Life Cycle Sustainability Assessment of Building Construction: A Case Study in China

Abstract

Life cycle sustainability assessment (LCSA) has been increasingly implemented in a wide spectrum of products. Considering the vital importance of buildings to human lives, it is surprising that there have been few LCSA case studies of buildings from mainland China, which boasts the largest developing economy in the world. This study aims to implement LCSA in a typical residential building project in China. The three areas of protections (AoPs) are integrated into an overarching LCSA framework by applying the analytic hierarchy process (AHP) method. It is found that the building project has less impacts of climate change, acidification and human toxicity, but greater impacts of ozone depletion and freshwater eutrophication, as compared to benchmarks of buildings. The sustainability single score is estimated to be 71.5/100, with 40.86% caused by the environmental impact, 29.68% by the economic impact and 29.46% by the social impact. The sustainability results of the studied case are further compared with an existing study in Hong Kong. The results would contribute to the knowledge and understanding of the sustainability performance of buildings in China. The methodology presented in this study can contribute to further improvements in LCSA evaluation, both regionally and globally.

1. Introduction

Life cycle sustainability assessment (LCSA) combines life cycle assessment (LCA), life cycle costing (LCC) and social life cycle assessment (S-LCA) and provides quantitative evaluations in the three areas of protection (AoPs), namely environment, economy and society [1,2]. LCSA can be dated back to Kloepffer [3], with a conceptual formula, LCSA = LCA + LCC + S-LCA. Ever since, LCSA has been adopted in different disciplines, including environmental science, engineering, energy, social science, business, management, accounting, economics, computer science, chemistry, etc. [4]. A growing trend of LCSA studies was observed in the last decade, with an annual publication peak of 26 articles in 2019 [5].

LCSA has been increasingly applied to the analysis of sustainability performance of buildings. Onat et al. [6] was one of the first attempts that applied LCSA to buildings. They studied residential and commercial buildings in the United States using an input–output-based hybrid model and analyzed 16 macro-level indicators. Hossaini et al. [7] integrated LCSA with the Analytical Hierarchy Process (AHP) to compare wood and concrete structures for a six-story building in Vancouver. Janjua et al. [8] compared two residential buildings in Australia, based on LCSA, by evaluating six sustainability categories, i.e., greenhouse gases, embodied energy, cost, gross benefit, working conditions and equal opportunity. In integrating the three pillars and trying to select the best option, the multi-attribute decision making (MADM) method has been adopted in the LCSA of buildings and construction [9,10]. Recently, LCSA has also been combined with building information modeling (BIM). For example, Filho et al. [11] developed a framework based on BIM and LCSA to select materials for low-income house in Spain.

The LCSA case studies of building were mostly carried out in the developed or the English-speaking countries, for example, the United States [12], Malaysia [13], Singapore [14], Australia [15], Brazil [16], India [17] and Spain [18]. Considering the largest developing country, China, the building industry contributes to 25% of its Gross Domestic Product (GDP). The construction area in China increases at a rate of 2.5 billion m² per year [19,20]. Unfortunately, there are very few published LCSA studies of buildings in mainland China. Most of the existing studies adopted life cycle assessment (LCA) and focused on the single dimension of environment (e.g., [21,22]). Only recently have some studies integrated life cycle costing (LCC) and LCA to balance environmental and economic impacts of buildings [23]. The policies in China mainly focus on carbon reduction, while an integrated assessment of the other environmental impacts, together with the economic and social impacts, are less emphasized.

The lack of LCSA studies of buildings can lead to a range of problems for decision makers. In our previous studies, a series of life cycle models were established for building construction, namely the Environmental Model of Construction (EMoC), the Cost Model of Construction (CMoC) and the Social-impact Model of Construction (SMoC) [24,25,26]. These models were developed based on the building industry in the Hong Kong Special Administrative Region (HKSAR) and successfully applied to a typical public housing project. Considering mainland China, several research questions need to be answered: (i) What are the life cycle environmental, economic and social impacts of a building project? (ii) What are the differences in sustainability performance between buildings in cities in southern and northern China?

In order to fill these research gaps, this study attempts to apply the three models, i.e., EMoC, CMoC and SMoC, to typical residential building projects in mainland China. As demonstrated in Figure 1, the three models are integrated into a framework of LCSA. The analytic hierarchy process (AHP) method is employed to normalize the indicators, including 18 midpoint and 3 endpoint indicators in LCA, 2 indicators in LCC and 13 indicators in S-LCA. The LCSA case study is subsequently conducted for a building project in the city of Qingdao, China. Lastly, the results from this study are compared with our previous studies. As one of the first attempts to apply LCSA in buildings in mainland China, this study can help pave the way for the applications of LCSA in China. The methodology presented in this study may contribute to further improvements in LCSA evaluations regionally and globally.

2. Methods

2.1. Life Cycle Models

The three life cycle models, namely EMoC, CMoC and SMoC, were applied and a set of functional worksheets were designed to facilitate data input, calculation, data documentation and the presentation of results [24,25,26]. The three models share a consistent system boundary to cover the “cradle-to-end-of-construction” processes, including raw material acquisition, material manufacturing, transportation and on-site construction. The results from EMoC and CMoC can be linked to the construction area, while the results from SMoC are only applicable to the entire building project. Details of each model and the adjustments made in this study are described as follows.

EMoC [24] contains 11 worksheets with different functions of instruction, input, calculation, data documentation and results presentation. The model gives midpoint and endpoint results based on ReCiPe [27,28]. At the midpoint level, the model provides analysis of the following impact categories: particulate matter, ozone depletion, ionizing radiation, human toxicity (cancer), human toxicity (non-cancer), global warming, photochemical oxidant formation, freshwater ecotoxicity, freshwater eutrophication, terrestrial ecotoxicity, terrestrial acidification, agricultural land occupation, urban land occupation, natural land transformation, marine ecotoxicity, metal depletion and fossil resources. At the endpoint level, three damage categories are analyzed: human health, ecosystems and resources. The normalization and the weighting are also provided in EMoC based on ReCiPe 2008. To adjust EMoC in accordance with the context of other cities, in particular for the case building located in Shandong, China, the “Input” worksheet provided options of four project regions: Shandong, Shenzhen, Hong Kong and other places in China. The electricity mix in the four regions was provided in the “Energy” worksheet. The model shall provide results of the total impacts of the building project, as well as impacts per gross floor area (GFA) for over 200 items.

Analogue to EMoC, the model CMoC was developed for the cost [26]. It contains 9 worksheets, including Welcome, Input, Resources, Material, Plant, Labor, Waste treatment, Externalities and Results. In the “Input” worksheet, users enter project-specific information, such as the project information of location and number of units, resource consumption, material and components, plants, employment, waste treatment and externalities. The externalities are calculated using the endpoint damage results from EMoC. In the “Results” worksheet, the costs of over 100 items of the building project are provided in six categories, i.e., material, resource, plant, labor, waste and externality.

SMoC is an S-LCA model of building projects [25]. The model contains 9 worksheets, including Welcome, Input, Calculation, sLCIA, Construction, National (background data) and Results. In the “Input” worksheet, the building project information of resource consumption, materials and components, and on-site construction activities should be entered. The “Results” worksheet provides the social impacts of resource, material and construction. SMoC is capable of calculating 13 subcategories for the three stakeholders, i.e., worker, community and society. The results are subject to normalization and weighting. A single score is calculated to represent the social performance of the building.

2.2. Integration of the Three Pillars

The harmonization of the three pillars has been regarded as one of the main challenges in the methodology of LCSA of buildings [29]. According to Alejandrino et al. [30], three approaches are available for the integration of the three pillars: (i) multi-attribute decision making (MADM), (ii) multi-objective decision making (MODM), and (iii) data envelopment analysis (DEA). The MADM methods have been recognized as the most widely adopted in LCSA case studies [31]. For example, Balasbaneh et al. [32] conducted LCSA for prefabricated construction and applied MADM to reveal the best option. However, sometimes with MADM, the decisions were made based on multiple but conflicting criteria [33]. The analytic hierarchy process (AHP) is an appropriate MADM scheme that can combine the multiple criteria and include the opinions of stakeholders, leading to reasonable final results for decision making [30]. AHP is selected for the LCSA integration in this study, as it is the most widely used approach for decision making and has been extensively applied in LCSA [10]. The hierarchy of the proposed AHP integration method is shown in Figure 2. There are four levels of the hierarchy: Level 1 is the integrated sustainability single score, Level 2 refers to the three pillars, Level 3 is for the endpoint or stakeholder categories and Level 4 refers to the impact categories.

The calculation of the environmental score is according to the standard procedures of LCIA, including characterization, normalization and weighting. The environmental single score is calculated using ReCiPe Endpoint World H/A, giving:

$$ENor{m}_i={CharaEnd}_i\times ENormFac{t}_i$$

(1)

$$ED{Norm}_j=\sum _{i\in J}ENor{m}_i$$

(2)

$$ES=\sum _{j}EDNor{m}_j$$

(3)

where $ENor{m}_i$ is the environmental normalization result of the ith impact category, ${CharaEnd}_i$ is the endpoint characterization of the ith impact category and $ENormFac{t}_i$ is the endpoint normalization factor of the ith impact category. $ED{Norm}_j$ is the normalization result of the jth damage category and $ES$ is the environmental score.

The economic score is the construction cost of the studied project. The social score is calculated following a procedure based on Dong and Ng [25],

$$SS{H}_j=\frac{\sum _{i\in J}SC{h}_i\times {SN}_i\times S{W}_i}{13}$$

(4)

$$SS=\sum _{j}SS{H}_j$$

(5)

where $SS{H}_j$ is the result of the jth social stakeholder, $SC{h}_i$ is the social characterization results of the ith impact category, ${SN}_i$ is the social normalization factor of the ith impact category and $S{W}_i$ is the social weighting factor of the ith impact category. $SS$ is the social score of the studied project.

The sustainability single score $SSS$ can then be calculated as follows:

$$SSS=ES\times {N_E\times W}_E+EcoS\times N_{Eco}\times W_{Eco}+SS\times N_S\times W_S$$

(6)

where $EcoS$ is the Economic score. $N_E$, $N_{Eco}$ and $N_S$ are the normalization factors of the environment, economy and society pillars. $W_E$, $W_{Eco}$ and $W_S$ are the weighting factors of the three pillars, respectively.

2.3. Description of the Studied Case

The studied building project is located in Qingdao, Shandong Province, China. The building project has two towers, with a construction area of 35,000 m², providing 204 apartments. The structure of buildings is reinforced concrete. The functional unit of this study is the building project, while LCA and LCC results are normalized to 1 m² of the construction area. We selected this building project as the study case for the following reasons: (i) the building project is a typical residential building with apartments of 2 or 3 bedrooms and 15–20 floors; (ii) the location of the building is in the northern part of China, in contrast with our previous in the southern part of China; (iii) the completeness of the LCA model was evaluated [34], so that the quality of the data input can be guaranteed.

2.4. Goal and Scope Definition

The life cycle includes the “cradle to end of construction” stages. The use stage and the end-of-life stages are excluded for two reasons: (i) the lack of information in the two stages; and (ii) the three models, EMoC, CMoC and SMoC, do not cover the two downstream stages. The studied system is presented in detail in Figure 3. In the pre-construction stage, raw material acquisition, manufacturing and transportation to the construction site are included. Primary materials are accounted for, including concrete, brick, block, paint, aluminum, timber formwork and rebar. At the construction site, construction activities are considered, including concreting, placement of concrete, installation and recycling of construction wastes. The main concrete type used in the project was C30, together with C15 and C20. The timber formwork was reused and then delivered back to the factory for recycling. The waste concrete was used for on-site pavement, and the remaining waste concrete was recycled. The waste steel was further processed to embedded parts. The rest of waste steel was recycled to the factory. Electricity, water, diesel and gasoline consumption are considered.

2.5. Life Cycle Inventory

The input data for EMoC, CMoC and SMoC were obtained from a questionnaire survey to the project manager, followed by telephone interviews. After several rounds of telephone interviews to the project manager, we obtained more project information and the data were further updated as compared to Dong et al. [34].

The input data for the LCA model (EMoC) and LCC model (CMoC) are given in

Table 1. Data input of LCA and LCC models (partially based on Dong et al. [34]).

Category	Item	Amount	Unit
Material	Concrete C15	1000	m3
	Concrete C20	800	m3
	Concrete C30	17,200	m3
	Brick	8000	m2
	Aluminum	12,000	m2
	Cement	60,000	kg
	Plaster	15,000	kg
	Rebar	2750	ton
	Glass	150,000	kg
	Timber formwork	12,000	m2
Transport	Ready-mix concrete	5	km
	Cement	5	km
	Plaster	5	km
	Aluminum	5	km
	Timber formwork	5	km
	Rebar	10	km
	Brick	25	km
	Glass	5	km
	Tower crane	10	km
	Hoist	10	km
	Excavator	10	km
Energy and Resource	Electricity	225,000	kWh
	Diesel	1000	L
	Water	20,000,000	L
	Gasoline	6800	L
Construction Waste	Waste concrete	1%
	Waste rebar	2%
	Waste brick	2%
	Waste cement	1%

. The concrete types (C15, C20 and C30) are specified and the transport of materials and the equipment are accounted for. The information about the equipment was provided by the project manager in an equipment list. The transport of the on-site equipment is considered. Waste concrete and rebar are recycled, while timber formwork is reused on-site and then recycled. The other construction wastes are delivered to the landfills.

The inputs of the S-LCA model include the profile of the respondent, general project information, resource consumption, material and components and on-site construction. The country of origin of the materials and resources should be selected, as this can determine the social background of the project. The building project was located in Shandong, China, and all the materials and components were purchased in China. Therefore, the country of origin for all the variables is China. For the on-site construction, the model SMoC provides a list of construction activities, as shown in

Table 2. On-site construction activities of the building project.

Item	Included in the Project (Yes/No)
Precast concrete element	No
Dust reduction by spraying water	Yes
Dust reduction by hard pavement	Yes
Dust or noise reduction by physical barrier	Yes
Adoption of biofuel	No
Waste material recycling	Yes
Adoption of EURO 5 trucks	Yes
Generation of on-site renewable energy	No
Natural ventilation	Yes
Steel formwork	No
Lift modernization program	No
LED Bulkhead Light Fittings and two-level Lighting System	No
Twin water tanks and rainwater harvesting system	No
On-site measures, e.g., metal hoarding and scaffolding	Yes
Green roof and enhanced tree protection measures	No
Specification, e.g., VOC free deep penetrating water proofing treatment	No
Application of dual flush water and sensor faucet	No
On-site stormwater management	No
Safety provisions on site for workers to use	Yes
Waste sorting room in building	No
Design (recycling at source)	No
Water capture + recycling	No
Apprenticeships	No
Communication with local schools/groups	Yes

.

3. Results

3.1. LCA Results

The midpoint characterization results of the studied building project are given in

Table 3. Midpoint and endpoint LCA results of environmental impact categories for the studied building project.

Impact Category	Midpoint				Endpoint
	Project	Per Unit	Per GFA (m2)	Unit	Project	Per Unit	Per GFA (m2)	Unit
Climate change	1.75 × 107	8.59 × 104	5.01 × 102	kg CO2 eq	2.45 × 101	1.20 × 10−1	0.00070078	DALY
Climate change Ecosystems					1.39 × 10−1	6.81 × 10−4	3.97 × 10−6	species.yr
Ozone depletion	1.08	5.30 × 10−3	3.09 × 10−5	kg CFC-11 eq	2.82 × 10−3	1.38 × 10−5	8.0642 × 10−8	DALY
Human toxicity	6.21 × 106	3.04 × 104	1.77 × 102	kg 1,4-DB eq	4.34	2.13 × 10−2	0.00012409	DALY
Photochemical oxidant formation	4.74 × 104	2.32 × 102	1.35	kg NMVOC	1.85 × 10−3	9.06 × 10−6	5.2827 × 10−8	DALY
Particulate matter formation	3.16 × 104	1.55 × 102	9.02 × 10−1	kg PM10 eq	8.10	3.97 × 10−2	0.00023458	DALY
Ionizing radiation	3.26 × 106	1.60 × 104	9.33 × 101	kg U235 eq	5.35 × 10−2	2.62 × 10−4	1.5296 × 10−6	DALY
Terrestrial acidification	5.50 × 104	2.70 × 102	1.57	kg SO2 eq	3.19 × 10−4	1.56 × 10−6	9.1158 × 10−9	species.yr
Freshwater eutrophication	5.57 × 103	2.73 × 101	1.59 × 10−1	kg P eq	2.45 × 10−4	1.20 × 10−6	6.9894 × 10−9	species.yr
Marine eutrophication	2.56 × 103	1.26 × 101	7.33 × 10−2	kg N eq				species.yr
Terrestrial ecotoxicity	2.07 × 103	1.01 × 101	5.92 × 10−2	kg 1,4-DB eq	2.63 × 10−4	1.29 × 10−6	7.5158 × 10−9	species.yr
Freshwater ecotoxicity	1.38 × 105	6.77 × 102	3.94	kg 1,4-DB eq	3.59 × 10−5	1.76 × 10−7	1.0265 × 10−9	species.yr
Marine ecotoxicity	1.43 × 105	6.99 × 102	4.07	kg 1,4-DB eq	1.14 × 10−7	5.59 × 10−10	3.2607 × 10−12	species.yr
Agricultural land occupation	2.70 × 106	1.32 × 104	7.70 × 101	m2a	3.02 × 10−2	1.48 × 10−4	8.6282 × 10−7	species.yr
Urban land occupation	1.58 × 105	7.74 × 102	4.51	m2a	3.05 × 10−3	1.49 × 10−5	8.7043 × 10−8	species.yr
Natural land transformation	2.99 × 103	1.47 × 101	8.55 × 10−2	m2	4.65 × 10−3	2.28 × 10−5	1.3291 × 10−7	species.yr
Water depletion	1.63 × 105	7.99 × 102	4.66	m3				$
Metal depletion	2.95 × 106	1.45 × 104	8.42 × 101	kg Fe eq	2.11 × 105	1.03 × 103	6.02	$
Fossil depletion	4.07 × 106	1.99 × 104	1.16 × 102	kg oil eq	6.54 × 107	3.20 × 105	1.87 × 103

. The LCA results are also presented per unit apartment and per 1 m² floor area. It was found that the entire building project emits 1.75 × 10⁷ kg CO₂ eq, and this is equivalent to carbon emissions generated by 2305 citizens in one year in the city of Qingdao, China (7.6 tons CO₂ eq per capita per year). Dong et al. [35] provided the median emissions of seven impact categories of buildings, which can be referenced to understand the results of the studied building project. The building project emits 500 kg CO₂ eq/m², and this is similar to the median emission of residential buildings, 498 kg CO₂ eq/m². For the ozone depletion, the project emits 3.09 × 10⁻⁵ kg CFC-11 eq/m², which is greater than the median emission of residential buildings at 9.3 × 10⁻⁶ kg CFC-11 eq/m². The large impacts of ozone depletion are mainly caused by concrete (48%), aluminum (63.6%) and rebar (29.6%). For acidification, the studied project generates 1.57 kg SO₂ eq/m², and this is much lower than the median emission of residential buildings (2.79 kg SO₂ eq/m²). For the freshwater eutrophication, the studied project has 0.159 kg P eq/m² (0.487 kg PO₄ eq/m²), and this is larger than 0.270 kg PO₄ eq/m² of the median residential building. The large eutrophication impacts are also caused by concrete, aluminum and rebar in the material stage. For human toxicity, the studied project emits 177 kg 1,4-DB eq/m², which is less than the median of buildings, 284 kg 1,4-DB eq/m².

The contributions from processes/materials to each impact category are shown in Figure 4. The breakdown details are given in the Supplementary Material (Table S1). It is found that materials contribute the most for all impact categories (>92%). For the impact categories of ionizing radiation, freshwater eutrophication, marine eutrophication, terrestrial ecotoxicity, freshwater ecotoxicity and marine ecotoxicity, materials contribute more than 99% to the impacts of the pre-use stages. Most of the emissions are attributed to aluminum, rebar and concrete. On the other hand, energy and waste have much smaller emissions. For instance, the on-site energy consumption contributes only 3% to the pre-use carbon emissions and 2% to the pre-use energy consumption.

The midpoint and endpoint normalization results of the impact categories are shown in Figure 5. The midpoint normalization results are apparently larger than the endpoint normalization results. For the midpoints, marine ecotoxicity, human toxicity, freshwater ecotoxicity and freshwater eutrophication are larger than 10,000 pt. On the other hand, agriculture land occupation, terrestrial ecotoxicity, natural land occupation and ozone depletion are lower than 500 pt. The midpoint normalization result of climate change is 2542 pt, ranked 12th among all impact categories. The endpoint results of fossil fuel depletion and climate change are ranked the highest, while the third significant impact category is particulate matter formation. Ironically, marine ecotoxicity, which is ranked the highest in the midpoint normalization results, is ranked the lowest in the endpoint results.

The endpoint results are calculated for each impact category, as well as for the damage categories (Table S1). The project leads to 1.06 × 10⁻³ DALY/m² of human health, 5.08 × 10⁻⁶ species. yr/m² of ecosystem, and 1873 USD/m² loss of resources. In Figure 6, the breakdown of the endpoint weighting results is shown. The inner pie shows the contributions from damage categories. It is found that human health accounts for 62% of the weighting score, mainly contributed by climate change–human health (41%), human toxicity (7%) and particulate matter (14%). Resources is the second largest contributor to the weighting score, contributing 33%, which is mainly due to fossil depletion. Ecosystems account for only 1% of the weighting score, mostly contributed by climate changes in the ecosystem.

3.2. LCC Results

The construction cost of the studied project is 3633 RMB/m². In addition to the internal construction cost, the external cost due to environmental impacts was calculated. Unfortunately, the environmental cost is much greater than the construction cost, which is 8.26 × 10¹¹ RMB/m². In CMoC, the external environmental cost is calculated using the damage cost to human health, ecosystem and resources. According to Heijungs [36], the environmental cost of 1 DALY is USD 60,000 and 1 species*yr is USD 1.75 × 10¹¹. Therefore, if the external environmental cost is evaluated based on damage cost, the results of the external costs will be much higher, as shown in this case.

3.3. S-LCA Results

The characterization results of S-LCA are shown in Figure 7 and the detailed data are provided in Table S2. It was found that the studied project has positive impacts for most of the impact categories, in particular for local employment, fair salary, working hours and health and safety, with social impact indicators larger than 0.75. The positive impacts of these categories are mainly caused by the positive impacts of materials (>60%). In addition, the positive impacts of safe/healthy living conditions, public commitments to sustainable issues and community engagement are due to the positive impacts of on-site construction (>60%). On the other hand, the two categories, freedom of association and collective bargaining and forced labor, have negative impacts, primarily due to the negative background value of materials.

The weighting results are given in

Table 4. S-LCA weighting results of the studied project.

Stakeholder	Impact Category	Resource	Material	Construction	Total
Worker	1 Freedom of association and collective bargaining	−1.36 × 10−2	−2.91	0.00	−2.93
	2 Child labor	6.99 × 10−3	1.50	0.00	1.51
	3 Fair salary	1.67 × 10−2	3.59	−5.45 × 10−2	3.55
	4 Working hours	1.55 × 10−2	3.33	−1.01 × 10−1	3.25
	5 Forced labors	−4.59 × 10−3	−9.87 × 10−1	−9.07 × 10−2	−1.08
	6 Equal opportunities/discrimination	3.00 × 10−3	6.43 × 10−1	−4.88 × 10−2	5.97 × 10−1
	7 Health and safety	1.07 × 10−2	2.31	1.01	3.33
Local Community	8 Access to material resources (e.g., sanitation, school)	4.40 × 10−3	9.45 × 10−1	4.77 × 10−2	9.97 × 10−1
	9 Cultural heritages	0.00	0.00	8.91 × 10−2	8.91 × 10−2
	10 Safe/healthy living conditions	2.98 × 10−3	6.41 × 10−1	1.22	1.87
	11 Community engagement	−3.90 × 10−3	−8.37 × 10−1	5.82 × 10−1	9.03 × 10−1
	12 Local employment	−3.90 × 10−3	−8.37 × 10−1	3.43 × 10−1	3.30
Society	13 Public commitments to sustainability issues	1.49 × 10−3	3.20 × 10−1	1.14	1.14
Worker		1.37 × 10−2	2.94	5.49 × 10−2	6.44 × 10−1
Local Community		0.00	0.00	1.76 × 10−1	5.83 × 10−1
Society		2.68 × 10−3	5.75 × 10−1	8.77 × 10−2	9.56 × 10−2
Score		1.74 × 10−3	3.73 × 10−1	3.18 × 10−1	1.32

. It was found that the weighting results of most impact categories are positive, except for freedom of association and collective bargaining and forced labor. This finding is consistent with the characterization results. The rankings of the impact categories in terms of the weighting results are also analogue to the characterization results. The results of stakeholders are 0.64 for the worker, 0.58 for the local community and 0.095 for society. The social single score is 1.32 for the entire project, which is a positive figure. The single score is 49% contributed by workers, 44% by the local community and 7% by society.

3.4. Integration of the Three Pillars

The sustainability single score $SSS$ is calculated using Equation (6). In this study, the equal weighting factors of 33.33% are used for the three pillars. It was found that the studied project has a $SSS$ of 71.5, with 100 being the best and 0 the worst. The contributions from the three pillars to the $SSS$ are shown in Figure 8. The weighted environmental score is 29.2 (40.86% of the $SSS$), the weighted economic score is 21.2 (29.68% of the $SSS$) and the weighted social score is 21.1 (29.46% of the $SSS$).

3.5. Interpretation

The results of the Qingdao case are compared with our previous work of a residential building project in Hong Kong [26]. The characterization results of midpoint impact categories and endpoint damage categories of Qingdao and those of Hong Kong are analyzed to calculate the ratio of the results of two building projects. In order to fairly compare the two case studies, the per construction area results are used to calculate the ratios. As shown in Figure 9, it was found that the environmental impacts of the Qingdao case are apparently smaller than the Hong Kong case, as most of the ratios are less than 100%. For most of the impact categories, the environmental impacts of the Qingdao case are only less than 70% of the Hong Kong case. In terms of the damage categories, the ratio of human health is 68%, that of ecosystems is 60% and that of resources is 69%, implying that the environmental performance of the Qingdao case is better than that of the Hong Kong case.

The social impacts of the two case studies are compared and the results are shown in Figure 10. Analogue to the comparison of environmental impacts, the ratios of results are calculated for the subcategories and the stakeholders. It was found that the Qingdao case had larger impacts on freedom of association and collective bargaining, fair salary and equal opportunities/discrimination, while the Hong Kong case had better performance in terms of child labor, working hours, health and safety, access to material resources, cultural heritage, safe/health living conditions, community engagement, local employment and public commitments to sustainability issues. The social impacts to stakeholders are also provided. It was found that the ratios of worker, local community and society are 53%, 51% and 92%, indicating the social impacts of the Hong Kong case are in general better than those of the Qingdao case.

4. Discussion

This study investigates the sustainability performance of a residential building in the city of Qingdao, China. The environmental results of five impact categories are validated with average emissions derived in our previous analyses on 105 buildings [35]. It is found that the LCA results of the studied building are in the reasonable range for climate change, ozone depletion, acidification, freshwater eutrophication and human toxicity, indicating the LCA results are reliable. It is found that the greater impacts on ozone depletion and freshwater eutrophication are attributed to the material stage, in particular those caused by concrete, aluminum and rebar. Therefore, the adoption of recycled construction material is highly recommended. In addition, the cradle-to-site cost of the studied project is 3633 RMB/m², which is reasonable as the average construction cost of residential building in China ranges from 2000 to 5000 RMB m² [37]. The social impacts of the studied residential building are compared with our previous study in Hong Kong, and it is found that the results are comparable.

There are mainly three shortages of this study. First, the current study covers the pre-use phases of a building’s life cycle, namely from the cradle to the end of construction. However, the downstream processes of operation, maintenance, demolition and recycling are not included within the research scope. This is a primary limitation of this study and should be further improved in the near future. Second, S-LCA involves three stakeholders, i.e., the worker, the local community and society, while the consumer and the value chain actor are not analyzed. The exclusion of the consumer is mainly due to the exclusion of the downstream processes. The value chain actor is not considered, since it is difficult to obtain the data and information of the upstream value chain actors. A comprehensive sLCIA method should be developed to cover all the relevant stakeholders throughout the entire life cycle of a building project. Thirdly, this study adopted AHP and applied equal weighting factors to integrate the three pillars (for LCSA evaluation). However, an integrated method, i.e., hybrid use of other MADM methods, may be useful for such an evaluation. In addition, fuzzy parameters are not incorporated into this LCSA case. Fuzzy numbers can be specified for the weighting factors in further studies.

As one of the first attempts at LCSA in China, we identified several important aspects to be improved in future. Since 22 September 2020, when China pledged to achieve carbon neutrality, LCA has been increasingly applied in the building industry. From April 2022, life cycle carbon analysis was mandated for all newly constructed buildings in China. On the other hand, the LCSA studies of buildings in China are still scarce. The experience of economic development as a single goal while ignoring the problems caused by extensive combustion of fossil fuel already taught us a lesson. Therefore, it is strongly suggested to carry out LCSA to building projects and evaluate the three dimensions instead of a single-category analysis on global warming. The methods of LCA, LCC and S-LCA should be established. The case studies on different building types, structures, regions, life spans and construction areas should be carried out. It is also necessary to conduct comparative analysis on different case studies to establish a benchmark system.

LCSA is still undergoing rapid development [38]. In an LCSA study, the problems may exist for two main aspects: data and methods. It is not easy to obtain all the data for an LCSA, in particular for a building project of which the life cycle is usually over 50 years. The lack of data leads to several subsequent problems in terms of model completeness, reliability of results, fair comparison, accuracy, etc. In this study, the Qingdao case was compared with the Hong Kong case, as these two case studies were under the same modeling framework. Nevertheless, the methods of LCSA are usually not consistent among different studies. It is not easy to compare the LCSA results of this study with other literature, since the methods in different studies are not comparable. In particular, there has been no agreement on the method of S-LCA.

An LCSA of buildings can greatly help the participators to understand the sustainability performance of a building project in a balanced way. Future research may focus on both the methodology development and the implementation of LCSA in the building industry. LCSA can be integrated with technologies, such as building information modeling (BIM), geographical information system (GIS), digital twin, machine learning, etc. The forecast of carbon emissions should incorporate the triple bottom line (TBL) and LCSA can thus serve as a methodological choice. The bottom-up analysis based on LCSA can be linked to the United Nations (UN) Sustainable Development Goals (SDG).

5. Conclusions

The LCSA study of buildings in China is scarce but needed. This study attempts to answer two research questions: (i) What are the life cycle environmental, economic and social impacts of a building project in mainland China? (ii) What are the differences of sustainability performance between buildings in southern and northern cities in China? To fulfill the research gap, we conducted a life cycle sustainability assessment (LCSA) study on a residential building project in the city of Qingdao, China.

The results show that the residential building project emitted 500 kg CO₂eq/m², which is mostly contributed from the material stage. The endpoint results of the studied project show that the damages are mostly due to the impacts to climate change, fossil depletion, human toxicity and particulate matter. The contributions from damage categories are 62%, 33% and 1% from human health, resources and ecosystems, respectively. The social single score of the studied project is 1.32, indicating that the studied project has positive social impacts. The three pillars are integrated using the analytic hierarchy process (AHP) method and the sustainability single score is found to be 71.5/100, 40.86% from environmental impacts, 29.68% from economic impacts and 29.46% from social impacts. The comparative analysis is conducted to compare the Qingdao case with the Hong Kong case. It is found that the Hong Kong case has a better social performance, while the Qingdao case has a better environmental performance.

The LCSA results of this study were compared with previous studies. The limitations on research scope, stakeholders of S-LCA and fuzzy numbers are discussed. LCSA is recommended as an instrument to evaluate the triple bottom line (TBL) of sustainable development. Future research on LCSA is suggested to focus on case studies, methodological development, data acquisition, benchmarking of LCSA results, integration with new technologies and linking LCSA to SDG. As the first attempt to implement LCSA in buildings in mainland China, this study can help improve the LCSA methodology and promote the understanding of sustainability performance for the building industry.