Whole Life Carbon Assessment of Buildings: The Process to Define Czech National Benchmarks

Abstract

In recent years, there has been a growing interest in addressing human-induced impacts on the environment, with a particular focus on transitioning to sustainability and achieving carbon neutrality. However, the current implementation of Whole Life Carbon (WLC) and Life Cycle Assessment (LCA) in the construction sector in the Czech Republic is hindered by several challenges. These include gaps in stakeholders’ knowledge, limited availability of LCA data on construction products and buildings, insufficient market incentives, and low institutional capacity. This study, conducted as part of the INDICATE project, aims to streamline the process of WLC calculation and establish a consistent national assessment method specific to the Czech context. The project encompasses various phases, i.e., a case study collection of office, multi-family, single-family, education, and logistic hall buildings, followed by the development of a comprehensive unified materials database, classification of building parts and uniform work with the bill of quantities, stakeholder engagement, an LCA of case studies with a sensitivity analysis, and WLC policy suggestions, including the quality of the project data, simplifications, and a benchmarks definition. The Global Warming Potential (GWP) is calculated throughout the entire life cycle of each considered building, utilizing the EU Level(s) methodology incorporated in the OneClick LCA software. By adhering to these newly developed methodological steps, benchmarks for multi-residential buildings are shown. The same methodology could be replicated by stakeholders in other countries to enhance their evaluation processes and ensure consistent results across their projects.

1. Introduction

1.1. Background

In recent years, there has been a growing interest in mitigating human-induced effects on the environment, with a clear focus on transitioning towards sustainability and carbon neutrality. The importance of sustainability is increasingly recognized in the building and construction industry, with efforts to incorporate it into quality assurance frameworks [1,2,3]. Green building certification systems, such as LEED [4], BREEAM [5], DGNB [6], and SBToolCZ [7], exemplify this trend. Whole Life Carbon (WLC) assessment is one of the sustainability criteria, expressed by the Global Warming Potential (GWP) in kg-CO₂ equivalents. The concept of life cycle carbon assessment is also newly included in related legislation—the recently approved Energy Performance of Buildings Directive (EPBD) [8] and the Energy Efficient Directive (EED) [9].

Around 39% of the GWP is associated with the building and construction sector, where operational energy use and material consumption play significant roles. Indeed, in 2019, energy consumption in residential and non-residential buildings contributed 50% and 32%, respectively, to the CO₂ emissions from buildings, while embodied emissions accounted for 18% of the global CO₂ emissions from the building sector [10,11]. There is an increasing need to look at the total impact of buildings throughout their entire life cycle [12,13,14]. Life Cycle Assessment (LCA) has become pivotal in quantifying and contrasting the environmental effects of construction materials and buildings [15]; it is currently supported by European standards, particularly EN 15804 + A2 [16] and EN 15978 [17].

LCA methodology evaluates the environmental effects of products and considers their complete life cycle. This includes the environmental impacts from the acquisition and production of raw materials to the manufacture of the product itself, its usage phase, and the eventual disposal, reuse, or recycling of its materials. The evaluation of product environmental impacts entails analyzing the material and energy exchanges between the system in question and its surroundings, particularly the environment [18,19].

1.2. Indicate Research Project

The INDICATE project, formally titled “The National Building LCA Data Accelerator” aims to provide a combination of financial support and technical guidance regarding life cycle analysis data for buildings alongside national policy advocacy [20]. This is directed towards establishing a robust foundation of data through a collaborative approach and engagement to secure essential endorsements from industry stakeholders and policymakers for the utilization of these data. This effort aims to accelerate progress towards achieving a fully decarbonized building stock for both operations and construction [21]. It plays a direct role in extracting information on the status of respective national building stocks and identifying the carbon reduction potential inherent in various national strategies. In particular, the project supported three pilot countries: the Czech Republic, Spain, and Ireland. In this study, the Czech method is described in detail.

1.3. Definition of a Czech National Method

The current state of WLC and LCA implementation in the building sector in the Czech Republic is characterized by several factors: stakeholders’ knowledge gaps, limited availability of LCA data on construction products and buildings, insufficient market incentives, low institutional capacity, and some reluctance from governmental entities [22,23,24]. The country lacks a comprehensive decarbonization strategy specifically tailored to the building sector, and responsibilities for construction regulations are fragmented among multiple ministries, suggesting a need for better coordination.

Although the operators of national subsidy programs for building renovations demonstrate a willingness to support carbon footprint monitoring, there is a proactive stance within the banking and real estate sectors to align with the EU Taxonomy [25] and EPBD standards. Notably, the recent approval of the EPBD for revision by the EU Parliament includes an updated mandate for the calculation and reporting of buildings’ carbon footprint in accordance with EN 15978 [17] and Level(s) [26] standards, which are applicable to buildings exceeding 1000 m² by 2028 and to all buildings by 2030 [27]. However, this transition will require the calculation of WLC and will bring to light a lack of awareness of WLC among policymakers, compounded by limited government support, as well as other stakeholders in the building sector.

To expedite the process of WLC calculation, the INDICATE project aimed to tackle these obstacles by examining current national building LCA case studies. These studies serve as the foundation for the establishment of benchmarks for WLC within the building stock of the Czech Republic. Thus, the objective of this work was to develop a meticulous calculation methodology and datasets that could pave the way for prospective benchmarks concerning the GWP associated with buildings in the Czech Republic throughout their complete life cycle.

Based on this methodology, upcoming benchmarks can be potentially defined, and stakeholders are guided to improve evaluation and ensure consistent results for their projects.

1.4. Motivations and Objectives

Buildings are complex structures, and conducting LCAs on buildings requires large amounts of data that are not always available; therefore, making assumptions is typically a necessity when going through an LCA, mostly during the inputting of data into the LCA calculation tool and the selection of the environmental datasets [28], but these different assumptions may influence the LCA results [29]. A national LC methodology is preferable instead of relying on European or global approaches due to significant variations in electricity mixes and primary energy sources for material production. For instance, the Czech Republic still heavily depends on coal and lacks sufficient renewable energy sources. As a result, environmental data for building materials and operational energy must be localized to ensure accurate and representative results. This need for localization is emphasized in the data quality selections.

Countries such as Finland, Sweden, and Denmark have introduced LCA-based limit values for WLC using similar methodologies where variations reflect different national weightings [30], but many other countries in Europe and around the world lack the WLC methodology and benchmarks for their regions. Therefore, the methodology presented in this paper can be beneficial to them. The proposed individual steps are replicable, and if not all of them are necessary, only those relevant to the local situation can be selected.

2. Materials and Methods

Figure 1 provides a workflow diagram of the main phases of the methodological process and the related interconnected outputs. In a few cases, several phases proceeded simultaneously.

2.1. Phase 1—Case Studies Selection

To establish a consistent and effective methodology and benchmarks, 50 real building case studies were gathered, including new constructions as well as renovations. This effort was not only driven by the objectives outlined in the INDICATE project; primarily, it was also to foster a deeper understanding of the GWP in various types of buildings, as previously explored by Zimmermann et al. [31] to develop LCA benchmarks for the Danish construction sector. When selecting these 50 case studies, the main objective was to choose different building typologies that were representative of the most common types in the Czech building stock. Consequently, the initial phase involved collecting and categorizing the case studies per typology (i.e., single-family houses, multi-residential buildings, office buildings, educational facilities, and logistic halls). Care was taken to ensure a diverse representation in these categories and inclusion of only real projects. Within each building type, various material variants (e.g., structures, insulation materials, and other key characteristics) were included to cover as many variations as possible within the given scope to obtain a representative sample for the Czech building stock without the need to select cases based on geographic location since there are no location-specific regulations for construction practices. Indeed, understanding the distinctions among buildings of the same type but constructed with different materials and dimensions is crucial for identifying the most environmentally sustainable solutions.

The case studies were sourced from prior research, such as SBToolCZ-certified buildings [32], or obtained through requests from Czech partners who normally work with the team in charge of these LCAs. The documentation was furnished for the developed design or construction design phase, comprising sections of architectural and structural technical documentation, building services systems’ documentation, energy performance certificates, Bills of Quantities (BoQs), and drawings. In numerous instances, this information was accompanied by a Building Information Modelling (BIM) model of the case study.

2.2. Phase 2—Definition of a Materials’ LCA Database

An LCA construction materials database plays a crucial role in conducting WLC assessments as it gathers environmental datasets for the most significant and frequently used products in the building construction industry and considers the local energy mix and primary energy sources for material production to ensure accurate and representative results. This database must be meticulously planned, organized, and implemented over time. This involves defining each piece of data, identifying its source, and assigning responsibility for its input into the database.

In the Czech Republic, only a very limited national environmental database with specific LCA data is available, the so-called CENIA database [33], based on the Environmental Product Declaration (EPD); this database contains slightly more than 200 datasets, which do not cover all the product groups needed for the whole building WLC assessment. Therefore, it was necessary to establish a unified internal database, based on available data, to assess all the case study calculations.

Configuring such a database is essential for establishing a consistent dataset dictionary at the earliest opportunity, thus avoiding the need for multiple inputs and data maintenance. Specifically, the database was developed between March 2023 and May 2023, primarily sourcing EPDs [34] and generic data based on the Ecoinvent database [35] stored within the database of the OneClick LCA software (OCLCA) [36]. These datasets were chosen based on their representativeness as generic data for the Czech market, as recommended by Silvestre et al. and Hodkova and Lasvaux [37,38].

Therefore, basic data quality assessment was carried out according to the quality criteria given by CEN/TR 15941 [39], including geographical, technological, and time-related coverage, as well as consistency, ensuring transparency throughout the entire data utilization process. The completeness of the data was ensured by the OCLCA software and uncertainty was an aspect that was taken into consideration during the sensitivity analysis.

Initially, the selection of the basic material items required for building calculations was based on the existing environmental database of SBToolCZ [40], which already contains a range of typical materials used in building construction [34]. Additional materials were incorporated during the assessment process of the case studies.

However, an important consideration is that OCLCA incorporates the contextualization of environmental datasets to a specified location (e.g., Czechia) through its internal algorithm, which considers the difference in energy mix between the original country and the destination country; therefore, for the materials datasets, data primarily from the Czech Republic were utilized, followed by data from European countries with similar emission factors of the electricity mix values (such as Italy, Poland, and Germany) and close market proximity to ensure technological representativeness. Expired data were neglected, and newer data were used instead.

Furthermore, an additional classification based on the GWP level of each product was implemented. In this regard, the most impactful materials in terms of GWP were taken into account as a first choice to ensure that the pessimistic—worst-case-scenario—results were always considered. This step ensures that the initial emerging WLC benchmarks for buildings are not overly stringent, and there is a need to allow for tightening in later stages as well. This approach is mainly because in the Czech Republic, it is still necessary to work with LCA data from foreign countries, and therefore, the representativeness of the results is still questionable. However, sensitivity analysis could be performed with other datasets, considering deviations in raw materials, energy sources, and waste management. Therefore, the consistency of the datasets used and the computational steps performed is of the highest importance.

The internal database was accessible to all members of the team in charge of performing the assessment.

2.3. Phase 3—Material and Products Classification

The amount and type of building materials and building products are key information for the LCA of a building and are based on the BoQ, which is usually prepared by a quantity surveyor or cost consultant to define the quality and quantity of works and materials. Today, the main reason for the BoQ is to determine the quality, quantity, and final cost of the construction work and consists of a list of materials, products, works, and services required to build and complete a project.

The BoQ can be processed as a detailed list of materials, products, and construction works or as a list of aggregated items describing complete structural parts containing materials and construction works together. In both cases, the first step in LCA processing is to derive the materials and products from the construction works and services.

The BoQ consists of hundreds or thousands of items which must be structured, grouped, and paired with hundreds and thousands of items from the material databases with environmental properties, service lifetimes, etc.

According to the large amount of data, the process must be as efficient and automated as possible [41]. Therefore, a classification system is needed where input data from the BoQ and BIM are compatible with the material database and the required LCA data structure.

The project data for the LCA should cover the whole building, including structural parts and building service systems. This represents thousands of items that should be systematically structured and processed to evaluate their environmental impact throughout the life cycle of the building. Therefore, building classification is essential to facilitate comprehension of the most environmentally significant categories and to analyze the environmental impact of structural parts and materials throughout the whole life cycle.

In the Czech Republic, various systems are employed for classifying buildings and structures and are typically grounded in pricing methodologies. The most common local pricing methods and software (SW), such as the ÚRS price system (CS ÚRS) [42] and the RTS pricing system [43], are based on the national classification JSKO (in Czech Jednotné Klasifikaci Stavebních Objektů) defined by Regulation No. 124/1980 Sb. and TSKPstat, administrated by the Czech Statistical Office [44]. JSKO and TSKPstat are used for the classification of construction works not included in CZ-CPA. The national version of the European classification of building construction CZ-CC (Classification of Types of Constructions) [45,46] and the CZ-CPA building products (Classification of Product by Activities) [47] are mandatory for the Czech environment.

The classification systems mentioned above are used in the design and building phase of the project but are not sufficient for the LCA because they are not covering the entire life of the building. Therefore, another classification system based on functional parts of the building is used for the LCA classification.

Additionally, for BIM-based projects, other classification systems are used. IFC (Industry Foundation Classes) is an open, international, vendor-neutral, and widely accepted data structure (ISO 16739-1:2024 [48]) for built environments, including buildings and civil infrastructure. IFC enables the collaboration and cooperation of BIM users regardless of which SW they are using, but other different classification systems, such as Uniclass, Omniclass, CoClass, CCI and many others, which are compatible with IFC, are used for different BIM data processing, actors, project stages, geographic areas, etc. In the Czech Republic, the RDS (Reference Designation System) based on ČSN EN ISO 23386 [49] and ČSN EN ISO 23387 [50] is currently used as a standard for BIM classification at the national level. The CA classification used in international assessment methods such as Level(s), OCLCA, etc., is based on the functional components approach; classification in the Czech national complex quality assessment method SBToolCZ is based more on the national classification systems JSKO and TSKPstat and is linked to the locally used pricing SW ÚRS and RTS.

Within the INDICATE project, the international Level(s) classification framework, which OCLCA has adopted, was used for the environmental analysis and to present the assessment results (Figure 2). Therefore, the national data structure must be adjusted to the required version.

During this phase, limitations were established to focus solely on the building itself, encompassing structural elements and building services while excluding external facilities, outbuildings, and external works. Moreover, a predetermined level of detail was chosen, resulting in the omission of certain materials from the assessment, such as small connectors and screws, in alignment with EN 15978 [17] and EN 15804 [16].

To facilitate the definition of the classification system per material, as well as the appropriate environmental dataset, an MS Excel template was designed. This template automates the connection process, reducing time consumption, especially considering that only one dataset per material was identified in the internal database.

2.4. Phase 4—Stakeholders Engagement

The collection of data, the ongoing methodological development, and the final successful dissemination and implementation of the results in building practice would not have been possible without the participation of the relevant stakeholders in the construction sector [51,52]. They need to be part of any preparatory processes as they are the ones affected by the implementation of the WLC and need to be aligned with what is realistically achievable.

Stakeholders can provide project data for assessment, participate in roundtables, workshops, and webinars, and contribute their know-how to the development of the WLC methodology for the Czech Republic. They are also a target group for follow-up education and capacity building.

2.5. Phase 5—Exportation of the Bill of Quantities

The BoQ of each case study was exported in two ways, respectively, from the stakeholders’ Excel sheets derived from pricing methods or the BIM model. In both scenarios, the primary objective was to arrange and categorize all elements to facilitate their seamless integration into OCLCA for calculation purposes.

When dealing with a BoQ in .xls format, the entire building is organized by building categories, such as internal partitions or foundations; a list of materials and associated works is given below, detailing quantities and costs for each item.

Hence, the initial step involved removing irrelevant rows and columns that were unrelated to the technical specifications and descriptions of the elements, such as redundant cost details, to streamline the file as much as possible. Subsequently, each row was meticulously examined manually, with items filtered using a numerical classification:

• a value of 0 indicated that the item would not be considered (e.g., works and processes);
• a value of 1 indicated that the item would be included in the calculation (e.g., materials and products);
• a value of 2 indicated minor items and elements that could be considered negligible (e.g., connectors, small components for HVAC elements, etc.).

Following this, only items classified as 1 passed through the second phase. As the WLC assessment aims to obtain as complete a picture of the building as possible, the building was divided into building parts, as the Level(s) framework suggests, such as foundations, external walls, façade openings, etc., as described in Section 2.2.

Afterwards, each eligible material or product was assigned to a specific category of the Ecoinvent database, which was then linked to a corresponding OCLCA dataset that referred to the internal database specially created for this purpose. This automated matching process, connecting Ecoinvent materials to their respective datasets (whether specific EPDs or generic datasets), was vital for maintaining consistency and comparability across all 50 case studies.

It is important to note that the materials or products listed in the BoQ are specified with particular units of measure, which must align with the units utilized in the OCLCA dataset. Failure to match units would result in the software disregarding the item in the calculation. Therefore, the next step involved confirming whether the units of the eligible materials matched those of the dataset. If not, conversion (often into kilograms or cubic meters) was necessary to ensure they could be included in the calculation.

In the case of a BIM model-based BoQ, the categories and the classification system are organized according to the way the elements must be extracted, grouped, or listed for calculation purposes. To facilitate the comparison of any variation, it is of utmost convenience to adopt at least the Level of Developments (LOD) 300 [53], which is close to the project documentation required for a building permit. The model should contain as many material details as possible to facilitate a systematic mapping process and to reduce approximations due to estimation. The main output from this phase was the BoQ for each case study that would then be used in the OCLCA plugin directly available in the BIM software.

In both scenarios, the water and energy consumption directly associated with the building, including heating, cooling, humidity control, mechanical ventilation, lighting, user electricity [expressed in MWh/year], and hot water preparation [expressed in m³/year], was extracted from the energy performance certificate, known as “Průkaz energetické náročnosti budovy” (PENB) [54] in Czech.

2.6. Phase 6—Life Cycle Assessment

An LCA study consists of four basic phases: definition of objectives and scope, inventory, life cycle impact assessment, and life cycle interpretation [55]. The main objective is not to know all the details and to assess as accurately as possible the environmental impacts of all the individual processes and emissions, but rather to provide an overview of the whole product system and to identify the processes that contribute significantly to the environmental impacts. The overall overview obtained is then used to compare possible technological solutions or to compare the environmental impacts of products that perform the same function in the sphere of consumption or use.

In the first phase of the LCA, what will be assessed and how must be clearly defined. This primarily involves a clear specification of the product under assessment and its function. The complexity of the LCA study is determined by the boundaries of the system [56]. To assess the life cycle impacts, the group of impact categories to be used and the method of the environmental impact of the elementary flows—the characterization model—must already be selected in this step of the study. In addition, the assumptions and constraints made should be stated.

The second phase of the LCA, called inventory, is used to identify and quantify all the material and energy flows entering the product life cycle and especially those leaving it and affecting the environment. The essence of the inventory is the modelling of the product system, which is usually carried out using specialized database software. Inventorying involves data collection. It is the collection of information on the individual life cycle processes of the product, and the energy and material intensity of all processes involved. The output of the inventory analysis is a dataset summarizing the material flows entering and leaving the boundaries of the product system. In simple terms, these are data on what quantities of substances enter the environment in the form of various emissions during the product life cycle and what quantities of natural raw materials have been consumed.

The next stage of the LCA is the conversion of the inventory dataset to product values for each impact category, which is conducted using the so-called characterization models. These make it possible to express the impact of emission flows on specific environmental problems.

The last phase of the LCA is life cycle interpretation. In this step, the most impacting life cycle phase is highlighted, as well as where the greatest consumption of materials, energy, etc., come from. This step also involves relating the results to appropriate units, i.e., defining the reference area (gross internal floor area) or the reference per capita (user), or determining the reference service life (in our case, 50 years according to Level(s)). The correct determination of the values in this step has a major impact on the results and their comparability at the national and international levels.

These findings are then subjected to further testing, such as in the form of sensitivity analysis, which assesses the impact of assumptions, limits, simplifications, and estimates on the results of the LCA study.

The result of the LCA study is a set of findings and a set of conditions for their applicability.

In this study, the LCA is performed considering the “cradle-to-cradle” approach according to the stages highlighted in Figure 3, namely product and construction process (A), use stage (B), end of life (C), and benefits (D).

The substages (A1–A3) are characterized by embodied impacts due to the extraction and manufacturing of raw materials. The sub-stage (A4) refers to the impacts related to the transportation of building materials from the production site to the construction site. Sub-stage (A5) includes emissions and energy used for installation. (B4 and B5) refer to the replacement and refurbishment of building components. (B6) mostly refers to operational energy, which is considered the primary part of the total energy used in buildings for cooling, heating, ventilation, lighting, and heating water. (B6) therefore requires operational energy. (B7) covers operational water consumption. Substages (C2) and (C3) consider the transport and process of the waste, while (C4) includes the disposal impacts. Stage (D) considers the positive impacts on the environment of certain materials when reused/recycled or from energy recovery. For reasons of necessary simplification and because some life cycle phases are known to have minimal impacts relative to the whole, phases B1-B3 and C1 have been omitted [57,58]. The specifics of the LCA are listed in

Table 1. Specifics for the LCA of the building case studies.

Parameter
Functional equivalent		Building
System boundaries		A1–D (excluded B1, B2, B3, and C1)
Service life		50 years
Cut-off rules		95%
Data quality assessment	Geographic coverage	Czechia followed by Poland, Italy, and Germany
	Technological coverage	The most typical production technology
	Time-related coverage	Temporal validity max 5 years
	Consistency	Ecoinvent background database High GWP datasets
LCA impact assessment		EN 15978 + Level(s)
Environmental indicator		GWP-100

.

The reference study period of 50 years is used for the LCA of 50 case studies. The decision to adopt a 50-year timeframe was influenced by Level(s), which predominantly utilizes this study period [26]; however, the service life of the building can be longer than that.

The process is implemented using OCLCA [36], a software tool used in more than 140 countries; its database accounts for EPDs in accordance with the EN 15804+A1 [34] and EN 15804+A2 [16] standards. On the one hand, the BoQ derived from the case studies and processed during Phase 5 can be uploaded into the software to calculate their impacts. On the other hand, compatibility with BIM software is guaranteed through a plugin readily accessible in the BIM software, specifically Autodesk Revit.

For the evaluation of environmental impacts, all the datasets were localized for the Czech Republic conditions. This has a direct impact on the conversion factor for the operational stages and selection of datasets as well as the A4 and C2 stages related to transportation.

The reference study period (i.e., 50 years) alters the replacement of construction products used in the building (B4 phase). Construction products with a service life shorter than the reference study period must be replaced one or more times during the reference study period. In the case of this specific work, the service life for the individual building parts is based on the dataset (either EPD or generic dataset) from OCLCA; the default value is given by the software being used. The description of how a case study is assessed can be graphically illustrated by four main steps, as Figure 4 shows.

Of course, at the end of each assessment, a third person carried out a validation check to eliminate errors in the calculations, which were mainly caused by incorrectly assigned datasets in terms of technological representativeness or incorrectly stated values from the bill of quantities and their relation to the selected LCA dataset.

Sensitivity Analysis

Choosing a method for assessing environmental impacts in LCA involves uncertainty. Various methods evaluate impacts using different datasets and characterization factors, but there is not a single correct choice [59,60]. Therefore, LCA practitioners must rely on subjective judgment when making their selections. Three kinds of deviations were considered for the sensitivity analysis to highlight the influence of each dataset [61] (Figure 5):

• Deviation in building materials; this impacts mostly the A and D modules of the life cycle.
• Deviation in energy source; this impacts the B6 module of the life cycle.
• Deviation in waste management; this impacts the C and D modules of the life cycle.

Considering the first option, since the primary approach of this study aimed to consider the most impactful datasets in terms of GWP, and to account for the “worst-case scenario” possible, a sensitivity analysis can be conducted to provide results for realistic and optimistic scenarios. Following the completion of the LCA, this analysis involves transitioning from the most impactful materials (e.g., concrete datasets, rebar datasets, etc.) to the most environmentally friendly ones in terms of GWP. Notably, the internal database outlined in Section 2.2 was updated with two additional datasets per item, focusing only on the most frequently occurring materials/products identified through environmental assessment (i.e., the so-called hotspots). This update facilitated an understanding of potential improvements if the most impactful material datasets of each case study were altered, prioritizing Czech datasets initially and, if not available, datasets from neighboring countries with similar energy mixes for materials production.

The second option involves choosing a dynamic emission factor (EF) of the electricity mix for the operational stage of the building. In the pessimistic scenario, the B6 value was calculated based on the standard Czech electricity mix used for energy calculations, with an EF according to Decree No. 480/2012 [62] of 0.78 kg CO₂ e/kWh. In contrast, for the recently published realistic scenario, the EF for electricity by the Czech Ministry of Environment (MoE) was used, which was equal to 0.37 kg CO₂ e/kWh [63]. Lastly, in the optimistic scenario, the emission factor from Norway was adopted as a possible future prospect or the use of renewable sources directly in buildings, primarily due to its reliance on renewable sources, which equals 0.0241 kg CO₂ e/kWh.

Regarding deviations in waste management, this option works with two different scenarios for the end-of-life phase of the building and the integrated building elements. Both the pessimistic and realistic scenarios assume landfilling or energy recovery as usual processes in the Czech Republic. The optimistic scenario includes recycling or reuse, as the need to save the consumption of primary raw materials is essential.

2.7. Phase 7—WLC Policy Suggestion and Lessons Learned

Policymakers are crucial to the successful implementation of the WLC in practice. It is vital to meet with them on a regular basis to discuss methods and interim outcomes, as well as to provide the groundwork for actual implementation.

Developing supporting documentation to familiarize policymakers with the topics they must understand and spread is of great importance. These comprise at least a position paper, a national policy brief containing the development of the findings of the case studies and benchmarks, and a white paper outlining the recommended WLC guidelines and their application in practice. It is also essential to take inspiration from recommendations abroad, where analogous processes are already successfully underway, and to communicate with relevant foreign partners.

The following paragraphs outline the most important topics that need to be addressed with stakeholders and consistently explain the associated issues.

2.7.1. Quality of Project Data

The quality of the input and output data is the most important aspect in the effort to obtain quality, representative, and consistent results. Errors in the input data can substantially affect the resulting WLC values, and there is always a subjective human factor involved. This aspect applies to both the input data from the bill of quantities or BIM and the input environmental data from the LCA database used.

2.7.2. Methodological Simplifications

The development of a detailed WLC assessment is highly time-consuming; thus, it imposes significant financial and capacity constraints, while also leaving room for human errors [28].

The imperative to streamline computational methodologies to accommodate the processing of approximately 25 thousand assessments annually for new building developments within the Czech Republic constitutes a fundamental precondition for the expeditious implementation of the EPBD. This imperative underscores the necessity of introducing simplified procedures based on a statistically significant sample derived from comprehensive assessments, as was carried out, for example, in Denmark [64].

2.7.3. Benchmarks Definition

The setting of the WLC benchmarks is necessary for their use in various policy instruments, such as subsidy programs or green public procurement, but above all for real reductions in the carbon footprint of the building stock in accordance with EPBD and other relevant legislation.

The benchmarks are to be set by a chosen statistical method (e.g., median or percentile) based on good quality and a sufficiently large statistical sample; they are likely to vary for different building typologies and need to be enshrined in legislation.

The benchmark development should consider the sensitivity analysis of the case studies, regarding the possible influence of the LCA background data quality, representing the location, time, and technological coverage, reliability, and consistency.

3. Results and Discussion

3.1. Phase 1—Case Studies Selection

The data utilized for developing the methodology and the future benchmarks are sourced from a variety of projects, including those originally certified by SBToolCZ, external projects from partners, and new life cycle assessments conducted as part of this activity, resulting in a total of 50 distinct case studies. These buildings are classified into five types: single-family houses, multi-residential buildings, administrative buildings, educational buildings, and logistic buildings, encompassing both new constructions and renovations—

Table 2. Overview of WLC case studies.

Case Study Typology	Planned		Actual status
	New Construction	Renovation	New Construction	Renovation
Single-family house	11	10	11	4
Residential building	7	6	11	1
Office building	7	0	11	4
Educational building	4	5	2	1
Logistic hall	-	0	5	0

.

Table 3. Example of case studies’ main information.

Typology	Source	Gross Internal Floor Area (m2)	Energy Class	Structure	Main Materials
Office	Partner	1324.18	A	massive brick
Office	Partner	248.10	C	no data
Multi-family house	Partner	1304.70	B	massive wood	Timber, wood
Multi-family house	Partner	1081.00	A	massive brick
…	…	….	…	…	…

describes the building types according to source, energy class, gross internal floor area, construction type, and main materials.

3.2. Phase 2—Definition of a Materials’ LCA Database

Table 4. Internal database structure.

SBToolCZ Material/Process	Dataset Name from OCLCA	Data Source	Location	Upstream Database	Unit	Notes
Bituminous coating	Asphalt, generic, compacted, 5/95% bitumen–aggregate ratio, 2350 kg/m3	Lucobit (Manufacturer)	Czechia	Ecoinvent	kg, ton, m3	…
…	…	Generic	Italy	Ecoinvent	kg, ton, m3, m2	…
…	…	…	…	…	…	…

illustrates how the internal database is structured. Throughout the process, it was constantly updated with new datasets (if any new ones were necessary during the WLC assessment of the case studies) to ensure that all the materials, even those that were not completely defined at the beginning of the process, were accounted for. The internal database as of April 2024 accounted for slightly more than 290 datasets. Approximately 55% of the datasets are sourced from the Czech market, with the remainder drawn from countries with comparable electricity mixes, such as Poland, Italy, and Germany.

3.3. Phase 3—Material and Products Classification

To facilitate comprehension of the most environmentally significant categories, a thorough classification of the building is essential, under which materials/products belonging to the building can be listed. Consequently, the classification systems outlined in Level(s), the SBToolCZ system (which is in accordance with Czech building practice), OCLCA, and the INDICATE project were analyzed to determine their correlation and the final selection of categories.

Table 5. Building classification systems defined by OCLCA, Level(s), and the INDICATE project.

OCLCA Structure	Level(s) Structure	Indicate Result Classification
FOUNDATION	1.1 Foundations	Ground (i.e., substructure, foundation, basement walls, etc.)
	1.1.1 Piles
	1.1.2 Basements
	1.1.3 Retaining walls
WALL	1.2 Load-bearing structural frame	Structure (i.e., structural frame, walls, floors, roofs, etc.)
EXTERNAL WALL/COLUMN	1.2.1 Frame (beams, columns, and slab)
BEAM	1.2.2 Upper floors
EXTERNAL WALL	1.1.3 External walls
	1.2.4 Balconies
SLAB/INTERNAL WALL	1.3 Non-load-bearing elements	Internal (i.e., partitions, int. finishes, etc.)
SLAB	1.3.1 Ground floor slab
INTERNAL WALL/DOOR	1.3.2 Internal walls, partitions, and doors
SLAB	1.3.3 Stairs and ramps	Structure (i.e., structural frame, walls, floors, roofs, etc.)
EXTERNAL WALL	1.4 Facade	Envelope (i.e., openings and external finishes)
	1.4.1 External wall systems, cladding, and shading systems
WINDOW	1.4.2 Façade openings
VERTICAL FINISH	1.4.3 External paints, coatings, and renders
ROOF	1.5 Roof	Structure (i.e., structural frame, walls, floors, roofs, etc.)
	1.5.1 Structure
	1.5.2 Weatherproofing
FINISH	2.1 Fittings and furnishings	Structure (i.e., structural frame, walls, floors, roofs, etc.)
	2.1.1 Sanitary fittings	Appliances (i.e., fixed facilities, mobile fittings, etc.)
	2.1.2 Cupboards, wardrobes, and worktops	n/a
HORIZONTAL FINISH	2.1.3 Ceilings	Internal (i.e., partitions, int. finishes, etc.)
VERTICAL FINISH	2.1.4 Wall and ceilings finishes
HORIZONTAL FINISH	2.1.5 Floor coverings and finishes
BUILDTECH	2.2 In-built lighting system	Appliances (i.e., fixed facilities, mobile fittings, etc.)
	2.2.1 Light fittings
	2.2.2 Control systems and sensors
	2.3 Energy system	Services (i.e., mechanical, electrical, renew. energy, etc.)
	2.3.1 Heating plant and distribution
	2.3.2 Cooling plant and distribution
	2.3.3 Electricity generation and distribution
	2.4 Ventilation system
	2.4.1 Air handling units
	2.4.2 Ductwork and distribution
	2.5 Sanitary systems
	2.5.1 Cold water distribution
	2.5.2 Hot water distribution
	2.5.3 Water treatment systems
	2.5.4 Drainage systems
	2.6 Other systems	Appliances (i.e., fixed facilities, mobile fittings, etc.)
	2.6.1 Lifts and escalators
	2.6.2 Firefighting installations
	2.6.3 Communication and security installation
	2.6.4 Telecoms and data installation
OTHER	3. Not defined	Not defined (i.e., energy/water consumption or any other building part)

illustrates in a comprehensive way the classification system of OCLCA and the Level(s) framework, along with the INDICATE system, to present the assessment results in a clear and transparent manner for the national context.

3.4. Phase 4—Stakeholders Engagement

Stakeholder engagement stands as a pivotal practice toward the definition of an accepted WLC national method.

First, potential case study providers were approached with the help of the project consortium (Czech Technical University—University Centre for Energy Efficient Buildings, Czech Green Building Council and Chance for Buildings). Approximately 65 case studies were purposively collected from them. From these, representatives of each typology and material solution were then selected.

Subsequently, various stakeholders involved in the implementation of EPBD [36] in Czech practice were approached—developers, investors, LCA and sustainability consultants, energy specialists, architects, planners, and of course policymakers. Both the selection of case studies and the ongoing methodological steps and results were discussed with them on an ongoing basis during work group meetings, workshops, and seminars. Especially with the policymakers, the compliance of calculation procedures with the expected future EPBD requirements and the possibilities of the Czech market were addressed—the implementation of WLC into currently used calculation tools for buildings, possibilities for simplification, capacity provision, and benchmark development.

A successful interaction was facilitated by numerous pathways—four workshops, two roundtables, two workgroups, two webinars, and five bilateral meetings between March 2023 and March 2024—each serving as a nexus for exchange and innovation. The issues raised during these activities included:

• Calculating LCA is time-consuming and costly.
• There is a lack of a methodological framework for preparing BoQs and BIM for LCA calculations at the national policy level.
• Results can vary significantly depending on the database and environmental datasets used.
• There is a need for a national tool to facilitate WLC calculations.
• There is a lack of capacity for performing WLC calculations.
• There were also four meetings with discussions and subsequent recommendations from the foreign partners BPIE, KU Leuven, and WGBC, who are experienced leaders in WLC implementation.

Thanks to all these meetings, a network of contacts and long-term cooperation with other interested parties in the Czech Republic, such as the Institute of Circular Economy, the Passive House Centre, or the Czech Chamber of Architects, has been established, which will certainly contribute to a smoother implementation of the directive in practice.

More discussion with stakeholders and training activities can lead to better understanding of and agreement with the approach, making implementation easier, doable, and sustainable.

3.5. Phase 5—Exportation of the Bill of Quantities

3.5.1. Manual Filtration of Materials

Table 6. Example of an extract of BoQs.

Item Name from BoQs	Numerical Consideration (0/1/2)	Classification Level(s)	Dataset Name from OCLCA	Unit	Quantity	Notes
Installation of formwork for foundation slabs	0	…	…	…	…	Not considered, work process description
Single-layer masonry of cavity brick 240 mm thick	1	1.2.3 External walls	Clay bricks, Porotherm Profi, Porotherm T Profi… (Wienerberger, Novosedly plant)	2880	kg	Calculation: 15 m2 × 0.24 m × 800 kg/m3
Bolts or screws installation over 150 to 300 mm long	2	…	…	1	set	Not considered, small connecting materials are negligible

was manually completed for each case study according to the methodology described in Section 2.5—Phase 5—Exportation of the Bill of Quantities. For example, for single-family houses, the number of elements varied around 500 items, while for large buildings, like office buildings or hospitals, the number ranged between 3000 and more. The process proved to be highly time-consuming and complex due to the need for the individual analysis of a large number of items to determine their inclusion in the subsequent steps. For instance, in a case study of a single-family house comprising 345 items in the BoQ, approximately 148 items (roughly 40%) were excluded from consideration for the assignment of environmental datasets. These exclusions were primarily construction work, for example the excavations, installations, or mass transfers, which are usually considered since the BoQ is primarily used for building costs estimation and small connecting elements.

Another challenge involved ensuring the proper conversion of material units to match the corresponding units required by the environmental datasets. Each environmental dataset is linked to specific units of measurement, and failure to adhere to these units may result in the OCLCA software failing to recognize the alignment with the dataset. Therefore, meticulous conversion to the appropriate unit of measure, ideally in kilograms of material, was necessary for those materials/items requiring it.

The next action was to complete the template (.xls format) provided by OCLCA, including the list of materials with their respective quantities, units, classification by Level(s), and the exact dataset name, for importing into the OCLCA. This ensured that each item could be easily recognized by the software and appropriately evaluated during the assessment.

3.5.2. BIM-Based BoQ

The BIM-based workflow was straightforward. Before exporting model data to OCLCA, the specifics of the model simplification must be taken into account. These include the neglect of structures and substructures, insufficient material descriptions, and simplified feature modelling. These specifics concern, in particular, foundations, façade elements (solid profiles), plasterboard partitions (neglected substructure), railings (insufficiently described materials), windows and doors (solid profiles), etc. In these cases, the appropriate amount of material is manually inserted into the tool, for example, according to the product data sheet of the product in question.

In some cases, separate individual models of building parts are developed by different stakeholders, e.g., three models for a facade, load-bearing structures, and foundations of a building. Consequently, there arises a need to export data from each of these models separately into the process, a task prone to errors and time consumption. All the points mentioned should be specified in the project brief, e.g., the Employer’s Information Requirement (EIR), described in ISO 19650 [65].

The export itself to OCLCA is conducted using an add-in to the Revit 2023 software in two ways: either the datasets are paired directly in Revit or in the web interface, in a similar manner to the import described in Section 3.5.1.

3.6. Phase 6—Life Cycle Assessment

The WLC assessment findings for each case study can be analyzed and directly downloaded from OCLCA. To facilitate comparison of the outcomes, individual case study result sheets were generated to enhance understanding of the impact across each LC phase and Level(s) classification category. For instance, Figure 6 and Figure 7 illustrate the results for a residential building, wherein the GWP is segmented across LC phases to highlight the most impactful one.

Conversely, Figure 8 presents the results for the embodied impacts, closely linked to the material/product production and replacement phases for the same project. Figure 9 presents the results for the whole LC. These results are categorized by building part according to the cumulative Level(s) categories:

• Ground (i.e., substructure, foundation, basement walls, etc.);
• Structure (i.e., structural frame, walls, floors, roofs, etc.);
• Envelope (i.e., openings and external finishes);
• Internal (i.e., partitions, internal finishes, etc.);
• Services (i.e., mechanical, electrical, renewable energy, etc.);
• Appliances (i.e., fixed facilities, mobile fittings, etc.);
• Not defined (i.e., energy/water consumption or any other building part).

Figure 9 presents the building parts’ impacts during the whole life cycle (from module A to module C).

Another crucial aspect to consider is the ratio between the embodied impacts (across the entire of module A, B4–B5, C2–C4) of building materials and building technical systems. For instance,

Table 7. GWP ratio between construction materials and building technical system in a single-family house case study.

	Building Parts	GWP [kg CO2 e/m2a]	Ratio
Construction materials	Foundations + basements + ground floor slab	6.13	53%
	Vertical load-bearing system	2.56	22%
	External walls	0.34	3%
	Internal walls, partitions, doors	0.16	1%
	Stairs, ramps	0.00	0%
	Finishes external/internal, horizontal/vertical	1.23	11%
	Roof	0.94	8%
	Façade openings	0.19	2%
	total	11.54	100%	90%
Building technical system	Sanitary fittings	0.02	2%
	Water, gas, drainage	0.44	36%
	Ventilation	0.08	7%
	Heating	0.54	45%
	Cooling	0.00	0%
	Lighting systems and electricity generation	0.12	10%
	Control systems and sensors	0.01	0%
	total	1.21	100%	10%

demonstrates the extent to which construction materials affect the final GWP value in comparison to the building technical system in a case study of a single-family house. For instance, numerous cases of family house case studies have been shown to account for approximately 90% of the impact, with technical systems contributing only 10%.

Sensitivity Analysis

Through the sensitivity analyses conducted for each case study, insights were gained into how the LCA results vary when different input data are inserted. This analysis focused on three main deviations: (i) variations in LCA datasets for building materials, (ii) changes in energy sources, and (iii) adjustments in waste management, across three distinct scenarios: pessimistic, realistic, and optimistic.

For instance, in the examination of building materials, Figure 10 illustrates the outcomes of a multi-residential building case study. Here, 10 critical materials (i.e., hotspots) were identified (such as concrete M25/30, rebars, rockwool insulation, etc.), and their datasets were modified to those with lower GWP, as outlined in Section “Sensitivity Analysis”. Across various case studies, it was observed that the difference between the pessimistic and optimistic scenarios ranged around a 20% improvement in terms of reduced GWP values.

When the energy source is the subject of change, there is approximately a 30% enhancement in terms of GWP, assuming the energy mix remains primarily sourced from Czechia. Typically, the electricity mix powers lighting, ventilation, and cooling systems. Figure 11 demonstrates improvement not only due to variations in the energy mix but also in building materials. In the optimistic scenario, where a Norwegian energy mix is considered, which is primarily derived from renewable sources, the improvement amounts to 55% compared to the standard scenario (B6 phase).

In terms of waste management, the pessimistic scenario adopts the default end-of-life (EOL) scenarios provided by OCLCA, which are either derived from manufacturer-specific EPDs or generic data from the Ecoinvent database. For instance, when looking at the building mentioned in the previous examples of deviations, OCLCA automatically linked each dataset from the 10 hotspots to a particular end-of-life scenario. In this instance, the result is 36.28 kg CO₂ e/m²a, which simultaneously represents the pessimistic and the most realistic scenario. Conversely, considering recycling and landfilling, or the reuse of those materials/products, the result would yield values of 49.23 kg CO₂ e/m²a, and 48.98 kg CO₂ e/m²a, respectively.

3.7. Phase 7—WLC Policy Suggestion and Lesson Learned

Through the case studies calculation process and the meetings and workshops with stakeholders, held to ensure the successful implementation of the WLC assessment of buildings into Czech practice, the following recommendations for policymakers should be considered:

• Establish a national LCA database: There is a need for a centralized database that contains verified and up-to-date life cycle assessment data for various building materials and construction methods. This will help streamline the assessment process and ensure consistency in the data used and the representativeness of the results.
• Approve a consistent methodology: A national methodology for conducting whole life carbon assessments must be standardized and anchored in legislation. This will help ensure that assessments are conducted consistently and transparently, making it easier to compare results across different projects.
• Provide guidelines for consistent Bills of Quantities: Common guidelines on how to prepare BoQs that include relevant data for conducting LCAs shall be prepared. This will help simplify the WLC assessment process and make it easier for professionals to incorporate it into their project planning.
• Leverage BIM advantages: BIM technology can facilitate the integration of WLC assessments into the design and construction process. Policymakers should encourage the use of BIM tools.
• Develop a national WLC calculation tool: A user-friendly and standardized calculation tool for conducting WLC assessments would simplify the process for professionals. Policymakers should invest in the development of such a tool to support the widespread adoption of sustainability practices in the construction industry.
• Conduct more case studies: Fifty case studies are not a sufficient statistical sample; they are only a starting point. At least 200 case studies should be conducted to help build a repository of best practices and lessons learned that can inform future policy decisions and industry practices.
• Implement WLC simplifications: Due to the highly time-consuming nature of detailed WLC studies, it is necessary to set up possible simplifications that will reduce the time and thus the financial requirements. These simplifications must be based on the statistical sample mentioned above and could include the evaluation of some building parts by percentages (e.g., GWP percentages for HVAC), by evaluation of buildings based on the composition of the main building structures (composition of 1 m² of external walls, roof, footprint, and floor), by the volume of the main masses, by specific penalties in the case of simplified LCA, etc.
• Invest in education and capacity building: Finally, policymakers should prioritize education and capacity-building initiatives to increase awareness and understanding of WLC assessments among professionals in the construction industry. This will help build the knowledge and skills needed to effectively implement them in practice.

3.7.1. Quality of the Project Data

To obtain relevant results, project data must be of high quality. At a minimum, third-party data checking is required, which can significantly increase the time-consuming nature of the studies performed. However, checking can be simplified if boundary conditions are clearly defined and input data entry processes are set up as simply as possible to prevent human error.

These include (i) a more accurate and unified preparation of the bill of quantities for LCA purposes—e.g., converting all items to weight to avoid errors due to the use of the wrong unit of measure, clear cut-off rules, and defined classification of construction parts; (ii) a clear definition of generic LCA datasets—a single generic LCA database for use for generic building materials in the early stages of building design; (iii) automation of the assignment of LCA datasets to items from the bill of quantities as much as possible; and (iv) automatic checking of outputs with warning of suspicious items.

3.7.2. Methodological Simplifications

Based on the findings gathered from the extensive computational analysis of numerous case studies, it can be asserted that simplification of WLC calculations will be necessary and may include: (i) establishing assessment detail levels based on project size or investment, with greater scrutiny reserved for larger projects necessitating detailed LCAs; (ii) streamlining GWP calculations based on statistical data for individual building components—such as the percentage contribution of foundations, building services systems, or the load-bearing structure to the overall structure; and (iii) implementing WLC assessment into existing tools used by Czech energy or budgeting specialists because of the market’s particular capacities.

Nevertheless, achieving such simplification necessitates a substantially larger statistical sample than the 50 case studies processed within the framework of the INDICATE project.

3.7.3. Benchmarks Definition

Benchmarks from the resulting GWP values can be set either as a weighted average, a median, or a percentile value. Another parameter is to determine the need to save a certain amount of GWP within a given timeframe, e.g., by 2030 or 2050, i.e., in line with a national decarbonization strategy. Unfortunately, the Czech Republic does not have such a strategy yet; therefore, it is only possible to take inspiration from abroad or to set benchmarks politically, e.g., it is necessary to start with softer limits and gradually tighten as the calculations become more precise and the energy mix changes.

In Denmark, for example, the GWP benchmarks for different building typologies are set for the 67th percentile of the developed case studies, i.e., GWP values in two-thirds of the overall ranking of values [64].

Figure 12 presents an example of possible GWP benchmarks for the newly constructed multi-residential buildings in the Czech Republic. It presents an assemblage of five case studies of existing multi-residential buildings, two of which were subjected to sensitivity analyses with changing input LCA datasets following the optimistic, realistic, and pessimistic scenarios. Thus, there are 11 GWP values in total, all of which can be considered relevant and representative of the Czech national WLC context.

The case studies include multi-story buildings built of reinforced concrete, sand–lime bricks, and hollow ceramic bricks, with common thermal insulation systems of polystyrene as well as mineral wool; so, they are quite a representative sample of housing construction in the Czech Republic.

The results show that GWP values range from 20.17 to 36.28 kg CO₂ e/m²a. The median value is equal to 26.45 kg CO₂ e/m²a, while the arithmetic average is 28.30 kg CO₂ e/m²a. However, these values do not meet the need to set softer benchmarks in the first stages of WLC implementation in practice.

If considering the same approach used in the Denmark benchmark settings [64], the values would be set at the 67th percentile and, therefore, at 26.45 kg CO₂ e/m²a. Indeed, in the current situation, where the Czech Republic lacks a decarbonization strategy, this would probably be the recommended value. However, given the unavailability of sufficient representative LCA data for building materials on the Czech market, it is possible to set the benchmark even more moderately, at the 90th percentile for example, which in this case comes out to 35.94 kg CO₂ e/m²a.

This may also be due to the fact that LCA is nowadays mainly commissioned by projects where it is assumed that their investors are interested in more environmentally friendly solutions, and therefore, the resulting GWP value may be relatively lower compared to that of conventional construction.

3.7.4. Theoretical and Practical Implications

This study provides a robust methodological framework for selecting LCA data and clarifying building parts or structures effectively for the assessment. It outlines a systematic approach that enhances the understanding of life cycle calculations, facilitating the development of a comprehensive methodology that stakeholders have requested and that could potentially be implemented in any other national context.

Practically, this research establishes a foundation for future statistical sample treatments in Czech practice. It promotes effective connections between stakeholders and ensures close communication with those involved in EPBD implementation. Additionally, it highlights the need for a unified and practical common methodology for preparing BoQs and BIM for LCA calculations within the national policy, ensuring usability and feasibility for stakeholders.

4. Conclusions

Numerous countries in Europe and worldwide do not have the Life Cycle Assessment (LCA) methodology and benchmarks specific to their needs. This paper offers a methodology that can be valuable for them. The methodological approach is replicable, allowing countries to adopt the entire process or only the parts that are most relevant to their circumstances for defining national WLC assessment methods.

The WLC assessment of 50 building case studies stands as the most extensive compilation of LCA data for various typologies ever assembled for the Czech Republic. This is largely attributed to the consistent utilization of the same environmental datasets database. This was meticulously crafted to evaluate and compare results using the same LCA software (OCLCA), following a uniform methodological process, which involves a judicious choice of case studies, unified classification, bill of quantities exportation, sensitivity analysis, and benchmark setting.

The selection of case studies was purposefully diverse, encompassing various building types, energy classifications, materials, and other relevant factors. This comprehensive approach ensures that the benchmark values derived are as inclusive and representative as possible for the national Czech market, accommodating the inherent disparities between buildings.

This approach to LCA, after preparing the unified template for national use (Figure 6) and completing the sensitivity analysis step, could be integrated into building practices. This integration could lead to recommendations for policymakers and private companies that can be used in assessing the whole life cycle of their projects. The paper also emphasizes the importance of encouraging the market to adopt benchmark definitions and simplifications for policymakers through the step-by-step WLC assessment approach.

The primary objective behind establishing benchmark values for the Global Warming Potential (GWP) is to provide a definitive reference point for evaluating the environmental performance throughout a building’s lifecycle. Such standardized benchmarks can serve as the cornerstone for tender specifications, public regulations, or any other form of benchmarking initiatives already available in energy performance, indoor climate management, or similar areas. Importantly, they try to fill a crucial gap by extending this framework to encompass the lifecycle-based environmental impact, a dimension that is so far absent in the Czech Republic’s regulatory landscape.

The results of 11 multi-residential building case studies, including several sensitivity analyses of different LCA data inputs, showed an average GWP value of 28.30 kg CO₂ e/m²a. However, to establish benchmarks relevant for a future successful WLC implementation, softer numbers must be applied at the first stage; this leads to a recommendation to use higher percentile results, such as those with a value of 31.13 kg CO₂ e/m²a for the 67th percentile or 35.94 kg CO₂ e/m²a for the 90th percentile. Still, the availability of LCA data for building products from the Czech market, the creation of an accessible national calculation tool and database, and the approval of national WLC methodology are crucial for the further development and refinement of national GWP benchmarks. Also, processing a significantly larger statistical sample of case studies than the actual one is a prerequisite for the above. They can then be gradually applied to save time, money, and capacity in the construction sector.

The quality of data extracted from BIM models or the standard BoQ should be investigated in a specific and clear manner to ensure that stakeholders do not perceive the process as complex and time-consuming. The LCA results must be presented in a unified format for the market, making them easy to understand and compare. Finally, there is a need to develop educational materials, training programs, and incentives to gradually increase the capacity of the construction sector stakeholders to cover the WLC assessment area. Each of these measures will contribute towards fulfilling the mandate to mitigate the environmental impacts of the construction industry activities in the Czech Republic.

Once the national WLC calculation tool is developed, the results and corresponding benchmarks must be adjusted accordingly. Future work will focus on analyzing more case studies to create a larger sample of the Czech building stock, potentially leading to further simplifications based on updated knowledge. One of the main limitations of the study was the consideration of only 50 case studies and the use of a large amount of foreign environmental datasets to develop benchmarks. However, this paper aims to present the methodology rather than definitive benchmarks for the Czech market and serves as a starting point for their calculations. Additionally, other environmental parameters, such as recycled content, acidification potential, or toxicity, will be considered in the future to expand the assessment from a holistic LCA perspective, aligning with policymakers’ interests.