Assessment of Carbon Neutrality Performance of Buildings Using EPD-Certified Korean Construction Materials

Abstract

Achieving carbon neutrality in the building sector is essential for addressing the global climate crisis. However, the production stage—which contributes to over 29% of a building’s life cycle carbon emissions (CE)—poses significant challenges for consistent carbon performance assessment due to the diversity of building materials and the uniqueness of individual building projects. These factors often lead to inconsistent evaluation results across assessors and the fragmented management of carbon data at the project level. This study proposes the Zero Carbon Building Index (ZCBI), a quantitative assessment method that incorporates embodied carbon from raw material extraction, transportation, and manufacturing. ZCBI enables the evaluation of carbon neutrality performance at the material level and supports the identification of reduction potentials in the production stage. A classification system was developed to evaluate CE during production, creating reference buildings for residential and non-residential purposes. Additionally, a Korean Environmental Product Declaration (EPD) database was established by incorporating CE data from 797 EPD-certified materials. Carbon reduction (CR) and ZCBI values were analyzed by categorizing CE variations across manufacturers into the lowest, average, and highest values. The results showed that CR for apartment complexes ranged from 42.1 to 311 kgCO₂e/m², with ZCBI values between 8.84% and 65.30%, and those for business facilities ranged from 40.9 to 264 kgCO₂e/m², with ZCBI values from 8.59% and 55.43. The proposed ZCBI framework provides a basis for optimizing material selection to reduce emissions and may evolve into a comprehensive carbon neutrality assessment covering the entire construction process.

1. Introduction

In October 2018, the intergovernmental panel on climate change proposed a pathway to achieve carbon neutrality by 2050, aligning with the Paris Agreement’s goal of limiting the global temperature rise to 1.5 °C [1,2]. Since then, the urgency of addressing the climate crisis has been emphasized at the UN climate action summit (September 2019) and the conference of the parties to the United Nations Framework Convention on Climate Change (November 2021), thereby accelerating global discussions on carbon neutrality [3]. Particularly, after the COVID-19 pandemic, the growing recognition of the climate crisis has prompted major countries to officially declare their commitment to achieving carbon neutrality [4]. The record-breaking global heat observed in 2024 suggests an increased likelihood that the planet is approaching the 1.5 °C threshold set by the Paris Agreement [5,6].

Korea announced the 2050 carbon neutrality goal, aiming for net-zero emissions by 2050 and a 40% reduction in CE across all industries, from 727.6 million tons in 2018 to 436.6 million tons by 2030 [7]. To achieve this goal, Korea introduced the Korean New Deal policy in 2020 and enacted the framework act on carbon neutrality in 2022 as part of its carbon neutrality efforts [8,9]. In the building construction process, the production stage contributes 29% of the total CE, whereas the operation stage accounts for 65%, highlighting the importance of reducing emissions in both stages [10,11]. To date, many countries have primarily focused on reducing energy consumption during the operational phase of buildings through initiatives such as Zero Energy Buildings (ZEBs) and the use of renewable energy [12]. However, to achieve full carbon neutrality in the building sector, it is essential to address the production stage, which accounts for a significant proportion of the total life cycle [13].

In order to evaluate CE and assess CR performance during the production phase, it is necessary to first derive the “material information” and “quantity information” of the construction materials used in buildings and then convert these into “greenhouse gas information” [14]. While numerous studies have been conducted individually at either the material level or the building level, there is a lack of research that integrates “material information” and “quantity information” into a unified framework to comprehensively evaluate carbon neutrality performance [15]. In practice, many global companies require carbon neutrality performance results for buildings to meet the standards of global initiatives such as renewable energy (RE) and carbon-free energy (CFE). However, such assessments are typically conducted on a project-by-project basis when requested, resulting in inconsistencies across evaluators and reduced reliability and comparability of results [14,16].

Therefore, this study aims to propose a methodology for evaluating carbon neutrality performance during the production stage. A database was developed for various types of “material information” used in buildings, and a comparative analysis of CE ranges was conducted. To derive “quantity information”, a reference building was constructed. Based on this, a quantitative evaluation methodology for carbon neutrality performance was established, and the “greenhouse gas information” was derived for both residential and non-residential buildings. This approach integrates currently fragmented material- and building-level assessments, providing a quantitative evaluation framework that supports construction stakeholders in making informed decisions from the design planning stage to achieve optimal carbon neutrality performance. In particular, the data and methodology proposed in this study are presented with detailed calculation procedures and results to ensure practical applicability in the construction industry.

2. Methodology and Flow of Research

Regarding “material information,” it is necessary to obtain the “CO₂e reference value,” which represents the standard CE for each type of construction material, as well as the “CO₂e actual value”, which reflects the actual emissions of the materials applied in the building. In terms of “quantity information”, the amount of materials used can vary significantly depending on factors such as building size, function, location, and structural type. Therefore, a standardized “reference quantity” is required for accurate comparison and analysis. “Greenhouse gas information” refers to the environmental impact data used to calculate CE, CR, and ZCBI based on the collected material and quantity information. Specifically, for “material information”, this study used certified products from the Environmental Product Declaration (EPD) system operated by the Korea Environmental Industry & Technology Institute (KEITI) [17]. For “quantity information”, data were extracted from completed life cycle assessment (LCA) cases under Korea’s Green Standard for Energy and Environmental Design (G-SEED), administered by the Korea Institute of Civil Engineering and Building Technology (KICT) [18]. “Greenhouse gas information” was also based on data provided by KEITI. The “CO₂e reference value” was derived from Korea’s national LCI database managed by KEITI, while the “CO₂e actual value” was obtained from certified EPD product data [19]. A more detailed research flow is as follows.

First, an _A1–A3CE database was established for building materials used in Korean construction that have obtained environmental product declaration (EPD) certification. Furthermore, a reference building for evaluating the _A1–A3ZCBI was developed by establishing a classification system based on region, building purpose, structural form, and scale. _A1–A3CR and _A1–A3ZCBI were derived by comparing the _A1–A3CE data from the Korean LCI database with _A1–A3CE-based data from the EPD database. This analysis considers the lowest, average, and highest values of _A1–A3CE from each EPD database, which may vary depending on the manufacturer and model, even for identical products. Finally, major construction materials were identified from the perspective of _A1–A3CE.

The data collection and management framework, evaluation methodology, and analytical procedures developed in this study are considered to be broadly applicable through adaptation to systems currently implemented in other countries or regions. In particular, the global expansion and standardization of such an evaluation framework may contribute to the establishment of a universally applicable integrated system for assessing carbon neutrality in the future. Figure 1 presents the overall flow of this study.

3. Literature Review

3.1. Environmental Labeling (International Organization of Standardization (ISO) 14020s)

Eco-friendly product certification is a key method for ensuring superior environmental performance compared to other products in the market [20]. Environmental labeling provides information that helps consumers recognize and choose products with superior environmental performance, encouraging the purchase of eco-friendly alternatives while motivating companies to develop environmentally friendly products [21]. Since 1993, the ISO has developed the ISO 14020 series as an international standard for the environmental management of products. The ISO standard for environmental labeling is presented in

Table 1. International standard for environmental labeling (International Organization of Standardization (ISO) 14020s).

Standard	Year (yyyy.mm)	Environmental Labeling
ISO 14020 [23]	2000.09	Environmental Labels and Declarations (general principle)
ISO 14021 [24]	1999.09	Type II (self-environmental claim)
ISO 14024 [25]	1999.04	Type I
ISO 14025 [26]	2006.07	Type III

[22].

Type I environmental labeling is granted to products whose environmental impact has been evaluated across various life cycle stages—production, distribution, consumption, and disposal—by an independent third-party certification agency [27]. This concept was first introduced in 1979 by Germany’s Blue Angel environmental label and later adopted by Japan, the United States, and the European Union [28]. As of 2015, this labeling is used in 47 countries worldwide and is known as EPD products in Korea, managed by the Korea Environmental Industry & Technology Institute (KEITI). The EPD applies to products for which the environmental impact is quantitatively assessed across seven major environmental categories, covering all stages from raw material collection to production, distribution, use, and disposal [25].

Type II labeling is defined in ISO 14021 as a type of labeling applicable to products that can be labeled without independent third-party certification if the company demonstrates secured environmental performance [22]. Many companies display symbols or phrases indicating their product’s eco-friendliness on packaging and engage in green marketing [29]. Several countries, including the United States, Canada, Japan, and those in Europe, have adopted ISO 14021 to enforce regulatory standards aimed at preventing false or exaggerated advertising by companies [22]. In Korea, this labeling is applied by KEITI to low-carbon products that have undergone additional CE reductions [17]. Low-carbon certification is granted to products with a carbon footprint below the maximum allowable CE or exceeding the minimum required CR rate. The maximum allowable CE refer to cases below the average CE for the product group, whereas the minimum reduction rate refers to a reduction of 3.3% or more in CE compared with similar products. KEITI comprehensively manages both Type I and Type II EPD-certified products, as well as low-carbon EPD-certified products [30].

Recently, the social recognition and importance of carbon neutrality have grown, increasing demand for reducing embodied carbon in the production stage of materials. Consequently, the number of EPD-certified products, for which environmental impact is evaluated across all stages and CE are further reduced, continues to increase. Figure 2 illustrates the status of EPD-certified products in Korea [17].

3.2. Life Cycle Assessment (ISO 14040s)

Life cycle assessment (LCA), as defined by ISO 14040 [31], identifies the environmental load generated throughout all stages of products or systems and evaluates its impact on the environment to identify measures for reduction and improvement [32]. The assessment categories cover six major environmental impacts: global warming potential, abiotic depletion potential, ozone depletion potential, acidification potential, eutrophication potential (EP), and photochemical oxidation creation potential [10,18].

In Korea, assessments are conducted as per the LCA preparation guideline for additional items in the innovative design field under the Green Standard for Energy and Environmental Design (G-SEED) [10]. The assessment categories of building LCA are divided into four stages based on the system boundary [18]. The production stage (A1–A3) encompasses the environmental impacts generated throughout all stages, including raw material extraction, transportation, and manufacturing, involved in producing construction materials used in building construction. The construction stage (A4–A5) covers the environmental impacts generated during the transportation of construction materials and the actual construction process. The operation stage (B1–B7) includes the environmental impacts resulting from the use of operational energy throughout a building’s lifespan, as well as those caused by the replacement of construction materials during repairs and maintenance. The disposal stage (C1–C4) covers the environmental impacts generated during the demolition of buildings, transportation of waste construction materials, and disposal of waste construction materials [33]. According to the G-SEED LCA guideline, the LCA results must include the production stage (A1–A3), construction stage (A4–A5), replacement (B4) and use of operational energy (B6) during the operation stage, and demolition (C1), transportation (C2), and disposal (C4) during the disposal stage. In addition, the embodied carbon associated with the production stage (A1–A3), construction stage (A4–A5), and disposal stage (C1–C4) pertains solely to building materials and does not include equipment materials such as mechanical and electrical systems [34,35]. Figure 3 shows the system boundary according to the LCA preparation guideline.

In LCA, the production stage is calculated by applying the environmental unit of each material to the quantity of materials used in the building. This is achieved by converting various construction materials into mass units (tons) by product category [33]. The major construction materials, which account for over 99% of the cumulative mass contribution, primarily include ready-mixed concrete, rebar, cement, masonry, insulators, aggregates, stone, glass, and tiles [35].

3.3. National Life Cycle Inventory (LCI) Database

The LCI databases are used as basic data for conducting LCAs of products. Such data include the quantities of inputs and outputs into a product system during the collection of raw materials needed for production, transportation and distribution, use, and disposal per functional unit of the product [19,36].

Countries and research institutes have conducted studies comparing the environmental performance of buildings using each nation’s LCI (Life Cycle Inventory) database. However, these studies face limitations due to insufficient databases for construction materials and difficulties in comparing evaluation results at the project level. In particular, the absence of integrated data combining material input quantities with environmental impact data has hindered the ability to quantitatively present CR potential and overall carbon neutrality performance.

Table 2. Review of the existing literature.

Year	Authors	Main Contents	Differences in This Study
2015	Lasvaux et al. [37]	Compared and analyzed data developed in France with data from Europe.	Previous studies had limitations in the number of materials analyzed and lacked a methodology for deriving comparative results across actual buildings.
2016	A. Martínez-Rocamora et al. [38]	Established criteria for selecting LCA databases when inconsistencies exist between the database and building conditions.	Although selection criteria have been suggested, no study has proposed constructing a database that satisfies those criteria and allows for application to real building cases.
2021	Mohebbi, G et al. [39]	Proposed carbon input calculation criteria within the UK context.	While UK data are available, they lack comprehensive coverage of materials used throughout the full construction process.
2024	H.J Jang et al. [40]	Developed and improved an environmental impact database for construction materials in China.	Lacked the concept of a reference building and evaluation methodology, making it impossible to estimate carbon reduction (CR) potential.
2025	Jie-Fu Zheng et al. [41]	Proposed an evaluation model for managing whole-process carbon emissions (CE) in buildings.	Did not present a structured database or a quantitative method for estimating carbon reduction (CR) performance.

highlights the key distinctions between previous studies and this present study [37,38,39,40,41]. Table 2 shows the differences between this study and previous studies in the LCI database.

In the case of Korea, energy and resources, basic materials, building materials, industrial products, transportation and logistics, waste treatment, etc., have 747 LCI databases, of which 61 are construction materials. This database is managed by the Korea Environmental Industry and Technology Institute (KEITI), a governmental organization, and is publicly accessible through its official website [19]. In January 2025, KEITI plans to develop new national guidelines for LCI database development, aiming to update and expand the existing LCI database, which is currently outdated or insufficient [42].

Table 3. CE (kgCO₂e) of major construction materials from Korea’s Life Cycle Inventory (LCI) database.

Construction Materials	Detail	Unit	Carbon Emissions (CE)	Construction Materials	Detail	Unit	Carbon Emissions (CE)
Ready-mixed concrete	18 MPa	m3	4.09 × 102	Insulator	Expanded polystyrene (EPS)	kg	1.96 × 100
	24 MPa	m3	4.14 × 102		Extruded polystyrene (XPS)	kg	3.28 × 100
	27 Mpa	m3	4.14 × 102		Glass wool	ton	1.90 × 102
Masonry	Concrete brick	kg	1.23 × 10−1	Cement	Cement	ton	1.06 × 103
	Autoclaved lightweight concrete (ALC) block	kg	6.57 × 10−1		White Portland Cement	kg	1.22 × 100
Aggregate	Sand	m3	3.87 × 100		Mortar	kg	4.31 × 10−1
	Gravel	m3	1.13 × 101	Gypsum board	Square edge-type board	ton	1.38 × 102
Rebar	-	kg	4.38 × 10−1		Fire protection	ton	1.38 × 103
Tile	-	kg	3.53 × 10−1	Glass	Double-glazed Glass	m2	2.24 × 101
Stone	Granite	m3	2.90 × 10−1		Tempered Glass	m2	1.0 × 100
	Artificial marble	kg	1.64 × 101		Plate glass	ton	7.89 × 102

presents the CE data from the Korean LCI database for major construction materials.

4. Analysis of Zero Carbon Performance in Production Stage

4.1. _A1–A3ZCBI Calculation Method

This study introduces the Zero Carbon Building Index in the production stage (_A1–A3ZCBI) to quantitatively represent carbon neutrality performance during the production phase. This index provides a comparable evaluation framework that enables the performance of various buildings to be assessed consistently and managed in an integrated manner.

The _A1–A3ZCBI proposed in this study represents the percentage ratio of carbon emissions (CE_{LCI DB}), calculated using Korea’s national LCI database under the existing building LCA preparation guideline, to _A1–A3CR achieved through the use of EPD-certified products to minimize embodied carbon in buildings. An optimal _A1–A3ZCBI can be achieved in the initial planning stage by either reducing the denominator through efficient design to minimize material input or increasing the numerator by incorporating EPD-certified products with low CE. Equation (1) presents the calculation of _A1–A3ZCBI, which indexes carbon neutrality performance in the production stage.

_A1–A3ZCBI (%) = _A1–A3CR ÷ CE_{LCI DB} × 100

(1)

• _A1–A3ZCBI: Zero Carbon Building Index in production stage (kgCO₂e/m²).
• _A1–A3CR: Amount of Carbon Reduction in production stage (kgCO₂e/m²).
• CE_{LCI DB}: Carbon Emissions in the production stage through Korea’s national LCI database (kgCO₂e/m²).

_A1–A3CR in the production stage, serving as the numerator of _A1–A3ZCBI, is defined as the difference between carbon emissions (CE_{LCI DB}) calculated using Korea’s national LCI database and carbon emissions (CE_{EPD DB}) determined using the EPD database. Equation (2) presents the calculation of _A1–A3CR, which is the numerator of _A1–A3ZCBI.

_A1–A3CR (kgCO₂e/m²) = CE_{LCI DB} − CE_{EPD DB}

(2)

• _A1–A3CR: Amount of Carbon Reduction in production stage (kgCO₂e/m²).
• CE_{LCI DB}: Carbon Emissions in the production stage through Korea’s national LCI database (kgCO₂e/m²).
• CE_{EPD DB}: Carbon Emissions in the production stage through Korea’s EPD database (kgCO₂e/m²).

4.2. Establishment of EPD Database of Major Materials

In Korea, the EPD certification system has been effective in evaluating environmental impacts across all product stages and granting certifications by KEITI. EPD is categorized into EPD-certified products (Type I) and low-carbon certified products (Type II). A total of 1832 cases have obtained certification, including 1372 EPD-certified cases and 460 low-carbon-certified cases [17]. A database for EPD-certified products (hereafter, EPD DB) was created for 797 cases of essential construction materials used in building construction. For the created EPD DB, _A1–A3CE was determined by converting the product specifications into weight (tons) according to the building LCA preparation guideline.

The EPD DB for major construction materials comprises 797 cases, including 632 EPD-certified products and 165 low-carbon-certified products, with low-carbon-certified products accounting for approximately 20%. Out of the 797 cases in the EPD DB, ready-mixed concrete accounts for 770 cases, or about 96% of the total. Notably, aggregates and stones, key materials in construction, lack certified products. Therefore, diversifying certified products is considered crucial for reducing _A1–A3CE.

Table 4. EPD DB development information for major construction materials.

Category	Ready-Mixed Concrete	Rebar	Masonry	Insulation	Aggregate	Stone	Cement	Gypsum Board	Total
Total certified products	770	2	4	11	0	0	7	3	797
EPD-certified	610	2	4	8	0	0	7	1	632
Low-carbon certified	160	0	0	3	0	0	0	2	165
Unit conversion	m2 > ton	kg > ton	m2 > ton	m2 > ton	-	-	kg > ton	m2 > ton	ton

shows the details of the EPD DB of major construction materials established in this study.

Table 5. CE ranges (kgCO₂e/m²) of EPD-certified products for major construction materials.

Major Materials	Detailed Specification	Certifications	Lowest (1)	Average (2)	Highest (3)
Ready-mixed concrete	18 MPa	12	1.08 × 102	1.91 × 102	2.72 × 102
	21 MPa	163	1.12 × 102	2.25 × 102	3.22 × 102
	24 MPa	214	1.01 × 102	2.39 × 102	3.87 × 102
	27 MPa	164	1.59 × 102	2.71 × 102	3.88 × 102
	30 MPa	132	1.70 × 102	2.83 × 102	4.05 × 102
	35 MPa	63	1.67 × 102	2.99 × 102	3.95 × 102
	40 MPa	22	2.67 × 102	3.73 × 102	3.73 × 102
Rebar	Steel bars for reinforced concrete (RC)	2	4.54 × 10−1	N/A	N/A
Masonry	Concrete brick	N/A	N/A	N/A	N/A
	ALC block	4	2.77 × 102	3.03 × 102	3.37 × 102
Insulation	Fiber insulation	3	4.68 × 100	5.43 × 100	6.19 × 100
	EPS	3	2.40 × 102	3.36 × 100	4.64 × 100
	XPS	N/A	N/A	N/A	N/A
Aggregate	Sand	N/A	N/A	N/A	N/A
	Gravel	N/A	N/A	N/A	N/A
Stone	Granite	N/A	N/A	N/A	N/A
Cement	Cement	4	8.83 × 102	9.24 × 102	9.65 × 102
	Mortar	3	1.99 × 10−1	2.41 × 10−1	2.83 × 10−1
Gypsum board	Square edge-type board	3	5.92 × 10−1	6.62 × 10−1	7.03 × 10−1

⁽¹⁾ Lowest carbon emissions (CE) among EPD-certified products. ⁽²⁾ Average carbon emissions (CE) among EPD-certified products. ⁽³⁾ Highest carbon emissions (CE) among EPD-certified products.

and

Table 6. Four classification systems for the reference building.

Classification System	Utilized Data	Analysis Result	Selection Result
Region	Green Standard for Energy and Environmental Design (G-SEED) certification	- Capital area, 65% - Metropolitan, 14% - Provincial city, 21%	Capital area (Seoul, Gyeonggi, Incheon)
Building purpose	G-SEED certification	- Business facilities, 32% - Apartment houses, 28% - Schools, 16% - General buildings, 15% - Accommodation facilities, 4% - General houses, 4% - Sales facilities, 1%	Residential: Apartment houses Non-residential: Business facilities
Structural form	G-SEED life cycle assessment (LCA) certification	- RC structure, 75% - Steel-reinforced concrete structure, 14% - RC + steel structure, 18%	RC structure
Structural scale	G-SEED LCA certification	- Average total floor area of 56 apartment houses - Average total floor area of 41 business facilities	Total floor area, 99,119.31 m2 Total floor area, 19,275.24 m2
Building Lifespan	G-SEED LCA guideline	- 50 years (assuming same energy usage each year)	50 years

were developed and analyzed based on the eight major materials and fifteen product categories identified as key construction materials in the reference building established in Section 5.

The EPD DB showed varying CE for products within the same product groups, depending on the manufacturer and model. To assist the decision-making process for stakeholders in construction concerning construction materials, it is essential to analyze the range of CE across different products. Thus, the EPD DB was organized based on the lowest, average, and highest CE of each product. As Hyundai Steel products are the only ones used for rebar, the lowest, average, and highest values were applied consistently. Additionally, concrete brick, extruded polystyrene insulation, aggregates, and stones were excluded from the _A1–A3CR analysis due to the absence of EPD-certified products. Table 5 presents the lowest, average, and highest CE values for each product in the EPD DB.

5. Construction of a Reference Building

5.1. Establishing Classification Systems

A reference building was created to comparatively analyze the _A1–A3CE, _A1–A3CR, and _A1–A3ZCBI; this was the primary goal of this study. Four classification systems—region, building purpose, structural form, and structural scale—were established to account for factors that can influence _A1–A3CE and _A1–A3CR in the production stage. Data on the established classification systems were collected from G-SEED and G-SEED LCA certification cases, which conducted building LCA in Korea [18].

For the region, the focus was on the capital region of Seoul, Gyeonggi, and Incheon, which have the highest number of G-SEED certification cases. For the building purpose, apartment houses were chosen for residential buildings and business facilities for non-residential buildings based on the highest number of G-SEED certification cases. For the structural form, reinforced concrete structures were selected, as they account for 75% of the G-SEED LCA cases. For the structural scale, G-SEED LCA case data for apartment houses and business facilities, based on the building purpose classification system, were collected and set as the average total floor area [10]. The details of the classification systems are outlined in Table 6.

5.2. Setting Input Quantity of Major Construction Materials

As per Korea’s building LCA preparation guideline, _A1–A3CE is calculated by multiplying the quantity of construction materials by the environmental unit of each material [33]. The quantity of materials used in building projects can vary significantly depending on project characteristics or design techniques; thus, establishing a standard quantity is essential. Therefore, in this study, a standard quantity of major construction materials was established by utilizing data from previous research that determined the standard quantities of key materials for each building type in Korea [17]. The calculation was performed in terms of weight (tons) per unit area (m²) for major construction materials, with the standard quantity set for materials that account for the top 99% or more by weight. This literature, based on the Korean building LCA preparation guideline, demonstrates high reliability, with an error rate of less than 5%. It identifies 14 major construction materials, including ready-mixed concrete, steel, masonry, insulation, and cement.

Table 7. Standard quantities per unit area (kg/m²) of major construction materials.

Major Construction Materials	Apartment House (RC)	Business Facility (RC)	General Building (RC)	Major Construction Materials	Apartment House (RC)	Business Facility (RC)	General Building (RC)
Ready-mixed concrete	2184.72	2141.75	1869.92	Cement	50.88	22.43	18.42
Rebar	63.64	106.73	84.58	Stone	2.43	7.82	2.92
Section steel	0.00	0.00	1.19	Aggregate	43.46	46.87	79.53
Glass	8.22	6.23	8.56	Wood	1.36	0.89	0.00
Masonry	88.49	63.10	53.27	Paint	2.77	1.41	1.03
Insulation	2.22	2.89	2.30	Iron	0.50	1.36	4.23
Gypsum board	7.75	5.15	4.84	Tile	7.13	4.03	5.08

presents the standard quantities per unit area of major construction materials derived from the reference literature [43].

The total floor area of the reference buildings for apartment complexes and office facilities, established based on the classification system described in Section 5.1, can be determined by calculating the total input quantity using the standard quantity per unit area from Table 7. The final selection of major construction materials includes ready-mixed concrete, steel rebar, masonry, insulation, aggregates, stone, cement, and gypsum board. Apartment houses involve seven types of these materials, excluding stone, whereas business facilities include seven types, excluding gypsum board.

Table 8. Input quantity of major construction materials in production stage.

No.	Major Construction Materials	Specification	Unit	Input Quantity for Apartment Houses	Input Quantity for Business Facilities
1	Ready-mixed concrete	18 MPa	ton	13,640.91	1910.76
		24 MPa	ton	202,906.35	7835.24
		27 MPa	ton	N/A	31,536.25
2	Rebar	Steel bars for RC	ton	6307.93	2057.22
3	Masonry	Concrete brick	ton	7211.30	924.88
		Autoclaved aerated concrete block	ton	1535.54	291.37
4	Insulation	Fiber insulation	ton	N/A	9.98
		EPS	ton	59.87	45.73
		XPS	ton	156.66	N/A
5	Aggregate	Sand	ton	4307.71	793.37
		Gravel	ton	N/A	110.05
6	Stone	Granite	ton	N/A	150.73
7	Cement	Cement	ton	1945.07	432.34
		Mortar	ton	3098.10	N/A
8	Gypsum board	Square edge-type board	ton	768.17	N/A
Total			ton	241,937.61	46,097.92

lists the input quantities of major construction materials applied in the reference building.

5.3. Derivation of Carbon Emissions

The reference building’s _A1–A3CE was calculated to analyze the _A1–A3CR and _A1–A3ZCBI by applying the EPD DB, which is the ultimate goal of this study. The _A1–A3CE must be determined using standard values for the input quantity of construction materials and the environmental unit cost of each material for the reference building. The input quantity of construction materials was determined using the standard quantities from Table 8, whereas the environmental unit was calculated based on Korea’s national LCI DB, as presented in Table 3. CE from stages other than the production stage, such as the operation stage, were estimated using the average values from G-SEED LCA cases collected during the classification system setup for the reference building.

Table 9. CE (kgCO₂e/m²) assessment results of the reference building.

System Boundary			Apartment Houses		Business Facilities
			Carbon Emissions (CE)	Ratio	Carbon Emissions (CE)	Ratio
Production stage	A1–A3	Production	4.77 × 102	29.90%	4.76 × 102	20.57%
Construction stage	A4	Transportation	1.92 × 101	1.20%	1.88 × 101	0.81%
	A5	Construction	5.89 × 100	0.37%	6.04 × 100	0.26%
Operation stage	B4	Replacement	1.09 × 103	68.35%	1.81 × 103	78.25%
Disposal stage	C1	Demolition	2.41 × 100	0.15%	2.36 × 100	0.10%
	C2	Transportation	5.95 × 10−3	0.00%	5.55 × 10−3	0.00%
	C4	Disposal	4.35 × 10−1	0.03%	2.46 × 10−1	0.01%
Total			1.59 × 103	100%	2.31 × 103	100%

presents the details of the reference buildings for apartment houses and business facilities.

6. Assessment of Carbon Neutrality Performance in Production Stage

6.1. Derivation of _A1–A3ZCBI for Apartment Houses

As the input quantities of construction materials generally remain unchanged after the design phase, the key factors influencing _A1–A3CR and _A1–A3ZCBI are the _A1–A3CE of each material used in construction projects. Therefore, for the EPD DB established using EPD-certified products applied in real production and buildings, the lowest, average, and highest _A1–A3CE values were identified and compared with _A1–A3ZCBI.

“Lowest” refers to the low-carbon product with the minimum _A1–A3CE within the same product category. “Average” represents the mean _A1–A3CE of all products in the category, while “Highest” indicates the product with the maximum _A1–A3CE. The reason for classifying product-specific CE values in the EPD database as “lowest,” “average,” and “highest” is that CE can vary within the same product category depending on the manufacturer, model, production technology, and factory facilities. Therefore, instead of presenting the _A1–A3CE of a single product, this study provides the range of _A1–A3CE and _A1–A3ZCBI values within each product category. This approach supports informed material selection decisions during the design and planning phase, contributing to the optimization of carbon neutrality performance from the early stages of a project.

According to Table 9, the _A1–A3CE for the reference building of apartment houses is 4.77 × 10² (kgCO₂e/m²). When applied to the lowest EPD DB product, the _A1–A3CE is 1.65 × 10² (kgCO₂e/m²), and the _A1–A3ZCBI is 65.30%. When applied to the average EPD DB product, the _A1–A3CE is 2.96 × 10² (kgCO₂eq/m²), and the _A1–A3ZCBI is 38.00%. When applied to the highest EPD DB product, the _A1–A3CE is 4.35 × 10² (kgCO₂e/m²), and the _A1–A3ZCBI is 8.84%.

A comparison between the lowest and highest _A1–A3CE values in Korea’s EPD DB revealed that _A1–A3CR ranged from 4.21 × 10¹ (kgCO₂e/m²) to 3.11 × 10² (kgCO₂e/m²), and the _A1–A3ZCBI ranged from 8.84% to 65.30%. When the _A1–A3CR was compared with the total CE of all stages for the reference apartment house (1.59 × 10³ kgCO₂e/m²), the ZCBI across all stages ranged from 2.64% to 19.52%.

6.2. Derivation of _A1–A3ZCBI for Business Facilities

The _A1–A3ZCBI for the reference building of business facilities was derived using the same method as for apartment houses. The _A1–A3CE for the reference building of business facilities, as presented in Table 9, is 4.76 × 10² (kgCO₂e/m²).

When applied to the lowest EPD DB product, the _A1–A3CE is 2.12 × 10² (kgCO₂e/m²) and the _A1–A3ZCBI is 55.43%. When applied to the average EPD DB product, the _A1–A3CE is 3.21 × 10² (kgCO₂e/m²) and the _A1–A3ZCBI is 32.56%. When applied to the highest EPD DB product, the _A1–A3CE is 4.35 × 10² (kgCO₂e/m²) and the _A1–A3ZCBI is 8.59%.

Similarly, a comparison between the lowest and highest _A1–A3CE values in Korea’s EPD DB revealed that _A1–A3CR ranged from 4.09 × 10¹ (kgCO₂e/m²) to 2.64 × 10² (kgCO₂e/m²) and _A1–A3ZCBI ranged from 8.59% to 55.43%. When the _A1–A3CR was compared with the total CE of all stages for the reference business building (2.31 × 10³ kgCO₂e/m²), the ZCBI across all stages ranged from 1.77% to 11.40%.

Table 10. Assessment result (kgCO2e/m²) of _A1–A3ZCBI for apartment houses and business facilities.

Apartment Houses
Category		Reference Building	Lowest (1)			Average (2)			Highest (3)
Major Materials	Specification	CE	CE	CR	A1–A3ZCBI	CE	CR	A1–A3ZCBI	CE	CR	A1–A3ZCBI
		(A)	(B)	(C) = (A) − (B)	(C)÷(A)	(D)	(E) = (A) − (D)	(E)÷(A)	(F)	(G) = (A) − (F)	(G)÷(A)
Ready-mixed concrete	18 MPa	2.45 × 101	6.47 × 100	1.80 × 101	3.78%	1.14 × 101	1.31 × 101	2.74%	1.63 × 101	8.21 × 100	1.72%
	24 MPa	3.68 × 102	8.99 × 101	2.79 × 102	58.42%	2.13 × 102	1.56 × 102	32.66%	3.44 × 102	2.40 × 101	5.04%
Rebar	Steel bars for RC	2.79 × 102	2.89 × 101	−1.02 × 100	−0.21%	2.89 × 101	−1.02 × 100	−0.21%	2.89 × 101	−1.02 × 100	−0.21%
Masonry	Concrete brick	8.88 × 100	8.88 × 100	N/A	N/A	8.88 × 100	N/A	N/A	8.88 × 100	N/A	N/A
	ALC block	5.30 × 100	2.23 × 100	3.06 × 100	0.64%	2.44 × 100	2.85 × 100	0.60%	2.72 × 100	2.58 × 100	0.54%
Insulation	EPS	1.18 × 100	1.45 × 10−3	1.18 × 100	0.25%	2.03 × 10−3	1.18 × 100	0.25%	2.80 × 10−3	1.18 × 100	0.25%
	XPS	5.18 × 100	5.18 × 100	N/A	N/A	5.18 × 100	N/A	N/A	5.18 × 100	N/A	N/A
Gypsum board	Square edge-type board	1.07 × 100	5.44 × 10−4	N/A	N/A	3.53 × 10−3	N/A	N/A	5.45 × 10−3	N/A	N/A
Cement	Cement	2.08 × 101	1.73 × 101	1.07 × 100	0.22%	1.81 × 101	1.07 × 100	0.22%	1.89 × 101	1.06 × 100	0.22%
	Mortar	1.35 × 101	6.49 × 100	3.47 × 100	0.73%	7.86 × 100	2.67 × 100	0.56%	9.23 × 100	1.86 × 100	0.39%
Aggregate	Sand	1.05 × 10−1	1.05 × 10−1	6.98 × 100	1.46%	1.05 × 10−1	5.61 × 100	1.18%	1.05 × 10−1	4.24 × 100	0.89%
Total		4.77 × 102	1.65 × 102	3.11 × 102	65.30%	2.96 × 102	1.81 × 102	38.00%	4.35 × 102	4.21 × 101	8.84%
Business Facilities
Ready-mixed concrete	18 MPa	1.76 × 101	4.66 × 100	1.30 × 101	2.73%	8.24 × 100	5.91 × 100	1.24%	1.17 × 101	5.91 × 100	1.24%
	24 MPa	7.32 × 101	1.79 × 101	5.53 × 101	11.63%	4.22 × 101	4.77 × 100	1.00%	6.84 × 101	4.77 × 100	1.00%
	27 MPa	2.95 × 102	1.13 × 102	1.81 × 102	38.13%	1.93 × 102	1.85 × 101	3.89%	2.76 × 102	1.85 × 101	3.89%
Rebar	Steel bars for RC	4.67 × 101	4.85 × 101	−1.71 × 100	−0.36%	4.85 × 101	−1.71 × 100	−0.36%	4.85 × 101	−1.71 × 100	−0.36%
Masonry	Concrete brick	5.85 × 100	5.85 × 100	N/A	N/A	5.85 × 100	N/A	N/A	5.85 × 100	N/A	N/A
	ALC block	5.17 × 100	2.18 × 100	2.99 × 100	0.63%	2.38 × 100	2.52 × 100	0.53%	2.65 × 100	2.52 × 100	0.53%
Insulation	Glass wool 48K	1.01 × 100	2.50 × 10−2	9.90 × 10−1	0.21%	2.90 × 10−2	9.82 × 10−1	0.21%	3.31 × 10−2	9.82 × 10−1	0.21%
	EPS	7.78 × 100	9.53 × 10−3	7.77 × 100	1.63%	1.33 × 10−2	7.76 × 100	1.63%	1.84 × 10−2	7.76 × 100	1.63%
Cement	Cement	2.38 × 101	1.98 × 101	3.97 × 100	0.83%	2.07 × 101	2.13 × 100	0.45%	2.16 × 101	2.13 × 100	0.45%
Aggregate	Sand	9.92 × 10−2	9.92 × 10−2	N/A	N/A	9.92 × 10−2	N/A	N/A	9.92 × 10−2	N/A	N/A
	Gravel	1.38 × 10−2	1.38 × 10−2	N/A	N/A	1.38 × 10−2	N/A	N/A	1.38 × 10−2	N/A	N/A
Stone	Granite	1.88 × 10−2	1.88 × 10−2	N/A	N/A	1.88 × 10−2	N/A	N/A	1.88 × 10−2	N/A	N/A
Total		4.76 × 102	2.12 × 102	2.64 × 102	55.43%	3.21 × 102	1.55 × 102	32.56%	4.35 × 102	4.09 × 101	8.59%

⁽¹⁾ Lowest carbon emissions (CE) of the same product group among EPD-certified products. ⁽²⁾ Average carbon emissions (CE) of the same product group among EPD-certified products. ⁽³⁾ Highest carbon emissions (CE) of the same product group among EPD-certified products.

and Figure 4 and Figure 5 present the _A1-A3ZCBI analysis results of apartment houses and business facilities.

6.3. Derivation of Major Construction Materials Based on Contribution to Cumulative CE

To assist the decision-making process of construction stakeholders regarding building materials, the contribution of major materials to CE was analyzed by identifying products having a cumulative _A1–A3CE of 99% or higher. Major construction materials with a cumulative _A1–A3CE(CO₂e) of 99% or higher for both apartment houses and business facilities include ready-mixed concrete, steel rebar, cement, and masonry. In contrast, insulation, aggregates, stones, and gypsum boards were considered major materials based on their cumulative weight (ton) contribution of 99% or higher when accounting for all input quantities in the production stage. However, they are excluded from the list of major materials in terms of _A1–A3CE due to the relatively low quantity used in the building or minimal environmental impact.

Ready-mixed concrete was identified as the most critical material, contributing over 70% to _A1–A3CE, as its input weight accounted for more than 85% of all major materials. Rebar was identified as the second most significant material, contributing around 10% to _A1–A3CE in apartment houses and approximately 17% in business facilities. Cement was identified as the third most significant material, contributing around 9% in apartment houses and approximately 7% in business facilities. Masonry contributed around 4% in apartment houses and 3% in business facilities.

The _A1–A3CR and _A1–A3ZCBI were analyzed based on the lowest, average, and highest _A1–A3CE values of EPD-certified ready-mixed concrete, steel, cement, and masonry, which collectively contributed 99% or more to the cumulative _A1–A3CE. For ready-mixed concrete, the _A1–A3CR ranged from 3.00 × 10¹ (kgCO₂e/m²) to 2.97 × 10² (kgCO₂e/m²), whereas the _A1–A3ZCBI ranged from 6.21% to 67.16%. This material accounts for 76.95% to 96.94% of _A1–A3CR for major construction materials, highlighting that utilizing low-carbon ready-mixed concrete is crucial for achieving _A1–A3CR and _A1–A3ZCBI.

For rebar, Hyundai Steel Co., Ltd. products are the sole option available in Korea, and the _A1–A3CE of EPD-certified products was found to be 1 (kgCO₂e/m²) higher than the value in Korea’s national LCI DB. Given that rebar accounts for over 10% of total _A1–A3CE as the second-largest contributor after ready-mixed concrete, the development of low-carbon technologies and diversification of certified rebar products are essential for achieving significant CR across various building types. Consequently, the _A1–A3ZCBI could potentially increase by more than 5%.

For cement, the _A1–A3CR ranged from 2.13 × 10⁰ (kgCO₂e/m²) to 1.08 × 10¹ (kgCO₂e/m²), whereas the _A1–A3ZCBI ranged from 0.45% to 2.25%. Cement is also important as it accounts for at least 7% of _A1–A3CE, but only seven EPD-certified products are available. Therefore, the development of low-carbon cement and the diversification of available products is needed.

Owing to the absence of concrete bricks, which have a relatively high material input, in the EPD DB, autoclaved lightweight concrete (ALC) blocks were analyzed instead. ALC blocks had an _A1–A3CR ranging from 2.51 × 10⁰ (kgCO₂e/m²) to 3.06 × 10⁰ (kgCO₂e/m²), and an _A1–A3ZCBI ranging from 0.53% to 0.59%. For masonry, achieving _A1–A3CR will require promoting a variety of EPD-certified products, including both concrete bricks and ALC blocks.

Table 11. _A1–A3CE and _A1–A3ZCBI of major construction materials with ≥99% cumulative CE.

Use	Major Materials	Cumulative A1–A3CE Contribution	Lowest		Average		Highest
			CR	A1–A3ZCBI	CR	A1–A3ZCBI	CR	A1–A3ZCBI
Apartment houses	Ready-Mixed Concrete	74.98%	2.97 × 102	62.27%	1.68 × 102	35.35%	3.25 × 101	6.83%
	Rebar	10.48%	−1.00 × 100	−0.21%	−1.00 × 100	−0.21%	−1.00 × 100	−0.21%
	Cement	9.00%	1.08 × 101	2.25%	8.62 × 100	1.81%	6.50 × 100	1.36%
	Masonry	4.59%	3.06 × 100	0.64%	2.85 × 100	0.60%	2.58 × 100	0.54%
	Total	99.08%	3.10 × 102	64.95%	1.78 × 102	37.55%	4.06 × 101	8.52%
Business facilities	Ready-Mixed Concrete	71.70%	3.17 × 102	67.10%	1.43 × 102	30.31%	3.00 × 101	6.21%
	Rebar	17.36%	−1.70 × 100	−0.36%	−1.70 × 100	−0.36%	−1.70 × 100	−0.36%
	Cement	7.53%	4.00 × 100	0.84%	3.05 × 100	0.65%	2.13 × 100	0.45%
	Masonry	3.12%	2.98 × 100	0.63%	2.78 × 100	0.59%	2.51 × 100	3.84%
	Total	99.71%	3.22 × 102	68.21%	1.47 × 102	31.19%	3.29 × 101	10.14%

presents the analysis results of the cumulative _A1–A3CE contribution of major construction materials in terms of carbon neutrality performance in the production stage.

7. Discussion

Currently, materials such as ready-mixed concrete and steel, which are primarily used in the structural components of buildings, are identified as the most critical contributors in terms of carbon emissions (CE) and carbon reduction potential (CR). However, to achieve truly embodied carbon neutrality, it is necessary to develop and promote evaluation systems for carbon-neutral materials—such as wood and biomass—that exhibit low CE and are compatible with resource circulation.

Moreover, for a comprehensive assessment of embodied carbon during the production stage, the scope should extend beyond conventional construction materials to include all material categories, such as mechanical, electrical, and communication systems. In particular, renovation work related to the service life and replacement cycles of each material must be incorporated into the evaluation.

Given the vast variety of materials, evolving technologies, and changing regulations, it is essential to establish an integrated system capable of efficiently responding to these numerous potential variables. Such a system could involve the development of intelligent platforms from a technological perspective or the institutionalization of integrated certification systems from a regulatory and administrative standpoint.

Notably, the LCI database used as a reference for evaluating A1–A3 CR and A1–A3 ZCBI includes many outdated datasets and suffers from a lack of continuous updates. To enable meaningful comparative analysis with newly developed and currently produced materials, it is necessary to establish a framework that ensures temporal consistency in the database.

Based on the results of this study, future research will expand the quantitative evaluation of CE and CR to the entire life cycle—including the construction, operation, and end-of-life stages—and develop a comprehensive methodology for whole-life ZCBI assessment. In doing so, we plan to address the limitations identified in this study, consider a broader range of potential variables, and ultimately enhance the system into an integrated management framework linked with certification schemes.

8. Conclusions

The aim of this study was to quantitatively assess carbon neutrality performance by examining carbon emissions (CE) and carbon reduction (CR) throughout the production stage of a building’s entire life cycle, leading to the following conclusions.

• The _A1–A3ZCBI was introduced to evaluate carbon neutrality performance by assessing _A1–A3CE and _A1–A3CR during the production stage.
• To analyze the _A1–A3CR and _A1–A3ZCBI, an EPD database was created for 797 building materials, sourced from 1832 EPD-certified products manufactured in Korea.
• As EPD-certified products exhibit various _A1–A3CE values depending on the manufacturer or model within the same product group, the lowest, average, and highest _A1–A3CE values were identified for each group. This distinction facilitated decision-making in product selection and analysis of _A1–A3CR and _A1–A3ZCBI.
• To analyze the proposed _A1–A3ZCBI, reference buildings were created based on four classification systems: region, building purpose, structural form, and structural scale.
• The _A1–A3ZCBI analysis of major construction materials showed that the _A1–A3ZCBI ranged from 8.84% to 65.24% for apartment houses and from 8.58% to 55.40% for business facilities. Additionally, the ZCBI across all stages based on _A1–A3CR ranged from 2.65% to 19.56% for apartment houses and from 1.77% to 11.42% for business facilities.
• Finally, the key materials contributing to the top 99% of cumulative carbon emissions during the production stage (_A1–A3CE) were identified. For both apartment houses and business facilities, these materials, ranked by impact, were ready-mixed concrete, steel, cement, and masonry.