The primary focus of this research study has been to analyse cost savings, time- savings, and the productivity improvement achievable with the use of panelised/framed prefabrication in place of the alternative traditional building system. The following sub- sections summarise the findings as previously discussed in earlier chapters.
7.2.1 Cost Saving, Time Saving and Productivity Improvement: Case Study Results
The first objective of the study has been to quantify the benefits that panelised prefabrication technology can offer in terms of cost savings, time savings and productivity
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improvements, over and above the corresponding benefits achievable with the use of traditional building system. The results are discussed in the following sub-sections.
7.2.1.1 Cost Savings
In relation to cost savings, the results show that using prefabrication in place of the traditional building system resulted in an average 21 percent cost savings in the five building types investigated in the case studies. This result was not significantly different across the three major cities delineated for the study - Auckland, Christchurch and Wellington. The results further showed that of the five building types, for community building projects, maximum cost saving of 30 percent was observed. The least cost savings of 13.4 percent were observed in the isolated house types of residential building projects. And 21.5 percent, 21.3 percent and 18.6 percent cost savings was observed for educational, apartment and commercial building projects, respectively.
Overall, the findings of this study show a reasonable reduction in the project completion costs by the use of prefabrication technology in place of traditional building system. This provides the basis to acknowledge ‘cost savings’ associated with the use of prefabrication technology as a key benefit of this system.
7.2.1.2 Time Savings
In regard to time savings, the results showed that using prefabrication in place of the traditional building system resulted in an average of a 47 percent saving in completion times for the five building types investigated in the case studies. This result was also not significantly different across the three major cities delineated for the study - Auckland, Christchurch and Wellington. Comparatively, a maximum time savings of 65 percent was observed for housing projects. On the other hand, apartment buildings offered the least time savings of 37 percent. The time savings for the other building types are as follows: Commercial buildings (45 percent), community buildings (45 percent) and educational buildings (41 percent).
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The findings of this study clinches ‘time saving’ as an important benefit of prefabrication technology that can stimulate the improved uptake of this technology. The fact that prefabrication takes the bulk of the construction activities from construction sites to factory-controlled environments was among the most cited reasons for the superior time saving benefits of the prefabrication system.
7.2.1.3 Productivity Improvement
The results related to productivity improvement showed that, when used in place of traditional building system, prefabrication can offer an average of 10 percent improvement in productivity in the five building types investigated in the study and across the three New Zealand cities. The highest productivity improvement value of 15 percent was observed for community building projects while the least productivity improvement of 8.5 percent was observed for housing projects. The productivity improvement values for the other projects were 9.8 percent (for apartments), 9.03 percent (for educational), and 8.9 percent (for commercial building projects).
The above productivity improvement results are very encouraging. The most frequently mentioned reasons for the superior productivity improvement benefits of prefabrication included just-in-time procurement, safer working conditions and reduced need of skilled labour (Hamilton, 2007, Winter et al., 2006).
7.2.2 Factors Influencing Prefabrication Benefits: Survey Results
The second objective of the study was to identify and prioritise the factors that can significantly influence the benefits that are achievable by the use of prefabrication technology.
Accomplishing this objective was one of the principal aims of the qualitative pilot study and quantitative industry survey. Seventeen factors were identified at the pilot study phase. Respondents’ ratings regarding the relative influences of the identified factors were analysed using SPSS factor analysis.
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Results showed that all 17 factors were rated moderate to a very high influence on the 5- point Likert rating scale used. No factor was rated low or very low. Additional factors supplied by the respondents in the open-ended section of the questionnaire were found to be rewordings of the factors already included in the list. This means during the survey no new factors were suggested.
Of the 17 factors, three rated ‘moderate’ in influence and contract type occupied the top of this group. Seven factors were rated ‘high’ in terms of their influence, with environmental impact topping the list. Factors with a ‘very high’ influence rating comprised building type and location as the most influential of all of the 17 factors. The lowest standard deviations associated with these two factors relative to the others showed that the respondents were more consistent in their ratings than for the others. This indicated a strong consensus among the respondents concerning the high influence of these factors on the potential benefits prefabrication offers.
Building type as the most influential factor means that the amount of benefit the technology can offer could vary significantly depending on the type of building. This survey finding is consistent with the results of case studies, which showed variation in cost savings, time savings and productivity improvement across the five different building categories investigated in this research. This however is in contrast with a number of previous studies (Hamilton, 2007; Lusby et al. 2004) that reported prefabrication benefits across the board without qualifying the benefits in relation to the purpose group of the building.
Location as the second most influential factor on potential prefabrication benefits is understandable and is in agreement with the popular buzzword in the property circle that the three most important underpinnings of the attractiveness and value of a residential property value are ‘location’, ‘location’ and ‘location’. In a previous study, Burgess et al. (2013) noted their expectation that the benefits of prefabrication might mainly be limited to seven main cities in New Zealand including: Auckland, Christchurch, Dunedin, Hamilton, Napier, Tauranga and Wellington. Together with the third most influential factor – logistics, location impacts heavily on the potential benefits of prefabrication
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technology, depending on the distance between the construction site and the prefabrication factory site, as well as the logistics and other challenges involved in transporting the prefabricated components. Factors like cost of transportation, traffic challenges and risks of delay in supply make the use of prefabrication a less preferred alternative to the traditional construction method in remote areas.
The type of prefabrication is also listed as having a very high influence on the prefabrication benefits. This is because, for instance modular prefabrication is more suitable for high-rise buildings then a residential house due to the economies of scale. Similarly, whole building prefabrication is most suitable for motels and portable buildings.
7.2.3 Reliability and Validity of Research Outcomes
The third objective of this study was to examine how the benefits analysed from case studies of completed project records compared to survey results that involved feedback from industry stakeholders.
Achieving this objective required the use of the Student t-test to examine whether or not the average values of time and cost savings and productivity improvement analysed from the survey ratings would fit into the confidence interval value ranges established for these benefits in the case study results. The results showed no significant differences between the time and cost savings and productivity improvement values analysed from the case studies and the survey feedback. There was therefore empirical evidence to support the reliability and validity of the research findings based on the external construct validity test results. It could also be concluded that the findings of the study could be generalised beyond the study scope to wider settings.