Modern methods of construction: Risks

Summary

Modern methods of construction have the potential to address a number of the current key concerns in the construction industry, ranging from improving productivity to managing the anticipated skill shortages of an ageing workforce. MMC is also seen as helping the construction industry improve its environmental and safety aspirations through more efficient use of materials, reduced waste, reduced human input and maximising fabrication of major elements within controlled quality controlled off-site environments.

Offsite vs. On-site: Current Building Regulations Part L
Source: Offsite housing review, Construction Industry Council, Feb 2013

Although MMC delivers many opportunities, there are risks - from land acquisition, design, construction, maintenance and ultimately to demolition/re-cycling - that clients, designers and constructors need to manage through the full lifecycle of the project.

This article will provide a brief look at the wide range of risks that need to be addressed in developing a project adopting MMC, including risks in respect of project promotion, liability, insurance, technical design, construction and safety. This article generally considers the “project team” as encompassing the client, designer, contractor, specialist supplier/fabricator and the supplier’s designer since to maximise the benefits of MMC to the project comes from a collaborative approach amongst these team members from very early stages of the project.

What are modern methods of construction?

There are numerous definitions of MMC within the available literature. The Ministry of Housing, Communities & Local Government (MHCLG) MMC working group produced a seven-category framework. This framework is outlined below and for the purposes of this article MMC will be taken to encompass:

MMC Definition framework
Source: MHCLG MMC Working Group, 2019

Offsite volumetric modular systems (volumetric, Cat 1): Where prefabrication is used to create complete “three dimensional” structural units (that may or not be fully fitted out with services and internal fittings) that are delivered and assembled on-site to form the final structure.

Offsite panel systems (or flat panel systems) (panel, Cat 2): Where “two dimensional” panels are prefabricated, delivered to site and lifted into position, then connected to form the structure. Finishes and services are usually installed on-site after the structure is assembled.

Offsite hybrid systems (hybrid): Which may combine volumetric or panel systems with other precast elements and/or a primary structural frame.

On-site MMC methods (on-site methods): Which include productivity, labour reduction and assurance improvements such as robotics, measures to protect working environment or standardisation of temporary works.

As can be seen above this covers a wide range of systems/methods of construction. To help present the risks within such a wide range of systems and methods, this article will focus on the first and most extensive use of MMC, namely volumetric systems, as it encompasses most of the key risks for this topic.

Why consider MMC?

Modern methods of construction have the potential to address many of the current concerns in the UK construction industry including low productivity, skill shortages, low predictability of cost and programme, quality and improvements in health and safety. These benefits are achieved by transferring many of the traditional site activities into a factory environment or to offsite fabrication yards that produce project elements that can be readily assembled on-site.

Transfer of such site activities into a factory environment can lead to significant benefits, such as:

• Overlapping of initial site preparation works with superstructure fabrication leading to shorter on-site construction phases
• Rapid achievement of weather-sealed working environments
• Reliable delivery of factory quality structures or components
• Safer operations through fewer site operations and fewer site operatives
• Cost savings for lower site overheads due to reduced time on-site and reduced site establishment. Though this may be balanced by higher initial costs for prototyping of designs and assembly set up
• Reduced environmental impacts with smaller quantities of site waste from materials, fewer site deliveries, whilst waste produced in a factory can be more easily recycled and lifetime energy use can be better achieved through better airtightness and thermal performance obtainable in factory conditions

Benefits of MMC
Source: Adapted from the RIBA Plan of Works 2013 Designing for Manufacturing and Assembly

Risks

However, this departure from more traditional methods opens up the possibility of unusual risks that need to be balanced against the possible benefits in assessing the potential success of MMC for the project’s lifecycle as it progresses through the stages:

1. Preparation and definition of brief
2. Development of concept design
3. Development of preliminary design
4. Production of detailed technical design
5. Construction
6. Handover, in-use and end of use

It is not unusual for projects to have these phases overlapping to varying degrees, with design commonly continuing into the construction phase. For the purposes of this article, they will be treated as discrete phases with the some of the considerations mentioned overlapping into adjacent stages; the RIBA DfMA overlay to the RIBA Plan of Work is taken as the basis for this approach.

Project definition, planning and design development (Stages, 1, 2 and 3)

These initial phases face significant risks that should be considered in concert with clients at the outset of the project. The adoption of volumetric methods in particular needs to be established early in the project life to maximise their potential benefits and minimise the associated risks being built into the project. However, the adoption of each method of MMC should be factored into the development of the design prior to detailed design commencing.

Suitability of the project to MMC

It may be a heresy to question the suitability of MMC at this time, considering the promotion of MMC by the UK government and industry, but it is a key question for all parties. A considered assessment needs to be undertaken at the start of a project on whether a volumetric system, a panel system, a hybrid or a traditional on-site approach best suits the project. Similar to other forms of construction such as precast segmental construction, volumetric construction should not be “retrofitted” to a detailed design. Careful assessment of whether the scope of the project, the limits of applicability, supply chain availability and permitted environmental conditions are appropriate to the adoption of MMC needs to be carried out in an open and realistic manner. Where such an assessment is not carried out, there will remain a significant risk of delays and disruption due to the variations needed to make the method “fit” to the project. This risk is exemplified by the late involvement of key suppliers, fabricators, and contractors resulting in, at best, the benefits of MMC not being fully incorporated or at worst details that compromise the integrity of key aspects of the structure such as fire resistance, robustness and water tightness.

Other early considerations include fundamental constructability issues such as determining the ability to transport to the site, availability of space and equipment to lift elements into place and availability of space for storage prior to lifting. Different skillsets from traditional construction may also be needed to facilitate construction on-site and these may not always be in place within a practical catchment area of the project.

Acceptability of MMC

Having confirmed the suitability for the adoption of MMC within the project team, they will need to look outward and address the risk of potentially poor perception from warranty providers, the local authorities and the targeted end users of a structure produced using MMC. Perceptions that may need to be addressed include:

• Potential for poor quality and defective construction
• A lack of understanding about the performance of MMC under fire situations
• Designs lack the potential for customisation
• Smaller room sizes are inevitable due to controls on handling and transportation constraints of volumetric units
• Poor consideration of tolerances will lead to lack of fit when erected on-site with resulting robustness or durability concerns
• Damage might accrue during transport, or prior to making structures watertight, leading to damage from water penetration

These adverse perceptions can result in difficulties in obtaining acceptance from local authorities, hence delaying the project. These perceptions may also make it difficult to achieve financing, insurance, and assurance of the project.

Some of these perceptions can be addressed by highlighting 21^st century technologies and processes which are now used in defining, fabricating and assembling buildings to achieve higher quality, safer and more cost-effective construction. But, early planning involvement, demonstrable quality control measures and communication of what is going into production of a structure’s MMC components appear to be the fundamentals of overcoming these perception risks.

Contractual

Traditional forms of contract have, to varying degrees, allowed for some development of design and completion of detailing at late stages in the design process or even during construction. When employing MMC, such finalisation of details at a later stage of the project generates the following risks:

• Abortive prototyping and wastage of materials of already fabricated units
• Delays to the programme as the details are resolved
• Problems for installation on-site such as lack of fit from inadequate consideration of tolerances
• Problems for resolving clashes between the volumetric units and the site constructed items such as foundations and utilities
• Problems of integrating building services when they have not been adequately considered early in the design

To realise the benefits of MMC volumetric and panel systems requires a “product-led” approach built into the contract where the arrangement, details and integration of the volumetric modules need to be finalised prior to production of the units. Errors, incompatible arrangement, assumptions within an incomplete design will be built into all the units risking cost and delays for remedial works or even worse defective units that must be scrapped and new units produced.

As a working principle, the greater the extent of work offsite, the earlier the key decisions must be taken and the sooner the client’s design requirements must be frozen. Thus, the processes and responsibilities for the “freezing” of the design needs to be built into the details of the contract and clearly communicated to all parties along with the risks for post-freeze changes.

As with stability in the design, successful factory production requires stability in product demand. Large scale projects have been dealing with offsite precast or fabricated components for many years, with key contractual questions arising when placing such a large essential proportion of a project with a single supplier/fabricator. These fabricators will likely use proprietary details and factory processes that require a significant outlay for setting up and maintaining, which depend on a steady and predictable throughput to preserve the essential quality facilities and a skilled labour force. However, the building market has been noted for its cyclical nature leading to risks in engaging such a single key supplier/fabricator. Assessing the risk of such a key component supplier going out of business during the project remains a very important early activity and requires discussions with the relevant professionals for appropriate contractual and insurance provisions needed to protect the project.

One approach to addressing the question of stability of the supplier is to allow for the use of  international suppliers that can use the fluctuations among different national building industries to balance the demands on their factories. However, the potential for the company to fail still exists and is potentially complicated further by differing legal frameworks when trying to recoup committed expenditure or compensation for delays and disruption. It can also introduce additional risks related to unforeseen differences in code requirements, design standards, working standards and, again, legal frameworks within which the supplier exists. The use of suppliers registered with Buildoffsite Property Assurance Scheme (BOPAS) and NHBC Accepts scheme should form part of the assessment of the project against such risks along with consideration of contractual arrangements that provide the client with access to all interim payments.

Insurance

Insurance risks for the project will range from consideration of the fabrication, delivery, and installation to concerns over the form and materials being built into the project, including questions of professional indemnity.

The project team will need to include the skills to assess the project requirements regarding:

• Insurance of the design for the proprietary units: Design insurance will need to consider the usual design liability issues along with issues particular to the inclusion of MMC. The article Professional indemnity insurance considerations when adopting modern methods of construction, published by the Institution of Structural Engineers, raises a number of key indemnity issues for the project team to consider when approaching projects with MMC components. Some of the key aspects associated with MMC may render the standard PI inappropriate and adequate specific clauses for items such as re-use of designs should be adopted. A major issue for the project is the potential for design flaws not being identified and corrected during design development or during reviews and prototyping of the design which will result in repeat flaws within every unit in the project with potentially disastrous results. This places a greater emphasis on design reviews and freezing of the design but can lose the potential for continuing innovation. To allow for the potential for ongoing project improvements, the project team need to put in place processes and relationships among the project team to assist in managing late innovation risks. Furthermore, identifying the criteria to be used to assess whether the benefit of further innovation outweighs the cost and programme impact of introducing the innovation changes would need to be developed. This desire for continued innovation needs to be balanced against the risks being shared across the team and how any liability can be equitably shared
• Insurance of units during fabrication: Although primarily the responsibility of the fabricator, the project team will need to consider the implications of loss of units to the overall project. Simple replacement costs of units in the factory are unlikely to be sufficient to compensate the project when key units are not available to meet the master project programme
• Insurance of units in storage: Whether in the fabricator’s yard and/ or on-site, unless there is a “just-in time” approach to the project there is a need to insure the modules at the temporary stockpile location. This location can be at the fabricators yard, at a separate designated storage location or on the project site if space is available. Each location has differing levels of obligations for each member of the project team, extending from the obvious material damage and loss due to fire, vandalism and weather, to storage location security, safety, and environmental compliance
• Insurance during transport: Risk of damage to the units during transport may not only have the consequence of requiring remediation/repair to a single damaged unit but may impact on the progress of the work. Furthermore, unless the units are all of a standard design, the damaged units may need to be replaced with newly fabricated units that must fill the space left by a damaged unit that cannot be repaired. Insurance may not cover all risks associated with export and import of MMC components and planning of transportation will need to try and remove risks such as intentional or unintentional contravention of border security and biosecurity regulations through appropriate inspections and security seals
• Insurance of the partially installed units: The partially completed structure can be highly susceptible to fire and water damage where the fire breaks, partitions and outer fabric have not yet been installed.  The structure is at its most vulnerable to arson and water damage during construction when the insulation/structure is exposed and the building is not yet weather tight. At this time there is every opportunity, given the amount of ventilation in the open structure, for a small fire to spread rapidly. Insurers may have the perception that MMC sites could be a particular risk to arson on major elements of the structure, and again the security of the site (and the structure itself) will be a critical aspect of the potential damage risk assessment. The proximity of the structure to the site boundary and surrounding buildings will play a role in the risk assessment along with access to and around the site
• Insurance of the completed structure: From a fire safety, water resistance and general insurance point of view, comments from insurance companies raise concern with MMC that an enhanced fire load may have been introduced into the structure or the vulnerability to fire or water damage may have been increased. This concern extends to the on-site fire and water protection works required

The key item from the insurer's perspective is to have full knowledge of the items going into the building and consultation on the risk mitigations. It is essential that the project team establishes clear and concise requirements and responsibilities for the modules throughout every stage of the module’s life. In doing this, the project team should consider:

• A risk assessment to back up the suitability of a chosen construction method in light of the intended occupancy. Any risk assessment or fire safety strategy, considering the fire protection/detection and design, should also be undertaken to include the property protection point of view, rather than only covering life safety. However, life safety must be given the highest priority
• The experience of the contractor in other similar modular/panel build systems
• The use of automatic fire protection and detection systems
• Details of the third-party inspection and certification schemes for both products and installation
• Full design details of the composition of any prefabricated pods (eg shower rooms) and material specifications
• The factory quality assurance procedures
• The handling procedures within and from the factory to installation and completion of the overall structure
• Consideration should be given to a role and position, such as a on-site Clerk of Works, being re-introduced as a means of ensuring on-site compliance during installation/ construction
• The extent and location of combustible elements within the structure and their potential susceptibility to an ignition source
• Fire breaks, fire stopping and compartmentation to limit internal fire spread
• Fire test results and data to verify the appropriateness of the chosen system and materials
• Water protection systems and details for maintaining the fabric of the modules through delivery, storage, and installation
• Details of the site-applied fire stopping (materials, products, and design)
• The risks associated with the introduction of items such as commercial catering facilities or solar PV systems

These contractual and insurances risks can be addressed through early discussion with contractors, fabricators, and insurance companies. In this discussions, clear responsibilities need to be defined for the overall structural designer, MMC supplier and other specialists. The design may be so specialist that the overall designer may not be able to check it and an expert third party peer review would need to be commissioned. The fundamental risk is the failure to understand that most of the MMC methods require a different approach to procurement, project insurance and risk assessment.

Project design phase: Stage 4 – Technical design

General principles

The Royal Institute of Chartered Surveyors (RICS) has stated that “while the method of manufacture and construction are important, many of the key risks with MMC are mitigated in the design; without a complete and viable design the method of manufacture, quality procedures, tolerances, construction method and interfaces with site conditions cannot be determined. Design underpins everything.”

The progress of MMC into the detailed design continues the efforts needed to mitigate the potential risks for the project. However, the effort needed to fully design and detail an MMC system can be underestimated, particularly the need to finalise design coordination which leads to an increased level of complexity at earlier stages of an MMC design. Drawings and specification of all components go beyond what is required in conventional construction.  For example, jointing elements need specifications setting out the colour, location, length, width, allowable tolerance, and temperature at which the jointing can be made along with to what level and how frequently it is to be inspected to guarantee an assured installation.

Inadequate planning of the design development can lead to omission of such key details for the design. Although this situation occurs with traditional design, MMC is potentially impacted to a greater degree by the introduction of inaccurate information, defective design and change orders.

It is necessary  to have a clearly defined scope since no single MMC system is suitable for all sites, building shapes or planning requirements though these restrictions are often not defined by the manufacturer. The best designs appear to come from a simple, core product to which further features may be added. When MMC systems have such a clearly defined scope, the limits of applicability and permitted environmental conditions can be fully specified. This then allows any variations to be fully designed and detailed.

Codes and standards

There is currently a lack of bespoke design codes, guidelines and standards for the application of MMC in the UK, particularly modular integrated construction. However, it should be noted that the BSI PAS 8700: Modern methods of construction is currently in draft form as is a standard by NHBC.
Additionally, international standards do exist such as:

• Monash University & Modular Construction Codes Board (2017) Handbook for the design of modular structures
• International Code Council and Modular Building Institute (2021) ICC/MBI 1200-2021 - Standard for off-site construction: planning, design, fabrication, and assembly

It is highlighted in the CROSS Report ID 1065 - Volumetric modular buildings and fire that “...volumetric modular buildings are not necessarily a ‘common building situation’, so it is essential that the design teams consider the issues holistically, without ‘blindly’ relying on prescribed guidance.” This indicates a need for designers who have sufficient knowledge and skills to approach the design situations from first principles. The advice that national documents such as the Approved Documents are only giving guidance for designers is raised again in CROSS Report ID 1179 – Modern Methods of Construction and Robustness. This report (1179) notes that adoption of MMC components needs to be approached on a case-by-case basis with a systematic risk assessment carried out covering such topics as fire protection, robustness, positive fixity to foundations, etc.

A more direct confirmation of the status of the limitation of the use of the Approved Documents is provided in CROSS Feature Article Report Cross-laminated timber (CLT) in multi-storey buildings wherein it states “It is the opinion of the CROSS-UK Fire Safety Expert Panel that the use of CLT in multi-storey buildings is not a “common building situation” as defined in the Approved Documents as they are currently published.” This is again reflected in the statements in CROSS Report ID 1243 - Fire Hazards in historical modular timber framed buildings, that many types of MMC cannot be regarded as a common building situation.

The National Fire Chiefs Council in their position paper published in 2022 also emphasised their concerns about the lack of understanding of the performance of MMC and promoted more research and entire system testing which could underpin demonstration of compliance with building regulations and fire safety procedural guidance.

It is noted that there are accreditations for the use of MMC: the Buildoffsite Property Assurance Scheme (BOPAS), NHBC Accepts and the BRE’s BPS7104, the first two being the most commonly used. However, these schemes set their own standards and do not have a specific focus on aligning with the Building Regulations across the UK. Thus, accreditations under these schemes does not automatically demonstrate compliance with all UK building regulations and standards.

For the project team, a fundamental risk is that the current standards, codes, and details may not adequately cover the specifics of the MMC proposed for the project. To address these risks, time and effort needs to be allowed at the start of the design development for risk assessments on key details along with consultations from specialists on topics such as fire resistance and building regulation compliance.

Critical design detail risks

The adoption of MMC (particularly volumetric construction) has inherent design risks that the project team need to identify and confirm how the risks have been mitigated.

Performance risks: If not carefully detailed and specified, MMC components can suffer risks for poor project performance in:

• Means of escape for both module design and overall layout
• Sound transmission due to their lightweight nature, unless measures such as resilient floor materials are adopted, finishes are selected carefully, floor mass is increased, or vertical structural connections are carefully developed
• Achievement of desired fire ratings balanced against minimising size and mass of the components
• The structural functions such as diaphragm action if plane bracing is not provided or site bolting with oversized holes are used
• The stiffness of the structure to support external secondary elements such as balconies and cladding
• Overall stability, smoke control and cladding efficiency when the layout deviates from the standardised planning grid
• The ability of the structure to cater for moist air/entrapped water
• Resistance to water ingress through continuous voids in volumetric construction

A feature of MMC components that has come under a significant amount of scrutiny is the fire performance of the components. As mentioned earlier, the fire performance of the units, from the perspectives of both safety of the occupants and for the fire and rescue services entering buildings, is of very real concern. This concern extends from the basic materials used in the components to the effectiveness of the installation process and completion of the fire protection systems and successful fire compartmentation of the structure.

Lack of continuity risks: Modular units themselves are generally inherently stable and robust. However, the overall assembly is a collection of components that have no intrinsic structural continuity across adjacent modular units and would tend to behave separately under lateral loads without careful detailing of the on-site connections. This raises the risks associated with the design and detailing of the continuity across adjacent modular units. The design must also consider how to build in alternative load path routes to mitigate against progressive/disproportionate collapse, structural integrity, and robustness against accidental loads.

Connections between components need to be robust, accommodate tolerances and maximise accessibility since the nature of this form of construction can block access to the inner nodes of the structural frame. The design of the joints between modules is further complicated by the need to retain the integrity of fire, moisture, and air membranes between units. Good practice will allow for lapping of these critical membranes, visible inspection of the integrity of joints and consideration of how these connections are formed on-site.

Volumetric MMC introduces voids between the walls of modules, intermediate floors, and subfloors. Factory-fitted fire barriers are then often hidden from view such that the practicalities and ease of inspection of this safety-critical element needs to be considered at the design stage. Such forms of construction open the potential for unseen and uncontrolled rapid fire spread through these voids and beyond the designated fire compartments. This includes modules sitting only at corner pads which results in a void in the subfloor beneath party walls. Designers need to consider whether the void is to be subdivided on the party wall line to match compartments above these foundations.

Tolerance and differential movement risks: A major challenge in MMC design is the dimensional and geometric variability arising from multiple sources during manufacturing processes, transportation and installation. Even if precise methods of production and advanced inspection technologies are used, risks will still exist between the precision achieved in the fabrication and that of the larger site tolerances, as well as deflection or distortion effects occurring during transportation and handling. MMC designers need to understand the realities of site conditions and to build in sufficient tolerance to allow their systems to be effectively and efficiently assembled. This includes consideration of items such as:

1. Designing for tolerance effects
2. Designing for differential shortening
3. Allowing for the resulting load redistribution from 1. and 2. above
4. Allowing for eccentric load effects from tolerances among MMC units
5. Designing for eccentricities with foundations
6. Designing for tolerances in incoming sewerage, water, electricity and telecommunications services

However, making allowances to encompass this range of tolerance can have the side effect of generating risks of eccentric loading of posts and connections.

Depending on the project experience of the fabricator, the operatives fabricating the MMC components may or may not have skills specific to the structure requiring a higher level of detail in the drawings and specification to achieve a satisfactory product. This high level of specification would need to extend to the ease of connections details and methods (eg pressure fittings, where permitted) and how the tolerances in these fittings are maintained during fabrication, delivery and installation. Detailed co-ordination between fabrication plans and site arrangements is required to avoid incompatibility risks of the units with the incoming service locations. This includes particular care at penetrations for service pipes and electrical sockets, especially if standard locations line up between units creating potential penetrations of fire and sound barriers.

Stage 5 – Fabrication, transportation and construction

Fabrication

Fabrication of MMC components within a factory environment has the fundamental advantage of managment of the fabrication quality within a controlled environment, provided that quality assurance procedures have been established and implemented. However, new or bespoke systems may not have such procedures fully implemented, and an assessment of the maturity of the applicable QA system should be undertaken.

As with the works on-site, there is a potential for fabricators to replace specified details and/or materials with proprietary details and available material which may:

• Place the designed performance at risk
• Result in incompatible performance with other elements of the project
• Deviate from previously obtained permits or building warrants

Transportation and storage

To reduce the risk of damage to MMC components during transportation it is necessary to consider aspects of the transportation such as:

• Access to site and the ability to deliver components without damaging or adjusting the components from the fabricated condition
• Loads applied during loading, transport and off-loading and whether they have been allowed for, (Reference can be made to Driver and Vehicle Standards Agency: Securing loads on HGVs and goods vehicles which covers transport loads on this issue)
• Support during storage - whether this matches the designed support conditions
• Storage environment - whether there is a potential for water to enter the fabric of the components or for the storage conditions to adversely affect the factory applied finishes
• Storage arrangements and whether the proposed arrangement that has been allowed for in the loading and detailing. Also, whether the arrangement has the potential to damage critical items such as the fire stopping and damp proofing or whether there is sufficient space for inspection and safe handling

As with other forms of prefabricated components, delivery disruption posses a risk to the overall project. Delayed delivery or a fabrication location no longer being available will need to be considered in the overall risk assessment of the project and suitable mitigation measures such as stockpile space, alternate delivery routes and alternative fabrication sources being considered.

Construction/installation

An information gap between the designer documentation and fabrication/installation directions can lead to modular fabrication/installation failure and defects that halt the on-site installation process, especially with just-in-time delivery. Mitigation of this would focus on careful modelling, detailing and specification of the design. Component systems can be less susceptible to this since standard components can be applied across multiple projects and delivered to replace defective elements.

Weather disruptions, delays in modular delivery, and crane failure can cause delays in the scheduled performance of MMC projects. Crane failures can be mitigated through contingency planning, but early and careful consideration of crane placement and operation will reduce the potential risks to the installation programme and safe crane operation.

Enhanced quality control is needed on-site to ensure all measures for structural integrity, fire integrity, waterproofing and ventilation are satisfactorily constructed. This may include such matters as ensuring inspection of structural connections, fire protection and waterproofing prior to covering them, using inspection and test plans developed from the designer’s specification. Poor practice and lack of supervision during installation can lead to hidden voids through which smoke, toxic gases and water can pass through a building.  Even a small amount of water penetration or small fire can lead to damage that is out of proportion to the original cause. Once modules are connected, proper inspection of the installation is not practical and consideration of a higher degree of inspection and more extensive records of inspected as components are assembled should be considered.

Other site based risks to be considered include:

• Product/component substitution resulting in deviation from the original design, particularly at the structural, fire and waterproofing connections
• Damage from follow on trades to pre-installed fire and water barriers
• Inaccuracy in foundations, particularly for volumetric systems
• Insufficient placement tolerance resulting in modules overhanging in successive levels and “creeping” out of position

Risks involving such site based issues can be reduced through training for the site teams and potentially engaging with the fabricator for site inspections.  Experience in Hong Kong is indicating that as MMC works are expanding there is a need to possess competence and knowledge for the particular form of work and particular training courses have been set up by CIC HK, including “Foundation Certificate in MiC (Lifting, Installation and Disassembly)”.

Sustainability

A greater emphasis needs to be placed on the circular economy aspects of the project during the design phases since risks or benefits will be multiplied in the production process such as:

• Provision of good levels of thermal insulation
• Adoption of efficient construction methods and energy use in construction and use of materials
• Use of 100% recyclable materials with consideration of ease of deconstruction and reuse
• Reduction of transportation movements
• Reduction of noise, dust vibration and waste materials
• Improved health and safety performance

Safety

A key benefit of MMC is its overall improvement in safety for construction through the reduction of on-site operations and maximising construction of elements within controlled environments. However, there are risks inherent in the MMC, including:

• During lifting and handling of fabricated units in the fabrication, transport, storage and installation
• During transportation of fabricated units
• Increased risk associated with work performed in close proximity to modules; in some cases, this may occur without the scaffolding measures typically utilised in traditional construction
• Ensuring tolerances are accommodated
• Lack of specialist knowledge for installation leading to inadequate risk assessments
• The potential for unsecured cut metal edges in units for the initial installation of the units, and then for any post-installation or connection of services
• The need for “incidental lifts” of the incomplete modules to enable the assembly of the complete unit which can include the uncontrolled use of forklifts to move large components. There is a potential for a lack of appreciation that every lift is a new application of loads and involves risks which must be eliminated through appropriate design and practice
• Exposed screw tips and nails in void spaces that may have safety implications for works on subsequent activities
• Abrasion of insulation materials resting on metal edges
• Pinch points in connections
• Surfaces which can retain rainwater and pose safety and durability issues
• Activities requiring work at heights to install and control large units

Stage 6 - Handover, in-use and end of use

Decisions made in the initial stages 1 to 4 can increase the number of, or magnify, the risks encountered at the handover, in-use and ultimately demolition phases in the project life cycle, including:

• Use of systems where a partial loss may result in the need for complete demolition and rebuild
• Use of suppliers/fabricators where it is difficult to obtain spare parts and components, especially for bespoke or limited-run systems
• Maintenance access not having been followed through in developing the design
• Lack of consultation with owners and operators on practical maintenance regimes
• Lack of handover of information on the design principles, details and materials used
• The installation of new services through walls and floors or the installation of electronic equipment/devices breaching fire compartmentation and that, in the event of a fire, allow much more rapid and extensive fire spread into hidden voids
• Use of systems where demolition must follow defined sequences to maintain stability
• Use of materials requiring particular handling methods to achieve the desired sustainability goals

Structures using MMC can be particularly impacted if any aspect of a development is altered during its lifecycle and this can impact the safe habitation of the structure and its safe demolition at end of use. Lack of knowledge and hence control of any changes or renovations of firebreaks, water barriers or service connections can compromise the safe and durable performance of the structure. Original construction and upgrade or repair data must be clearly documented and maintained to ensure contractors (including those involved in minor day to day maintenance) have an awareness of the complexities and limitations of the building – including such aspects as fire protections, service routes and protections, and structural integrity. Such information is also important for fire and rescue services to understand the form of structure they are entering and making decisions with respect to stay in place advice.

Key views

New methods of construction have the potential to contribute to the solution of many of the construction industry’s issues.

However, there have been notable failures of structures built using MMC in recent years, leading to the buildings being condemned and demolished. These failures have occurred for a variety of reasons, including, but not limited to, a lack of structural integrity, a lack of fire integrity, and inadequate consideration of moisture leading to excessive damp and decay. It is essential that future projects learn from these failures.

To successfully implement these new methods will require a willingness to adopt new and wider thinking approaches to:

• Design
• Procurement
• Installatio
• Maintenance,
• Handover and close out
• Demolition and re-use

All parties need to think about projects in new ways, with a systematic and realistic approach to risk, sustainability and innovation. The nature of modular construction emphasises the need to put into practice the concepts and details behind the Golden Thread principles being promoted within the industry, with clear transfer of information and responsibility through the life of the structure.

Successful delivery of MMC projects hinges on effective management of the risks being built into the early phases of the project lifecycle and followed through in a clear, documented, and managed process to completion and handover.

References

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