1. Introduction
Since the beginning of the 21st century, technological advancements and industrial development led to significant increases in greenhouse gas emissions, exacerbating the global greenhouse effect and resulting in frequent extreme weather events and natural disasters [
1]. In response to these challenges, global attention to environmental issues intensified. In 1992, the United Nations General Assembly adopted the United Nations Framework Convention on Climate Change (UNFCCC), which aimed to reduce greenhouse gas emissions to mitigate dangerous disruptions to the climate system caused by human activities. In 2005, the Kyoto Protocol came into force, setting binding emission reduction targets for participating countries. This was followed by the Paris Agreement, which took effect in 2016, focusing on global cooperation to address climate change and limit global warming. At the end of 2020, China’s National Development and Reform Commission (NDRC) released the Action Plan for Carbon Peaking and Carbon Neutrality (2021–2025), which outlined the national goals for achieving peak carbon emissions and carbon neutrality for the first time. During the 75th session of the United Nations General Assembly, China pledged to peak carbon emissions by 2030 and achieve carbon neutrality by 2060, setting an ambitious “dual carbon” goal to completely eliminate or offset carbon dioxide emissions.
The Chinese government has long been committed to implementing carbon reduction policies. Starting in 2005, China introduced a series of new energy development plans focused on expanding clean energy sources such as wind, solar, and nuclear power. These initiatives aimed to increase the share of clean energy in the energy mix and decrease reliance on fossil fuels [
2]. In 2011, China began experimenting with carbon emissions trading by establishing pilot markets in cities such as Beijing and Shanghai. This marked the country’s initial foray into carbon trading mechanisms. By the end of 2020, China had officially launched a nationwide carbon emissions trading market. This market encompasses a wide range of sectors, including electricity, heat, cement, chemicals, metals, petrochemicals, automobiles, and public buildings [
3]. These policies significantly advanced China’s carbon reduction efforts, demonstrating the country’s commitment to mitigating climate change and transitioning towards a more sustainable energy system [
4].
The carbon emissions of China’s construction industry in 2020 were approximately 850 million tons of carbon dioxide, accounting for over 40% of the country’s total carbon emissions [
5]. Whether the Chinese construction industry can effectively reduce energy consumption became one of the main constraints on whether China can achieve the “dual carbon” goals on schedule. With the increase in China’s urbanization rate, the construction industry is expected to continue to grow to a certain extent, which will bring huge obstacles to the smooth implementation of China’s future carbon reduction plans [
6,
7]. Prefabricated buildings are recognized as one of the effective means to alleviate China’s current carbon emission contradiction due to their low cost, low energy consumption, and reduced material waste characteristics [
8,
9,
10]. In 2016, the State Council of China released the “Opinions of the State Council on Promoting High-Quality Development of the Construction Industry and Building Materials Industry”. This document directed provincial authorities to provide subsidies for projects that adhere to certification standards for prefabricated green buildings. Additionally, it emphasized the promotion of technological and process innovations related to prefabricated components within the construction sector [
11]. In the same year, the Ministry of Housing and Urban-Rural Development of China issued the “Action Plan for the Development of the Prefabricated Building Industry (2016–2020)”. This plan aimed to expedite the application of prefabricated materials in construction projects and set a target for the use of prefabricated technology in new buildings to exceed 30% within ten years Additionally, the Chinese government established 30 demonstration pilot cities and initiated 119 demonstration projects [
12]. which clarified the guiding ideology, overall goals, and key tasks for the development of prefabricated buildings in China in the next five years and pointed out the direction for the development of the industry. In the process of promoting prefabricated buildings, whether it can effectively promote the diversification of China’s construction industry’s energy structure is also one of the possible entry points for promoting China’s low-carbon transformation and development [
13,
14]. Therefore, this study evaluates the carbon reduction benefits of China’s prefabricated building policies by analyzing the energy efficiency of the construction industry across various regions before and after the implementation of these policies.
This article treats the implementation of prefabricated building policies as a quasi-natural experiment and employs the difference-in-differences (DID) method to assess the impact of these policies on carbon emissions associated with the output value of the construction industry. Utilize the propensity score matching with difference-in-differences (PSM-DID) methodology to conduct a further validation of the benchmark results. Additionally, a randomized repeated experiment was conducted to perform a placebo test. Mechanism analysis was carried out to identify the factors influencing the carbon emissions related to prefabricated building policies, explore the policy’s action mechanisms, and investigate strategies to enhance the policy’s effectiveness. The study also offers policy recommendations aimed at providing guidance for policy implementation and promotion.
2. Literature Review
The prefabricated construction industry chain encompasses a supply chain network that integrates various entities such as prefabricated component production factories, design units, transportation services, and construction firms. This chain is centered around the factory production of building components and includes upstream activities such as development and design, as well as downstream processes such as transportation and assembly. Internationally, countries such as the United States, the United Kingdom, Japan, Sweden, and Singapore are recognized as leaders in advancing the development of prefabricated buildings [
15,
16,
17]. In foreign countries, where prefabricated construction was established for a longer period, the industry achieved maturity in terms of its industrial chain, policy frameworks, and practical application of components. This maturity led to notable successes in addressing labor shortages and reducing building carbon emissions.
The factory production mode of prefabricated buildings is conducive to the rational allocation of resources and can achieve dual carbon reduction goals. Energy is considered one of the factors that have the greatest impact on buildings, and process innovation in the manufacturing stage of prefabricated components has a significant effect on improving energy efficiency [
18,
19]. The results of the literature review and investigation by Zhang et al. indicate that the use of prefabricated construction technology in China reduced the use of wood templates in construction equipment by 87% and water consumption by 70% [
20]. Compared to traditional cast-in-place buildings, the production process of prefabricated building components can reduce hidden carbon emissions by 15.6% and operational carbon emissions by 3.2% [
21,
22,
23], reducing energy consumption by 20.49% [
24,
25,
26]. Liu and Ying found through their research on a typical prefabricated building in Shanghai that adopting prefabricated building technology can effectively reduce the use of building materials and the generation of solid waste [
27]. By establishing a calculation model for energy consumption and waste flow, Chen et al. found that the use of prefabricated processes reduced material usage and energy consumption by 20%, as well as the production of greenhouse gases, such as carbon dioxide, by 20% [
24]. The above results indicate that prefabricated construction technology has a significant effect on reducing environmental benefits such as energy consumption, carbon emissions, and even acidic gases and water in the construction industry.
At present, research on carbon emission measurement methods for the entire industry is mainly divided into two categories [
28,
29,
30]: One type is based on the production end, which only considers the carbon emissions of the product production point (including exports) and no longer considers the product usage end. The other type is based on the consumer end, which is exactly opposite to the production end, that is, only considering the carbon emissions of the product’s consumer end (including exports), without considering the production end [
31,
32]. Currently, what is more widely recognized in academia is the consumption-based carbon emission calculation, such as Zhang et al., who used the consumption-based method to complete the carbon emission accounting for Chinese cities [
33]. Steininger et al. argued through a comparative study of two methods that consumer-based carbon emission policies are more conducive to improving the cost-effectiveness and fairness of industries [
31]. Guan et al. believe that consumer-based carbon emission accounting can effectively alleviate global climate issues [
34]. The traditional research methods for carbon emissions in the construction industry mainly include process analysis, the input–output method, and mixed method [
35,
36]. Process analysis is based on the energy consumption and other characteristics of the entire life cycle of buildings, combined with carbon emission factors based on the Intergovernmental Panel on Climate Change (IPCC) and the China Life Cycle Database (CLCD) [
22]. We can accurately calculate the carbon emissions value throughout the entire lifecycle of the building [
37,
38]. Regarding the output method, some scholars used input–output analysis to study the carbon emissions and energy consumption of buildings in Ireland, and found that infrastructure generates approximately 11.7% of carbon emissions [
39]. The mixed rule is a method that combines process analysis and input–output methods to produce results. Considering the complexity of the construction industry involving multiple industrial sectors and the need for research, this article adopts a combined approach based on consumer end and construction process analysis to study the carbon emission accounting of prefabricated construction industry. This means that the entire construction industry process, including materials, manpower, transportation, and other aspects, consumes a large amount of energy such as oil, electricity, and coal, which are all accounted for.
The research methods for calculating energy consumption are also becoming more mature, mainly divided into single factor energy efficiency (SFEE) and total factor energy efficiency [
40,
41]. Single factor measurement considers energy itself as the sole input factor [
42], and all factor energy efficiency measures energy efficiency by considering the actual energy consumption of the entire building [
43]. The current mainstream analysis of total factor energy consumption is the economic heat index, which refers to the ratio of economic output to energy consumption of an industry as an indicator of energy efficiency. The method of total factor energy efficiency analysis needs to fully consider various outputs and inputs of the industry, including not only energy consumption, but also many industrial factors such as capital and labor [
44]. At present, experts in the industry have different opinions on the accurate selection of input and output factors, and consensus is yet to be formed, which is still in the exploratory stage [
45]. Compared to this, the measurement process of single-factor energy efficiency is more direct and simple. Therefore, this article adopts the ratio of economic output to energy consumption in the single factor energy efficiency research method as the method to measure the energy efficiency of the construction industry.
In the field of analyzing factors affecting carbon emissions, Li and Liu et al. believe that energy, building materials, and machinery are the main sources of carbon emissions in the construction industry [
46]. Agi, Diabat et al. divided the factors that affect carbon emissions in the construction industry into five major factors: government, market, technology, society and culture, and supply chain coordination, and emphasized the importance of policies [
47,
48,
49]. Sun Shao nan et al. divided the influencing factors into five aspects when considering the effect of prefabricated carbon reduction: design planning, building materials, energy use, building environment, and construction organization [
50]. Liang et al. identified urbanization, per capita GDP, technology and equipment ratio, energy consumption structure, innovation support, environmental regulation, industrial contribution rate, and industrial concentration as external factors affecting carbon emissions in the construction industry [
4]. Du, Zhou, and others believe that the mechanical equipment rate and technological innovation of construction enterprises are important factors affecting building carbon emissions [
51]. In addition, as prefabricated buildings are an emerging technology, the introduction of relevant policies will to some extent promote technological innovation in relevant regions, and technological innovation will also have a significant impact on building carbon emissions. Therefore, this study considers regional technological innovation as one of the factors that may affect carbon emissions in the construction industry.
It is evident from the above results that while current research methods and systems for studying carbon emissions in the construction industry are relatively comprehensive, there remains a significant gap in the systematic evaluation of the overall effectiveness of China’s prefabricated building policy system. This study introduces several key innovations compared to prior research: (1) Provincial-Level Systematic Evaluation: It is the first comprehensive assessment of the overall energy consumption impacts of prefabricated building policies on the construction industry from a provincial perspective. This approach addresses the existing gap in the quantitative evaluation of these policies’ environmental benefits in China. (2) Advanced Methodology: By employing the difference-in-differences (DID) model and utilizing provincial panel data, the study effectively minimizes the impact of randomness and micro-level specificity. This enhances the objectivity of the results, providing a more reliable basis for policy reference. (3) Confirmed Benefits and In-Depth Analysis: The study validates the positive effects of prefabricated building policies and offers a systematic analysis of the influencing factors. These insights contribute practical recommendations for the further refinement and promotion of these policies, offering valuable guidance for decision-makers.
6. Mechanism Variables Analysis
Following the benchmark regression and robustness testing, the study confirms the benefits of prefabricated building policies on carbon emission efficiency and validates the experimental results. The next phase involves examining how these policies affect carbon emission efficiency through mechanism analysis. This analysis will categorize carbon emissions in construction into labor, materials, and machinery. Using Model (2), the study will assess labor productivity, material utilization rates, and mechanical power rates as mediating variables to explore their roles in the relationship between the policy and carbon emission efficiency.
Table 8 mechanism analysis shows that the core explanatory variable’s coefficient for labor productivity is positive and significant at the 1% level in both columns (1) and (2), demonstrating that the prefabricated construction policy enhances labor efficiency. The bootstrap algorithm’s parameter interval [0.0892–0.4568] supports the confidence in the coefficient of 0.432 in column (3) in
Table 8, confirming that labor productivity significantly mediates the relationship between the policy and carbon emission efficiency. Thus, the prefabricated building policy improves carbon emission efficiency by enhancing labor productivity in the construction industry.
In column (4) of
Table 8, the coefficient for the mechanical power rate is positive and significant at the 1% level, indicating that prefabricated construction policies enhance the mechanical power rate in construction enterprises. This aligns with the benchmark regression’s finding that a higher per capita technical equipment rate negatively correlates with carbon emission efficiency. The use of prefabricated components appears to increase machinery utilization and encourages the updating of construction equipment, leading to better resource allocation. The coefficient for mechanical power rate as an intermediary variable in column (6) is 0.470 within the confidence interval of [0.0758, 0.4870]. This confirms that prefabricated construction policies contribute to the optimal allocation of mechanical resources, thereby improving carbon emission efficiency.
In columns (7) and (8) of
Table 8 the core explanatory variable coefficients for material utilization are positive and significant at the 1% level. This suggests that prefabricated building policies enhance the material utilization rate in construction enterprises. Prefabricated construction shifts component production from sites to factories, where skilled workers operate in controlled environments, leading to more efficient production, reduced energy consumption, less waste, and fewer defects. The coefficient in column (9) is 0.438, which falls within the bootstrap algorithm’s confidence interval [0.0931, 0.4553]. Thus, it is evident that prefabricated building policies improve material utilization efficiency, contributing to better carbon emission efficiency in buildings.
8. Conclusions and Policy Recommendations
8.1. Research Conclusions
The study aims to assess the carbon emission efficiency of China’s construction industry by analyzing the total output value per ton of carbon dioxide emitted. Utilizing various methods, including the double difference method, parallel trend test, benchmark regression, robustness and heterogeneity analysis, and mechanism analysis, the research explores the impacts of prefabricated building policies. The key conclusions are:
Improvement in carbon emission efficiency: The implementation of prefabricated building policies significantly enhanced the carbon emission efficiency of China’s construction industry. As the industrial chain matures, the benefits of these policies are expanding.
Policy focus areas: the prefabricated construction policy positively influences carbon emission efficiency through improvements in labor productivity, mechanical power rate, and material utilization rate.
Effects of control variables: In addition to the core variables, regional technological innovation, per capita GDP, and environmental protection also positively impact carbon emission efficiency. Conversely, energy structure and the technology assembly rate of construction enterprises negatively affect carbon emission efficiency.
8.2. Research Limitations
This study adopts a provincial-level perspective on the construction industry and relies primarily on macro panel data. Given the varying priorities placed on economic development and environmental policies across different provinces, as well as their fluctuations over time, there may be discrepancies in the implementation and promotion of prefabricated building policies across different years. To maintain the coherence and feasibility of the research, this study idealized these changing factors. Consequently, further investigation is recommended to more precisely evaluate the carbon emission benefits of prefabricated buildings, considering these temporal and spatial variations. Secondly, there is a current lack of precise quantitative measurement systems for assessing the impact of various variables on carbon emissions in the construction industry. Developing a comprehensive indicator system to evaluate the effects of these variables on carbon emissions may be an area for future research.
8.3. Policy Recommendations
The policy recommendations based on the research findings are as follows: (1) Sustainability and delays: Recognize that the benefits of prefabricated building policies may experience delays. Governments should ensure the sustainability of policy implementation, focus on the maturity of the industrial chain, and consider the time and capital costs associated with technology. (2) Technological innovation: Promote technological research and innovation by establishing special funds for new prefabricated building technologies. Offer innovation subsidies and tax incentives to encourage enterprises to invest in R&D, enhance technological innovation, and accelerate the industry’s maturation. Implement policies to improve material utilization and recycling in prefabricated construction, encourage the use of high-performance, eco-friendly materials, and establish standards for material usage and waste reduction. (3) Energy structure adjustment: Introduce policies to adjust the local energy structure by replacing traditional energy sources with clean energy and diversifying energy sources. Enforce restrictions on excessive carbon emissions, establish a coal consumption cap with gradual reductions, and support the technological transformation of prefabricated construction enterprises to enhance energy efficiency. (4) Performance evaluation and management: Develop performance evaluation systems to improve construction enterprise management, provide systematic training for construction workers, and boost labor productivity. Implement incentive mechanisms to phase out inefficient machinery, reduce wasteful equipment, and adopt efficient construction techniques to optimize resource allocation and enhance mechanical power efficiency.