Modular Construction: Design Considerations and Opportunities Vikrom Laovisutthichai 1*, Weisheng Lu 2, and Fan Xue 3 This is the authors’ pre-print version (before peer review) of the paper: Laovisutthichai, V., Lu, W., & Xue, F. (2020). Modular construction: design considerations and opportunities. Proceedings of the 25th International Symposium on Advancement of Construction Management and Real Estate (CRIOCM2020), Springer, in press. Outstanding Paper Award. This file is shared for personal and academic use only, under the license CC BY-NC-ND 4.0 (Non-Commercial, No Derivatives, and with an Attributed citation when you use). The final published version of this paper can be found at: [LINK_TO_SPRINGERLINK]. Any uses other than personal and academic purposes must obtain appropriate permissions from Springer first. Abstract: The realization of Modular Construction (MC) is impeded by several barriers, e.g., initial investment, logistics constraints, and negative perception. Design, a profoundly creative process to alleviate difficulties in the built environment, is prospected to enhance this construction method. Under this circumstance, many guidelines, recommendations, and avoidances have been proposed to design. However, every coin has two sides. This research, therefore, argues that MC also provides new design opportunities, which have not been yet extensively investigated. It does so by comprehensive literature review and detailed archival study of successful case studies. The result unveils that although MC, by nature, may impose several design limitations, e.g., design simplification, standardization, and limited dimension, it can also serve demands and construct an outstanding architectural design by, for example, a composition of three-dimensional unit, mass customization, and product prototype. This research creates a balanced view of MC in a design process, and highlights the new approach for further design and research development in this discipline. 1* Laovisutthichai Vikrom Corresponding author, Department of Real Estate and Construction, The University of Hong Kong, Hong Kong E-mail: Vikrom@hku.hk Weisheng Lu Department of Real Estate and Construction, The University of Hong Kong, Hong Kong 2 3 Fan Xue Department of Real Estate and Construction, The University of Hong Kong, Hong Kong Keywords: Modular Construction; Architectural Design; Design for Excellence; Design for Manufacturing and Assembly. 1 1 Introduction 2 Modular Construction (MC) is an innovative construction method, basically comprising the 3 room-sized free-standing integrated units manufacturing in a factory-like environment, 4 logistics, and installation to form an architecture [1, 2]. These units are preassembled with 5 finishes, fixtures, and fittings to minimize work in-situ [3]. If comparing this prefinished 6 volumetric unit to the other prefabricated products, MC is classified a high level of 7 prefabrication [4]. This construction method has been applied to many building types, 8 especially in cellular-type building, including hotels, student dormitory, governmental 9 building, and social housing [5]. 10 MC is becoming more widely used, since it has offered numerous advantages to the 11 industry. They include quality improvement [6], construction time reduction [5, 7], 12 productivity enhancement [8], workforce safety [9], and waste minimization [5, 10]. In spite 13 of these various benefits, MC also experiences criticism. The method implementation in the 14 real-world cases is undermined by, for example, the significant investment on the production 15 line establishment [11], and transportation regulations and constraints [12]. In addition, this 16 modernized construction process and machinery need an experienced workforce and 17 technician for operation [13]. These shifts in the procedures also require more attempts from 18 stakeholders and alterations in construction practices [14]. Moreover, there is a somewhat 19 stereotypical perception in the architecture, engineering, and construction (AEC) industry, or 20 even the general public that architectural design is limited by the drawbacks of MC [15, 16]. 21 Many efforts have already been made to support this innovative construction realization. 22 Design, as an initiation process shaping the following activities [17], is currently prospected 23 to be a new faith to alleviate MC difficulties. In such circumstance, organizations and 24 researchers worldwide provide MC design requirements, recommendations, lessons, 25 instructions, and practice examples for practitioners [18-20]. Nonetheless, everything has two 26 sides. While design considerations and avoidances for MC have been extensively studied, 27 the new design possibilities occurred from MC have not been widely debated in the previous 28 29 research. This paper, therefore, aims to explore both benefits and limitations of MC to an 30 architectural design process. It is also expected to highlight new design opportunities, derived 31 from MC, for the further design and research development. This is achieved by reviewing 32 literature and revisiting successful case studies. The remainder of this paper consists of four 33 sections. Section 2 provides the background information of MC and architectural design. It is 34 followed by the research methods adopted. Section 4 displays the design considerations and 35 prospects, distinguished in this study. Finally, it reaches the discussion and conclusion parts. 36 2 Literature Review 37 2.1 Modular Construction 38 Modular Construction (MC), sometimes called volumetric prefabricated construction, refers 39 to a construction process of prefinished 3D unit assembly to be a part of or create the whole 40 building [1, 2]. In general, MC consists of three main stages. It begins with manufacturing in 41 a factory-like environment. This system borrows the concept of the production line, the 42 industrial workstation, and repetitive duties, to reduce the amount of work in-situ [21]. Then, 43 a wide range of such modules, from basic structure to fully furnished units, are transported to 44 construction sites for assembly. Finally, all modules are installed, and structural, mechanical, 45 electrical, and plumbing (MEP) systems are connected to form buildings [2]. The method 46 current application includes student accommodations, hotels, hospitals, and governmental 47 buildings [5]. 48 Gibb [4] provides a taxonomy of such units: Level 0 A system uses zero forms of 49 prefabricated units; Level 1 Component and sub-assembly (e.g., lintels); Level 2 Non- 50 volumetric assembly such as 2D precast concrete wall panels or tie beams without usage 51 space enclosed; Level 3 Volumetric assembly such as kitchen, bathroom, utility rooms with 52 usable space enclosed; and Level 4 Modular building like a living unit with full usable space 53 enclosed and some utilities installed. If sticking to the above definition, MC can be 54 considered in Levels 3 or 4 in Gibbs’ taxonomy, representing a higher level of sophistication 55 in terms of production, transportation, and assembly. 56 57 The characteristics of MC offers numerous advantages to the industry. For example, product quality improvement is given by the factory-like environment in the production line 58 [6]. It makes a variety of actions in construction more repetitive, controllable, and reliable, 59 and contributes to an accurate monitoring system and immediate inspection. Secondly, the 60 settings of MC provide labourers with a safe working environment and reduce their risky 61 behaviours. The number of accidents can be decreased by 80% if adopting MC [5, 9]. Its 62 production line system also boosts the construction productivity by a process revitalization 63 and efficient project schedule [8]. Furthermore, construction waste management gains several 64 benefits from the natures of volumetric prefabrication. It is able to minimize waste from 65 timber formwork, plastering, and smoothening process. By using MC, solid landfill waste can 66 be decreased by 70% [5, 10]. Finally, as on-site and production line tasks can be done 67 simultaneously, it is estimated that the use of 3D unit prefabrication can decrease construction 68 time by 50% and saved 7% of the total project finance [5, 7]. For developers, the shortening 69 of time means a considerable reduction in interest charges and early return of investment 70 capital [22]. 71 On the other hand, MC is also challenged by several drawbacks. Firstly, MC incurs an 72 increase of total construction cost, including the significant initial investment required for the 73 production line establishment and operational cost afterwards. Against the stereotypical view, 74 MC is more expensive than traditional cast-in-situ construction [11]. Moreover, the use of 75 machinery requires experienced technicians, labourers, and experts to handle the modernized 76 processes [13]. In addition, logistics becomes a fundamental concern in MC. One must 77 investigate transportation regulations, routes, and traffic before design, since the delivery 78 limitations directly affect the size, weight, and dimensions of modules [12]. A paradigm shift 79 in architectural design and construction professional practices is also required to implement 80 MC. Due to its restrictions, early coordination among stakeholders, and additional project 81 planning and design efforts are necessary to ensure the construction possibility, prevent the 82 risks, and facilitate the flow of the operations [14]. Finally, MC is suffering from a poor 83 image resulted from technical problems, poor workmanship, short material lifespan, and 84 building performance limitations during the first age of MC [15]. Some stakeholders rejected 85 the use of MC amid the anxieties of building aesthetics and the fear of monotony in an 86 architectural form [16]. 87 During the past few decades, researchers have introduced several means to mitigate these 88 barriers, such as process supervision, computational technologies integration, construction 89 knowledge sharing, and materials and joints durability improvement [16]. Recently, the trend 90 has shifted the focus to design, as described in the following section. 91 2.2 Architectural Design 92 Design, in architecture, is generally a highly dynamic process, involving a number of 93 explorations, examinations, discussions, and determinations, to resolve difficulties in the built 94 environment [23, 24]. It handles with wide ranges of qualitative and quantitative 95 requirements, e.g., regulations, building codes, functionality, buildability, feasibility, 96 programs, sites, context, and human resources [25]. The Roman architect Vitruvius 97 articulated that the process outcome, an architecture, should be of “durability”, “utility”, and 98 “beauty”, if expressed in modern English [26]. Unlike painting or sculpture, this creative 99 process’s outcome has a huge impact, since it shapes the following activities, namely 100 manufacturing, logistics, construction, occupation, renovation, as well as demolition [17]. 101 Due to the recognition of its significant, design is prospected to mitigate many 102 difficulties and enhance MC. Many recommendations are generated to encourage this 103 strategy. For instance, the Building and Construction Authority of Singapore (BCA) publishes 104 Prefabricated Prefinished Volumetric Construction (PPVC) guidebook to provide 105 fundamentals, requirements, and practical tips on how to design MC [18]. This report 106 introduces many design concerns, e.g., transportation constraints, module configuration, 107 machinery performance, and joints. The American Institute of Architects (AIA) supports 108 design for MC by giving practice examples and lessons discovered from the previous cases 109 [19]. In addition, the book, “Design in Modular Construction”, reviews the generic types of 110 modular construction, displays the application examples, and offers background information 111 for design [20]. Furthermore, previous research encourages an integrated design process and 112 early collaboration for effective design decision making [27]. Another study also highlights 113 the demand for MC design guidelines further development [28]. 114 While many efforts have already been done to corroborate design suggestions and 115 avoidances, the new design opportunities, emerged from MC, have not been extensively 116 explored in the previous literature. Until now, there are many notable modular architectures 117 and successful case studies to be investigated. The new design prospects learned from these 118 cases are expected to be beneficial for designers, and finally, increase the MC adoption. 119 3 Research Methods 120 This research adopted a 3-step method to investigate both design constraints and 121 opportunities, emerged from MC, as shown in Figure 1. It started from a literature review of 122 MC definitions, advantages, and drawbacks, to understand its characteristics and current 123 circumstance. The process and significance of architectural design are also clarified in this 124 step. Then, the second step intended to explore design guidance, suggestions, limitations, as 125 well as new options, arisen from MC. This was achieved by a comprehensive literature 126 review related to architectural design and MC. At this stage, the archives of notable modular 127 architectures, e.g., records from designers, research papers, and drawings, are also revisited. 128 By using these methods, it is able to examine a complex dynamic of architectural design and 129 construction projects from a real-life context, provide an explanation, and identify the 130 causality [29]. Finally, this research analyzed the collected data, and highlighted both design 131 restrictions and possibilities, derived from MC. 132 133 Figure 1 Research Methods 134 In this paper, Nakagin Capsule Tower (NCT) and Habitat 67 were selected to be the case 135 studies. NCT, designed by Kisho Kurokawa, was studied, as it is the first successful high-rise 136 modular architecture for actual use in Japan in the early 1970s (see Figure 2) [30]. Located at 137 the centre of Tokyo, NCT is a residential building, which consists of two core structures and 138 140 fully furnished capsules. Described by the architect, NCT aims to create an architecture 139 in anticipation of a new age, achieve full mass production for living modules, and promote 140 industrialization technology in the industry [31]. Praised in the New York Times, the tower is 141 one of the notable magnificent architectures [32]. It has been recorded an architectural 142 heritage by Documentation and Conservation of Buildings, Sites, and Neighbourhoods of the 143 Modern Movement (DoCoMoMo) organization since 2006 [30]. 144 145 Figure 2 Nakagin Capsule Tower (NCT) [33] 146 Habitat 67, designed by Moshe Safdie, is a prototype project for fully mass-produced 147 construction system in Montreal, Canada (see Figure 3) [34]. As the Canadian Pavilion for 148 the World Exposition in 1967, this experiment intends to indicate the construction industry 149 shortcomings and pave the way towards the new direction. Composed of 354 precast concrete 150 modules for 158 living units, the building offered high-quality housing with a variety of 151 spaces for dwellers [35]. It was also able to avoid monotony form in the dense urban 152 environment. This case is currently recognized as iconic architecture, influencing the 153 architectural design throughout the past few decades [36]. 154 155 Figure 3 Habitat 67 [37] 156 4 Results 157 4.1 Design Considerations 158 After a comprehensive review of previous literature and case studies, several concerns should 159 be pondered during design to encourage MC efficiency, as described below. 160 Collaboration: Collaboration means a professional practice, which involves 161 stakeholders to work together from the project initiation until the construction completion. It 162 is recommended, since the architectural design for the modular building requires various 163 information from different stakeholders for a precise determination [27]. Both research and 164 practice agree that this approach can improve MC efficiency, prevent redesign and rework, 165 ensure the project constructability, as well as minimize waste generated during construction 166 [38-40]. The early collaboration also provides designers with a clear idea of MC and 167 maximize flexibility in design options [19]. In NCT, designers collaborated with consultants, 168 manufacturer, and main contractor during design to ensure the manufacturability, 169 transportability, and feasibility of the project [31]. 170 Design standardization: This suggestion refers to the repetitive use of industrial 171 components or modules in design [38]. Based on the characteristics of a manufacturing line, 172 MC requires a larger number of repetition in design for construction feasibility [34]. In NCT, 173 It was adopted to ensure the capsule manufacturability in the container factory and enable 174 mass production in construction [40]. The architect of Habitat 67 also realized this issue and 175 applied the repetition of single standardized three-dimensional precast modules to the design. 176 However, the architecture could still provide 15 different house types by combining one, two, 177 or three modules together [34]. 178 Design simplification: It is generally a design method, which aims to reduce a complex 179 design to basic forms or elements. In the mass production system, the complexity of form 180 means additional tasks, efforts, and costs. In both cases, although several choices of interior 181 design and finishing were offered, all capsule’s structure and exterior were kept to be as 182 simple as possible to support the production flow [31, 34-35]. 183 Logistics constraints: Unlike the traditional in-situ construction, MC requires the 184 transportation of a large module from a manufacturing line to a construction site. 185 Transportation-related concerns should be pondered carefully from the project initiation [19]. 186 They may vary, depending on a project condition, transportation route, as well as production 187 location, which can be on-site, off-site, or even off-shore [41]. The case of NCT provided a 188 practice example related to module logistics. According to the architects, the factory and 189 construction locations, transportation route, legal restrictions, stopover point, on-site storage, 190 and delivery schedule, were studied from the project initiation. The module’s design, shape, 191 weight, and dimensions, followed these restrictions to ensure the module transportability [31, 192 42]. 193 Connection: Apart from logistics, a joint or connection between modules is another 194 critical element in MC. While developing a design proposal, the design team is recommended 195 to consider the joint’s manufacturing, structural system, thermal performance, water 196 penetration rate, fire resistance, as well as aesthetics. Collaboration is also suggested to assist 197 in this detailed design [19-20]. 198 4.2 Design Opportunities 199 Although the concerns above could be regarded as the agents of design restrictions and shifts 200 in architectural design practice, MC also offered new design potentials. This is realized by 201 detailed archival studies of previous cases, as follows. 202 A composition of three-dimensional units: Unlike the focus on the composition of 203 planar elements in conventional construction, MC allows designers to form an architecture by 204 locating standardized volumetric modules together to create various architectural forms and 205 combinations [20]. The way to arrange these modules during design resembles the action of 206 installing prefabricated components together in construction. This is ratified by both cases. In 207 NCT, the architect recognized this opportunity, and introduced “a sum of parts” to make a 208 distinctive architectural form by the composition of the manufactured living cells [31, 38]. 209 While, the form of Habitat 67 was clustered from the grouping of elements [34]. This 210 innovative design technique, together with MC, was able to meet demands and avoid 211 monotony architectural form, while the capsule’s price was still reasonable [31, 34]. 212 Mass customization: Mass customization refers to “the ability to provide individually 213 designed products and services to every customer through high process flexibility and 214 integration” [43]. It is utilized as both manufacturing and business competitive strategies. In 215 construction, MC, together with this concept, can serve a variety of space required and enable 216 variations in design. In NCT, it provided eight options of interior design [44]. It allowed users 217 to express themselves by selecting or altering several standardized parts like a vehicle, e.g., 218 interior finishing materials, colour, and alternative equipment [31]. This strategy can be 219 220 adopted to design outstanding architecture and increase client satisfaction. Product prototyping: One of the advantages of MC is an exemplary product model from 221 original materials and structure. The capsule prototype can also be considered as a reliable 222 method to demonstrate the design ideas and engineering system to buyers. In the case of 223 NCT, the actual capsule was placed on the ground in front of the sales office to make clients 224 have more explicit ideas about the product before purchasing [31]. 225 Product mobility: Architects have proposed many ideas about architecture as a living 226 organism, which needs to be grown, renovated, and renewed during the building life cycle. 227 MC moves this rhetoric closer to reality by producing mobile modules, which can be 228 transported, attached, detached, and relocated. In NCT, the capsules were attached to the 229 main structure by high-tension bolts, allowing the module detachment or replacement without 230 affecting others. This responded to the architect’s belief that architecture can metabolize [45]. 231 5 Discussion and Conclusion 232 5.1 Discussion 233 Grounded on the comprehensive literature review and successful case studies revisit, the above 234 section substantiates that MC, by its nature, may establish several additional criteria to 235 architectural design, i.e., collaboration, standardization, simplification, logistics constraints, 236 and connection. However, it also enables several design techniques, i.e., a composition of three- 237 dimensional units, mass customization, product prototyping, and product mobility. 238 This research creates a balanced view between design limitations and possibilities, when 239 adopting MC. Both of them can be utilized as a guide for design proposal development. It also 240 initiates the discourse about the new design possibilities emerged from MC, which have not 241 been extensively debated. In addition, the outputs from this study support the ongoing 242 development of Design for Manufacturing and Construction (DfMA) in construction. The 243 recent study raises a critical issue that currently, many DfMA suggestions in construction 244 emerges from manufacturing industry background without considering the differences between 245 two industries [46]. The key terms and explanations, identified from the construction cases in 246 this study, can be regarded as a part to support construction-oriented DfMA principles. 247 On the other hands, this research also has its constraints. First, it is structured based on the 248 literature review and detailed archival study. More investigations from real-life practice and 249 feedback from implementation are necessary. Moreover, this is merely a preliminary study of 250 design considerations and opportunities emerged from MC. The application may include, but 251 not limited to, these design directions. Future research is recommended to focus on both sides 252 to expand the knowledge in this discipline. 253 5.2 Conclusion 254 Although Modular Construction (MC) has brought various benefits to the construction sector, 255 it still experiences several barriers. From the project initiation point, design is prospected to 256 mitigate difficulties hindering MC implementation. To support this promising strategy, a 257 plethora of design principles, guidelines, and avoidance are generated; on the contrary, the new 258 design possibilities acquired from MC have not yet been expanded. This research, therefore, 259 reviews previous literature and revisits successful case studies to explore both sides. 260 Eventually, five design considerations and fours opportunities are identified. The outcome 261 corroborates that MC, liked every construction method, may impose several additional 262 concerns to design, but also provides new design prospects. 263 This research illustrates a balanced view of MC in an architectural design process, and 264 paves the new way for future research development to concentrate on the new design 265 possibilities, occurred from MC. Both identified limitations and opportunities can be utilized 266 to achieve a higher level of stakeholders’ satisfaction. The findings also support the current 267 application of DfMA concept in construction. However, the design directions, identified in this 268 study, are merely examples of thousands. More studies and real-life case studies are demanded 269 to develop this sector further. 270 271 272 273 274 275 References [1] Construction Industry Council (CIC). (2020). About MiC. Retrieved from https://bit.ly/35XSgYS [2] Gibb, A. G. (1999). 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