Analyzing CO₂ Emissions by CSI Categories: A Life Cycle Perspective

Abstract

As the construction industry continues to evolve, energy consumption of buildings, particularly CO₂ emissions, has become a critical focus for sustainable development. The need for effective design decisions regarding the selection of materials throughout the project life cycle is apparent, yet the link between specifications and CO₂ emissions has not been set yet. This study presents a comprehensive life cycle assessment (LCA) of CO₂ emissions across various Construction Specifications Institute (CSI) categories, aiming to identify the carbon footprint of different building systems and materials. The methodology focuses on using 3D building model case studies to evaluate the design decisions versus their impact on global warming potential (GWP). The results of this study emphasize that within CSI categories, concrete divisions consistently emerge as the predominant contributors to GWP, exceeding 75% in several instances. Following closely, metals contribute approximately 50% in multiple projects. The study also explores sustainable design options across CSI divisions to provide insights into building components contributing most to a building’s overall carbon footprint. This deeper understanding of sustainable design principles regarding CSI divisions and their impact on carbon footprint reduction will help sustainable designers and construction managers to implement carbon-conscious material choices and design strategies early in the planning phase.

1. Introduction

With the construction industry rapidly growing in the last two decades, environmental concerns regarding the consumption of natural gas and energy have become prominent. According to the 2018 Commercial Buildings Energy Consumption Survey (CBECS), U.S. commercial buildings consumed 6.8 quadrillion British thermal units (BTUs) of energy, with electricity and natural gas being the main energy sources [1]. According to the Global Status Report for Buildings and Construction, the construction sector consumes 32% of global energy and contributes 34% of the global CO₂ emissions [2]. Additionally, the report states that materials like cement and steel, essential for construction, are responsible for 18% of the global emissions. As sustainable development becomes crucial for the building sector, the selection of materials throughout a project’s life cycle emerges as a critical factor.

The life cycle assessment (LCA) method offers researchers the ability to analyze environmental impacts, including CO₂ emissions, associated with the production, transportation, and installation of building materials [3]. Studies showed that LCA stretches across more phases of the building life cycle, including the production of building materials, construction, operation, demolition, and deconstruction of buildings [4]. Several studies were conducted related to the CO₂ emissions of specific construction materials. One of the recent studies focused on investigating the carbon footprint of precast concrete piles, specifically during the building construction stage, in China, with an aim to quantify and analyze the environmental impact of this construction material [5]. In another study, Wang et al. combined Building Information Modeling (BIM) with advanced Dynamo visual programming to enhance tunnel design and assess CO₂ emissions, which showed that integrating CO₂ emissions data into the BIM model can lead to more sustainable engineering practices [6].

There are multiple studies in the recent literature combining BIM with LCA. Lu et al. (2021) [7] integrated LCA and Life Cycle Cost (LCC) by using BIM. Their four-step methodology framework included defining system boundaries, inventory analysis, obtaining environmental impact and cost results, and analyzing and optimizing the results for the best project applications [7]. Another paper by Dormohamadi et al. (2024) compared the environmental and economic impacts of earth-based and conventional walling materials and provided suggestions for alternative materials with lower environmental impacts [8]. Some of these studies specifically focused on the use of BIM to observe CO₂ emissions. Zhao et al. (2024) [9] focused on hospital buildings to unite BIM and LCA in calculating CO₂ emissions. The operational CO₂ emissions of hospital buildings were found to be the main source of emissions, showing hospital buildings how to promote efficient building performance [9]. Sun and Park (2020) focused on the construction process and presented a methodology for calculating CO₂ emissions using BIM [10]. Osorio-Gómez et al. (2025) concentrated on various environmental impacts, including global warming potential, over a 50-year period, by integrating BIM and LCA [11]. Mah et al. (2011) [12] established a baseline for CO₂ emissions in residential construction by integrating emission data into a 3D BIM model. They identified the key stages for higher emissions as foundation and framing [12].

The literature is also rich with studies focusing on the LCA of construction materials and methods. A recent review by Barbhuniya & Das (2023) focused on a comprehensive analysis of LCA principles, phases, and key parameters specific to construction materials, including inventory analysis, impact assessment, and uncertainty analysis. LCA studies on materials like cement, concrete, steel, and wood were examined, and the results emphasized a need for data quality, standardization, and integration of social aspects [13]. Balashbaned & Sher (2024) [14] performed a systematic literature review to evaluate the LCA process of certain materials such as cross-laminated timber (CLT), glued laminated timber (GLT), and laminated veneer lumber (LVL). Their study revealed significant CO₂ emissions for manufacturing cross-laminated timber, and they proposed a framework to identify the best material alternatives for engineering wood [14]. Lin et al. (2025) explored LCA in connection with Environmental Product Declaration (EPD) data and circular principles focused on mass timber’s end-of-life [15]. Their research highlighted a lack of comprehensive data for end-of-life practices of timber and mentioned challenges of integrating material data into LCA frameworks. A similar study by Wang and Lan (2024) performed a cradle-to-grave LCA on the cross-laminated bamboo and included circular aspects like recycling rates and end-of-life scenarios, paired with a Monte Carlo analysis of uncertainties [16].

Choi and Tae (2024) [17] proposed a comprehensive Life Cycle Sustainability Assessment (LCSA) framework for concrete, integrating environmental, economic, and social dimensions. Their framework emphasized the importance of considering social impacts alongside environmental and economic factors in the sustainability assessment of concrete and made it possible to quantitatively evaluate concrete sustainability [17]. Another recent study by Chen (2025) [18] explored the integration of LCA with Geographic Information Systems (GIS) and Artificial Intelligence (AI) to optimize recycling and reuse strategies in building construction. They found that the use of GIS can help decrease CO₂ emissions by locating recycling sites and distribution networks on the map [18]. Kumar et al. (2024) [19] performed a whole-building LCA comparing mass timber, steel, and concrete buildings of varying heights, and have had one of the few studies based on the International Building Code provisions. Their findings indicated that mass timber buildings have significantly lower global warming potential compared to their steel and concrete counterparts [19].

Using LCA in the early stages of the project allows design and construction parties to have informed choices that minimize environmental impacts and optimize resource use, as mentioned by Moncaster et al. (2018) [20]. Najjar et al. (2017) proposed a framework for integrating BIM with LCA to assess environmental impacts during the early design stages of an office building. They used Autodesk Revit and associated tools to evaluate the life cycle impacts of building materials. Their study highlighted the power of BIM-LCA integration for a sustainable design and decision-making process [21]. Mohebbi et al. (2023) [22] performed a similar study by focusing on the whole life carbon of three construction methods in the UK by using Autodesk Revit. Their study emphasized the role of BIM in performing carbon assessments and the importance of selecting construction methods with lower carbon footprints [22]. With LCA’s ability to provide measurable data, project parties can set clear sustainability goals and make effective design decisions related to the selection of materials throughout the project life cycle.

While the importance of utilizing LCA and BIM technology in making effective design decisions, particularly in the selection of construction materials, throughout the project life cycle is widely acknowledged, there remains a significant gap in directly linking these material specifications to their associated CO₂ emissions. Recent studies highlight that while BIM–LCA methods are advancing, CO₂ emissions data are still missing or poorly integrated across several material categories, which can be linked to CSI divisions. As an example, Parece et al. (2024) stated that the current approaches have limitations, such as a lack of standardized geometry modeling and information management [23], which implies the current BIM-LCA tools struggle to link material databases correctly to 3D models and CSI classifications. BIM&CO, a well-known source for BIM objects that are used in 3D modeling, mentioned a lack of data for technical equipment [24], which can be linked to a lack of data in Division 22-Plumbing, Division 23 -HVAC, and Division 26-Electrical among the CSI divisions. Another study examined the BIM-LCA combination with two different LCA tools and found that the procedure is limited to data entry, interoperability with different software packages, and the intricacy of the LCA tools [25].

When studies related to BIM and LCA are further examined, several limitations were identified as a lack of alignment with domain models, such as BIM [26], and a lack of data on using waste and recycled materials as new building materials [27]. Despite its limitations, the BIM-LCA combination was found to be the optimal procedure to achieve sustainable development, and the application of building materials was suggested to be examined for this purpose [21]. While design choices can be made based on broader structural categories, or cost and availability of materials, integrating CO₂ emissions into the early stages of planning and specifications is rather new. In light of the previous studies, these limitations have been considered to support sustainable design decisions through linking material configurations to CSI divisions in this study.

CSI categories refer to the standardized divisions and subdivisions used in the Construction Specifications Institute (CSI) [28]. The CSI MasterFormat is widely used in the U.S. and Canada as the standard for the organization of construction specifications in commercial and institutional building projects. The scientific basis of CSI categories lies in their role as a taxonomy for the built environment. The CSI MasterFormat was created with 16 divisions and expanded to 50 divisions in 2004. Divisions represent the broad categories of construction work as concrete, masonry, and so on. Sections are created within these divisions to represent more detailed scopes of work as organized by type, function, or product. This organization of divisions and sections helps standardize the presentation of information. CSI MasterFormat also enhances interdisciplinary coordination and collaboration among project parties by organizing specifications across project phases and facilitating more structured data classification that helps BIM and LCA.

Opportunities to reduce CO₂ emissions across multiple CSI categories are frequently overlooked. Bridging this gap requires the integration of BIM and LCA to observe the variability in CO₂ emissions between CSI categories. This study conducts a comprehensive LCA of CO₂ emissions across multiple CSI divisions, with the goal of quantifying the carbon footprint associated with different building systems and material categories. The findings will allow construction practitioners to determine which building components contribute most to a structure’s overall carbon footprint and implement carbon-conscious material choices accordingly.

2. Materials and Methods

The methodology of this study includes 5 main steps: (1) select case studies, (2) create Autodesk Revit 3D models of case studies, (3) use a BIM-integrated software tool to perform material-based LCA for buildings, (4) calculate CO₂ emissions throughout the building’s life cycle phases, (5) group and analyze the results per CSI divisions. These steps are shown in Figure 1.

2.1. Selection of Case Studies

To evaluate sustainable design principles regarding CSI divisions and their impact on carbon footprint reduction, ten diverse case study projects were selected. The selection of the ten case studies was based on focusing on commercial or similar projects that use steel-framed systems. It was observed that the relevant building codes and regulations mandate the use of steel framing for commercial and similar building types due to requirements related to structural strength, fire resistance, and durability. Within this study, the case studies were deliberately structured to provide variation across other critical dimensions, including project type, size, function, and material configurations within steel-framed systems.

Further information about the case studies is presented in

Table 1. Case study properties in detail.

Project No	Project Type	Location	Gross Area (SF)	Main Materials Used
Project 1	Fraternity building	Lincoln, NE	8772	Concrete, steel framing, wood, fiberglass insulation, brick veneer
Project 2	Campus building	Philadelphia, PA	10,084	Steel framing (with extra metal bracing), concrete, wood, batt and fiberglass insulation, hollow core Concrete Masonry Unit (CMU)
Project 3	Campus building with a lab	Chester County, PA	15,268	Concrete, steel framing, sound attenuation blanket for insulation, rigid insulation with exterior grade plywood sheathing, exterior gypsum sheathing, R−11 batt insulation, manufactured stone veneer, aluminum and galvanized steel doors, double-panel glazing, special curtain walls, specific interior paint requirements
Project 4	Office building	Bucks County, PA	59,128	Concrete, precast concrete columns, steel framing, aluminum window frames, double glazed windows, double glazed spandrel panels, aluminum and galvanized steel doors, special curtain walls, brick veneer
Project 5	Dormitory	Clemson, SC	12,558	Concrete, precast concrete, steel framing, precast lintel, architecturally exposed structural steel, CMU, high-performance coating, elastomeric coating
Project 6	Office building	Greenville, DE	21,659	Cast-in-place concrete varying from 2500 to 3000 psi, precast concrete columns, steel framing
Project 7	Office building	Philadelphia, PA	119,717	Lightweight and structural cast-in-place concrete with 3000 psi strength, steel framing
Project 8	Hospitality	North Wildwood, NJ	67,250	Soundproofing, specific finishes, thermal and moisture requirements, concrete, steel
Project 9	Dormitory	Wilmington, DE	22,490	Concrete, acoustic insulation, specific finish requirements per room, steel
Project 10	Campus building	Tucson, AZ	54,805	Steel, cold-formed structural steel, galvanized steel decking, hot-rolled structural steel, concrete, finishes, specific interior paint requirements, generic bricks, hollow-core CMU

, which includes key details such as the type of project, its geographical location, the building’s total gross floor area, and the primary construction materials used. This information provides essential context for interpreting the results and understanding the characteristics and scope of each case study. The cases selected in this study varied significantly in scale, with floor areas ranging from approximately 8700 to 120,000 square feet (SF), allowing for analysis across both small- and large-scale developments. The range from 8700 SF to 120,000 SF ensured the representation of both smaller and larger commercial-like buildings. Larger buildings typically have more complex systems and higher energy demands, influencing their carbon emissions differently from smaller buildings.

Another reason for selecting these cases was their diverse building types. Case studies spanned various types of projects, including campus, office, and hospitality projects. By including these building types, the study covers a range of building functions and operational characteristics. Each type has distinct energy usage patterns, occupancy rates, and HVAC requirements, influencing their carbon footprint. Some of the campus projects were dormitory projects, which doubled as housing. These project types, while serving different occupants, were chosen to reflect a broad spectrum of functional requirements, design strategies, and material usage patterns commonly found in the built environment. In terms of functional requirements, the design of these projects requires clear pathways for the movement of people, whether the occupants are students, residents, or guests. In every one of them, safety and security systems are essential, and they comply with the Americans with Disabilities Act (ADA) standards. Whether the use of spaces changes, they each need to adapt to the changing needs of occupants, such as having multipurpose rooms. Most importantly, sustainability features, such as energy efficiency, water use, and proper waste management, have increasingly become standards in campus, housing, and hospitality projects. Each of these project types brings unique material demands and construction practices, making them ideal for a comparative LCA. Additionally, for the specific purposes of this study, all of the case studies selected have material categories based on CSI divisions. Overall, the selection of diverse case studies in terms of size and type enhanced the comprehensiveness and applicability of the carbon emissions in this study, providing valuable insights for reducing environmental impact in the construction and operation of buildings by using the BIM-LCA combination.

As the final and critical reason for selecting these ten case studies, the potential for seamless BIM-LCA integration was considered. This integration plays a pivotal role in enhancing the precision and reliability of carbon emissions assessments throughout all stages of a building’s life cycle-from material extraction and construction to operation and eventual deconstruction or reuse. For this integration to be effective, it is essential to have a comprehensive and well-structured BIM model using Autodesk Revit. Such a model must include accurate geometric data and detailed information about the materials utilized in the project for generating meaningful LCA results. Achieving this level of model detail required researchers to engage in close collaboration with project stakeholders to refine the Revit models and ensure they aligned with the material configuration requirements of the LCA software application.

Ultimately, the selection of these particular projects was not only driven by building type or size, but also by practical accessibility and data quality, ensuring that the BIM-LCA integration would be both technically feasible and methodologically successful. This approach allowed the study to produce accurate, consistent, and comparable carbon emission outputs, reinforcing the validity and relevance of its findings.

After selecting the majority of the case studies, it was realized that these case studies primarily lay in the same climate zone across the United States (U.S.) based on the International Energy Conservation Code (IECC) climate classification. As it is well-known, building energy use and carbon emissions are highly sensitive to climate. In colder climates, heating loads dominate the energy use, while in hotter regions, cooling and ventilation are critical factors for energy use and carbon emissions. Similarly, when material selection criteria are considered, buildings in hot–humid climates may use reflective roofing and moisture-resistant materials, while cold regions may prioritize thick insulation and triple-glazed windows. All of these preferences would affect the carbon emissions distributed among the CSI divisions. As the primarily selected case studies were in the U.S Climate Zone 4 A, limiting the study to this mixed–humid climate would provide insights specific to this zone, yet would fail to account for how buildings perform in hot–dry, hot–humid, cold, or marine climates. In order to capture the influence of regional environmental conditions on sustainable design strategies, three more case studies were added to the mix to represent a mix of climate zones. The geographic diversity might help the research account for variations in temperature, humidity, and seasonal weather patterns, all of which play a critical role in shaping energy performance and material selection. Additionally, expanding to other zones allows the study to capture a full range of operational energy demands, which significantly affect life cycle carbon emissions, which is the primary purpose of this study. The final list of case studies with their U.S. climate zones is given in

Table 2. Case studies.

Project No	U.S. Climate Zone	Classification
Project 1	Zone 5 A	Cool–Moist
Project 2	Zone 4 A	Mixed–Humid
Project 3	Zone 4 A	Mixed–Humid
Project 4	Zone 4 A	Mixed–Humid
Project 5	Zone 3 A	Hot–Humid
Project 6	Zone 4 A	Mixed–Humid
Project 7	Zone 4 A	Mixed–Humid
Project 8	Zone 4 A	Mixed–Humid
Project 9	Zone 4 A	Mixed–Humid
Project 10	Zone 2 B	Hot–Dry

.

2.2. Creating Autodesk Revit 3D Models of Case Studies

The information collected from the case studies was used to develop Revit models of these buildings by considering that these cases represent a diverse range of building materials and design alternatives. The detailed BIM model for each case study captured the architectural, structural, mechanical, electrical, and plumbing (MEP) components. Firstly, the architectural 3D model of the building featuring a traditional design was created using Revit. This model was meticulously crafted to include precise geometry, authentic materials, and essential building components. Following this, additional elements crucial for the structural integrity and MEP systems were integrated. This included incorporating air terminals, lighting fixtures, and Heating, Ventilation, and Air Conditioning (HVAC) equipment into the model. An example 3D view of the Revit model of Project 4 is shown in Figure 2. The 3D view of the Revit model for each case study plays a valuable role in understanding the significance of carbon emissions across the CSI divisions using Tally. Tally calculates embodied carbon based on material quantities derived directly from the Revit model. By looking at the 3D view in this figure and the LCA results, researchers can visually connect emissions data to specific building elements such as walls, slabs, and roofs. This will help them to understand which parts of the building are most material-intensive and, therefore, carbon-intensive. The material-intensive parts should be linked to different CSI categories, which can be used as a virtual checkpoint to understand the distribution throughout the structure. In this example, Project 4 is expected to have carbon emissions distributed into primary construction material categories, as well as considerable secondary categories for openings.

As the goal was to use these models for LCA and specifically calculate carbon emissions, a full list of model elements, as well as materials and components that needed to be created in these models, was developed beforehand. Additional data related to the materials used, such as scope boundaries for each life cycle stage and the impacts associated with the specific material or component, was also collected at this stage. It was decided to use the following phases in the Revit models as given below:

• 01—Existing
• 02—Demo
• A10—Substructure
• B10—Superstructure
• B20—Exterior Enclosure
• C10—Interior Construction
• C20—Interior Finishes
• E20—Furnishings
• New Construction
• Project Completion

These phases enabled users to list each material or component with its service life, or the period of time after installation it is expected to meet the service requirements prior to replacement or repair. This information was coupled with the values for transportation distance or service life.

At this stage, it was important to know which LCA software would be used to develop model elements correctly to integrate with the LCA tool. Tally was selected as a powerful tool for conducting building LCAs, which will be discussed in detail in the next section.

2.3. LCA Analysis with Tally

Tally is a BIM-integrated LCA tool that focuses on the material-based environmental impacts. It was developed jointly by KT Innovations, Thinkstep, and Autodesk as a BIM software plugin [29]. Tally was recognized as one of the three primary LCA tools alongside Athena Impact Estimator and SimaPro. Being developed specifically for buildings located in North America, Tally was noted for its ability to be implemented early in the design process and seamlessly integrated with BIM, supporting iterative design decisions [30]. The UN Environment Programme (UNEP 2025) states that the effective use of Tally would help construction parties understand the trade-offs between their material decisions vs. major environmental impacts [2].

Tally exemplifies the integration of digital technologies into LCA by directly utilizing Revit’s materials and components. In this study, the researchers selected Tally for several key reasons. First, Tally functions as a plug-in for Autodesk Revit, allowing for seamless integration with BIM technology [30]. This integration extends to Revit’s material database, including access to manufacturer-specific Environmental Product Declarations (EPDs) [15]. Considering the LCA process, Tally’s LCA methodology aligns with international standards such as ISO 14040–14044 and EN 15804, ensuring credibility and consistency in its assessments [31]. It has the capability to provide real-time feedback to architects and engineers on how different materials and design choices impact the building’s carbon footprint [25], which is essential in selecting sustainable design options.

However, Tally has limitations due to its reliance on a predefined material database from GaBi, which, like many other LCA databases in the industry, includes only specific material types [32]. As a result, Tally primarily focuses on structural and conventional building systems modeled in Revit. While prior studies have explored the potential to expand Tally’s analysis to cover systems such as plumbing, HVAC, and electrical via BIM, this remains an area for development [30]. When compared to other tools like the Athena Impact Estimator, Tally has a clear advantage in BIM integration. Unlike Tally, Athena operates as a standalone application. It requires users to export bills of quantities for LCA, which disrupts the workflow and limits its ability to support early-stage design decisions within the modeling environment, posing a significant constraint [33].

2.4. Embodied Carbon Calculations

As per its previously mentioned benefits, Tally was used to calculate the CO₂ emissions of ten case studies. Tally contains its own database of materials and their corresponding carbon emissions data. For each project, Tally performed a material assessment of each material and component created in Revit. As it evaluated materials and assemblies directly from the Revit model, at this step, users went back and forth between Revit and Tally to make sure the 3D model created served Tally’s LCA calculation purposes. Tally calculated the CO₂ emissions of each material used in the project, such as concrete, steel, insulation, finishes, and so on. The CO₂ production associated with the entire life cycle of a building, from extraction of raw materials to manufacturing, construction, operation, and end-of-life disposal, was considered in these calculations. The results per life cycle of the building were presented as global warming potential (GWP) in kg CO₂ eq. The sample results from Project 8 are shown in Figure 3.

Among the life cycle stages of Tally, the product stage (A1–A3) corresponds to the material extraction, transportation to the facility, and manufacturing [34]. Transportation/construction stage (A4) involves transportation to the site and installation/construction of materials. Use stage (B2–B5) includes maintenance, repair, and replacement. End of Life (C2–C4) is demolition and disposal. Finally, Module D (D) covers the end of the building’s life after the building is demolished. It represents the “beyond the system boundary” stage of an LCA, as defined by the EN 15978 standard. Mainly, it shows how much of the materials can be reused; therefore, Module D can be expressed as the “reuse” stage in Figure 3.

2.5. Analysis of CO₂ Emissions per CSI Divisions

Following up on the results per life cycle of the building, the researchers further focused on the GWP results for each CSI division. The actual results will be provided in the Section 3.

3. Results

In this section, the GWP of the ten case studies and the CO₂ emissions per CSI divisions are presented. As shown in the previous section, Tally has powerful graphical images and provides detailed reports on CO₂ emissions, breaking them down by material type, construction phase, and building system. The GWP results from ten cases were collected and presented in

Table 3. Summary of GWP of case studies.

	Global Warming (kg CO2eq)
Project No	Product Stage [A1–A3]	Construction Stage [A4]	Use Stage [B2–B5]	End of Life Stage [C2–C4]	Module D [D]	Total (Except Model D)	Total per SF (Except Model D)
Project 1	1335,026	18,106	291,590	177,569	−402,646	1822,291	207.74
Project 2	385,714	7616	122,856	53,050	−140,448	569,236	56.45
Project 3	213,451	5233	58,725	73,139	−33,567	350,548	22.96
Project 4	820,789	7964	111,414	102,926	−59,683	1043,093	17.64
Project 5	942,998	9743	20,302	141,394	−82,496	1114,437	88.75
Project 6	886,061	9128	67,738	138,339	−49,952	1101,266	50.85
Project 7	2995,894	30,541	184,052	389,734	−349,463	3600,221	30.07
Project 8	1472,527	45,429	12,181,947	411,734	−148,117	14,111,637	209.84
Project 9	1369,542	14,269	177,045	320,632	−78,733	1881,488	83.66
Project 10	4979,613	56,593	344,774	140,467	−1768,908	5521,447	100.75

. The GWP per life cycle stage, as well as the total CO₂ emissions of products, construction, and use stages, are presented in this table. Module D, the stage that corresponds to the reuse of materials after the lifetime of the project, is intentionally excluded from this total. Module D represents “benefits and loads beyond the system boundary” [35], meaning it accounts for the potential reuse or recycling of material categories after demolishing the building. Therefore, Module D is accounted for as a credit, not a direct CO₂ emission amount. Additionally, as the actual amount of reuse or recycling of materials after the building’s life cycle is very challenging to project at the beginning of the project, the researchers decided to exclude the Module D results to improve the reliability of this study.

As shown in Table 3, the total GWP (kg CO₂ eq) amounts vary widely per project from around 350,000 to 14,000,000 kg CO₂ eq. This variation in the overall total carbon emissions depends on several factors. Firstly, building type significantly impacts emissions. Commercial buildings, campus buildings with lab facilities, and offices each have distinct energy demands, operational characteristics, and material use patterns that influence their carbon footprint. As an example, the hospitality project (Project 8) ended up having higher carbon emissions than office and campus buildings. Secondly, materials utilized in the project play a critical role in the life cycle carbon emissions, as emphasized in this study. For instance, Project 7 has a larger size than Project 8, yet Project 8 has considerably higher carbon emissions than Project 7 due to its specifically required insulation and soundproofing material, whereas Project 7 uses more traditional material options with the exception of lightweight concrete and steel, which improved its carbon emission results through the life cycle of the project. Finally, the location and climate zone of the project impact its energy consumption for heating, cooling, and transportation of materials, thus influencing carbon emissions. For example, Project 5 is located in a hot and humid climate with no winters, and Project 1 is located in a cool, moist climate with four seasons. Although the size of Project 1 is much smaller than Project 5, Project 1′s carbon emissions are higher due to higher heating demands.

A comparison among these projects is only possible by finding the kg CO₂ eq emissions per SF, which is also presented in this table. According to the total GWP per SF results, Project 8 and Project 1 have the most CO₂ emissions, while Project 4 has the least CO₂ emissions. The highest carbon emissions in total and per SF are both from Project 8 due to the building function of this project. As Project 8 is a hospitality project, it has specific finish and insulation requirements. The fact that hospitality buildings have more finishes and furnishings, like decorative elements, results in more material use per SF and increases carbon emissions. Additionally, it should be noted that hospitality projects are operated 24/7, whereas office projects like Project 4 only operate during weekdays. When the operational (use stage as stated in Tally) is reviewed for Project 8 and Project 4, the significant difference in carbon emissions can be observed. Project 1 has a different situation where the product stage carbon emissions are driving the high carbon emissions per SF. This can be explained by stating that this is a fraternity building and the client requested premium materials in finishes as well as for insulation, which resulted in higher embodied carbon results per SF. Overall, it was beneficial to note the ranking of CO₂ emissions in total per SF, as it allowed a fairer comparison among the carbon emissions of these ten case studies.

Per the aim of this study, the results need to be further investigated to observe the itemized CO₂ emissions per CSI divisions. For this purpose, the Tally results were further filtered to isolate and focus on the primary CSI divisions that represent the highest levels of raw material consumption and intensive material installation activities. This targeted approach enables a clearer understanding of which construction components and systems contribute most significantly to the overall embodied carbon footprint of the project. Below are the CSI divisions utilized in this study:

• Division 03—Concrete
• Division 04—Masonry
• Division 05—Metals
• Division 06—Wood/Plastics/Composites
• Division 07—Thermal and Moisture Protection
• Division 08—Openings and Glazing
• Division 09—Finishes

For each project, the itemized results were itemized per the CSI divisions, as each division’s percentage of contribution to CO₂ emissions. The sample results are shown for Project 8, also known as the case study with the highest GWP per SF, in Figure 4.

The itemized results per CSI divisions for each of the ten case studies are combined and presented in

Table 4. Results per the CSI divisions of the case studies.

	Percentage of GWP (kg CO2 eq)
Project No	Div. 03 Concrete	Div. 04 Masonry	Div. 05 Metals	Div. 06 Wood	Div. 07 Thermal and Moisture	Div. 08 Openings	Div. 09 Finishes
Project 1	10%	4%	44%	0%	36%	0%	6%
Project 2	24%	14%	27%	0%	7%	7%	21%
Project 3	43%	3%	14%	0%	8%	11%	21%
Project 4	81%	0%	0%	0%	0%	12%	7%
Project 5	85%	5%	5%	0%	0%	5%	0%
Project 6	76%	5%	8%	0%	3%	4%	4%
Project 7	84%	0%	3%	1%	3%	2%	7%
Project 8	15%	0%	2%	1%	51%	5%	26%
Project 9	56%	5%	3%	0%	21%	7%	8%
Project 10	13%	13%	58%	0%	0%	4%	12%

. In order to interpret these percentages of the GWP results better, one needs to understand the means and methods associated with the case study projects. It should be noted that the percentage contribution of some categories was less than 1%, which was rounded to 0% in this figure.

Among the ten case studies, Projects 4, 5, 6, and 7 have the highest percentage of Div. 03—Concrete contribution to GWP, with a more than 70% result according to Table 3. Project 7, an office building and headquarters in an urban location, was designed with lightweight and structural cast-in-place concrete with 3000 psi strength, which was supported by steel bar joists, C-stud metal framing, and wide flanges. Although Div. 05—Metals was used in framing, and the CO₂ emission contribution of the selected steel elements was way less than that of the concrete used. Similarly, Project 6, an office building and a corporate center, used cast-in-place concrete varying from 2500 to 3000 psi with precast concrete columns. The contribution of Div. 05—Metals due to metal studs and decking were more than Project 7, yet still very much less than concrete itself. Project 4 was also an office building and had considerable CO₂ emissions in the Div. 08—Openings category in comparison to Projects 6 and 7. Project 4 used precast columns like Project 6. Among these projects with the highest percentage of Div. 03—Concrete GWP results, Project 5 is different in the sense that it was a dormitory project with a precast structural panel.

When Div. 04—Masonry ranking is evaluated, Project 2, which is a campus building, has the highest percentage of GWP in Masonry with 14%. This project used hollow core Concrete Masonry Unit (CMU) walls, which explains the high percentage of masonry. Project 10 has the second-highest GWP percentage regarding Masonry. Project 10 is also a campus building and uses a variety of masonry elements from generic bricks to hollow-core CMU and more.

Regarding Div. 05—Metals, Project 10 has the highest percentage with a variety of steel elements such as cold-formed structural steel, galvanized steel decking, hot-rolled structural steel, and more. Project 1, a fraternity building, is the second highest in the Metals category. This was a surprising result, as this building included a basement and consumed a considerable amount of concrete with reinforcement, yet did not make it to the top ranks in concrete, but the GWP results of its steel use were unexpectedly high.

The GWP percentages of Div. 06—Wood category varied around 1% for all the projects and was generally low compared to the other divisions. This is due to two main reasons: (1) Due to the codes and the project sizes, these ten case studies were majorly steel framed and used a limited amount of wood products only for the interior partitions in the form of gypsum wallboard and similar. (2) As expected, wood is a more sustainable material compared to others due to being a renewable material and requiring less energy to be produced compared to other materials like steel. As wood is lighter in weight, its transportation environmental impact is considerably lower.

Div. 07—Thermal and Moisture Protection category is interesting in the sense that Project 8′s more than half of the GWP is assigned to this category. When Project 8 is further evaluated, it can be seen that this hospitality project is a hotel building from one of the well-known chains. The high GWP results in both Div. 07 and Div. 09—Finishes can be explained by the material components used in a hotel construction. Soundproofing and the visibility requirements for how the guest rooms and common areas should look impacted the amount of insulation and finish materials used. In this case, the results were affected by the quantity of the material rather than the selected material types.

Div. 08—Openings had similar GWP percentages, with Project 3 and Project 4 having the highest rankings. Project 3 is a campus building with a lab, and Project 4 is an office building. The highest percentages and carbon emissions in this case are caused by the variety of material components used. Each project utilized aluminum and galvanized steel doors, double-panel glazing, and special curtain walls, which caused higher GWP results.

Div. 09—Finishes were expected to be higher in Project 8, the hotel project, which exactly happened. With 26% of GWP, Div. 09 was one of the highest carbon emission CSI divisions in Project 8. This was followed by Project 2 and Project 3. As both projects were campus buildings, specific finish material requirements were in place for faculty offices and classroom areas. Additionally, Project 3 included labs, which resulted in various types of finish material in both walls and floors. One example is paint. As some rooms needed to use a certain type of paint, it has been a challenge to control the Volatile Organic Compound (VOC) content. As the production, transportation, and application of high-VOC paints contribute negatively to CO₂ emissions, the GWP percentage for Div. 09 was high for both Project 2 and Project 3. Project 10 was fourth in the GWP ranking for Finishes, and it was also a campus building with specific interior paint requirements.

Further assessment was performed to identify the top three major GWP contributions among the CSI divisions of these ten case studies. As shown in

Table 5. Ranking of the CSI Divisions per each case study.

	CSI Divisions
Project No	Rank 1	Rank 2	Rank 3
Project 1	Div. 05 Metals	Div. 07 Thermal and Moisture	Div. 03 Concrete
Project 2	Div. 05 Metals	Div. 03 Concrete	Div. 09 Finishes
Project 3	Div. 03 Concrete	Div. 09 Finishes	Div. 05 Metals
Project 4	Div. 03 Concrete	Div. 08 Openings	Div. 09 Finishes
Project 5	Div. 03 Concrete	Div. 05 Metals	Div. 04 Masonry
Project 6	Div. 03 Concrete	Div. 05 Metals	Div. 04 Masonry
Project 7	Div. 03 Concrete	Div. 09 Finishes	Div. 05 Metals
Project 8	Div. 07 Thermal and Moisture	Div. 09 Finishes	Div. 03 Concrete
Project 9	Div. 03 Concrete	Div. 07 Thermal and Moisture	Div. 09 Finishes
Project 10	Div. 05 Metals	Div. 03 Concrete	Div. 04 Masonry

, Div. 03—Concrete has been the top contributor in six projects out of ten. Concrete has been shown to be one of the top three contributors of GWP in all the case studies. Following concrete, Div. 05—Metals has been the top contributor in three projects and has been in the top three in four more projects. Following concrete and metals, Div. 09—Finishes has been observed as a second or third rank contributor repeatedly. One of the cases, Project 8, the hotel project, had Div. 07—Thermal and Moisture Protection as the top CSI division contributor, followed by finishes and concrete. These results suggest the dominance of concrete and metals in CO₂ emissions, regardless of the project type and location, with the exception of hospitality projects.

As the carbon footprint of different building systems and materials was identified and ranked according to CSI divisions, the main goal of this study was completed at this stage. In the final phase of this study, ten case studies were evaluated to implement sustainable decision-making approaches to these highly ranked CSI divisions to observe their implications on CO₂ emissions. The first two highest categories were targeted to apply sustainable design principles to decrease the CSI category-based GWP. Below are the alternatives applied to each case study:

• Project 1: The target categories were Div. 05—Metals and Div. 07—Thermal and Moisture Protection. Instead of a galvanized steel lintel, which was used in exterior walls to support openings, a stainless-steel alternative with high recycled content was selected. The recycled stainless steel offered the same strength and corrosion resistance without zinc galvanization. Zinc galvanization is an energy-intensive process, increasing CO₂ emissions. Omitting this process positively contributed to LCA results and decreased the product-stage GWP. Additionally, instead of a vendor in another state, a vendor in the same state with less trucking distance was selected. For the second rank CSI division, a high thermal resistance (R-value) roof insulation of R−38 Fiberglass was selected among certified products from GREENGUARD. The certified product came with detailed emissions testing reports and helped support the life cycle impacts related to Div. 07.
• Project 2: The target categories were Div. 05—Metals and Div. 03—Concrete. Three 5/8” metal stud framings were the main contribution in Div. 05. The material selection for the metal stud framing was pretty basic for this project, so it could not be changed. As this was a Leadership in Energy and Environmental Design (LEED)-certified building, the metal studs were already chosen from regional suppliers. In this case, the researchers concentrated on the second-ranked category of concrete. It should be noted here that Div. 03—Concrete does not only correspond to the material concrete. Div. 03 covers the material assembly of concrete. An assembly of concrete generally includes concrete itself, formwork for cast-in-place concrete, reinforcing steel (also known as rebar), and accessories such as water stops and concrete fasteners. The list can be extended to include concrete chemicals and precast concrete as needed. For Project 2, cast-in-place concrete was utilized. The sustainability approach in this case included decreasing the life cycle impacts of concrete, formwork, and/or rebar used in this project. One approach was to use ready-mix suppliers with carbon-efficient operations at the site and plan to minimize waste. Although both actions are valid, it is very hard to measure their impact on GWP during the early stages of the project. Therefore, another approach was implemented to choose concrete with published Environmental Product Declarations (EPDs) from local suppliers, which decreased both the product- and transportation-stage GWPs.
• Project 3: The target category was Div. 03—Concrete. The same approaches in Project 2 were applied to concrete assemblies in Project 3.
• Project 4: The target category was Div. 03—Concrete. Considering the concrete assemblies, Project 4 required all the rebar to be manufactured from high-strength billet steel conforming to ASTM designation A615 grade 60. Although most U.S.-based A615 rebars use 80–100% recycled content, rebars with EPDs showing recycled content were selected as a sustainable alternative. Additionally, local suppliers from the same region of the project (Northeast Region in this case) were selected to be used.
• Projects 5 and 6: The target category was Div. 03—Concrete. The same approaches as in Projects 2, 3, and 4 were applied to decrease the GWP results.
• Project 7: The target category was Div. 03—Concrete. The same approaches as in Projects 2, 3, and 4 were applied to decrease the GWP results. Div. 09 Finishes were also targeted, yet a decrease in CO₂ emissions was not experienced.
• Project 8: The target category was Div. 07—Thermal and Moisture Protection. This was the hotel project discussed before regarding the use of soundproofing material. The sustainability practice included selecting low-VOC content and recycled soundproofing material such as mineral wool and cellulose insulation.
• Project 9: The target categories were Div. 03—Concrete and Div. 07—Thermal and Moisture Protection. Sustainable design practices above were applied to concrete assemblies, as in the prior projects. For Div. 07, roof canopy insulation was switched to a more sustainable alternative by suggesting a higher recycled material content and the use of rapidly renewable materials.
• Project 10: The target category was Div. 05—Metals. Composite floor decking was found as the main contributor in the metals category. As a sustainable alternative, a recycled steel deck with low-carbon concrete was used. The steel decking included around 90% recycled content, and the concrete mix was selected with a carbon-cure tech to improve the environmental impact results related to metals.

The GWP values were calculated once more after applying the sustainable design alternatives for each project as explained above. The results per the CSI divisions after applying sustainable material alternatives are presented in

Table 6. Results per the CSI divisions of case studies after applying sustainable material alternatives.

	Percentage of GWP (kg CO2 eq)
Project No	Div. 03 Concrete	Div. 04 Masonry	Div. 05 Metals	Div. 06 Wood	Div. 07 Thermal and Moisture	Div. 08 Openings	Div. 09 Finishes
Project 1	10%	4%	40%	4%	31%	5%	6%
Project 2	22%	14%	27%	2%	7%	7%	21%
Project 3	41%	3%	14%	2%	8%	11%	21%
Project 4	63%	5%	5%	2%	6%	12%	7%
Project 5	68%	5%	5%	3%	5%	5%	9%
Project 6	70%	5%	8%	6%	3%	4%	4%
Project 7	80%	0%	3%	3%	3%	2%	7%
Project 8	15%	1%	2%	3%	48%	5%	26%
Project 9	53%	5%	3%	6%	18%	7%	8%
Project 10	13%	10%	53%	4%	4%	4%	12%

. These results will be discussed in the next section.

4. Discussion

The results of this study presented the major contributions of CO₂ emissions among the CSI divisions as Div. 03—Concrete, Div. 05—Metals, and Div. 07—Thermal and Moisture Protection. In seven of the case study projects among ten, concrete assemblies were found to consume the highest amount of carbon. In four of these cases, the GWP of concrete was more than 75% among all the CSI divisions. Div. 05—Metals category’s GWP has fluctuated among the ten projects, yet it was around 50% for two of the projects. Finally, thermal and moisture protection is its highest contribution in a hotel project, and its GWP resulted in anywhere between 21% and 51% in three of the case study projects. Div. 09—Finishes can be accepted as the fourth powerful category in the CSI divisions, with its above 20% GPW results in three projects. Overall, ranking the GWP values according to the CSI divisions helps researchers and construction practitioners to know which areas of construction to focus on to decrease CO₂ emissions efficiently in a project. LCA results from the Tally-BIM combination in this study referred researchers to consider implementing sustainability measures for the most effective CSI divisions, which would result in the most feasible way of decreasing CO₂ emissions.

Some sustainability measures were discussed in the Results Section to show how the GWP values were improved in the ten case studies. Comparing the results in Table 3 and Table 5, it can be seen that applying sustainable design principles regarding the highest CSI divisions has drastically improved GWP, also known as CO₂ emissions, in all the case study projects. The percentage improvements in the largest CSI divisions ranged from 0% to 18%. The smallest percentage improvement was observed in the Div. 09—Finishes category, where the sustainable alternatives did not change the outcome, and the largest improvement was observed in the Div. 03—Concrete category, where Project 4 experienced an 18% decrease in GWP. In addition to concrete, Div. 05—Metals experienced 4–5% improvements in GWP per the applied sustainability principles. These results emphasize that when the largest CSI division is targeted, the Tally-BIM combination can be used to find out which material categories dominate CO₂ emissions, and sustainability improvements can achieve 5–18% success with only targeting these major categories.

It is worth mentioning that although Tally software and Revit models are powerful tools for estimating carbon emissions in building projects, they come with certain limitations. For starters, Tally relies on pre-defined environmental data sourced from the GaBi database. GaBi database includes certain material types, which have been the case for many LCA databases available in the industry. In this case, if a case study utilizes new construction technologies that are not available in GaBi, their environmental impact cannot be successfully reflected in the results. In this study, the case studies selected used industry-standard materials, so there was no issue in finding the exact material match in Tally. When researchers implemented the sustainable options, they selected options from Tally’s database, which resulted in the GaBi database benefiting the project rather than becoming a limitation. Secondly, Tally pulls quantity data directly from the Revit model. Therefore, Revit models with missing components would create a limitation in the LCA process with Tally. The Revit models utilized in this study went through a two-stage process, where the models were created with detailed material layers and construction assemblies, and then checked after a preliminary Tally run. After the preliminary Tally analysis, the models were further improved to make sure they are well-structured and LCA-ready. The Revit models also had the material quantities created for certain CSI divisions to run a quantity takeoff check to verify that the Revit model’s material values are realistic. Overall, a Tally-Revit combination comes with its limitations of the completeness of the Revit model and the scope of the LCA database used, yet these limitations have been overcome through detailed modeling and appropriate data usage.

When researchers reviewed the sustainable design principles applied, there were no major changes to the design. Although in some cases, like when the steel framing in the metals category was targeted, more sustainable framing alternatives were proposed, they could not be applied to the projects for two main reasons: (1) Building codes, such as those established by the International Building Code (IBC) in the U.S., dictates the minimum standards for framing materials and methods. These codes specify which types of materials are acceptable for various structural elements based on factors like building height, occupancy type, and structural loads. Therefore, it was not possible to alter the framing material in many cases. As an example, although steel framing is well-known for its high embodied carbon, it was not possible to switch to this material alternative with CLT framing, which has very low embodied carbon. (2) Specs and engineering calculations determine the appropriate type of framing based on the structural requirements of the building. These calculations consider factors such as building design, loads (e.g., gravity, wind, and seismic), and environmental conditions to select the most suitable framing type. In many cases, specs mandated the use of steel framing, which could not be switched to a more sustainable alternative.

As can be observed from the previous section, the sustainability implications were mainly based on using materials with higher recycled material content, using regional suppliers, using low-carbon equivalents, performing carbon-efficient operations at the site, and minimizing waste. All these tasks can be performed without drastically altering the design of the building. As an additional benefit to decreasing environmental impacts, many of these alternatives are cost savers for the project. As an example, using local suppliers would cut down on the transportation stage environmental impacts, as well as the delivery costs of construction materials.

Although there are no previous studies that can be used to directly compare the results of this study, a similar work was performed on a high-rise building using the Tally-BIM combination recently. This previous work by Ma et al. (2024) also found concrete as the top contributor in not only GWP, but also in other environmental impacts such as acidification potential, eutrophication potential, and similar [31]. This work was limited to a high-rise building in an urban location in the U.S. Their results also supported the findings of this study in terms of which material categories dominate the embodied carbon emissions. They stated the importance of focusing on the life cycle embodied carbon emissions of concrete and steel, especially due to their contribution to GWP at the product stage. Febriyani et al. (2021) also utilized BIM and Tally to analyze two types of curtain walls, including concrete and steel [36]. Their results showed the major GWP rankings in concrete (75% and 73% for alternatives A and B, respectively) and metals (11% and 5% for alternatives A and B, respectively). Another recent study by Najjar et al. (2017) integrated BIM and LCA to compare two types of multi-story office buildings in Brazil [21]. Their material components included both concrete and metals, along with masonry and finishes. The GWP results of this study showed that the highest contribution was experienced in walls and curtain wall mullions in Type A, and walls and floors in Type B. Although the percentages varied, the material components of walls, floors, and curtain wall mullions were mainly concrete and steel, which once again declared the dominance of concrete and steel categories regarding carbon emissions. As can be observed from the previous studies, the findings of this study are supported based on the concrete and steel material categories as the primary contributors of carbon emissions in an LCA analysis. The significance of this study comes from using CSI divisions as the primary organization of specs in the U.S. to direct construction practitioners on which categories to target for sustainable design implications. As mentioned before, the sustainability measures taken in this study were minor and cost-effective, yet the percentage of improvement in GWP was impressive. These strategies can be adopted and used for other material categories in the CSI divisions depending on the project types and needs. Therefore, it is important to identify the most prominent CSI categories to support the LCA of buildings and focus on the highest impact material assemblies to obtain the most effective result in decreasing the carbon emissions of buildings.

5. Conclusions

This study highlighted significant variations in CO₂ emissions across CSI categories throughout a building’s life cycle, identifying which components most impact the overall carbon footprint. The methodology included utilizing the Tally-BIM combination to perform LCA. A structured case study database of ten projects of various types and locations was developed to ensure the reliability of the research and to facilitate future replication.

The analysis revealed that Div. 03—Concrete and Div. 05—Metals are the primary contributors to embodied carbon. This study contributed to the body of knowledge of sustainable construction by showing construction parties where to direct their attention to alleviate carbon emissions. Sustainable design options applied across these divisions resulted in substantial reductions in GWP, demonstrating the practical impact of material choices on emissions. These low-key, sustainable design alternatives can be utilized to test their impact on future projects in managing carbon-conscious material choices and design decisions.

The methodology is applied mainly to office and campus buildings, with the inclusion of only one hospitality project, which might have limited the scope. Future research directions can include limiting the group of case study projects to one type, such as repeating this study on a set of campus projects vs. hospitality projects to see the highest impact GWP among the CSI divisions. Focusing on improving the highest GWP categories would help integrate environmental performance, material efficiency, and life cycle thinking and benefit the sustainable development in architecture. Overall, this methodology is beneficial for construction practitioners from all ends, i.e., designers and construction managers, and can be repeated to expand the pool of CSI categories and material components to support carbon-conscious construction via sustainable material selection.