoted as a radical innovative strategy to enhance the efficiency, quality, and environmental performance of house construction.”

To aid with the growth and economic viability of this sector, the government has been reported as putting forward an initiative to standardise modular products sector-wide via the construction industry. However, the fire safety of modular buildings is an area that still raises a number of concerns, especially given the serious damage reported as a result of fires in modular-type buildings that often leads to total loss of the building.

Last year, the National Fire Chiefs Council (NFCC) voiced concerns over the lack of understanding of the performance of modular construction in a fire scenario. The presence of extensive cavities and other inaccessible areas in modular construction is a detail that cannot be addressed in the factory as the cavity is not created until the modules come together on-site.

The release of the Morrell/Day report on construction product testing has also shown the work to be done in this sphere, which will in turn impact modular construction products. Another of the aspects raised by this report is the limited UK capacity for fire testing, and raises the question as to whether there is the capability, capacity, and standardised approach to testing to properly evaluate modular constructions for fire.

With so many questions around their fire safety, as well as the capacity of the industry to test and risk assess both new and existing modular buildings, the UK’s National Standards Body, BSI, has been tasked with looking at the standards surrounding this sector and provides an overview of the project to date.

F&RM: What is the background to this project?

BSI: The Department for Levelling Up, Housing, and Communities (DLUHC) are seeking to raise the quality and performance of off-site construction in the residential sector. BSI, as the National Standards Body, has a role of bringing industry together to set standards by consensus. This enables government and industry to come together to agree the level of benchmarking with all stakeholders.

What is the planned scope of the standard and who is it aimed at?

The draft scope of the standard is currently as follows: This Publicly Available Specification (PAS) specifies requirements for the use of modern methods of construction (MMC) in new build residential properties. It covers multiple build types and materials used in single use and mixed use residential MMC.

This PAS covers the following types of residential buildings:

  • Houses 
  • Low rise Apartments (< 5 storeys) 
  • Mid rise Apartments (6–9 storeys) 
  • High rise Apartments (10 storeys and above)

This PAS specifies requirements for individual elements and build types covering the entire lifecycle from design, through delivery and assembly, to repair and maintenance on material use and production, risk, safety, skills, information management and systems manuals. It does not cover industrial, commercial, hostels, care homes, hotels, prisons, or hospitals.

The PAS is intended for use by multiple audiences, for example, designers, manufacturers, installers and developers as well as by logistics providers, specifiers, and assurance and warranty providers. It may also be of use to valuers, insurers, and lending providers.

How will the drive for sustainability, one of the benefits of modular construction, impact fire and life safety?

The draft contents will address all aspects including:

  1. Design, specification, and materials
  2. Manufacture and production
  3. Transport, logistics, and storage
  4. Construction and assembly
  5. Risk management, performance, and safety
  6. Business operation, quality, and compliance
  7. Skills and training
  8. Information management

How will the standard impact on designers of new modular buildings and how will the standard change what currently happens on-site?

All stakeholders will be represented through a Steering Group, advisory panels, and public consultation. Consultation is an important stage in the development of a BSI standard, and can be accessed by any member of the public via BSI’s standards development public commenting portal. All comments submitted are finally resolved and agreed by the panel.

What impact will the introduction of the Golden Thread have in this sector?

The standard will be developed to work within both new and existing regulatory and standards landscapes.

The work on this standard is now underway, with updates to follow:

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