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Modular Prefabricated Classrooms: A New Zealand Study to Investigate Cost and Time Performance Potential

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Modular construction is proposed as a feasible solution for school classrooms construction at a lower cost and shorter period by the Ministry of Education (MOE), New Zealand. However, the traditional construction remains a plausible alternative. This paper aims to review the feasibility of using modular prefabricated classrooms in terms of cost and time performance compared to traditionally constructed ones in New Zealand. Data from construction costs and completion time estimates of a classroom model design was obtained from four prefabrication manufacturers and six traditional contractors to ensure data comparability. The data obtained showed that it is possible to isolate construction method data only from material inputs data as a plausible methodology for comparing modular prefabricated and traditional construction cost and completion time performance henceforth. This methodology was implemented to investigate whether modular prefabricated classrooms could be constructed at a lower cost and completed timelier than the traditional ones, and the cost estimated by the contractors can be implemented in practice. It is concluded that constructing modular prefabricated classrooms, particularly emphasising the construction method, is feasible and holds real potentials to deliver at the originally planned cost and completion time compared to traditionally constructing classrooms in New Zealand.
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1
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28 - 29 October 2021
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582
Modular Prefabricated Classrooms: A New Zealand Study to
Investigate Cost and Time Performance Potential
Christoffel Hendrick Roos1, *Ayokunle Olanipekun2, Wajiha Shahzad3 and Monty
Sutrisna4
1Construction Industry Services (CSI), chris81.cr50@gmail.com
2University of Wolverhampton, UK, A.Olanipekun@wlv.ac.uk
3&4Massey University, Auckland, New Zealand, w.m.shahzad@massey.ac.nz;
m.sutrisna@massey.ac.nz
Abstract
Modular construction is proposed as a feasible solution for school classrooms construction at
a lower cost and shorter period by the Ministry of Education (MOE), New Zealand. However,
the traditional construction remains a plausible alternative. This paper aims to review the
feasibility of using modular prefabricated classrooms in terms of cost and time performance
compared to traditionally constructed ones in New Zealand. Data from construction costs and
completion time estimates of a classroom model design was obtained from four prefabrication
manufacturers and six traditional contractors to ensure data comparability. The data obtained
showed that it is possible to isolate construction method data only from material inputs data as
a plausible methodology for comparing modular prefabricated and traditional construction cost
and completion time performance henceforth. This methodology was implemented to
investigate whether modular prefabricated classrooms could be constructed at a lower cost and
completed timelier than the traditional ones, and the cost estimated by the contractors can be
implemented in practice. It is concluded that constructing modular prefabricated classrooms,
particularly emphasising the construction method, is feasible and holds real potentials to deliver
at the originally planned cost and completion time compared to traditionally constructing
classrooms in New Zealand.
Keywords: Cost and time, Modular classrooms, New Zealand, Performance, Prefabrication
1 Introduction
Prefabricated construction is considered an innovative construction type where the built
elements are manufactured offsite mostly under a controlled environment and afterwards, the
manufactured elements are transported to construction sites for installation (Shahzad et al.,
2015; Antillón et al., 2014). The derivative is pre-assembly whereby the manufactured
elements can be directly installed as a sub-unit before transportation to construction sites
(Wasana et al., 2019). Compared with the traditional construction, prefabricated construction
offers more opportunities for higher precision in terms of designing, planning, and constructing
(Darlow et al., 2021; Wang et al., 2020). Also, the customisation of prefabricated elements
permits mass construction that can be based and relocated easily, and repeatedly constructed
elsewhere using the same expertise level (Sutrisna et al., 2019). As a result, numerous benefits
such as better cost, time, and quality performance than traditional construction (Arashpour et
al., 2018) have been put forward to increase the use of prefabrication for different construction
purposes in practice (Mao et al., 2016).
583
Modular Prefabricated Classrooms: A New Zealand Study to
Investigate Cost and Time Performance Potential
Christoffel Hendrick Roos1, *Ayokunle Olanipekun2, Wajiha Shahzad3 and Monty
Sutrisna4
1Construction Industry Services (CSI), chris81.cr50@gmail.com
2University of Wolverhampton, UK, A.Olanipekun@wlv.ac.uk
3&4Massey University, Auckland, New Zealand, w.m.shahzad@massey.ac.nz;
m.sutrisna@massey.ac.nz
Abstract
Modular construction is proposed as a feasible solution for school classrooms construction at
a lower cost and shorter period by the Ministry of Education (MOE), New Zealand. However,
the traditional construction remains a plausible alternative. This paper aims to review the
feasibility of using modular prefabricated classrooms in terms of cost and time performance
compared to traditionally constructed ones in New Zealand. Data from construction costs and
completion time estimates of a classroom model design was obtained from four prefabrication
manufacturers and six traditional contractors to ensure data comparability. The data obtained
showed that it is possible to isolate construction method data only from material inputs data as
a plausible methodology for comparing modular prefabricated and traditional construction cost
and completion time performance henceforth. This methodology was implemented to
investigate whether modular prefabricated classrooms could be constructed at a lower cost and
completed timelier than the traditional ones, and the cost estimated by the contractors can be
implemented in practice. It is concluded that constructing modular prefabricated classrooms,
particularly emphasising the construction method, is feasible and holds real potentials to deliver
at the originally planned cost and completion time compared to traditionally constructing
classrooms in New Zealand.
Keywords: Cost and time, Modular classrooms, New Zealand, Performance, Prefabrication
1 Introduction
Prefabricated construction is considered an innovative construction type where the built
elements are manufactured offsite mostly under a controlled environment and afterwards, the
manufactured elements are transported to construction sites for installation (Shahzad et al.,
2015; Antillón et al., 2014). The derivative is pre-assembly whereby the manufactured
elements can be directly installed as a sub-unit before transportation to construction sites
(Wasana et al., 2019). Compared with the traditional construction, prefabricated construction
offers more opportunities for higher precision in terms of designing, planning, and constructing
(Darlow et al., 2021; Wang et al., 2020). Also, the customisation of prefabricated elements
permits mass construction that can be based and relocated easily, and repeatedly constructed
elsewhere using the same expertise level (Sutrisna et al., 2019). As a result, numerous benefits
such as better cost, time, and quality performance than traditional construction (Arashpour et
al., 2018) have been put forward to increase the use of prefabrication for different construction
purposes in practice (Mao et al., 2016).
Among these benefits, cost and time savings from prefabricated construction are the most
compelling for its adoption and implementation in the construction industry (Shahzad et al.,
2014). Reinforcing this position, the growing number of studies that are evaluating the
feasibility of prefabricated construction are based on cost and time performance (e.g., Abdul
Nabi & El-adaway, 2021; Sutrisna et al., 2019). For instance, cost saving is achieved in
prefabricated construction by shifting onsite work cost into offsite manufacturing cost and
product transferring cost (Sutrisna et al., 2019). Also, the customisation of elements and
process design, plan, installation, transportation, and expertise contribute to time savings and
speedy prefabricated construction (Razkenari et al., 2020). Meanwhile, there are different
categories of prefabricated construction such as sub-assemblies and elements, panelised
construction, modular construction, whole building prefab and hybrid (Hong et al., 2018;
Shahzad et al., 2014; Sutrisna et al., 2019). However, the cost and time benefits that are reported
in the literature rarely differentiate between the different categories of prefabricated
construction (e.g., see Abdul Nabi & El-adaway, 2021). As a result, it may be challenging to
establish the feasibility of prefabricated construction in terms of cost and time performance in
a country like New Zealand, where the Ministry of Education (MOE) has prescribed the
modular prefabricated construction category as a feasible solution to overcome school
overcrowding at a lower cost and timelier completion (MOE, 2015).
Despite the benefits of prefabricated construction, modular construction has slowly taken off
and the construction stakeholders like everywhere else are undetached from the traditional
construction in New Zealand (Chen & Samarasinghe, 2020). Shahzad et al. (2014) established
that more prefabrication content potentially increases the cost and time performance in
prefabricated construction of commercial buildings and more investigation of the subject in
other building types in this country was suggested. With MOE’s proposal for modular
prefabricated classroom construction on one hand, and stakeholder attachment to traditional
construction, the paper explores the scope to compare the performance of both construction
types in New Zealand. The aim of this study is to determine whether modular prefabricated
classrooms are more feasible in terms of cost and time performance than traditionally
constructed ones in New Zealand. The MOE can use the results to decide whether to proceed
with modular schools’ construction in New Zealand. Also, the results can be used to benchmark
the cost and construction duration of modular school’s construction among industry
practitioners and school development policy makers in New Zealand and elsewhere in
Australasia.
2 Literature review
2.1 Categories of prefabricated construction type
Prefabricated construction type can be categorised according to the amount of prefabrication
implemented in the built product. Based on multiple sources (e.g. Wasana et al., 2019; Hong
et al., 2018; Shahzad et al., 2014), the four categories of prefabricated construction type that
are commonly implemented in practice are sub-assemblies and elements (prefabricated
building elements and units such as precast columns and beams), panelised construction (pre-
nailed trusses, and the precast wall and floor panels), modular construction (modules or pods),
and whole building prefab (complete building short of foundations and onsite service
connections). The hybrid has been described as fifth category and is the combination of both
non-volumetric and volumetric offsite construction elements in the same project (Sutrisna et
al., 2019). Regardless of the category, prefabricated construction projects need to be
competitive in terms of the cost and time performance be more acceptably implemented in
practice.
584
2.2 Prefabricated construction project cost and time performance
An increasing number of studies are evaluating the cost and time performance of prefabricated
construction (Sutrisna et al., 2019; Mao et al., 2016; Li et al., 2017). Also, these studies employ
relative evaluation approach by comparing prefabricated and traditional projects performance.
Evaluating the performance of an ongoing hospital project, (Antillón et al., 2014) revealed a
6% prefabrication cost premium over the traditional construction of the project, and this is
consistent with other (recent) findings irrespective of the project types (Wasana et al., 2019;
Sutrisna et al., 2019). As a result, reasons for prefabrication cost premium have been elucidated.
Hong et al. (2018) revealed that the materials that constitute prefabricated elements contribute
highly to the total prefabrication construction costs. Materials like precast concrete and steel
were estimated to contribute 30-55% of the total prefabrication construction cost (Hong et al.,
2018). Also, prefabrication construction cost is increased by the manufacturing costs of
prefabricated elements, especially those that are used for singular prefabricated project
constructed in isolation. For this kind of project, customisation costs that was accrued cannot
be spread across as would in the construction of a chain of prefabrication projects (Sutrisna et
al., 2019). Mao et al. (2016)’s analysis revealed that prefabricated construction project cost
drivers result from assembly, transportation and cast in-situ. Assembly costs comprise of
machinery cost, prime cost of installation, jointing cost, built-in fitting and support costs and
tower crane expenses. Transportation costs comprise of the cost of transporting raw materials
to the prefabrication sites and the prefabricated elements to the construction site (Hong et al.,
2018; Mao et al., 2016). Cast in-situ cost refers to the cost effect on the cast in-situ part of
prefabrication projects (Mao et al., 2016) since one hundred percent prefabrication is seldom
in practice (Hong et al., 2018). The onsite portion (or residual onsite activity) exposes
prefabricated construction projects to uncertainties (Sutrisna et al., 2019), and this is one reason
for a lesser prefabrication construction project time certainty than traditional construction
(Wasana et al., 2019). Particularly, prefabricated project construction time increases with
reduced prefabricated content (Wasana et al., 2019). This means that prefabricated project
construction time can be reduced by increasing the prefabricated content. For instance, Shahzad
et al. (2014) revealed that 74% prefab content can result to 100% or more-time efficiency in
light to medium commercial buildings. The prefabricated construction time saved is an
opportunity for costs savings (Smith & Rice, 2015) but this remains a research issue. Based on
reported literature, it is suggestive that prefabricated projects are still constructed at high costs
in comparison with the traditional ones, while the completion time can be reduced by increasing
the prefabricated content. However, the factors responsible for the current levels of
prefabricated construction project cost and time performance are elucidated and improvement
can be achieved as practitioners and researchers continue to consider them in practice.
3 Methodology
Among the categories of prefabricated construction, this paper is focused on modular
prefabrication proposed for school construction. However, the feasibility in terms of cost and
time performance was yet to be established in comparison with traditionally constructed
classrooms by MOE in New Zealand. Comparing modular prefabrication and traditional
construction project cost and time performance is often challenged by a lack of comparison
basis in research. Also, methods like comparing data obtained from projects with theoretical
and industry benchmarks and/or direct comparison of data obtained from unrelated projects
directly do not effectively overcome the challenge (Mao et al., 2016; Shahzad et al., 2014).
This paper employed a quantitative approach by obtaining estimated cost and time data from
prefabrication (4 number) and traditional (6 number) contractors in Auckland, New Zealand.
585
2.2 Prefabricated construction project cost and time performance
An increasing number of studies are evaluating the cost and time performance of prefabricated
construction (Sutrisna et al., 2019; Mao et al., 2016; Li et al., 2017). Also, these studies employ
relative evaluation approach by comparing prefabricated and traditional projects performance.
Evaluating the performance of an ongoing hospital project, (Antillón et al., 2014) revealed a
6% prefabrication cost premium over the traditional construction of the project, and this is
consistent with other (recent) findings irrespective of the project types (Wasana et al., 2019;
Sutrisna et al., 2019). As a result, reasons for prefabrication cost premium have been elucidated.
Hong et al. (2018) revealed that the materials that constitute prefabricated elements contribute
highly to the total prefabrication construction costs. Materials like precast concrete and steel
were estimated to contribute 30-55% of the total prefabrication construction cost (Hong et al.,
2018). Also, prefabrication construction cost is increased by the manufacturing costs of
prefabricated elements, especially those that are used for singular prefabricated project
constructed in isolation. For this kind of project, customisation costs that was accrued cannot
be spread across as would in the construction of a chain of prefabrication projects (Sutrisna et
al., 2019). Mao et al. (2016)’s analysis revealed that prefabricated construction project cost
drivers result from assembly, transportation and cast in-situ. Assembly costs comprise of
machinery cost, prime cost of installation, jointing cost, built-in fitting and support costs and
tower crane expenses. Transportation costs comprise of the cost of transporting raw materials
to the prefabrication sites and the prefabricated elements to the construction site (Hong et al.,
2018; Mao et al., 2016). Cast in-situ cost refers to the cost effect on the cast in-situ part of
prefabrication projects (Mao et al., 2016) since one hundred percent prefabrication is seldom
in practice (Hong et al., 2018). The onsite portion (or residual onsite activity) exposes
prefabricated construction projects to uncertainties (Sutrisna et al., 2019), and this is one reason
for a lesser prefabrication construction project time certainty than traditional construction
(Wasana et al., 2019). Particularly, prefabricated project construction time increases with
reduced prefabricated content (Wasana et al., 2019). This means that prefabricated project
construction time can be reduced by increasing the prefabricated content. For instance, Shahzad
et al. (2014) revealed that 74% prefab content can result to 100% or more-time efficiency in
light to medium commercial buildings. The prefabricated construction time saved is an
opportunity for costs savings (Smith & Rice, 2015) but this remains a research issue. Based on
reported literature, it is suggestive that prefabricated projects are still constructed at high costs
in comparison with the traditional ones, while the completion time can be reduced by increasing
the prefabricated content. However, the factors responsible for the current levels of
prefabricated construction project cost and time performance are elucidated and improvement
can be achieved as practitioners and researchers continue to consider them in practice.
3 Methodology
Among the categories of prefabricated construction, this paper is focused on modular
prefabrication proposed for school construction. However, the feasibility in terms of cost and
time performance was yet to be established in comparison with traditionally constructed
classrooms by MOE in New Zealand. Comparing modular prefabrication and traditional
construction project cost and time performance is often challenged by a lack of comparison
basis in research. Also, methods like comparing data obtained from projects with theoretical
and industry benchmarks and/or direct comparison of data obtained from unrelated projects
directly do not effectively overcome the challenge (Mao et al., 2016; Shahzad et al., 2014).
This paper employed a quantitative approach by obtaining estimated cost and time data from
prefabrication (4 number) and traditional (6 number) contractors in Auckland, New Zealand.
To prevent incomparable data and depart from the existing data collection approaches at the
same time, these contractors were provided with a case study of 78m² Revit model classroom
design (Plan shown in Figure 1) in conformity with the teaching space requirement in the
country (MOE, 2015). For either type of construction, the contractors were instructed to
provide the construction costs and completion time estimates for the Revit model classroom
elements on a pro forma. The elements include preliminary & general (P&G), foundation &
slab, framing & bracing, roof building wrap and services. Others are wall insulation & lining,
doors & windows, cladding and finishes. The prefabricated construction included the cost
estimates for transportation and site installation (Mao et al., 2016). With a pro forma,
continuous data can be obtained for parametric data testing (Kaur & Kumar, 2015). It allows
isolated request for missing data; therefore, it is a flexible means of collecting continuous
project data (Shahzad et al., 2014).
Furthermore, the contractors were instructed to provide estimated costs and completion times
expended on construction management tasks, and labour and plant inputs. As a result, the scope
of comparison was limited to the construction method to ease comparability. The contractors
were not asked to provide the estimates of cost and time expended on materials. This is because
they operate different supply chain strategies for sourcing materials that are difficult to
compare. Obtaining estimated data is akin to how efficiently the contractors can deliver either
project construction types. However, contractors’ efficiencies can vary, to the detriment of data
validity and reliability. Therefore, data obtained were initially compared on the face value and
outlier data from any contractor were removed from the analysis to increase data validity and
reliability. The methods of analysis that conform with the adopted quantitative methodology
were used are as follows. An arithmetic method comprising addition, subtraction and division
operations was computed for preliminary analysis of the prefabricated and traditional
construction cost and completion time estimates for the Revit model classroom elements.
Finally, independent samples t-test was computed to establish whether there is a significant
difference between prefabricated and traditional construction using the construction cost and
completion time estimates for the Revit model classroom elements.
586
Figure 1: Plan view of the 78m² Classroom
4 Findings
As shown in Tables 1 and 2, four prefabrication manufacturers providers (M1-M4) and six
contractors (T1-T6) provided cost estimates for the prefabricated and traditional construction
of the 78m² Revit model classroom design on elemental basis respectively as at 2019. For the
prefabricated construction, the cost estimates provided by M1 was much higher than those
provided by others (M2-M4). Similarly, the cost estimates provided by T2 was much higher
than other traditional contractors (T1; T3-T6). High-cost estimates provided by M1 and T2
(Yellow columns in Tables 1 & 2) may be due to the inclusion of material costs used in the
construction of the elements. This contradicts the research design to estimate based on
construction method only, but it provides an indication of the material cost impact on
prefabricated and traditional construction. Regardless, cost estimates by M1 and T2 are outliers
and were not used for further analysis. Of the remaining prefabrication contractors (M2-M4),
M4 provided the highest total cost estimate (NZ$60,000); the least was provided by M2
(NZ$35,700), and their average was NZ$50,066.67. Also, of the remaining traditional
contractors (T1; T3-T6), T1 provided the highest total cost estimate (NZ$128,000); the least
was provided by T4 (NZ$80,000), and their average was NZ$97,100.
Table 1: Prefabricated construction cost estimates supplied by different contractors
Prefab
elements
M1
M2
Average
Average
without M1
Preliminary
& General
$ 70,000.00
$ 7,800.00
$ 25,700.00
$ 10,933.33
Foundation
& Slab
$ 80,000.00
$ 5,500.00
$ 26,000.00
$ 8,000.00
587
Figure 1: Plan view of the 78m² Classroom
4 Findings
As shown in Tables 1 and 2, four prefabrication manufacturers providers (M1-M4) and six
contractors (T1-T6) provided cost estimates for the prefabricated and traditional construction
of the 78m² Revit model classroom design on elemental basis respectively as at 2019. For the
prefabricated construction, the cost estimates provided by M1 was much higher than those
provided by others (M2-M4). Similarly, the cost estimates provided by T2 was much higher
than other traditional contractors (T1; T3-T6). High-cost estimates provided by M1 and T2
(Yellow columns in Tables 1 & 2) may be due to the inclusion of material costs used in the
construction of the elements. This contradicts the research design to estimate based on
construction method only, but it provides an indication of the material cost impact on
prefabricated and traditional construction. Regardless, cost estimates by M1 and T2 are outliers
and were not used for further analysis. Of the remaining prefabrication contractors (M2-M4),
M4 provided the highest total cost estimate (NZ$60,000); the least was provided by M2
(NZ$35,700), and their average was NZ$50,066.67. Also, of the remaining traditional
contractors (T1; T3-T6), T1 provided the highest total cost estimate (NZ$128,000); the least
was provided by T4 (NZ$80,000), and their average was NZ$97,100.
Table 1: Prefabricated construction cost estimates supplied by different contractors
Prefab
elements
M1
M2
M3
M4
Average
Average
without M1
Preliminary
& General
$ 70,000.00
$ 7,800.00
$ 10,000.00
$ 15,000.00
$ 25,700.00
$ 10,933.33
Foundation
& Slab
$ 80,000.00
$ 5,500.00
$ 6,500.00
$ 12,000.00
$ 26,000.00
$ 8,000.00
Framing
& Bracing
$ 80,000.00
$ 7,500.00
$ 25,375.00
$ 7,166.67
Roof
$ 60,000.00
$ 1,600.00
$ 17,650.00
$ 3,533.33
Building
Wrap
$ 6,000.00
$ 800.00
$ 2,325.00
$ 1,100.00
Services
$ 30,000.00
$ 2,500.00
$ 9,625.00
$ 2,833.33
Wall
insulation
& lining
$ 10,000.00
$ 600.00
$ 4,400.00
$ 2,533.33
Doors
& Windows
$ 6,000.00
$ 800.00
$ 2,200.00
$ 933.33
Cladding
$ 15,000.00
$ 2,400.00
$ 6,850.00
$ 4,133.33
Finishes
$ 15,000.00
$ 1,600.00
$ 5,650.00
$ 2,533.33
Sub-total
$ 372,000.00
$ 31,100.00
$ 125,775.00
$ 43,700.00
Transport
$ 7,000.00
$ 3,000.00
$ 4,625.00
$ 3,833.33
Site
installation
costs
$ 3,000.00
$ 1,600.00
$ 2,650.00
$ 2,533.33
Total
$ 382,000.00
$ 35,700.00
$ 133,050.00
$ 50,066.67
*Cost data is presented in New Zealand dollars
588
Table 2: Traditional construction cost estimates supplied by different contractors
Construction
elements
T1
T2
T3
T4
T5
T6
Average
Average without T2
P&G
$ 5,000.00
$ 35,000.00
$ 5,000.00
$ 20,000.00
$ 15,000.00
$ 15,000.00
$ 15,833.33
$ 12,000.00
Foundation & Slab
$ 30,000.00
$ 30,000.00
$ 30,000.00
$ 14,000.00
$ 20,000.00
$ 15,000.00
$ 23,166.67
$ 21,800.00
Framing & Bracing
$ 14,000.00
$ 25,000.00
$ 10,000.00
$ 10,000.00
$ 8,000.00
$ 12,000.00
$ 13,166.67
$ 10,800.00
Roof
$ 18,000.00
$ 25,000.00
$ 9,000.00
$ 12,000.00
$ 15,000.00
$ 15,000.00
$ 15,666.67
$ 13,800.00
Building Wrap
$ 3,000.00
$ 3,000.00
$ 3,000.00
$ 3,000.00
$ 2,500.00
$ 1,000.00
$ 2,583.33
$ 2,500.00
Services
$ 6,000.00
$ 20,000.00
$ 6,000.00
$ 3,000.00
$ 4,000.00
$ 3,500.00
$ 7,083.33
$ 4,500.00
Wall insulation &
lining
$ 8,000.00
$ 5,000.00
$ 3,000.00
$ 4,000.00
$ 6,000.00
$ 6,500.00
$ 5,416.67
$ 5,500.00
Doors & Windows
$ 9,000.00
$ 25,000.00
$ 2,000.00
$ 2,000.00
$ 2,000.00
$ 2,000.00
$ 7,000.00
$ 3,400.00
Cladding
$ 20,000.00
$ 25,000.00
$ 15,000.00
$ 7,000.00
$ 8,000.00
$ 15,000.00
$ 15,000.00
$ 13,000.00
Finishes
$ 15,000.00
$ 10,000.00
$ 15,000.00
$ 5,000.00
$ 8,000.00
$ 6,000.00
$ 9,833.33
$ 9,800.00
Sub-total
$ 128,000.00
$ 203,000.00
$ 98,000.00
$ 80,000.00
$ 88,500.00
$ 91,000.00
$ 114,750.00
$ 97,100.00
Transport
$ -
$ -
$ -
$ -
$ -
$ -
$ -
$ -
Site installation
costs
$ -
$ -
$ -
$ -
$ -
$ -
$ -
$ -
Total
$ 128,000.00
$ 203,000.00
$ 98,000.00
$ 80,000.00
$ 88,500.00
$ 91,000.00
$ 114,750.00
$ 97,100.00
*Cost data is presented in New Zealand dollars
589
Table 2: Traditional construction cost estimates supplied by different contractors
Construction
elements
T1
T2
T3
T4
T5
T6
Average
Average without T2
P&G
$ 5,000.00
$ 35,000.00
$ 5,000.00
$ 20,000.00
$ 15,000.00
$ 15,000.00
$ 15,833.33
$ 12,000.00
Foundation & Slab
$ 30,000.00
$ 30,000.00
$ 30,000.00
$ 14,000.00
$ 20,000.00
$ 15,000.00
$ 23,166.67
$ 21,800.00
Framing & Bracing
$ 14,000.00
$ 25,000.00
$ 10,000.00
$ 10,000.00
$ 8,000.00
$ 12,000.00
$ 13,166.67
$ 10,800.00
Roof
$ 18,000.00
$ 25,000.00
$ 9,000.00
$ 12,000.00
$ 15,000.00
$ 15,000.00
$ 15,666.67
$ 13,800.00
Building Wrap
$ 3,000.00
$ 3,000.00
$ 3,000.00
$ 3,000.00
$ 2,500.00
$ 1,000.00
$ 2,583.33
$ 2,500.00
Services
$ 6,000.00
$ 20,000.00
$ 6,000.00
$ 3,000.00
$ 4,000.00
$ 3,500.00
$ 7,083.33
$ 4,500.00
Wall insulation &
lining
$ 8,000.00
$ 5,000.00
$ 3,000.00
$ 4,000.00
$ 6,000.00
$ 6,500.00
$ 5,416.67
$ 5,500.00
Doors & Windows
$ 9,000.00
$ 25,000.00
$ 2,000.00
$ 2,000.00
$ 2,000.00
$ 2,000.00
$ 7,000.00
$ 3,400.00
Cladding
$ 20,000.00
$ 25,000.00
$ 15,000.00
$ 7,000.00
$ 8,000.00
$ 15,000.00
$ 15,000.00
$ 13,000.00
Finishes
$ 15,000.00
$ 10,000.00
$ 15,000.00
$ 5,000.00
$ 8,000.00
$ 6,000.00
$ 9,833.33
$ 9,800.00
Sub-total
$ 128,000.00
$ 203,000.00
$ 98,000.00
$ 80,000.00
$ 88,500.00
$ 91,000.00
$ 114,750.00
$ 97,100.00
Transport
$ -
$ -
$ -
$ -
$ -
$ -
$ -
$ -
Site installation
costs
$ -
$ -
$ -
$ -
$ -
$ -
$ -
$ -
Total
$ 128,000.00
$ 203,000.00
$ 98,000.00
$ 80,000.00
$ 88,500.00
$ 91,000.00
$ 114,750.00
$ 97,100.00
*Cost data is presented in New Zealand dollars
Furthermore, as shown in Table 3, the same number of prefabrication and traditional
contractors provided the completion time estimates for different elements in the 78m² Revit
model classroom design as at 2019. Among the traditional contractors (T1-T6), T2 provided
the highest total estimated time to complete the Revit model classroom (75 days); the least was
provided by T5 (48 days), and their average was approximately 62 days. Among the
prefabrication contractors (M1-M4), M3 provided the highest total estimated time to complete
Revit model classroom (64 days); the least was provided by M2 (44 days), and the average was
approximately 54 days.
Table 4: Traditional and Prefabricated construction completion time estimates supplied by
different contractors
Constructed elements
Traditional Contractors
Prefabrication Contractors
T1
T2
T3
T4
T5
T6
Average
M1
M2
M3
M4
Average
P&G
3
10
3
20
10
10
9.33
7
10
20
25
15.50
Foundation & Slab
7
5
10
10
4
5
6.83
9
5
8
10
8.00
Framing & Bracing
12
15
12
12
8
10
11.50
7
10
10
5
8.00
Roof
8
10
8
8
5
8
7.83
6
3
8
3
5.00
Building Wrap
2
2
3
2
1
2
2.00
2
1
1
1
1.25
Services
2
5
4
2
1
2
2.67
4
3
2
2
2.75
Wall insulation &
lining
6
3
6
2
4
5
4.33
2
1
3
2
2.00
Doors & Windows
3
5
3
2
2
2
2.83
1
1
1
1
1.00
Cladding
15
10
6
5
8
5
8.17
3
4
3
5
3.75
Finishes
10
10
5
5
5
5
6.67
2
3
4
3
3.00
Transport
0
0
0
0
0
0
1
1
1
1
1.00
Site installation costs
0
0
0
0
0
0
1
2
3
3
2.25
Total
68
75
60
68
48
54
62.17
45
44
64
61
53.50
*Time data is presented in No. of days
The averages of the total estimated cost and completion time of the prefabricated and traditional
construction of the 78m² Revit model classroom design was computed (Table 5) to establish
the total estimated cost and completion time differences. As shown in the Table, the total sum
of estimated prefabricated construction cost was NZ$50,066.64. This value is 48.43% lesser
than the NZ$97,100 total sum estimated for the traditional construction cost. Similarly, the
total completion time estimated for the prefabricated construction was approximately 54 days.
This value is 13.94% lesser than approximately 62 days of completion time estimated for the
traditional construction. It could be seen that differences exist between the total estimated cost
and completion time of the prefabricated and traditional construction of the Revit model
classroom. The inference is that the prefabricated construction of the Revit model classroom
has a lower cost and can be completed timelier than employing traditional construction
methods.
Table 5: Averages of the total cost and completion time estimates
Constructed
elements
Average Prefab
Cost
Average Trad
Cost
Average Prefab
Completion time
Average Trad
Completion
time
P&G
$ 10,933.33
$ 12,000.00
15.50
9.33
Foundation & Slab
$ 8,000.00
$ 21,800.00
8.00
6.83
Framing & Bracing
$ 7,166.67
$ 10,800.00
8.00
11.50
590
Roof
$ 3,533.33
$ 13,800.00
5.00
7.83
Building Wrap
$ 1,100.00
$ 2,500.00
1.25
2.00
Services
$ 2,833.33
$ 4,500.00
2.75
2.67
Wall insulation &
lining
$ 2,533.33
$ 5,500.00
2.00
4.33
Doors & Windows
$ 933.33
$ 3,400.00
1.00
2.83
Cladding
$ 4,133.33
$ 13,000.00
3.75
8.17
Finishes
$ 2,533.33
$ 9,800.00
3.00
6.67
Sub-total
$ 43,699.98
$ 97,100.00
Transport
$ 3,833.33
1.00
0.00
Site installation
costs
$ 2,533.33
2.25
0.00
Total
$ 50,066.64
$ 97,100.00
53.50
62.17
Given the differences in the estimated total construction cost and completion time of both the
modular prefabricated and traditional construction of the Revit model classroom, this paper
further investigated whether the differences are significant. In practice, modular prefabricated,
and traditional construction are different construction types. Therefore, a significantly different
result would indicate that the construction costs and completion time estimates provided by the
contractors (T1-T6; M1-M4) reflect the type of construction and are practicable. The
independent t-test is used to compare means between two unrelated groups on the same
continuous, dependent variable (Laerd, 2018), and was employed. In this paper, the two
unrelated groups are modular prefabricated vs traditional construction, while the dependent
continuous variable is the estimated construction costs (and completion time) for individual
elements in the Revit model classroom. The premise of decision was based on the observed t-
value, the degrees of freedom and the statistical significance (p-value) (Laerd, 2018).
Following the analysis, the results are presented in Table 6. With p < .05, there was a significant
difference in the average estimated construction cost of the elements in the Revit model
classroom between prefabrication and traditional construction types, t(75.121) = -4.900, p =
.000 (Table 6). Similarly, there was a significant difference in the average estimated completion
time of the elements in the Revit model classroom between prefabrication and traditional
construction types, t(91.940) = -2.041, p = .044 (Table 6).
Table 6: Independent Samples Test
Independent Variables
Levene's Test for
Equality of Variances
t-test for Equality of Averages
F
Sig
t
df
Sig. (2-tailed)
Cost estimates
of Modular
Prefab vs
Traditional
construction
types
Equal variances
assumed
18.61
0.000
-
4.425
84
0.000
Equal variances
not assumed
-
4.900
75.121
0.000
Completion
time estimates
of Modular
Prefab vs
Traditional
construction
types
Equal variances
assumed
0.00
0.983
-
2.080
106
0.040
Equal variances
not assumed
-
2.041
91.940
0.044
591
Roof
$ 3,533.33
$ 13,800.00
5.00
7.83
Building Wrap
$ 1,100.00
$ 2,500.00
1.25
2.00
Services
$ 2,833.33
$ 4,500.00
2.75
2.67
Wall insulation &
lining
$ 2,533.33
$ 5,500.00
2.00
4.33
Doors & Windows
$ 933.33
$ 3,400.00
1.00
2.83
Cladding
$ 4,133.33
$ 13,000.00
3.75
8.17
Finishes
$ 2,533.33
$ 9,800.00
3.00
6.67
Sub-total
$ 43,699.98
$ 97,100.00
Transport
$ 3,833.33
1.00
0.00
Site installation
costs
$ 2,533.33
2.25
0.00
Total
$ 50,066.64
$ 97,100.00
53.50
62.17
Given the differences in the estimated total construction cost and completion time of both the
modular prefabricated and traditional construction of the Revit model classroom, this paper
further investigated whether the differences are significant. In practice, modular prefabricated,
and traditional construction are different construction types. Therefore, a significantly different
result would indicate that the construction costs and completion time estimates provided by the
contractors (T1-T6; M1-M4) reflect the type of construction and are practicable. The
independent t-test is used to compare means between two unrelated groups on the same
continuous, dependent variable (Laerd, 2018), and was employed. In this paper, the two
unrelated groups are modular prefabricated vs traditional construction, while the dependent
continuous variable is the estimated construction costs (and completion time) for individual
elements in the Revit model classroom. The premise of decision was based on the observed t-
value, the degrees of freedom and the statistical significance (p-value) (Laerd, 2018).
Following the analysis, the results are presented in Table 6. With p < .05, there was a significant
difference in the average estimated construction cost of the elements in the Revit model
classroom between prefabrication and traditional construction types, t(75.121) = -4.900, p =
.000 (Table 6). Similarly, there was a significant difference in the average estimated completion
time of the elements in the Revit model classroom between prefabrication and traditional
construction types, t(91.940) = -2.041, p = .044 (Table 6).
Table 6: Independent Samples Test
Independent Variables
Levene's Test for
Equality of Variances
t-test for Equality of Averages
F
Sig
t
df
Sig. (2-tailed)
Cost estimates
of Modular
Prefab vs
Traditional
construction
types
Equal variances
assumed
18.61
0.000
-
4.425
84
0.000
Equal variances
not assumed
-
4.900
75.121
0.000
Completion
time estimates
of Modular
Prefab vs
Traditional
construction
types
Equal variances
assumed
0.00
0.983
-
2.080
106
0.040
Equal variances
not assumed
-
2.041
91.940
0.044
5 Discussion of findings
The feasibility of prefabricated construction projects is demonstrated by comparing the
estimated construction costs and completion time with traditionally construction ones. Among
the categories of prefabricated construction, the modular construction category that has been
proposed for school construction in New Zealand was selected for the comparison.
Furthermore, comparable data derived from a 78m² Revit model classroom model was obtained
from four prefabrication and six traditional contractors in the country. The data was broken
down according to the Revit model classroom elements that enabled detailed comparative
analysis. However, the data reflected only the construction method encompassing the
construction management tasks, and labour and plant inputs. Results from comparing modular
prefabricated and traditional construction project have reportedly been poor due to an
inconsistent basis comparison (Antillón et al., 2014). In this paper, this problem may have been
circumvented by using data reflecting construction method only for comparative analysis.
Material inputs only data can also be sourced for such comparative analysis. Therefore, a new
methodology whereby construction method data or material inputs data can be isolated to
compare modular prefabricated and traditional construction performance may have emerged in
this paper.
The comparative analysis using the arithmetic method revealed that the modular prefabricated
construction of the Revit model classroom can be low in cost and can be completed in a timelier
manner compared to traditional construction. Also, based on the independent t-test analysis, it
was demonstrated that the realistic cost of the prefabricated construction of the Revit classroom
model design was estimated by the contractors and therefore can be implemented in practice.
Notably, this contradicts most literature findings who found otherwise (Wasana et al., 2019;
Sutrisna et al., 2019). It should be noted, these studies attributed the higher costs and
completion time of prefabricated projects than traditional ones to many reasons such as
assembly and transportation of prefabricated elements, and residual onsite activities (Mao et
al., 2016). In practice, the Australian and New Zealand construction supply chains work in
tandem and Sutrisna et al. (2019)’s reasons for high prefabricated construction project costs
can be related to both supply chains. Most prefabricated construction projects in both countries
are constructed singularly in isolation and this removes the customisation cost reduction
benefits that would accrue to a chain of prefabricated construction projects (Sutrisna et al.,
2019). This is expected to change, and improved prefabricated construction cost benefits can
be realised when MOE starts to build proposed classrooms to accommodate one hundred
thousand students under the National Education Growth Plan (NEGP) in New Zealand (Ardern
& Hipkins, 2019). Based on Shahzad et al. (2014)’s study in New Zealand, increasing the
prefabrication content of these classrooms will reduce their completion times and ensure they
are utilised earlier than traditionally constructed classrooms. However, the shorter construction
time demands high upfront cash inflows, about 80% of payment, to fabricate the modules
(Wuni et al., 2021).
In addition to the positive cost and time performance potential, studies in other developed
countries show that modular classrooms have learning benefits that are relevant for improving
academic learning experiences in New Zealand and Australasia. Modular classrooms can be
leveraged for research into learning environments to improve pedagogies in Australian higher
education (Newton et al., 2020). A Canada study reveals that they can be prototyped for hands-
on construction exercise for university students to develop specialised skills (Hegazy et al.,
2020). Rizkiyansah et al. (2020) report a strong sustainable modular classroom performance,
especially waste reduction in Indonesia. To corroborate, King (2020) reveals that modular
592
classrooms installed with energy efficient measures such as air-source-heat pump generate
about 35% lower carbon dioxide emissions than required by current UK regulations. However,
modular classroom indoor quality is lowered when in-use with the potential to cause discomfort
and health effects to pupils and teachers when the total volatile organic compounds (TVOC)
concentration of 200 μg/m3 is exceeded in a Slovakian case (Harčárová, 2020).
6 Conclusion, recommendation, implications
Prefabricated construction has become a paradox in New Zealand. It has been slow to take off
because construction stakeholders are undetached from traditional construction, while at the
same time, the Ministry of Education (MOE) has proposed it as a solution for school classroom
construction to accommodate one hundred thousand students at lower cost and timely
completion in the country. Therefore, it became imperative to determine whether modular
prefabricated classrooms are more feasible in terms of cost and time performance than
traditionally constructed ones in New Zealand. This paper departed from existing comparative
analysis methods to ensure data comparability by obtaining data from four prefabrication and
six traditional contractors derived from construction costs and completion time estimates of a
78m² Revit model classroom model design. The data obtained showed that it is possible to
isolate construction method data only from material inputs data as a plausible methodology for
comparing prefabricated and traditional construction cost and completion time performance
henceforth. This methodology was implemented to determine that the 78m² Revit modular
prefabricated classroom could be constructed at cheaper cost and completed timely compared
to the traditional method, and the realistic cost estimated by the contractors can be implemented
in practice.
It is concluded that constructing modular prefabricated classrooms, and emphasising on the
construction method only, is more feasible at lesser cost and timely completion when compared
to constructing traditional classrooms in New Zealand. In terms of implication, it has been
demonstrated that estimating the construction cost and completion time of prefabricated
construction by isolating construction method data from material inputs data can potentially be
done as a realistic approach with reasonable accuracy. In other developed countries like USA
and the UK, the potential of modular classrooms has been proven beyond cost and time
performance. Modular classrooms can enhance academic research and learning experiences for
users in these countries and elsewhere. Academic researchers can undertake fit-for-purpose
experimental research using modular classrooms. Students’ hands-on-experience of modular
classrooms help them to develop specialised construction project management skills that are
relevant in practice. In further research, the efficacy of the proposed methodological approach
can be further tested using real life data. The MOE can use the findings to decide whether to
proceed with modular prefabricated classroom construction in New Zealand. Clients and
contractors who may be sceptical about the benefits of prefabricated construction may find this
paper as the vehicle to present evidence and potentials that can change their views.
7 References
Abdul Nabi, M., & El-adaway, I. H. (2021). Understanding the Key Risks Affecting Cost and Schedule
Performance of Modular Construction Projects. Journal of Management in Engineering, 37(4),
04021023.
593
classrooms installed with energy efficient measures such as air-source-heat pump generate
about 35% lower carbon dioxide emissions than required by current UK regulations. However,
modular classroom indoor quality is lowered when in-use with the potential to cause discomfort
and health effects to pupils and teachers when the total volatile organic compounds (TVOC)
concentration of 200 μg/m3 is exceeded in a Slovakian case (Harčárová, 2020).
6 Conclusion, recommendation, implications
Prefabricated construction has become a paradox in New Zealand. It has been slow to take off
because construction stakeholders are undetached from traditional construction, while at the
same time, the Ministry of Education (MOE) has proposed it as a solution for school classroom
construction to accommodate one hundred thousand students at lower cost and timely
completion in the country. Therefore, it became imperative to determine whether modular
prefabricated classrooms are more feasible in terms of cost and time performance than
traditionally constructed ones in New Zealand. This paper departed from existing comparative
analysis methods to ensure data comparability by obtaining data from four prefabrication and
six traditional contractors derived from construction costs and completion time estimates of a
78m² Revit model classroom model design. The data obtained showed that it is possible to
isolate construction method data only from material inputs data as a plausible methodology for
comparing prefabricated and traditional construction cost and completion time performance
henceforth. This methodology was implemented to determine that the 78m² Revit modular
prefabricated classroom could be constructed at cheaper cost and completed timely compared
to the traditional method, and the realistic cost estimated by the contractors can be implemented
in practice.
It is concluded that constructing modular prefabricated classrooms, and emphasising on the
construction method only, is more feasible at lesser cost and timely completion when compared
to constructing traditional classrooms in New Zealand. In terms of implication, it has been
demonstrated that estimating the construction cost and completion time of prefabricated
construction by isolating construction method data from material inputs data can potentially be
done as a realistic approach with reasonable accuracy. In other developed countries like USA
and the UK, the potential of modular classrooms has been proven beyond cost and time
performance. Modular classrooms can enhance academic research and learning experiences for
users in these countries and elsewhere. Academic researchers can undertake fit-for-purpose
experimental research using modular classrooms. Students’ hands-on-experience of modular
classrooms help them to develop specialised construction project management skills that are
relevant in practice. In further research, the efficacy of the proposed methodological approach
can be further tested using real life data. The MOE can use the findings to decide whether to
proceed with modular prefabricated classroom construction in New Zealand. Clients and
contractors who may be sceptical about the benefits of prefabricated construction may find this
paper as the vehicle to present evidence and potentials that can change their views.
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... Luo et al. [47] and Yazdani et al. [48] derived a framework for the overall management of OSC projects based on a combination of existing architectural project management systems and manufacturing. Furthermore, some management systems have been used for real-world projects [36,49,50]. Sutrisna and Goulding [51] and Yang et al. [16] focused on system development to enhance the use of building information modeling (BIM) from the design stage. ...
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