Modern Methods of Construction Policy Position Statement

1. Issue Identification

The consequences of failure in buildings constructed using Modern Methods of Construction (MMC) are not yet well understood, in contrast to traditional methods where performance is well documented. A concern with some MMC approaches is that products can be engineered to achieve only the lowest performance necessary, for example, minimum thickness, size, or strength, often leaving little safety margin. This creates vulnerabilities when construction quality or maintenance vary, reinforcing the need for stronger evidence, oversight, and regulatory consistency. Without comprehensive system-level fire testing, MMC structures, especially modular and timber-based forms, could fail more rapidly and with less warning. This unpredictability poses a serious concern in high-rise or complex buildings, where rapid failure could hinder evacuation and emergency response.

The National Audit Office[i] report into dangerous cladding highlights that building defects continue to be uncovered at considerable cost. Fire and rescue services (FRSs) and the National Fire Chiefs Council (NFCC) remain concerned about risks to communities and future legacy issues linked to the alternative construction processes used in MMC. Greater precision is often cited as a benefit possible to achieve in factory settings, however our members remain concerned that quality can still be undermined by a lack of skill among construction teams onsite.

In April 2025, British Standards Institute (BSI) published PAS8700:2025[ii], the UK’s first publicly available specification for MMC in new-build residential properties. It outlines requirements for design, manufacture, and onsite assembly, with an emphasis on durability and safety. While this represents a positive step toward standardising MMC practices, PAS8700 focuses on process and oversight rather than offering the robust, system-level fire performance guidance NFCC deems essential to ensure MMC builds are safe from fire. NFCC continues to advocate for technical standards supported by full-scale fire testing and structural performance data to ensure fire safety is embedded in the design of higher-risk residential developments.

MMC-specific behaviours may necessitate revised operational tactics, greater water demand, and updated assumptions about collapse times, such as Cross Laminated Timber (CLT) delamination and modular void fire spread[iii]. To respond effectively, FRSs require robust information on how buildings will behave in a fire.

Unfortunately, there is a lack of large-scale fire test research and data on construction materials, especially with MMC. The Grenfell Tower Inquiry’s Phase 2 Report[iv] highlighted concerns around the validity of product test performance, claims, and certification. It recommended that a construction product regulator be responsible for assessing product conformity with legislation, statutory guidance, and industry standards, and for issuing certificates accordingly.

An independent study conducted by Harlow consulting and Edinburgh Napier University, commissioned by the Government[v], found that while risks in volumetric modular construction mirror traditional methods, specific concerns exist. These include regulatory gaps, poor fire and product testing, transit damage, unclear accountability, limited data, and skills shortages. The research paper identified that ‘deemed compliant’ products may not have been subject to the right test conditions. It also highlighted a risk specific to modular construction, is the possibility of disproportionate damage in the event of fire (or flooding). A follow-up study by the Buildings Safety Regulator[vi] (BSR) confirmed many of these risks, identifying fire safety issues such as poor compartmentation, defective fire doors, inadequate fire-stopping, unclear structural fire design, and difficulties with building control inspections. Although the scope of this follow-up study was limited in scope, the prevalence of issues it uncovered strongly suggests that the problem may be far more widespread. The findings indicate that more comprehensive investigations could reveal a problem of greater scale and complexity.

2. NFCC Position

NFCC supports the Government’s ambition to boost affordable housing supply and recognises the potential of Modern Methods of Construction (MMC) to drive productivity and innovation. However, this must not come at the cost of safety. The fire performance of MMC remains poorly understood due to limited testing requirements, creating significant uncertainty in the built environment. MMC also introduces complexities that existing regulatory guidance, such as Approved Document B (ADB), may not fully address. This creates a risk that traditional frameworks could fall short in ensuring compliance, oversight, and fire safety, particularly as these new methods are adopted at scale.

As identified by the Independent Review of Building Regulations and Fire Safety[vii] (the Independent Review), a significant cultural shift and improved competency are required across the construction industry. While NFCC has welcomed the ongoing reforms in building safety, insufficient progress towards these requirements has been made to ensure that MMC is used in a manner which provides safe buildings for all.

Clear competency requirements are crucial to enable the safe implementation of MMC. NFCC has published an Industry White paper[viii] on Remediation which calls for a cross-departmental Construction Skills Strategy. Strengthening skills, competence, capability, and capacity across the workforce is vital to addressing the systemic failures that contributed to the Grenfell Tower fire tragedy and ensuring future building safety. NFCC supported the Government’s Construction Products Reform Green Paper[ix], particularly its focus on improving third-party testing skills, but believes the proposals must go further.

3. Recommendations

• Clarify the scope of Approved Document B to confirm it applies to traditional construction methods only and is not suitable for complex or modern methods of construction, including mass timber and high-rise modular builds. While the FAQ for ADB offers guidance, this lacks the clarity and prominence needed, and risks being overlooked. NFCC recommends that clarification to the scope of ADB is strengthened and incorporated directly within the main body of the guidance.
• Develop dedicated fire safety guidance for MMC (building on PAS8700) ensuring that design and construction practices reflect the specific risks and requirements of offsite systems and engineered products.
• Create a robust pathway for demonstrating compliance with fire safety requirements in MMC buildings, including a large-scale, whole-system fire testing regime; the limitation of desktop studies (assessments in lieu of tests) to exceptional, controlled cases only; and clear standards for assessor competence and accountability.
• Establish a publicly accessible Construction Library, as recommended by the Grenfell Tower Inquiry, containing independent, system-level fire performance test data and peer-reviewed research on MMC and new construction methods.
• Define clear competency requirements for those designing, approving, and constructing MMC buildings—including developers, regulators, and fire engineers—backed by a mandatory competency framework and aligned with broader reforms.
• Publish a cross-sector MMC strategy, co-developed with industry experts, structural and fire safety professionals, and regulators. This strategy should integrate fire safety, research funding, regulatory alignment, and workforce development from the outset.

4. Supporting evidence

The Farmer Review of the UK Construction Labour Model (‘Modernise or Die’, 2016) identified opportunities to support more housebuilding with the use of MMC. Despite the opportunities identified, MMC continue to face barriers such as limited research and development funding, and risk aversion among warranty providers and insurers. Marsh McLennan’s 2022 report[x] notes that UK insurers are cautious in underwriting MMC projects due to limited loss data, reducing appetite in an already challenging insurance market. The 2024 House of Lords Inquiry[xi] into MMC and their letter[xii] to the Sunak Government stressed the need for a clear national strategy and deeper understanding of how the sector operates to unlock its potential.

Literature examining the fire safety challenges posed by MMC has highlighted how the complexity and prefabrication of MMC systems can complicate traditional regulatory and fire safety assurances.[xiii]

If MMC is to support the Government’s ambitions to “turbocharge”[xiv] housebuilding, help meet net zero, and address skills shortages, a coordinated, cross-sector strategy is essential. This must include Government leadership and sector-wide engagement to ensure that skills, knowledge, and fire safety especially structural performance are fully integrated from the outset.

NFCC has particular concerns for the following methods when in use for high rise buildings, buildings that are housing vulnerable occupants, buildings with a “stay put” strategy, or buildings with any form of delayed strategy including stay put: 3D Modular (Volumetric) construction – Category 1 of the MMC Definitions Framework (3D primary structural systems); and the use of engineered mass timber products e.g. Cross-Laminated Timber (CLT) and Glue-Laminate Timber (Glulam).

Some MMC systems may present disproportionate operational risks. For example, smouldering in mass timber can persist long after suppression, requiring extended fire service intervention and exposing crews to ongoing structural stability concerns. Similarly, non-traditional wall systems may behave unpredictably under simultaneous fire and wind loading. These operational realities emphasise the need for conservative, evidence-led design approaches that minimise reliance on traditional mitigation measures, which may be vulnerable to failure or later compromise.

Regulation

NFCC recognises the important role MMC can play in addressing housing and infrastructure needs but stresses that safety must be embedded in these construction methods and materials from the outset. The current regulatory framework, including guidance and manuals, requires strengthening to address MMC complexities. We urge the Government to provide clear guidance and standards for MMC and the offsite manufacturing sector, ensuring fire safety is integrated into design and construction, underpinned by rigorous testing and research to demonstrate MMC’s fire performance over time.

The Independent Review, along with the previous Government, acknowledged that the current building regulation system was not fit for purpose[xv] even for traditional construction. NFCC is concerned that MMC buildings are being designed and approved under a framework not suited even for traditional methods. Without added safeguards, there is a risk of future safety issues, as potentially unsafe MMC buildings may be constructed before essential regulatory reforms and updates to statutory guidance are completed.

Approved Document B is the main safety design guidance for typical new buildings. In 2022, the Government issued FAQs attempting to clarify its application to modular and combustible (e.g., timber) structures. It advised against using ADB for “tall, large or complex buildings”, though these terms remain undefined and ADB has no upper height limit. This still suggests ADB can be used for design across various purposes and occupancy types. Clearer, more explicit guidance is needed to confirm ADB is not suitable for certain MMC types referenced in this advice.

NFCC would like to see MMC be supported by the Government in an appropriate framework to assure safe design which is fully informed by research to fill the current knowledge gap on fire performance.

PAS8700 Standards

PAS8700 provides focus on effective processes to support the design, manufacture, and assembly of MMC buildings, focusing on procedural consistency and safety oversight. While a step forward, this lacks the technical depth and fire safety guidance needed for safe delivery. No standards yet provide practical guidance of this type to inform designs or help regulators assess suitability. NFCC stresses the need to embed system-level fire performance and competency within MMC frameworks, especially for high-risk settings. Further guidance is therefore still needed.

Testing and Research

As part of the ADB review, the Government has commissioned research projects, including large-scale fire tests, to build knowledge on MMC and inform new test methods and guidance. The Grenfell Tower Inquiry[xvi] recommended creating a Construction Library similar to Queensland’s Cladding Materials Library to give designers of higher-risk buildings access to key data, fire reports, and academic research. This was accepted by the Government.

Concerns about modular and engineered timber construction are acute. A report from the London Fire Brigade (Thematic Report – Modular Construction, September 2025) identifies recurring issues in modular builds, including poor fire stopping, cavity barriers, and a lack of system-wide testing. Engineered timber products like CLT pose risks such as smouldering fires, which are hard to detect and control, as highlighted by Fire safety engineering group Arup[xvii]. These concerns support the need for independent, full-system fire testing and a publicly accessible Construction Library of fire performance data, as recommended by the Grenfell Tower Inquiry.

FRSs continue to encounter proposals where MMC systems are presented with insufficient or incomplete evidence to demonstrate compliance with the functional requirements of the Building Regulations. In recent cases, systems such as CLT and Light Gauge Steel Frame (LGSF) were proposed with fire performance assumptions unsupported by robust data or testing. For example, LGSF load-bearing walls were assessed only under single-sided fire exposure in line with ADB Table B3, despite their likely exposure to fire on both sides in real-world scenarios. Similarly, proposals for unencapsulated CLT construction without sprinklers fell outside existing guidance, yet were advanced with limited evidence of performance. These examples highlight the inconsistency in how MMC proposals are scrutinised and reinforce the NFCC’s position that system-specific evidence must be presented and critically assessed to demonstrate compliance.

More traditional construction techniques offer known resilience backed by comprehensive large-scale testing, unlike modular and mass timber construction, where limited system-level fire data creates uncertainty, especially in high-rise settings. Understanding fire performance is essential to ensure safety. NFCC is concerned that current approaches test components individually rather than test systems as a whole. As the Independent Review recommended, testing must reflect real-world fire performance at the system level. Phase 2 of the Grenfell Tower Inquiry raised serious concerns over product testing validity, including retracted test reports. NFCC continues to receive reports of MMC projects proceeding without sufficient fire performance evidence, highlighting a systemic gap in transparency and safety.

NFCC previously welcomed and have supported[xviii] the Independent Review’s[xix] recommendation to significantly limit the use of assessments in lieu of tests (desktop studies) for approving changes to cladding and other systems. While well-prepared assessments referencing primary test data can be useful, the priority must be ensuring accurate application to avoid dangerous outcomes. When coupled with the general lack of research and test data, NFCC remains particularly concerned about the lack of evidence required within the regulatory framework about how MMC buildings may perform in a fire. The impact of innovative materials and techniques on structural stability, especially in tall modular and mass timber construction, is not fully understood, raising significant safety risks during fire events.

Robust and transparent controls over desktop studies are needed to prevent reliance on unsubstantiated opinion or conjecture. These controls should apply to both extended applications with classification reports and engineered approaches, ensuring bad practice is eliminated and assessors are held accountable. Assurance must be given that fire performance of materials and systems are fully tested, evidenced, and meet safety standards for residents and firefighters. If technical assessments are to be accepted for compliance, clear definitions of assessor competence and examples of required expertise should be established.

Competence

A recurring issue reported by FRSs is that designers and dutyholders often lack sufficient understanding of MMC fire behaviour. In practice, this can result in reliance on assumptions or incomplete submissions to Building Control, leaving the burden of evaluation to the FRS. Where detailed fire engineering input is not sought or heeded, there is a risk that non-compliant or unsafe designs could proceed unchecked. This underlines NFCC’s concerns about competency levels across the sector and the importance of ensuring clear accountability for demonstrating compliance.

The successful implementation of MMC relies heavily on quality control and the competence of installers. Without cohesive training, certification, and adherence to updated standards, MMC buildings risk falling short of safety requirements, especially in high-risk environments.

Ensuring competency of all actors, including those undertaking assessments, is crucial. Oversight within the construction sector needs strengthening. In 2019[xx], NFCC called for better regulation of construction competency through multiple measures. This included calls that the Government mandate that all key disciplines working on buildings in scope of the new Building Safety regime adopt appropriate competency frameworks; that assessing organisations be accredited or licensed by a third-party independent body; and that assessing organisations should maintain registers of competent persons.

While MMC offers improved build quality through factory precision, this advantage can be compromised by insufficient onsite skills during construction. Building safety depends on factors like proper welding, secure bolting, correct plasterboard fitting and maintenance, accurate module alignment without gaps, and properly installed fire stopping and cavity barriers. However, experience shows that assuming consistent build quality onsite is unreliable and cannot be taken for granted.

As above, FRSs have reported cases where insufficient information has been provided to demonstrate that methods of modern construction have met the functional requirements, or that their fire performance has been fully evidenced or understood.

When issues regarding construction material safety are coupled with concerns around competency and build quality, it becomes particularly concerning considering the use of MMC in high-rise residential buildings, with increasingly taller schemes coming forward, and where there are greater numbers of people living with vulnerabilities.

In 2020, the Industry Competence Group (ICG) published its final report, Setting the Bar^[xxi], and then in 2022 a requirement of the Building Safety Act 2022 was the creation of the Industry Competence Committee (ICC), a multi-stakeholder group coordinated by the BSR; this group first met in 2023.

While we welcome the development of a suite of Built Environment competence standards by the BSI and supported by Government, concerns around competency and consistency remain.

These developments are a good first step, and NFCC was the first stakeholder to update the FRS competency framework per the Independent Review. However, while FRS competency now has HMICFRS oversight, many industry standards remain voluntary, with the ICG’s remit limited. As noted within the ICG’s earlier reports, there remains a risk that the best in the industry become better, while still being ‘undercut’ by parts of the industry that are able to avoid requirements to be properly competent.

Competence is critical for keeping buildings safe for occupants and firefighters. It must cover the entire premises lifecycle of planning, design, approval, construction, occupation, management, and future alterations. Competence is also needed within the regulatory regime to ensure decisive action against non-compliance.

Operational Response

FRSs operate under the assumption that compliance with Building Regulations ensures a baseline of predictable building behaviour – an essential foundation for safe and effective fire intervention, particularly in high-rise scenarios. The Grenfell Tower Fire tragedy painfully demonstrated that when buildings fail catastrophically, the safety of both occupants and firefighters can no longer be assured.

Adding to this concern FRSs often receive insufficient or inconsistent information about construction methodologies, particularly regarding MMC. This lack of information hampers FRSs’ ability to understand building design and operational risks, especially in high-rise buildings. Analysis from visiting Professor at the University of Central Lancashire (UCLAN) Dr Jim Glockling[xxii] emphasises the potential impact on operational response resources arising from MMC, including the potential for fires that are larger, longer, and harder to fight, potentially requiring different tactics and equipment to locate, make accessible, and tackle fires that could be hidden in voids, or take days to put out. This highlights the need for clearer communication and better information sharing between designers, developers, and FRSs to ensure effective fire safety measures and operational preparedness.

FRSs are consulted during construction to assess compliance with the Regulatory Reform (Fire Safety) Order 2005 and can comment on Building Regulations and provide non-statutory advice. Procedural guidance currently includes a pro-forma intended to capture key building information, including construction methodology, for sharing with FRSs. However, FRSs report that this information is often incomplete or inconsistently provided, limiting their ability to understand the building they are expected to plan for and respond to. Consistency in the provision of this information remains a priority, particularly as MMC introduces new and less predictable risks.

While the inclusion of this requirement in national procedural guidance is welcome, NFCC notes that adherence is not mandatory, and compliance varies significantly. While FRSs are statutory consultees, they are not the approving authority for Building Regulations and as such their comments and observations may go unresolved or unaddressed. Improved oversight and accountability are needed to ensure FRS advice is consistently considered during the design process.

A major challenge is the lack of a database recording high-risk MMC buildings. MMC buildings are not always visually identifiable, yet FRSs need this information to plan operations, conduct risk assessments, and respond effectively to fires. NFCC has consistently highlighted the urgent need for a national dataset or register of high-risk MMC buildings to support effective operational planning, risk assessment, and emergency response by FRSs.

References

[i] Dangerous cladding: the government’s remediation portfolio – NAO report (www.nao.org.uk)

[ii] BSI publishes standard for modern methods of construction | BSI (www.bsigroup.com)

[iii] CROSS Safety Report – Volumetric module buildings and fire, December 2021

[iv] Grenfell Tower Inquiry: Phase 2 Report (2024), Chapter 113, paragraph 113.22

[v] www.gov.uk/government/publications/volumetric-modular-construction-research

[vi] RR1203: The impact of Permanent Volumetric Modular Construction (PVMC) on building safety – HSE (www.hse.gov.uk)

[vii] Independent Review of Building Regulations and Fire Safety: final report www.gov.uk

[viii] Remediation – Fire Service Policy and Operations- NFCC Industry White Paper (nfcc.org.uk)

[ix] Construction Products Reform Green Paper – www.gov.uk

[x] Insights publications May MMC Technical Paper (www.marshmclennan.com)

[xi] Modern-methods of construction-Whats Gone Wrong (committees.parliament.uk)

[xii] Letter written by Lord Moylan, Chair of Build Environment Committee to Cabinet Office (committees.parliament.uk)

[xiii] Fire performance and regulatory considerations with modern methods of construction | Buildings & Cities (www.journal -buildingscities.org)

[xiv] Press release from Jim Mcmahon OBE MP and The Rt Hon Angela Rayner MP (www.gov.uk/government/news/devolution-revolution-forges-ahead-with-more-powers-for-mayors

[xv] Interim report into the Review of Building Regulations and Fire Safety – GOV.UK

[xvi] Grenfell Tower Inquiry Phase 2: Recommendation 24 We have referred to the Cladding Materials Library set up by the University of Queensland, which could form the basis of a valuable source of information for designers of buildings in general. We recommend that the construction regulator sponsor the development of a similar library, perhaps as part of a joint project with the University of Queensland, to provide a continuing resource for designers, (www.gov.uk)

[xvii] Fire safe  design of mass timber buildings-may2024 (www.arup.com)

[xviii] NFCC_response_to_MHCLG_assessment_in_lieu_of_test_-_Final_24_May_2018-1.pdf (nfcc.org.uk/wp-content/uploads/2023/08/NFCC_response_to_MHCLG_assessment_in_lieu_of_test_-_Final_24_May_2018-1.pdf

[xix] Independent Review of Building Regulations and fire safety (https://publications.parliament.uk/pa/cm201719/cmselect/cmcomloc/555/55506.htm)

[xx] NFCC_Response_to_Raising the Bar.pdf 15 November 2019 (https://nfcc.org.uk/wp-content/uploads/2023/08/NFCC_Response_to_Raising_the_Bar.pdf)

[xxi] Construction Industry Council, “Setting the Bar”, October 2020 (www.cic.org.uk)

[xxii] ‘Building Designer’s expectations on the fire service – You expect us to do what?’

Equalities Impact Assessment

NFCC Modern Methods of Construction Policy Position Statement Equalities Impact Assessment