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Modular vs Conventional Construction: A Multi-Criteria Framework Approach

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Ahmed W.A. Hammad at UNSW Sydney
Ahmed W.A. Hammad
Ali Akbarnezhad
Ali Akbarnezhad
Ali Akbarnezhad
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34th International Symposium on Automation and Robotics in Construction (ISARC 2017)
Modular vs Conventional Construction: A Multi-Criteria
Framework Approach
A.W.A Hammada and A. Akbarnezhada
aSchool of Civil and Environmental Engineering, The University of New South Wales, Australia
E-mail: a.hammad@unsw.edu.au, a.akbarnezhad@unsw.edu.au
Abstract
The use of modular construction methods for
projects offers significant time and environmental
improvement relative to conventional construction
methods. Currently, there is a lack of appropriate
assessment approaches to capture the differences
between modular and conventional construction.
This paper proposes a framework to aid decision
makers in choosing between the latter construction
methods through the integration of building
information models with material libraries, project
schedules and machinery inventory. A fixed set of
performance parameters, whose attributes are
shared among both construction methods, are
defined to allow for a reasonable comparison across
multiple criteria, including embodied carbon,
productivity and total construction costs expended.
The dynamics of the project are incorporated by
modelling the various stages of the project within a
building information model. The proposed
framework is tested on a realistic case example,
highlighting its applicability as a decision support
tool for construction method selection.
Keywords –
Modular Construction; Construction Methods;
Prefabrication; Sustainable Construction; BIM
1 Introduction
The construction sector is known to occupy a
significant share of the annual GDP of economies
worldwide. The industry is also known for its great deal
of environmental breaches. In particular, according to
the intergovernmental Panel on Climate Change (IPCC),
the construction sector is classified as one of seven
dominant sectors responsible for substantial greenhouse
gas (GHG) emissions [1]. With the growing awareness
of the importance of sustainable construction, such that
economic, social and environmental factors are
accounted for concurrently, many construction
organisations have started to implement greater
sustainable measures in their design and construction
processes. One of the most critical determinants of the
economic and environmental performance of a project is
the construction method adopted [2]. As an example,
modular construction is known to have major economic
advantages compared to conventional construction [3].
Modular construction can be defined as a
construction system where volumetric components
forming a completed part of a building are produced
off-site and transported to the construction site for
installation [4]. It is the highest end of prefabrication,
where full sets of buildings are constructed off-site,
instead of only smaller components being produced
during the manufacturing process [5].
Some studies suggest the dominance of semi-
prefabrication methods over conventional construction
approaches in terms of minimising construction related
embodied carbon [6], and greenhouse gas emissions [7].
Though there are studies that have also attempted to
contrast separately the economic [8] or environmental
impacts [6], [9] of construction methods, no attempt has
however been made to contrast volumetric construction
methods such as modular with conventional methods
using an encompassing approach. A study undertaken to
highlight an exact quantification approach for
comparing between modular and conventional
construction across multiple criteria is therefore lacking.
The idea of modular construction has been around
since the 1960s, though its effective adoption as a
construction method has not been as wide as was
expected [10]. It is always challenging to incorporate
changes to the conventional construction methods,
which have been widely tested and used for long
periods [11]. Having said that, plenty of the research
conducted indicates that a controlled environment, such
as the one presented in modular construction methods,
where components are manufactured off-site in a
continuous flow process, allows a lot of benefits to be
achieved. These advantages can be realised in terms of
productivity, safety and environmental performance [4],
[12].
Motivated by the lack of a systematic procedure to
compare the trade-offs between modular and
conventional construction methods, this paper proposes
34th International Symposium on Automation and Robotics in Construction (ISARC 2017)
a methodology for integrating Building Information
Modelling (BIM), equipment libraries and
environmental databases, within a framework for use in
construction method selection, both for residential and
commercial buildings. The analysis forming the
framework is based on the life cycle cost assessment,
where economic considerations are embedded along
with the common environmental factors, to quantify the
overall building performance during all stages of a
project’s life excluding its operational phase.
The rest of the paper is organised as follows: Section
2 introduces the major components making up the
proposed framework. Section 3 presents a brief case
study on a realistic project for showcasing the
applicability of the proposed framework. Results are
discussed in Section 4. Finally, concluding remarks and
future work recommendations are presented.
2 Construction Method Comparison
Framework
This section describes the different modules making
up the proposed framework. Figure 1 depicts the overall
framework which is comprised of 4 principle modules;
the first set of modules incorporates the input data
required for the analysis; the second module is a BIM
representation of the project to be constructed and
which aggregates the input data. Associated with the
BIM is a Comparative Module that specifies the
different material composition that would be required
for each construction method adopted. The last of the
modules is a Criteria Analysis Module which embeds
the conditions necessary to perform a comparison
between the construction methods.
2.1 Input Module
Data is required to assess the differences between
the construction methods available. Modular
construction relies on an environment which is
drastically different to that of conventional construction.
As a result, differences would arise in the project
information regarding site preparation and building
layout, material to be used, equipment deployed during
the construction process, carbon factors of the
associated material with each construction method, and
the cost element related to the building components.
Each of the aforementioned information forms a
separate database which get utilised by the constructed
BIM.
2.2 BIM
As a form for linking the various information from
the input database, a BIM is associated with each
construction method. Depending on the size of the
project and its use type, different construction methods
will need different material compositions and hence the
building model produced for each method can vary.
Modular construction places large emphasis on the use
of timber and light gauge steel framing, as opposed to
brick and mortar in conventional construction. As a
result, the BIM produced for each construction method
will have to reflect this difference in element
composition. Materials and equipment can be mapped
according to the construction method use, and
information for the latter databases can then be
associated with the BIM of each construction method.
2.3 Comparative Module
The Comparative Module is where the BIM for
modular and conventional construction is used to extract
the necessary data required to evaluate the multiple
criteria defined. The criteria is evaluated in a way where
economic and environmental factors influenced by both
construction methods can be assessed. A total of 3
criteria are incorporated within the Comparative Module
of the framework, as discussed below.
2.3.1 Embodied Carbon
The first criteria, Eq. (1) minimises the total
embodied carbon emissions. Operational carbon is
neglected since it is assumed that irrespective of the
construction method used, the building will be operated
in the same manner; hence the operational carbon is
expected to stay be the same for both construction
methods.
,c c t e c e
c t c e
Q M ETD R P
 
(1)
where
c
Q
is the quantity of material making up
each building component
cC
,
c
M
is the emission
factor associated with each material component due to
its manufacturing phase within its life cycle, as obtained
from emission databases,
t
E
is the emission factor
associated with transportation truck
t
,
D
is the travel
distance traversed by the truck
t
,
is the number of
trips that need to be conducted by the associated truck,
,ec
R
is the emission factor associated with equipment
e
deployed on building component
c
, while
e
P
represents the duration of operation of equipment
e
.
34th International Symposium on Automation and Robotics in Construction (ISARC 2017)
Figure 1. Framework for comparing between modular and conventional construction methods
34th International Symposium on Automation and Robotics in Construction (ISARC 2017)
If on-site construction is used then the distance
parameter is calculated by summing the distance of
travel between material suppliers
i
and construction
site,
i
d
:
i
i
Dd
(2)
On the other hand, if modular construction is to be
used then the distance is equal to that between the
manufacturing place of modular components and the
construction site
:
Dd
(3)
2.3.2 Construction Project Duration
The different construction methods will have
different project durations, due to the nature of
operations and machinery used. To evaluate the
schedule duration of each construction method, a second
criteria is defined, Eq. (4).
e
ec ce
Q
F

(4)
where
e
Q
is the quantity of material to complete
activity
e
while
ce
F
is the productivity rate of crew
c
working on activity
e
.
2.3.3 Construction Cost
The third criteria, Eq. (5), computes the cost
estimate of each construction method. Each building
component is associated with a set of tasks.
qa qa
qa
N CC

where
qa
N
is the crew size of type
q
assigned to
task
a
, which reflects the total number of machinery
deployed on the respective activities, while
qa
CC
is the
unit cost of crew
q
assigned to task
a
.
3 Case Example
A project in the North-West of Sydney involves the
construction of a granny flat, with dimensions 14 m by
16 m. The builder has the choice of selecting between
modular and conventional construction methods; each
method is associated with a set of building components
as shown in Table 1. The framework of Figure 1 is
applied to compare between the two available
construction methods. Embodied carbon emission
factors are derived from databases such as [13], [14],
whereas cost rates and crew productivity rates are
obtained from RSMeans and Cordell [15], [16].
Common workflow patterns adopted for both
construction operations are shown in Figure 2.
Table 1. Material Composition associated with each
construction method
Modular
Conventional
Interior
Walls
Steel frame studs
with 5 mm poly
sheets
Partition walls with
wood studs and 10
mm gypsum
wallboards
Exterior
Walls
PFC cage with light
gauge enclosed
framing and
colourbond cladding
Double masonry
units with bitumen
insulation and brick
veneer cladding
Floor
Purlin joists with
CFC sheeting
Concrete slab on
grade with tile
finishes
Roof
Light gauge ceiling,
with plaster ceiling
panel, roof packers
and corrugated
ceiling sheeting
Timber framing
with metal tiling
Figure 2. Workflow process of construction
A workflow is adopted to evaluate material use,
crew requirement and resource utilization at each stage
of the project. A representation of the BIM used to
34th International Symposium on Automation and Robotics in Construction (ISARC 2017)
obtain all the required data for the project is given in
Figure 3. Piers are assumed to be adopted as the
substructure for supporting the granny flat in the case of
modular construction, whereas a simple flat slab acts as
the building pad for a granny flat constructed using on-
site methods. Site preparation for both methods is
assumed to be similar; as a result, the analysis excludes
substructure construction.
Figure 3. BIM model used for case study
4 Results and Discussion
Each criterion is analysed and the associated results
are given in Figures 3 – 5.
4.1.1 Embodied Carbon Emissions
Figure 4 shows the difference in total embodied
carbon of both construction methods, adopting the
material components of Table 1. The resulting
embodied carbon is a direct result of the quantities
derived from BIM along with the embodied carbon
factors obtained from databases listed above. It is
important to note that a total of 302
2
2/kg CO m
and
378
2
2/kg CO m
of embodied carbon is associated
with modular and conventional construction for the
granny flat project, respectively. Overall, modular
construction is responsible for 19% lower embodied
carbon in comparison to conventional construction
Figure 4. Comparing embodied carbon of the case
study using modular vs conventional construction
A pie chart showing the average contribution of each
material used in both construction methods to total
carbon emissions is given in Figure 5. In line with the
literature, timber has the highest embodied carbon levels
followed by concrete.
Figure 5. Contribution of material components to
total embodied carbon in granny flat case study
4.1.2 Productivity
Based on the crew rate productivity estimates and on
the material quantities derived from BIM, the total time
taken to complete the project under each construction
method is calculated. Results are shown in Figure 6.
Modular construction is found to have a 58% advantage
in terms of project delivery duration, compared to
conventional construction. This is attributed to the
influence of weather on work progress, where during
rainy conditions, on-site work needed to stop. Such was
not the case in the controlled environment of the
modular factory.
34th International Symposium on Automation and Robotics in Construction (ISARC 2017)
Figure 6. Comparing duration of project using
modular vs conventional construction
4.1.3 Costs
Total cost estimates for both construction methods
rely on the quantities from BIM and the rates associated
with the material components. Such rates incorporate
labour within them. Based on the flow process
delineated in Figure 2, the procedure can be mapped to
the cost rates obtained from RSMeans and Cordell.
Figure 7 shows the cost estimates of both methods.
Modular construction is on average cheaper than
conventional methods for this case example. The reason
behind this is due to the fewer materials used, and the
automated building process in modular construction,
which permits economies of scales to be realised.
Figure 7. Comparing cost of project using modular
vs conventional construction
5 Conclusion
With the growing awareness of sustainable
construction, many companies have shifted their focus
to sustainable design. This is particularly important
given the impact of the construction sector on the
economy and on the environment. One way suggested
to improve the sustainability of the construction and
building industries is through the use of modular
construction. This work presented a novel framework to
compare the modular construction method against a
conventional one. The framework focused on evaluating
three main criteria, namely embodied carbon,
productivity and monetary cost of the project.
Effectiveness of the proposed framework was confirmed
by application to a practical construction project.
Modular construction was found to be more effective in
terms of lower embodied carbon, higher productivity
and lower construction costs. Future research will focus
on incorporating additional parameters and criteria to
compare between the construction methods.
References
[1] Intergovernmental Panel on Climate Change,
“IPCC Fourth Assessment Report (AR4): Climate
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[4] Harvey M. Bernstein, John E. Gudgel, and Donna
Laquidara-Carr, “Prefabrication and
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[5] Alistair G.F. Gibb, Off-site Fabrication:
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34th International Symposium on Automation and Robotics in Construction (ISARC 2017)
[10] V. W. Y. Tam, C. M. Tam, S. X. Zeng, and W. C.
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In order to efficiently transform business processes (such as product design, product engineering, production, logistics, sales, deliveries, etc.) into digitally automated processes, new concepts have been introduced in both the manufacturing and construction industries. Under the term Industry 4.0, promising possibilities for high-performance production processes are emerging based on e.g., digital twins and cyber-physical systems. However, the construction industry lags behind in adapting these ideas, and is still facing severe productivity deficits. This paper addresses these deficits by assessing the hypothesis of Building Information Modeling—as the digital twinning methodology in construction—representing a key driver for digital automation and thus enabling more productive processes. To this end, we apply a design science research approach to develop artefacts using computational methods for the automation of business processes in a configure-to-order industry partner. The evaluation is done in the context of a pilot project together with this industry partner. The findings obtained in the pilot project revealed time savings in the phases of bid estimation and work preparation. Based on the findings, the applicability and utility of the suggested approach are discussed and allow for the conclusion that Building Information Model data can usefully streamline and automate many processes at the interface between design and production, if structured and preprocessed purposefully.
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Application of Decision Support Systems for Advanced Equipment Selection in Construction
Chapter
  • Oct 2019
  • Lect Notes Comput Sci
We consider the problem of supporting decision makers in construction projects for making the rational-best choice between the introduction of advanced technological solutions and the use of conventional approaches. The complexity, uniqueness, and uncertainty, typical of construction projects, are the main obstacles in this kind of decision problems. We propose a method for the development of decision support systems for such problems based on Bayesian decision theory. Bayesian decision theory is applied to capture and rationally solve such decision problems. We account for uncertainty and construction process specific criteria, for structuring the knowledge-base and easing the elicitation of the decision network. The applicability potential of the proposed approach is presented by means of an example application scenario.
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Economic comparison of industrialized building system and conventional construction system using building information modeling
Article
Full-text available
  • Dec 2015
The new construction method known as Industrialized Building System (IBS) offers several benefits compared to the Conventional Building System (CBS); however, IBS is perceived by most of the practitioners to be an expensive method for being utilized in construction industry. Whilst relatively numerous studies have been carried out on the subject of IBS and CBS methods, there has not been any exploiting building information modeling (BIM) as a useful tool to calculate quantities, time, and cost needed to construct building with each of the two aforementioned methods. The aim of this paper is to calculate cost of two similar buildings (one is constructed with IBS method and other one with CBS method) and compare them in terms of economy based on a chosen case study and same initial investment. To this end, the construction cost of buildings is calculated using BIM software, namely Revit Architecture and Navisworks Manage for modeling the chosen case study and estimating construction cost, respectively. The findings indicated that IBS was not economic in low investment of company; however, with investment on more than 100 units of IBS, this method was shown more economical compared to CBS method. In addition, the initial investment on IBS method could be returned when more than 200 units of IBS were implemented in the projects.
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Embodied energy and carbon in construction materials
Article
Full-text available
  • Jan 2008
The development of an open-access, reliable database for embodied energy and carbon (dioxide) emissions associated with the construction industry is described. The University of Bath's inventory of carbon and energy database lists almost 200 different materials. The data were extracted from peer-reviewed literature on the basis of a defined methodology and a set of five criteria. The database was made publicly available via an online website and has attracted significant interest from industry, academia, government departments and agencies, among others. Feedback from such professional users has played an important part in the choice of 'best values' for 'cradle-to-site' embodied energy and carbon from the range found in the literature. The variation in published data stems from differences in boundary definitions (including geographic origin), age of the data sources and rigour of the original life-cycle assessments. Although principally directed towards UK construction, the material set included in the database is of quite wide application across the industrial sector. The use of the inventory is illustrated with the aid of 14 case studies of real-world new-build dwellings. It was observed that there was little difference between embodied energy and carbon for houses and apartments until external works were taken into account (energy inputs for roads, connecting pathways, etc.).
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Comparative study of greenhouse gas emissions between off-site prefabrication and conventional construction methods: Two case studies of residential projects
Article
  • Nov 2013
  • ENERG BUILDINGS
Greenhouse gas (GHG) emissions in the construction stage will be more relatively significant over time. Different construction methods influence GHG emissions in the construction phase. This study investigates the differences of GHG emissions between prefabrication and conventional construction methods. This study sets a calculation boundary and five emission sources for the semi-prefabricated construction process: embodied emissions of building materials, transportation of building materials, transportation of construction waste and soil, transportation of prefabricated components, operation of equipment, and construction techniques. A quantitative model is then established using a process-based method. A semi-prefabrication project and a conventional construction project in China are employed for preliminary examination of the differences in GHG emissions. Results show that the semi-prefabrication method produces less GHG emissions per square meter compared with the conventional construction, with the former producing 336 kg/m(2) and the latter generating 368 kg/m(2). The largest proportion of total GHG emissions comes from the embodied emissions of building materials, accounting for approximately 85%. Four elements that positively contribute to reduced emissions are the embodied GHG emissions of building materials, transportation of building materials, resource consumption of equipment and techniques, and transportation of waste and soil, accounting for 86.5%, 18.3'36,10.3%, and 0.2%, respectively, of reduced emissions; one a negative effect on reduced emissions is the transportation of prefabricated components, which offsets 15.3% of the total emissions reduction. Thus, adopting prefabricated construction methods contribute to significant environmental benefits on GHG emissions in this initial study.
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The Ecoinvent database system: A comprehensive Web-based LCA database
Article
  • Nov 2005
  • J CLEAN PROD
The paper describes the general structure of the ecoinvent database developed by the Swiss Centre for Life Cycle Inventories. The database accommodates more than 2500 background processes often required in LCA case studies.Quality guidelines, established in order to ensure coherent data acquisition and reporting across the various institutes involved, are described. These include aspects such as the reporting of pollutants (e.g., heavy metals), or the nomenclature of processes and elementary flows.The data (exchange) format is also described. Processes are documented with the help of meta-information and flow data (including both unit process raw data and aggregated LCI results). The structure of the data format corresponds to the ISO/TS 14048 data documentation format. Data exchange between project partner institutes and between the database and its customers (database users) is based on XML-technology. Matrix inversion is used to calculate the cumulative LCA data using efficient algorithms and making use of the fact that LCA matrices are usually sparse.
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The innovation process: Adoption of information and communication technology for the construction industry
Article
The paper discusses innovation and uses information and communication technology (ICT) as an example. A general framework that is broad in the perspectives it examines is presented for the analysis of innovations and technology adoption in the construction industry. The framework is described in relation to the life cycle of a technological innovation and consists of two primary perspectives: a macroview (top) and a microview (bottom). The analysis models either determine characteristics or measure values. Each analysis model is discussed in some detail and applied to an ICT example. The relevance of the framework is summarized by a discussion of how these interrelated analyses are applicable to the decision-making process within a particular firm and of the mechanisms required by the industry to improve the innovation process. A framework is required that is comprehensive in its ability to look at information and knowledge flows in support of innovation within the industry and at the interrelationships between micro and macro influences. Gaps in current approaches include a lack of quantitative analysis tools, the ability to reflect the dynamic aspect of innovation, and industry knowledge of practical decision-making tools. Key words: innovation, technology adoption, information and communication technology, construction engineering.
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An embodied carbon and energy analysis of modern methods of construction in housing: A case study using a lifecycle assessment framework
Article
  • Jan 2011
  • ENERG BUILDINGS
There is a growing interest in comparing the energy and consequential carbon embodied in buildings using different methods of construction and alternative materials. This paper compares the embodied carbon in a low energy, affordable house constructed using a novel offsite panellised modular timber frame system, in Norfolk UK with two traditional alternative scenarios. A lifecycle assessment (LCA) framework is used to conduct a partial LCA, from cradle to site, of the construction. An inventory of the materials and fossil fuel energy utilised in the construction was used to calculate the primary energy consumed and the associated embodied carbon. The embodied carbon was found to be 34.6 tonnes CO2 for a 3 bedroom semi-detached house, 405 kgCO2 per m2 of useable floor area. When compared with traditional methods of construction the modern methods of construction (MMC) house resulted in a 34% reduction in embodied carbon. Despite timber being the predominant structural and cladding material, concrete is the most significant material (by proportion) in embodied carbon terms, responsible for 36% of materials related embodied carbon.
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Sustainable performance criteria for construction method selection in concrete buildings
Article
  • Mar 2010
  • AUTOMAT CONSTR
The use of prefabrication offers significant advantages, yet appropriate criteria for applicability assessments to a given building have been found to be deficient. Decisions to use prefabrication are still largely based on anecdotal evidence or simply cost-based evaluation when comparing various construction methods. Holistic criteria are needed to assist with the selection of an appropriate construction method in concrete buildings during early project stages. Following a thorough literature review and comprehensive comparisons between prefabrication and on-site construction method, a total of 33 sustainable performance criteria (SPC) based on the triple bottom line and the requirements of different project stakeholders were identified. A survey of U.S. experienced practitioners including clients/developers, engineers, contractors, and precast concrete manufacturers was conducted to capture their perceptions on the importance of the criteria. The ranking analysis of survey results shows that social awareness and environmental concerns were considered as increasingly important in construction method selections. Factor analysis reveals that these SPCs can be grouped into seven dimensions, namely, economic factors: “long-term cost,” “constructability,” “quality,” and “first cost”; social factors: “impact on health and community,” “architectural impact”; and environmental factor: “environmental impact.” The resultant list of SPCs provides team members a new way to select a construction method, thereby facilitating the sustainable development of built environment.
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Towards adoption of prefabrication in construction
Article
  • Oct 2007
  • BUILD ENVIRON
There is an urgent issue on huge quantities of wastage generation in construction. There should not be lack of environmental support from construction stakeholders. The current implementation of prefabrication seems unable to provide satisfactory results to the construction industry. This paper provides a feasibility analysis in adopting prefabrication in construction activities. Advantages, hindrances and future development on prefabrication's applications are provided based on a questionnaire survey. The suitability in adopting prefabrication of various project types is also examined. Furthermore, a financial analysis is also investigated by a local case study. It found that wastage generation can reduce up to 100% after adopting prefabrication, in which up to 84.7% can be saved on wastage reduction.
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