The Improvement Priority of Inhibitory Factor for Invigorating the Modular Building : Focused on Professional of Work Related to Modular Building

1.1. Background and purpose

Modular building has a big advantage as a construction method to maintain Korea’s land in environmentally friendly way with its strengths such as shortened construction periods, quick removal, and practical use of land. However, its market has yet to developed, and actual cases of construction based on modular building have been limited to military barracks, dormitory facilities, and single housing units. In an effort to invigorate modular building, the Housing Act was revised in 2016 to incorporate the entire or partial residential space into the range of industrialized housing, which was previously defined as major structures. The revision also improved its effectiveness by deleting a clause stating that construction shall start within 1 year after approval, but still there is no business obtained this approval showing its limitations in boosting modular building.

Therefore, surveys were conducted targeting modular building professionals, improvement priority was established, and then expert surveys were performed with an aim of uncovering practical factors to invigorate modular building. The results of this research are intended to be utilized as basis data in raising awareness of the public regarding industrialized housing and responding to government policies.

1.2. Research method and scope

This research is about establishing priorities to improve factors undermining the invigoration of modular building. Specific research methods and details are as follows:

First, factors discouraging modular building were identified through analysis of previous research and consultation with experts. Second, expert surveys were conducted for the purpose of resolving the uncovered factors that discourage modular building. Though understanding the current public awareness on modular building is important, survey targets were limited to professionals working in the modular building sector considering the unique nature of the Korean construction industry in which modular building has yet been invigorated. Third, based on the findings of the surveys, IPA analysis was carried out to establish the improvement priorities of the inhibitory factors. IPA (Importance Performance Analysis) method enables simultaneous analysis of how survey respondents recognize importance and satisfaction of survey items and prioritization of survey items. This method provides meaningful information to efficiently develop improvement items when a problem needs to be resolved with defined manpower and budget. Fourth, the results from IPA were verified through in-depth expert surveys.

IPA analysis results are displayed on a plane as in <Figure 1>. The first quadrant is the most important but least satisfactory area, meaning that it needs urgent improvement because survey respondents think the surveyed items important, but actually their satisfaction level is low.

Fig. 1.

IPA Matrix

The second quadrant in which respondents think the survey items important and feel satisfied is the area requiring improvements with close attention. In the third quadrant, respondents consider the importance of survey items as low, but their satisfaction level is high, meaning extra effort is not necessary. The fourth quadrant implies that respondents give low priority and satisfaction level is also low, requiring close attention and mid and long-term solutions.

2.1. Concept of modular building

Modular construction method refers to production and construction method of a building which is constructed by assembling individual modules produced from a factory, and modular building means buildings created using modular construction method and building activities. Modular building has advantages such as shortened construction period, lightweight, flexibility, and mobility.¹⁾

In Korean laws, the terminology, ‘industrialized housing,’ which is used in Japan, is also used, and the range of industrialized housing was expanded after the revision of the Housing Act in 2016. However, it only applies to detached or apartment housing, and there is no legal terminology for buildings for other purposes.

On the other hand, terminologies like modular, panelized, manufactured, off-site, prefabrication, format housing, and factory-produced housing are used.²⁾

2.2. industrialized housing approval system

The industrialized housing approval system was first introduced in 1992 to improve the quality and boost Korea’s industrialized housing, and has been revised as shown in <Table 1>. However, its low effectiveness such as lack of incentives (Article 53 of the Housing Act: If a person who has more than one architect and structural engineers, or has more than one architectural execution engineers construct, construction and inspection regulations are eased) resulted in only four recent (since 2010) approval cases of industrialized housing.

Table 1.

Status of Major Enactments and Amendments of the Industrialized Housing Approval System

Table 2.

Study of Existing Research Encouraging Modular Building

2.3. Previous research on modular building

Research on how to encourage modular building has been continued since 2010. In the study of Kim Hu-yong (2017), automation for mass production was proposed, and Lee Jun-sik (2016) tried to improve the awareness by standardizing exterior materials. Haisier, Abudukeha (2013) and Moon Yeong-a et al. (2013) examined Korean and overseas cases to study direct and indirect factors or classified factors into speed, flexibility, sustainability, economical efficiency. The encouragement method by regulations on industrial housing was suggested in research by Hwang Eun-Kyoung et al. (2016), Kim Hyeong-do et al. (2016), and Park Junyeong et al. (2013), while Lee Mun-seok (2016) presented a proposal of procurement contracts. The previous research was centered on the encouragement through technical or systematical improvements. However, improving all factors comes with many restrictions such as time and money. Therefore, to boost modular building, prioritization of these factors is necessary.

3.1. Research tool

Research tool used in this study is as follows: Based on the previous research and literature, factors hampering the expansion of industrialized housing were identified and the first preliminary survey of experts was conducted to validate the reliability of the tool. It was conducted three times from September 27 to December 10, 2016, targeting professionals working for industrialized housing production companies. By combining factors drawn from the previous research and the preliminary survey, the total of 37 factors inhibitory the encouragement of modular building in actual modular construction sites. This research applied Cronbach’s Alpha to measure the respondent reliability of the survey questionss by life cycle in relation to inhibitory factors.

The life cycle of industrialized housing is separated by seven phases, and Cronbach’s Alpha reliability by life cycles was analyzed as follows: planning and ordering phase (.649/8), design and authorization phase (.549/3), production and manufacturing phase (.747/6), packaging and shipping phase (.573/4), construction and inspection phase (.739/7), maintenance phase (.710/3), and dismantling phase (.754/3).³⁾

3.2. Identifying factors that inhibit the expansion of modular building

To identify inhibition factors, factors were drawn from previous research papers such as ‘Off-site Ultra High-speed Housing Construction Technology R&D,’ ‘Study of methods to encourage factory produced construction,’ ‘Study of methods to encourage industrialized building for the development of the professional construction industry,’ and ‘R&D of end-user oriented customized housing.’ In addition, basic survey of modular building experts was performed to add more factors.

Unlike general building, modular building includes packaging, shipping, preservation, dismantling and reusing in its life cycle, a unique characteristic of modular building.

Inhibitory factors are categorized into eight phases by life cycle including strategic phase for the expansion, maintenance phase, and dismantling and reusing phase.

Table 3.

Extraction of Factors that Discourage the Expansion of Modular Building

These inhibitory factors from research papers and the expert survey were categorized into seven life cycle phases and the public awareness and modular building market. As shown in <Table 4>, there are items that are duplicated or with similar meaning by each life cycle, so wording was reorganized to study importance and satisfaction.

Table 4.

Extraction of Factors that Discourage the Expansion of Modular Building

As a result, 37 factors were developed for the actual analysis required for this research, and the details are displayed in <Table 3>.

4.1. Data collecabtion and survey analysis

Surveys were performed targeting professionals working in various fields related to industrialized housing. 74 copies of the survey were distributed from May 16 to June 15, 2017 and 56 copies of them were collected. Among the collected survey sheets, 50 valid ones were used for the final analysis. Frequency analysis, technical statistics, IPA, and T-test analysis were conducted using IBM SPSS 23.0. Survey questions were shown in <Table 5>, consisting of items on general information of respondents such as field of work and experience, scope awareness level in relation to industrialized housing terms like image of industrialized housing terminology, necessity of improvements in terminology, and preferred terminology, and satisfaction and importance regarding 37 inhibitory factors <Table 3>. Concerning the priority ranking identified by IPA, additional opinions were collected through in-depth survey of experts for two days from August 3 and 4 in 2017.

Table 5.

Survey Questions

4.2. Survey results and discussion

1) General items on survey respondents

Fields of work consist of module production company, construction company, building design, research institution, and civil servant, and over 70% of respondents are working in construction company (40.8%) and module production company (34.7%). Also, the proportion of respondents with less than five years or five to ten years of experience was high. Details are shown in <Table 6>.

Table 6.

Perception of Industrialized Housing

2) Necessity of redefining industrialized housing terms

Through awareness on industrialized housing terminology, this study aimed to come up with the necessity of redefining the terminology and its priority.

The survey on terms considered as industrialized housing showed that Factory Production On-site Assembled Housing was the highest with 31.2% followed by Unit Modular Housing (30.1%), Wood-based Assembled Housing (16.1%), PC Assembled Housing and Container Housing (9.7%).

This survey used multiple response analysis, and the result implies that terms showing distinction to RC structure are recognized as industrialized housing.

Some experts claimed that negative perception of the general public, which comes from industrialized housing terms, inhibits the expansion of industrialized housing. Compared to Canada which has revised terminology twice since the introduction of CSA factory certification system in 2001,⁴⁾ Korea has never made revision to terms since the introduction of industrialized housing approval system in 1992.

In this context, the survey examined legal terminology’s negative impacts on the expansion of modular housing. 3-point Likert scale was used for analysis in which 1 means negative, 2 normal, and 3 positive. 48% of the respondents said negative and 12% positive.

Then, the priority of proper terms for terminology revision was surveyed. Respondents were asked to pick top 3 terms out of 10 candidate terms. As a result, modular housing (53.1%) ranked the top followed by prefabricated housing (30.6%) and assembly housing (18.4%).

Table 7.

Scope (Approved) of Industrialized Housing

Industrialized housing terms are legally defined, but among the public and in reality, various terms like modular housing and prefabricated housing are used together with industrialized housing. In other words, now it is time to redefine the terminology because other terms are mixed despite the existence of legal terminology.

3) Identifying inhibitory factors

To identify inhibitory factors, modular building was categorized into the 7-phase life cycle and the public awareness and modular building market, and inhibitory factors extracted from literature, previous research, and preliminary surveys were categorized into the life cycle and the public awareness and market.

In this research, IPA method was used to identify factors primarily improved based on the gap between current satisfaction and importance regarding inhibitory factors. The satisfaction and importance level of each factor using 3-point scale is shown in <Table 9>.

Table 8.

Need to Amend Legal Terms and Negative Effects of Industrialized Housing Vocabulary by Each Industry Segment

After IPA analysis, 11 factors were identified as top priority improvement item (1^st area), and 6 factors for improvement (2^nd area).

In the national awareness/market and life cycle phase categories, planning and ordering phase and construction and inspection phase have the most factors which were identified as top priority improvement and improvement items.

Below is the detailed analysis on the top priority improvement and improvement areas for the public awareness/market and life cycle phase categories.

Fig. 2.

Modular Building Invigorating MATRIX

In the national awareness/market category (a), out of 3 items, promotion of industrialized housing and negative public perception ((a)-1) was identified as the top priority (1^st area), and other factors ((a)-2, 3) were located in the gradual improvement area (3^rd area).

This result is similar to the analysis on legal terminology’s negative impact to the expansion of industrialized housing.

In the planning and ordering phase, out of 8 items, 3 factors ((b)-1, 2, 6) were identified as the top priority, and one factor ((b)-7) in the improvement area.

Table 9.

Priority Rankings to Encourage Industrialized Housing

In the design and approval phase, out of 3 items, 2 factors ((c)-1: standard modular design and MC design standard, (c)-2: professional designer level) were identified as the top priority.

In the production and manufacturing phase, out of 6 items, there was no top priority factor, but one improvement factor ((d)-1: standardization of construction materials, parts, and production facilities).

In the packaging, shipping, and preservation phase, out of 4 items, one factor ((e)-4: entry of equipment for urban construction projects) was identified as the top priority.

In the construction and inspection phase, out of 7 items, 3 factors ((f)-2: level of professional contractors that specialize in industrialized housing, (f)-3: secure fireproofing of joints during construction, (f)-6: division of roles and responsibilities between construction companies and producers) were identified as the top priority, and there was one improvement factor ((f)-1).

In the maintenance phase, all three items ((g)-1: maintenance manual, (g)-2: occurrence of burden of responsibility regarding defects between the manufacturer and builder, (g)-3: A/S that reflects the characteristics of the manufacturing industry or consistent maintenance of quality) were identified as improvement factors.

In the dismantling and reusing phase, out of 3 items, one top priority was identified, and the rest were located in the 4^th area meaning keeping the status quo. It can be inferred that dismantling and reusing cases are very rare, which is understandable considering the current status and marketability of industrialized housing, and thus the focus is on the technology development and market expansion, rather than the improvement in the dismantling and reusing phase.

The in-depth survey of experts was performed using the identified factors to collect additional opinions. For ((b)-8: absence of standards requiring the publicizing of primary costs), experts said standards of the unit cost for standard design needs to be sophisticated in practice since primary cost is volatile. For ((g)-3: A/S that reflects the characteristics of the manufacturing industry or consistent maintenance of quality), the suggestion for quality maintenance was to strengthen standards on performance or design rather than to improve repair methods. In addition, it was estimated that if the industrialized housing market is expanded first, improvements for ((b)-5: possession of an unreasonable industrialized housing production factory, (d)-3: specified manufacturing technologies for each unit module, (d)-4: efficiency of production and error mitigation when producing units, (d)-6: level of professional production and manufacturing offices) will be made naturally in accordance with supply and demand.