Embodied Carbon Emissions and Direct Construction Costs of Modular Residential Buildings

The construction industry is experiencing poor profit margins and falling orders, and there is a dire need to improve its productivity. Research in the journal Buildings takes a look at modular building as a means of reducing emissions and increasing productivity, using South Korea as a case study. 

Study: Comparison of the Embodied Carbon Emissions and Direct Construction Costs for Modular and Conventional Residential Buildings in South Korea. Image Credit: vipman/Shutterstock.com

Construction corporations have started showing a substantial interest in modular construction methods, in which units are built under protected conditions in factories and then transported to a location for assembly and construction. Modular construction—a technology-intensive dry construction method—enhances construction efficiency and productivity.

New research in the journal Buildings analyzes the embodied carbon emissions and direct construction cost for a modular residential building’s production phase, and compares the findings with those of a conventional residential building. The study focuses on the material production phase, as it is reported that this phase results in increased embodied carbon emissions when compared to project stages.

Individual modules are assembled into the final building on-site using one of the modular construction approaches illustrated in Figure 1:

Figure 1. Modular construction methods, adapted from ref. Image Credit: Jang, et al., 2022

Enhanced quality, a quicker construction period, and sustainable building methods are three main advantages of modular construction, as modules can be produced in the factory next to the foundation work that is being performed at the site, thereby reducing the overall construction period and cost. Lastly, modular construction offers environmental advantages, with reduced use of on-site wet construction methods.

Figure 2. Comparison of modular and conventional RC construction methods, adapted from ref. Image Credit: Jang, et al., 2022

The scientists performed an environmental impact analysis and economic assessment of modular construction material production phases. For this method, a study was designed and performed to compensate for the lack of existing research.

Methodology

A modular residential building was analyzed for this study. Table 1 and Figure 3 present an overview and the front view of the project.

Figure 3. Front view of target building. Image Credit: Jang, et al., 2022

Table 1. Project overview. Source: Jang, et al., 2022

As depicted in Figure 4, the building is divided into three areas. However, for this study, only the B-wing that was constructed using a column and beam support structure was chosen for examination and compared to the same residential building.

Figure 4. Division of target building. Image Credit: Jang, et al., 2022

The study examined the embodied carbon emissions produced during the production stage depending on the major construction materials. The embodied carbon emissions produced by construction materials and used for residential buildings as an outcome of modular and RC construction methods are compared in Table 2.

Table 2. Quantity of major construction material using the two building systems. Source: Jang, et al., 2022

Table 3 lists the factors of embodied carbon emission in the production stage for various major construction components.

Table 3. Embodied carbon emission factors in the production phase for major construction materials. Source: Jang, et al., 2022

Table 4 presents the unit costs of key construction elements.

Table 4. Unit material cost of major construction materials. Source: Jang, et al., 2022

* 1 United States Dollar (USD) = 1240 Korea Won (KRW).

Results and Discussion

The results of the analysis of the embodied carbon emissions of the key construction materials employed in this study are shown in Table 5.

Table 5. Results of the assessment of the embodied carbon emissions. Source: Jang, et al., 2022

A comparison between the embodied carbon emissions required for the modular and RC construction methods is shown in Figure 5.

Figure 5. Comparison of the modular and RC building embodied carbon emissions. Image Credit: Jang, et al., 2022

Based on a detailed report of the national modular public housing demonstration complex project, the direct construction costs of the RC construction method and the modular construction method were examined.

The findings of the direct construction costs of both methods are shown in Figure 6 and Table 6.

Figure 6. Comparison of modular construction and RC construction costs. Image Credit: Jang, et al., 2022

Table 6. Direct construction costs for the modular and RC construction methods. Source: Jang, et al., 2022

* 1 USD = 1240 KRW.

When the overall direct construction cost of RC and modular construction methods are compared, the modular construction costs were 8.1% higher approximately. Nevertheless, considering the possibility of reusing the individual modules, material cost reduction is possible due to mass module production and enhanced work productivity. Thus, a reduction in the production unit cost over the module’s entire lifecycle is possible.

Hence, the construction industry is using more of the latest modular construction methods to enhance productivity.

The embodied carbon emissions and direct construction costs of the RC and modular methods were examined and compared. This assessment considered both environmental and economic factors, thereby validating the modular method’s efficiency and value for money.

The study results prove that modular construction can reduce embodied carbon emissions in the material production phase, when compared to the RC structure, despite an expensive direct construction cost.

Similar to the results of equivalent previous studies, this result is also considered in the same context as the finding that the RC structures’ environmental influence is greater when compared with the environmental impact of modular (steel) structures and RC structures (Table 7).

In addition to the already identified benefits of modular construction, it is expected that the modular construction application will also provide environmental benefits.

Table 7. Characteristics summary table of RC method and modular method. Source: Jang, et al., 2022

Conclusion

The study analyzed and compared the produced embodied carbon emissions and direct construction costs that occurred during the material production stage of a residential building. The results are compared for the modular and RC construction methods, enabling the calculation of the cost involved in these two methods and the determination of characteristics through an assessment of their environmental cost and performance.

As a result, the modular construction method decreased embodied carbon emissions in the material production phase by around 36%, when compared with the conventional RC method. This is directly related to the amount of ready-mix concrete used, along with its high embodied carbon emissions.

The comparison revealed that the modular method was more expensive. Nevertheless, due to the benefits of the modular construction method, which offers high-recycling rates and ease of repair, the cost results were not considered, requiring a further cost review to obtain a full-lifecycle perspective. The study dealt only with the initial phase of material production and excluded the reuse possibility, so the results show only a partial scenario.

Journal Reference:

Jang, H., Ahn, Y., Roh, S. (2022) Comparison of the Embodied Carbon Emissions and Direct Construction Costs for Modular and Conventional Residential Buildings in South Korea. Buildings, 12(1), p51; Available Online: https://www.mdpi.com/2075-5309/12/1/51/htm

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