Comparative Life Cycle Assessment of Reconstruction and Renovation for Carbon Reduction in Buildings

Abstract

This study compares the environmental impacts of building reconstruction and renovation in aging building improvement projects and quantitatively assesses their carbon reduction potential from a life cycle perspective. A life cycle assessment (LCA) methodology was used to estimate greenhouse gas emissions across all stages—production, transportation, construction, operation, and disposal. A reinforced concrete (RC) structure in Seoul served as the case study, with three scenarios modeled: maintaining the existing structure, reconstruction, and renovation. Results show that renovation produced a carbon emission intensity of approximately 1.37 × 10³ kg–CO₂eq/m²—46.21% lower than the existing building and 22.34% lower than reconstruction. Renovation offered significant embodied carbon savings during the production and demolition phases. In the operational phase, emissions were reduced by 47.50% through upgrades such as high-performance insulation, better windows, and renewable energy systems. While reconstruction showed some emission reductions, its environmental burden remained higher due to the need for new materials and additional demolition waste. Overall, renovation demonstrates greater carbon reduction potential across the building’s life cycle. These findings underscore its value as a key strategy for achieving carbon neutrality in the building sector by 2050 and provide scientific evidence to inform design and policy decisions.

1. Introduction

Since the 1970s, South Korea’s construction industry has experienced rapid growth driven by economic development and urbanization, resulting in a steady supply of large-scale residential and commercial buildings. Consequently, over 41% of the nation’s building stock is now more than 30 years old—a figure that has continued to rise in recent years [1,2].

Aging buildings commonly suffer from structural degradation, reduced energy efficiency, and an inability to meet evolving user needs, making functional improvements difficult through routine maintenance alone [3]. These limitations highlight the need for comprehensive performance upgrades beyond simple repairs. In response, both reconstruction and renovation projects have expanded rapidly as viable strategies to enhance building performance, promote resource circularity, and reduce environmental impacts. Related policies and regulatory frameworks have been progressively refined accordingly [4].

However, reconstruction involves complete demolition, generating substantial construction waste and significant greenhouse gas (GHG) emissions from the production and transportation of new materials [5]. Numerous studies have emphasized the considerable environmental burden associated with waste processing and material production in reconstruction projects [6,7,8], raising concerns about its sustainability in the context of achieving carbon neutrality by 2050. In contrast, renovation retains much of the existing structure, reducing resource consumption and minimizing waste [9]. As a result, it is increasingly viewed as a compelling alternative. In advanced economies such as Europe and Japan, renovation is already considered a core strategy for carbon neutrality, with policy discussions supporting its expansion gaining momentum [10,11].

Nonetheless, the decision between reconstruction and renovation should not rely solely on economic feasibility or construction duration. Instead, it requires quantitative evidence on long-term environmental impacts across the entire building life cycle [12]. Most prior studies have focused narrowly on operational-phase benefits such as improved energy performance [13,14], while comprehensive life cycle-based environmental assessments remain limited [15]. Although the importance of reducing embodied carbon is gaining attention [16,17], few studies have evaluated the full life cycle—from material production and transport during manufacturing, to energy use and waste during construction, and the environmental burden at the end-of-life phase. This lack of comprehensive analysis hinders efforts to validate the environmental benefits of renovation and integrate them into policy.

Globally, building a life cycle assessment (LCA) based on the ISO 14040 series is widely recognized as a tool for quantitative comparison and policy guidance. However, studies directly comparing reconstruction and renovation—especially those quantifying carbon emissions based on real-world cases—remain scarce [18,19,20].

To address these gaps, this study presents a scientific and systematic decision-making framework by comparing the environmental impacts of reconstruction and renovation from a life cycle perspective. Using the ISO 14040-based LCA methodology, we quantify carbon emissions for three scenarios: maintaining the existing structure, renovation, and reconstruction. The results offer essential baseline data to evaluate the environmental validity of building improvement projects and inform future policies and design strategies aligned with carbon neutrality goals. Specifically, this study contributes to the literature in three novel ways. First, it provides a comprehensive life cycle-based comparison covering the production, transportation, construction, operation, and end-of-life phases, whereas most prior studies focused primarily on operational energy savings. Second, it presents empirical evidence from the Korean context by analyzing a real reinforced concrete building in Seoul, which addresses the lack of region-specific comparative LCA studies in East Asia. Third, it highlights explicit policy implications by linking the results to South Korea’s 2050 carbon neutrality roadmap, thereby offering actionable insights for both policymakers and design practitioners.

2. Life Cycle Assessment

2.1. Building Life Cycle Assessment

Building LCA is a standardized methodology for quantitatively evaluating the environmental impacts associated with a building throughout its entire life span. It follows the guidelines established by the International Organization for Standardization (ISO), specifically ISO 14040 and ISO 14044 [21,22]. ISO 14040 defines the overall principles and framework of life cycle assessment, outlining its four phases: goal and scope definition, life cycle inventory analysis, impact assessment, and interpretation. ISO 14044 complements this by specifying detailed requirements and procedures for each phase, including criteria for data quality, transparency, and consistency. Together, these standards ensure that LCAs are conducted in a scientifically rigorous and internationally comparable manner. By grounding this study in ISO standards, the results gain greater credibility and can be more readily applied to policy and practice both in South Korea and internationally.

In the building sector, LCA is increasingly applied from the design phase onward to guide carbon reduction strategies across all stages—from material production and construction to operation, maintenance, demolition, and disposal [23]. Unlike conventional assessments that focus on a single phase, LCA provides a comprehensive analysis of both embodied carbon (emissions from materials and construction processes) and operational carbon (emissions during building use).

Figure 1 illustrates the system boundary of a typical building LCA. Unlike general consumer products, buildings have long life spans and varying operational conditions. Therefore, assessments must account for both operational energy use and embodied carbon from material production and end-of-life demolition. Defining the full life cycle boundary helps avoid under- or overestimating environmental impacts by considering all relevant phases.

In the context of reconstruction and renovation, LCA plays a key role in comparative evaluation. Reconstruction involves demolishing existing buildings and constructing new structures, leading to substantial material production and construction waste—significantly increasing embodied carbon. Renovation, by contrast, retains much of the existing structural framework, minimizing resource inputs and waste generation during early stages. Using consistent system boundaries and functional units, LCA enables an objective, life cycle-based comparison of these alternatives, offering evidence that goes beyond simple cost analysis to assess environmental feasibility.

LCA also serves as a decision-making tool during the design phase, allowing quantitative prediction of long-term greenhouse gas emissions based on choices such as material selection (e.g., reinforced concrete vs. steel), energy systems (e.g., conventional vs. renewable), or envelope upgrades (e.g., high-performance insulation, windows). These insights provide a data-driven foundation for developing strategies to meet 2050 carbon neutrality goals in the building sector.

In this regard, life cycle assessment is not merely a tool for quantifying environmental burdens—it serves as a strategic framework for ensuring sustainability across the design, construction, operation, and end-of-life phases. Based on this approach, the present study compares reconstruction and renovation scenarios to offer scientifically validated insights that support strategy selection in building improvement projects.

2.2. Evaluation Scope and Methodology

This study conducts a comparative analysis of carbon emissions generated during reconstruction and renovation to support decision making and feasibility evaluation of renovation projects. The analysis focuses on an existing reinforced concrete (RC) building in Seoul, South Korea, with two above-ground stories and one basement level. The building was modeled as renovated into a mixed steel and RC structure with three above-ground stories and one basement level. Carbon emissions were quantitatively estimated for both reconstruction and renovation scenarios using the same reference building, and projected emissions for the existing building were also calculated to assess the reduction potential. In the renovation scenario, the existing reinforced concrete framework (columns, beams, and foundations) was retained, while envelope elements such as walls, roof, and floors were replaced. In contrast, the reconstruction scenario assumed complete demolition of the existing building and replacement with a new reinforced concrete and steel structure.

A 50-year assessment period was adopted to represent the building’s service life, consistent with standard guidelines for building LCAs [24]. The system boundary covers the entire life cycle: material production (production stage), transportation to the construction site (transportation stage), construction activities and equipment energy use (construction stage), building operation and maintenance (operation stage), and end-of-life processes including demolition and waste disposal (via incineration or landfill). The functional unit is defined as one square meter of floor area over a 50-year service life. The reference flow includes all materials and energy required to operate a general-purpose building over this period. For the operational stage, greenhouse gas emissions were calculated using carbon intensity factors from the Korean national LCI database, ensuring consistency with national standards [25].

This comprehensive scope allows for a robust evaluation of carbon emissions across the building’s full life cycle and facilitates a quantitative comparison of the environmental impacts of reconstruction and renovation as alternative improvement strategies.

Table 1. Overview of the analysis targets.

Category		Unit	Existing Building	Renovation
Site Area		m2	580,852.80	580,852.80
Structural System		-	Reinforced Concrete (RC)	Reinforced Concrete (RC), Steel
Building Scale		-	2 above/1 below	3 above/1 below
Building Area		m2	7639.10	15,989.80
Building Coverage		%	12.19	13.63
Floor Area Ratio		%	19.67	22.26
Floor Area	Above	m2	6050.00	21,080.76
	Below	m2	4622.00	5127.92
	Total	m2	10,672.00	26,208.68

shows the overview of the analysis targets.

2.3. Data Collection for Carbon Emissions Assessment

A building LCA approach was applied to quantitatively assess potential carbon emissions and environmental impacts over the full life span of the subject building. Construction material input data varied by scenario.

For the existing building, material quantities were estimated using the database, which compiles representative averages of buildings with similar use, structure, and construction period. This approach has been widely adopted in building LCA studies, and prior research has demonstrated that LCA databases provide sufficiently reliable and representative data for assessing environmental impacts of construction materials when project-specific information is unavailable [26]. In contrast, actual design documentation was used for the reconstruction and renovation scenarios. Material quantities and types were obtained directly from architectural drawings and material schedules to reflect the specific characteristics of each plan.

Energy demand during the operational phase was calculated according to international standards such as ISO 13790 and DIN 18599, which define methods for determining annual primary energy consumption [27,28]. For the existing building, thermal transmittance (U-values) of the envelope and window performance were based on 1980s South Korean regulations. For reconstructed and renovated buildings, current standards outlined in the Energy Saving Design Criteria for Buildings were applied [29]. Transport-related environmental impacts were evaluated by assigning transport modes to each material, following the 2025 Standard Construction Cost Estimating Guide [30].

3. Carbon Emissions Assessment for Renovation

3.1. Production Phase (A1–A3)

Accurate data on material types and quantities is essential for evaluating environmental impacts during the production phase. In this study, the subject building was assessed under three scenarios: maintaining the existing structure, reconstruction, and renovation.

For the existing building, design and construction documents were unavailable, making it difficult to determine exact material quantities. Therefore, material inputs were estimated using a life cycle assessment database of buildings with similar use and structural characteristics. Material quantities were required to establish a baseline for embodied carbon emissions during the production and demolition phases, enabling a consistent comparison with reconstruction and renovation scenarios. This approach allowed the calculation of average material composition and quantities, which were then used to assess environmental impacts.

For the reconstruction and renovation scenarios, detailed material data were obtained from actual design documents developed during the planning phase. Thus, estimated data were used for the existing building based on comparable cases. In the renovation scenario, concrete and reinforcing steel demand were significantly reduced compared to reconstruction because the structural frame was preserved. For example, ready-mixed concrete use was 9418 tons for renovation versus 33,372 tons for reconstruction, and reinforcing steel was 458 tons versus 1622 tons, respectively. On the other hand, new materials such as steel trusses, reinforcement plates, and metal panels were introduced in the renovation to support the upgraded structure and envelope. These differences in retained versus replaced elements formed the basis of the comparative analysis. Material quantity estimates for the production phase excluded temporary materials and reusable construction aids, focusing only on permanent materials incorporated into the building.

Table 2. The major material quantities by scenario.

Material	Amount (tons)
	Existing	Reconstruction	Renovation
Ready-mixed Concrete	24,540.05	33,372.43	9417.66
Reinforcing Steel	1192.71	1621.99	457.72
Brick	688.49	936.28	264.22
Cement	584.26	794.54	224.22
Aggregate	1421.76	1933.48	545.62
Steel Truss	-	1904.20	1904.20
Reinforcement Plate	-	0.07	0.07
Metal Panel	-	136.09	136.09

shows the major material quantities by scenario.

3.2. Construction Phase (A4–A5)

3.2.1. Transportation (A4)

To evaluate the environmental impacts of material transport during construction, the primary materials identified in the production phase were matched with appropriate transport modes and distances. For transportation-related impacts, transport modes were assigned by material type per the 2025 Standard Construction Cost Estimating Guide: ready-mixed concrete via mixer trucks; steel reinforcement, structural steel, aggregates, and metals via 20-ton trucks; and other materials via 8-ton trucks. A uniform transport distance of 30 km was applied, based on the Korean Green Building Certification System (G-SEED) guidelines [24]. A summary of the transport-related data is provided in

Table 3. Summary of transport-related data by scenario.

No.	Material	Transported Amount (tons)			Transport Distance (km)	Transport Mode
		Existing	Reconstruction	Renovation
1	Ready-mixed Concrete	24,540.05	33,372.43	9417.66	30	Ready-mixed Concrete
2	Reinforcing Steel	1192.71	1621.99	457.72	30	20-ton Truck
3	Brick	688.49	936.28	264.22	30	8-ton Truck
4	Cement	584.26	794.54	224.22	30	8-ton Truck
5	Aggregate	1421.76	1933.48	545.62	30	20-ton Truck
6	Steel Truss	-	1904.20	1904.20	30	20-ton Truck
7	Reinforcement Plate	-	0.07	0.07	30	20-ton Truck
	Metal Panel	-	136.09	136.09	30	20-ton Truck

.

3.2.2. Construction Process (A5)

Environmental impacts during the construction process were assessed by estimating the types and quantities of energy used for each construction activity. Since site-specific energy consumption data for the subject building were unavailable, energy usage was estimated using models based on similar building types [31].

3.3. Operational Phase (B4, B6)

Operational energy consumption was calculated using the Building Energy Demand Evaluation Report. The building was classified as a general-purpose facility, with energy use covering heating, cooling, hot water, lighting, and ventilation. A 50-year service life was assumed, as per national LCA guidelines. Seoul is located in a temperate climate with hot, humid summers and cold winters, which imposes high energy demand for both cooling and heating. This climatic context was explicitly incorporated into the operational energy assessment to ensure realistic simulation results.

Annual primary energy demand over the building’s operational life was calculated using energy simulations based on the methods outlined in ISO 13790 and DIN 18599.

For both the existing and renovated buildings, thermal insulation performance was assumed to match the legal U-values applicable at the time of the building permit. Specifically, the existing building’s envelope and window performance were assessed using standards from the 1980s Enforcement Rules of the Building Act [32], while the renovated building followed the current Energy Saving Design Criteria [33].

Due to limited data on mechanical equipment capacities, estimates were made using values from literature on comparable buildings [34].

Equipment replacement and maintenance cycles were considered: electric heat pumps (EHPs) were assumed to have an 8-year lifespan based on Environmental Product Declaration (EPD) scenarios [041 Air Conditioner]; gas boilers were assumed to last 15 years; and LED lighting was assumed to have a lifespan of 7000 h, based on the EPD scenario [027 LED Lighting] [35].

For ventilation systems, the existing building was assumed to lack a heat recovery system, as such requirements did not exist at the time of its construction.

Lighting power density was set at 7.5 W/m² for both the existing and renovated buildings, based on simulation parameters from the Korea Institute of Civil Engineering and Building Technology (2016) for GHG reduction potential modeling.

Finally, the capacity of the renewable energy system in the renovated building was estimated based on the 2025 mandatory renewable energy supply ratio (34%) stipulated by the Act on the Promotion of the Development, Use, and Diffusion of New and Renewable Energy [36].

Table 4. Building energy consumption assessment method.

Classification	Description
Assessment Method	Evaluation of energy consumption and primary energy consumption based on ISO 13790 and DIN V 18599 standards Energy consumption per unit area = ${\displaystyle \frac{E\left(cooling\right)+E\left(Heating\right)+E\left(Lighting\right)+E(Hot water)+E\left(Ventilation\right)}{A(floor area of the energy-demanding space)}}$ Primary energy consumption per unit area = Energy consumption per unit area × Primary energy conversion factor
Assessment Tool	ECO2-OD (developed and distributed by the Korea Energy Agency) A static energy consumption simulation tool based on ISO 13790 and DIN V 18599 Used in Korea’s “Total Energy Consumption Regulation” and “Green Remodeling Performance Evaluation”
Input Data for Assessment (Input data)	Climate Data	Regional weather data embedded in ECO2-OD (Monthly outdoor temperatures, solar radiation, etc.)
	Usage Profile	Building operation profiles by usage type (embedded in ECO2-OD) (Occupant schedules, equipment operation schedules, lighting schedules, indoor temperature setpoints)
	Architectural Parameters	Heated/cooled floor area Insulation Performance (U-values and coverage areas of walls, roof, and floor insulation) Window Performance (Window U-values, Solar Heat Gain Coefficients (SHGC), and window area)
	Mechanical Systems	Heating/cooling/domestic hot water systems (Rated capacity, efficiency (% or COP), fuel type) Ventilation (Airflow rate, external static pressure, power consumption)
	Electrical Systems	Total lighting system power consumption
	Renewable Energy Systems	Installation of Photovoltaic Modules (Module type, installed capacity and area, orientation) Installation of Geothermal Facilities (Heat pump capacity, efficiency, fuel type)
Output Data After Assessment (Output data)	Energy Demand	Energy required to maintain indoor comfort (e.g., thermal and lighting energy) under specific conditions (e.g., indoor/outdoor temperature, occupancy)
	Energy Consumption	Energy consumed by building systems to meet the energy demand
	Primary Energy Consumption	Energy consumption multiplied by a primary energy conversion factor, accounting for losses during electricity generation and fuel transport

summarizes the Building Energy Consumption Assessment Method, and

Table 5. Input data for energy consumption assessment using ECO₂-OD.

Classification		Input Item
		Existing Building				Renovation (Same as New Construction)
		Direct		Indirect		Direct		Indirect
Envelope U-value	External Wall (W/m2K)	0.582		0.582		0.240		0.340
	Roof (W/m2K)	0.582		0.582		0.150		0.210
	Floor (W/m2K)	1.163		1.163		0.200		0.290
Window Performance	U-value (W/m2K)	3.489		3.489		1.500		1.900
	Solar Heat Gain Coefficient	0.74		-		0.583		-
Heating System	Type	Electric Heat Pump				Geothermal Heat Pump
	Fuel Type	Electricity				Geothermal
	Capacity (kW)	1675.80				3609.32
	COP	3.46				5.4
Cooling System	Type	Electric Heat Pump				Geothermal Heat Pump
	Fuel Type	Electricity				Geothermal
	Capacity (kW)	1513.40				3350.82
	COP	2.77				4.19
Hot Water System	Type	Gas Boiler				Gas Water Heater
	Fuel Type	NG (Natural Gas)				NG (Natural Gas)
	Capacity (kW)	1569.75				1569.75
	Combustion Efficiency	90.1%				90.1%
Ventilation System	Air Volume (CMH)	25,500				30,500
	Static Pressure (Pa)	15				15
	Power Consumption(kW)	0.254 (kW)				0.254 (kW)
	Heat Recovery Status	Not applied				Applied
	Heat Exchange Efficiency (%)	Cooling	0	Heating	0	Cooling	52	Heating	72
Lighting System	Fixture Type	LED				LED
	Total Power Consumption (W)	33,000				81,500
Renewable System		Not installed				Geothermal	3609.32 kW

presents the input data for Energy Consumption Assessment Using ECO₂-OD.

Table 6. Energy consumption assessment results.

Classification		Description
Existing	Results Graph
	Consumption Assessment Results	Usage	Renewable	Heating	Cooling	Hot Water	Lighting	Ventilation	Total
	Energy Demand (kWh/m2·yr)		-	62.7	9.7	5.2	18.5	-	96.1
	Energy Consumption (kWh/m2·yr)		-	38.1	5.9	7.3	18.5	7.2	77.1
	Primary Energy Consumption (kWh/m2·yr)		-	104.7	16.4	8.1	50.9	19.8	199.9
Renovation	Results Graph
	Consumption Assessment Results	Usage	Renewable	Heating	Cooling	Hot Water	Lighting	Ventilation	Total
	Energy Demand (kWh/m2·yr)		-	21.9	9.1	5.2	18.5	-	54.7
	Energy Consumption (kWh/m2·yr)		−8.6	6.1	2.5	6.4	18.5	8.7	42.2
	Primary Energy Consumption (kWh/m2·yr)		−8.6	16.8	6.9	7.0	50.9	23.9	105.5

presents the energy consumption assessment results. Table 6 summarizes the results of the operational energy consumption assessment for the existing and renovated buildings. For the existing building, the total energy demand was estimated at 96.1 kWh/m²·yr, with heating (62.7 kWh/m²·yr) and hot water (18.5 kWh/m²·yr) accounting for the largest shares. The corresponding final energy consumption reached 77.1 kWh/m²·yr, while the primary energy consumption was 199.9 kWh/m²·yr.

In contrast, the renovation scenario showed significant improvements. The total energy demand was reduced to 54.7 kWh/m²·yr, representing a decrease of approximately 43% compared to the existing building. The greatest reductions were observed in heating, where demand fell from 62.7 to 21.9 kWh/m²·yr, and in cooling, from 9.7 to 9.1 kWh/m²·yr. With the integration of renewable energy systems, the final energy consumption decreased to 42.2 kWh/m²·yr, and the primary energy consumption was reduced to 105.5 kWh/m²·yr—almost half the level of the existing building.

These results indicate that renovation substantially improves operational performance by reducing heating and cooling loads through envelope upgrades, while renewable energy integration further decreases dependence on conventional energy sources. Overall, the renovation scenario demonstrates a considerable reduction in operational energy consumption, reinforcing its effectiveness as a strategy for achieving long-term carbon reduction goals.

3.4. End-of-Life Phase (C1, C2, C4)

3.4.1. Demolition Process

Assessment of environmental impacts during demolition requires data on the energy consumption of demolition equipment. In this study, an estimation model developed in previous research was applied to calculate demolition energy use, and the resulting values were incorporated into the end-of-life phase impact assessment [31]. In addition, demolition waste was quantified as the total amount of materials originally used during construction together with those added through maintenance over the building’s service life. In the renovation scenario, although the quantity of newly added materials is smaller than in the new construction scenario, the existing structural components that were retained are also assumed to be demolished at the end of the 50-year service life. For this reason, the final demolition waste volumes for renovation were treated as equivalent to those of new construction. This assumption was applied to ensure consistency in system boundaries across scenarios. The demolition scenario assumed the use of standard equipment typically deployed in practice—specifically, a 0.7 m³ breaker and a 1.0 m³ backhoe. Energy consumption and associated environmental impacts based on diesel use are presented in

Table 7. Energy consumption results for demolition phase by scenario.

Classification	Amount (ton)	Demolition Equipment	Fuel Type	Energy Consumption (ℓ)	Data Quality
Existing	28,427	Breaker (0.7 m3) + Backhoe (1.0 m3)	Diesel	103,532	Estimated
New Construction	40,699	Breaker (0.7 m3) + Backhoe (1.0 m3)	Diesel	148,226	Estimated
Renovation	40,699	Breaker (0.7 m3) + Backhoe (1.0 m3)	Diesel	148,226	Estimated

.

3.4.2. Transportation

To assess the environmental impact of transporting demolition waste, the transport volume was estimated based on the designated disposal methods. Waste materials were classified into three treatment types: recycling, incineration, and landfill. Waste processing rates (recycling, landfill, incineration) were derived from the 2023 Waste Generation and Treatment Report by the Ministry of Environment [35]. Transport volumes were calculated using material-specific disposal ratios. Results are summarized in

Table 8. Transport quantities by material processing method.

Classification	Transported Amount (tons)			Transport Distance (km)	Transport Mode	Data Quality
	Existing	New Construction	Renovation
Construction Waste Transportation (Site-Recycling Facility)	28,397.55	40,658.66	40,658.66	30	15-ton Truck	Estimated
Construction Waste Transportation (Site-Incineration Plant)	-	-	-	30	15-ton Truck	Estimated
Construction Waste Transportation (Site-Landfill)	29.72	40.42	40.42	30	15-ton Truck	Estimated

.

Transport was assumed to be carried out using 15-ton trucks, based on the 2025 Standard Construction Cost Estimating Guide. A uniform transport distance of 30 km was applied to all materials, as recommended by the Green Building Certification Guidelines (G-SEED, 2016) [24].

3.4.3. Disposal (Incineration and Landfilling)

Demolition waste was categorized into three disposal routes—recycling, incineration, and landfill—and corresponding quantities were estimated. The incinerated and landfilled quantities are provided in

Table 9. Quantities of waste construction materials by disposal method.

Classification	Waste Material Amount (ton)			Data Quality
	Existing	New Construction	Renovation
Incineration	-	-	-	Estimated
Landfilling	29.72	40.42	40.42	Estimated

.

The cut-off approach, recommended in national building LCA guidelines, was applied: waste materials designated for recycling were excluded from the system boundary upon collection and attributed to the waste management company rather than the building system.

3.5. Carbon Emissions Assessment Results

Global warming refers to the increase in the Earth’s average surface temperature due to the rising concentration of greenhouse gases (GHGs) in the atmosphere. Among the ~20 substances classified by the IPCC for global warming potential (GWP) are carbon dioxide (CO₂), methane (CH₄), nitrous oxide (N₂O), hydrofluorocarbons (HFCs), and sulfur hexafluoride (SF₆). Carbon dioxide is considered the most representative GHG [37].

This study conducted LCAs for three scenarios—maintaining the existing structure, reconstruction, and renovation—to estimate their respective GWPs.

Table 10. Results of carbon emission assessment by stage.

Classification		Emissions per Building (kg–CO2eq)			Emissions per Unit Area(kg–CO2eq/m2)
		Existing	New Construction	Renovation	Existing	New Construction	Renovation
Production Phase		5.65 × 106	9.97 × 106	4.46 × 106	5.29 × 102	6.87 × 102	3.07 × 102
Construction Process	Transportation Process	2.16 × 105	2.94 × 105	8.29 × 104	2.02 × 101	2.02 × 101	5.71
	Construction Process	6.44 × 104	8.76 × 104	2.47 × 104	6.04	6.04	6.04
Operation Phase	Operation Energy Process	2.13 × 107	2.74 × 107	2.74 × 107	2.00 × 103	1.05 × 103	1.05 × 103
	Replacement Process	0.00	0.00	0.00	0.00	0.00	0.00
End-of-life Stage	Demolition Process	2.81 × 104	4.02 × 104	4.02 × 104	2.63	2.77	2.77
	Transportation Process	6.59 × 101	1.61 × 102	1.61 × 102	6.17 × 10−3	1.11 × 10−2	1.11 × 10−2
	Disposal (Incineration, Landfill) Process	1.80 × 103	2.45 × 103	2.45 × 103	1.68 × 10−1	1.68 × 10−1	1.68 × 10−1
Total		2.73 × 107	3.78 × 107	3.20 × 107	2.55 × 103	1.77 × 103	1.37 × 103
Reduction vs. Existing (%)							46.21%
Reduction vs. New Construction (%)							22.34%

and Figure 2 present the detailed results.

• Existing building: total emissions = 2.73 × 10⁷ kg–CO₂eq; per-unit-area = 2.55 × 10³ kg–CO₂eq/m²
• Reconstruction: total emissions = 3.78 × 10⁷ kg–CO₂eq; per-unit-area = 1.77 × 10³ kg–CO₂eq/m² (30.59% reduction from existing building)
• Renovation: total emissions = 3.20 × 10⁷ kg–CO₂eq; per-unit-area = 1.37 × 10³ kg–CO₂eq/m² (46.21% reduction from existing building, 22.34% reduction from reconstruction)

In the operational phase, both reconstruction and renovation showed emissions of 1.05 × 10³ kg–CO₂eq/m²—representing a 47.50% reduction compared to the existing structure. This reduction was driven by improved insulation, window performance, and the integration of renewable energy systems such as geothermal heating.

In summary, reconstruction reduced per-unit-area emissions by approximately 30.59% compared to the baseline, while renovation achieved a greater reduction of 46.21%. Moreover, renovation outperformed reconstruction by 22.34%, primarily due to its ability to retain structural elements, reduce material consumption, and minimize waste. These results suggest that renovation is a more environmentally effective alternative to reconstruction.

4. Discussion

This study quantitatively compared the life cycle carbon emissions of reconstruction and renovation scenarios for aging buildings using LCA. The analysis showed that renovation resulted in approximately 46.21% lower greenhouse gas emissions compared to the existing building and 22.34% lower than reconstruction. These outcomes are attributable to reduced embodied carbon through the reuse of structural elements and improved energy efficiency during operation. This aligns with prior research highlighting the environmental benefits of renovation due to material reuse over reconstruction [37,38,39]. Importantly, this study addressed limitations in prior research that focused primarily on the operational phase by integrating both embodied carbon (from production and demolition) and operational energy consumption into a single comprehensive assessment. The environmental benefits of renovation were evident not only during the use phase but also in reduced resource input and waste generation during the early and end-of-life phases, underscoring the importance of LCA-based decision making in future building improvement projects.

From a policy perspective, the findings support the environmental validity of renovation-based improvement strategies for aging buildings. In particular, they provide valuable insights into how the building sector can contribute to the 2050 carbon neutrality roadmap. To shift development practices away from a reconstruction-centric approach and toward renovation, it is essential to implement incentive programs and design guidelines that reflect embodied carbon savings through LCA-based criteria.

Nevertheless, because this study was conducted at the planning stage, some input data relied on estimates from comparable buildings and existing databases, which may introduce uncertainties in areas such as demolition energy consumption and construction-phase material-specific energy inputs. Moreover, since the analysis was based on a single case study, the generalizability of the findings is limited. Future research should therefore expand to multiple building types and scales, ideally supported by on-site measured data, to improve robustness and applicability.

Finally, although this study concentrated on environmental impacts, it also recognizes that economic considerations—including construction costs, maintenance expenses, and long-term energy savings—are critical in decision making. While a detailed cost analysis was beyond the present scope, future studies that integrate environmental and economic perspectives would provide more comprehensive evidence for stakeholders and policymakers.

5. Conclusions

This study applied life cycle assessment (LCA) to quantitatively evaluate and compare the environmental impacts of reconstruction and renovation as improvement strategies for aging buildings. The analysis covered the full life cycle—production, transportation, construction, operation, and end-of-life—across three scenarios: maintaining the existing building, reconstruction, and renovation.

The results showed that renovation achieved a 46.21% reduction in carbon emissions per unit area compared to the existing building and a 22.34% reduction compared to reconstruction. This reduction was especially prominent in the production and demolition phases, where embodied carbon savings were most significant. During the operational phase, further reductions of approximately 47.50% were achieved through the use of high-performance insulation, upgraded windows, and renewable energy systems. While reconstruction did lead to emission reductions compared to the existing building, its overall environmental burden remained relatively high due to the production of new materials and construction waste generation. Similar patterns have also been observed in international studies, further supporting the robustness and generalizability of these findings. Comparative whole-building LCA research has shown that renovation consistently achieves substantially lower life-cycle emissions than new construction across different building typologies [12,40]. Likewise, Dragonetti et al. reported a life-cycle intensity of approximately 1.34 × 10³ kg–CO₂eq/m² over 50 years—closely matching the 1.37 × 10³ kg–CO₂eq/m² identified in this study [41]. These parallels confirm that the Korean case aligns well with international benchmarks, underscoring the broader international relevance of the results.

These findings suggest that renovation is a more environmentally favorable alternative to reconstruction, particularly in terms of resource conservation and greenhouse gas mitigation. Given South Korea’s national goal of achieving carbon neutrality by 2050, renovation provides a compelling strategy to reduce embodied carbon while enhancing operational energy efficiency.

Therefore, this study offers scientific evidence to guide decision making by clients, policymakers, and designers when selecting building improvement strategies. The results may serve as a foundation for the development of future policies, standards, and design guidelines related to renovation and reconstruction.