Appropriate Thresholds and Metrics for LEVEL(S) Key Performance Indicators (KPIs)

Abstract

The European Union’s LEVEL(S) framework establishes a standardized methodology for evaluating and documenting the sustainability of buildings across Europe, aiming to enhance the sustainability, competitiveness, and resilience of the EU’s built environment. This study investigates the theoretical foundations and practical applications of the LEVEL(S) framework in advancing sustainable building practices. The research begins with a systematic identification of gaps in existing sustainability indicators, such as the absence of specific metrics and undefined thresholds, identified in the author’s previous work. To address these gaps, the study introduces new thresholds informed by an extensive review of the relevant literature and performance data. Additionally, the research synthesized a comprehensive Table by analyzing EU user manuals, the related academic literature, and various Green Building Rating Systems (GBRSs), thereby facilitating the extraction of pertinent standards and regulations. Collectively, these findings provide valuable resources for policymakers and stakeholders, ensuring that the recommendations are closely aligned with the LEVEL(S) framework and can be effectively applied to real-world building projects throughout Europe.

1. Introduction

In 2022, the top CO₂-producing nations were China, United States, India, EU-27, Russia, and Brazil. EU-27 led by Germany accounts for producing 3.2 billion metric tons of global GHG emissions. Globally, buildings are the largest consumers of energy, responsible for nearly 33% of total final energy use and around 30% of global CO₂ emissions [1,2]. When their entire life cycle is considered, including construction, operation, and demolition, their impact becomes even more pronounced, contributing to almost half of the global energy demand and 50% of total CO₂ emissions [3,4]. In this context, the European Union is committed to achieving a fully decarbonized building stock by 2050 [5]. This progress can be achieved by encouraging renovations across member states, with a particular focus on the worst-performing buildings, as stated in the last recast of the Energy Performance of Buildings Directive (EPBD). In the residential building sector, member states are required to set national targets to reduce average primary energy consumption by at least 16% by 2030 and 20–22% by 2035 [6]. In parallel, for non-residential buildings, the revised Directive introduces a phased improvement pathway based on minimum energy performance standards, mandating the renovation of the worst-performing 16% of the stock by 2030 and 26% by 2033, with the entire building stock expected to comply by 2050 [7].

In this scenario, global sustainability rating systems play a prominent role in achieving the decarbonization goal [8]. Several certification systems are currently used in Europe to assess and promote sustainability in architecture and buildings, as well as to reduce carbon emissions. The most notable among them is the Leadership in Energy and Environmental Design (LEED), which, while commonly used in North America, has also gained popularity in some parts of Europe [9,10,11]. In Europe, the Building Research Establishment Environmental Assessment Method (BREEAM) is another widely used sustainability assessment method [9,12]. Additionally, the Passive House (Passivhaus) standard is well-known in Germany and Austria [13,14], while CasaClima enjoys widespread use in Italy and other European regions [15,16]. Moreover, the Carbon Risk Real Estate Monitor (CRREM) represents a research and innovation initiative that formulates science-based decarbonization roadmap for the commercial and residential real estate sectors [17].

As part of a well-established rating system, the European Commission, launched in 2017 after its inception in 2015, introduced a new framework for evaluating buildings called LEVEL(S) [18]. The objective of this framework is to enhance the sustainability of buildings within the European Union by establishing defined thresholds for some areas of analysis, thus facilitating the development of a robust scale system for future research. Implementing this framework is critical to promoting sustainable construction practices, and continuous advancements in LEVEL(S) could play a pivotal role in driving these efforts. Consequently, advancing research on the LEVEL(S) framework remains essential for its ongoing development and optimization. In support of these goals, LEED certification has recently strengthened alignment with the LEVEL(S) framework and the EU Taxonomy within the European market. As of April 2025, updated LEED criteria have been released to highlight key aspects of the EU Taxonomy, which directs investments toward sustainable activities, and reinforce compatibility with the LEVEL(S) framework [19].

Additionally, the New European Bauhaus (NEB) development is key to facilitating Europe’s green transition, linking the European Green Deal with practical aspects such as buildings and living spaces. NEB has recently introduced indicators, weighting factors, and thresholds that could strengthen the LEVEL(S) framework and potentially increase its adoption. By focusing on transforming the built environment to align with climate goals and enhance quality of life across Europe, NEB emphasizes sustainability, beauty, and inclusiveness. The sustainability theme focuses particularly on reducing energy use and emissions, as well as enhancing resource management, in alignment with LEVEL(S)’s indicators.

As the primary objective of this study is to establish scientifically grounded thresholds, aligning various tools remains a critical priority for the EU. Therefore, the proposed improvement by NEB will be systematically analyzed in this study [20]. Compared to other sustainability protocols, such as LEED and BREEAM, which are extensively used and tested in several buildings, there are currently no case studies that effectively highlight the potential strengths and weaknesses of the LEVEL(S) framework in implementing its goals.

In this context, the present work aims to analyze the Key Performance Indicators (KPIs) and thresholds outlined in LEVEL(S), supplementing any gaps with the literature review for KPIs where metrics or thresholds are not provided. Given the numerous indicators associated with this recent EU framework, the need for a clear scaling system to measure sustainability is evident. This study delinates threshold criteria. For macro-objectives that are insufficiently addressed in the existing literature, future work should be conducted on empirical assessments using real-world case studies. Furthermore, in cases where multiple options are available, the criteria for selecting the most suitable metrics and thresholds require careful consideration. For certain indicators, no thresholds have been reported in the literature; therefore, the paper highlights the missing aspects on which further research will be required, thereby pointing to areas where experimental studies should be developed to empirically assess and validate threshold values in real-world contexts. Accordingly, this study provides guidance for future research on the subject [21]. The whole work draws upon both the official website of the European Union’s LEVEL(S) framework for sustainable buildings and authoritative scientific sources, including the NEB report and established protocols such as LEED, BREEAM, GREEN STAR, CASBEE, and ITACA. While hundreds of sustainability protocols have been implemented worldwide, this study examines the most prominent examples from each continent [22,23]. This study is structured as follows: The first part explores the significance of decarbonization within the context of global sustainability rating systems (Section 1). Section 2 describes the methodology employed, which involves an extensive literature review utilizing sources from the official European Union website (User Manuals) to identify recent development gaps in the EU’s approach. Section 3 presents a thorough analysis of these gaps, focusing on a recent assessment of the LEVEL(S) Key Sustainability Indicators and discussing enhancements to LEVEL(S), with particular emphasis on the critical need to define precise thresholds and metrics. Section 4 methodically evaluates each indicator within the LEVEL(s), assessing the appropriate metrics and thresholds. This includes a comprehensive analysis of the thresholds established in LEVEL(S) against those found in other studies and regulations to identify the most effective benchmark.

It is important to note that not all indicators in the LEVEL(S) framework have defined thresholds or are suited to having thresholds established.

2. Research Method

The methodology of this study can be divided into several stages (Figure 1). First, an assessment of the LEVEL(S) structure and its gaps was carried out to gain a better understanding of this recent initiative launched by the European Union. The analysis centered on the structure of LEVEL(S), with a thorough explanation of its macro-objectives and corresponding indicators. This was followed by an evaluation of the weaknesses linked to each macro-objective and its indicators. Building on the gaps identified in the previous study of the present authors [21], this assessment aimed to define the most suitable thresholds for each indicator within the LEVEL(S) framework. This process involved determining the appropriate unit of measurement for each indicator and establishing a threshold to gauge target achievement effectively. To ensure robustness, these thresholds were evaluated through a comprehensive literature review, identifying the most appropriate benchmark for each indicator. Finally, a compiled threshold list was developed, presenting the values deemed most suitable by this study. As part of this process, an evaluation of the most prominent sustainability protocols worldwide, especially Green Building Rating Systems (GBRSs), such as LEED (United States), BREEAM (United Kingdom), ITACA (Italy), GREEN STAR (Australia), CASBEE (Japan), and LEVEL(S), was undertaken to identify common indicators between LEVEL(S) and the respective GBRS. The objective was to analyze the thresholds applied to equivalent indicators and to present these findings, following the table of common indicators provided at the end of each section addressing a specific macro objective from the LEVEL(S) framework. This comprehensive assessment facilitates a more robust analysis of various databases and enhances the overall understanding of sustainability metrics across different international contexts.

Furthermore, an in-depth analysis was conducted to examine the metrics associated with each indicator. Unlike other sustainability labeling systems that benefit from well-established scaling mechanisms and their application across various case studies, the LEVEL(S) framework requires a defined scale and methodology for measuring different thresholds across macro-objectives.

This literature review was conducted by the principles of the Critical Literature Review (CLR) framework. Each relevant source was systematically analyzed and critically evaluated to assess its potential contribution to the study [24]. Given the wide range of indicators encompassed within the LEVEL(S) framework, the initial stage involved a comprehensive examination of metric definitions, unit definitions, and threshold definitions for each indicator, with particular emphasis placed on identifying pertinent keywords associated with each. Special emphasis was placed on identifying key terms relevant to these dimensions. The resulting data, specifically, keywords related to metrics, thresholds, and units, served as search terms and inclusion criteria, thereby expanding the scope and comprehensiveness of the literature search. Extensive searches were conducted across electronic databases, including Google Scholar, and official documentation from recognized sustainability protocols worldwide. The review primarily concentrated on European contexts, except for GBRSs, to ensure a comprehensive perspective on the continent. The literature review process is depicted in the figure above.

3. Analysis of the Gaps in the LEVEL(S) Framework: Key Performance Indicators (KPIs) and Areas of Improvement

LEVEL(S) is based on a set of indicators [18,25,26,27,28,29,30,31,32,33,34,35,36,37,38,39] categorized into six macro-objectives reported hereafter [40]. This paper addressed the gaps associated with the indicators for the six macro-objectives of the LEVEL(S) framework, evaluated in the previous study [21]. An overview of these identified gaps is provided first, followed by a detailed discussion in Section 4. The evaluations associated with each indicator of the LEVEL(S) framework reveal distinct gaps (

Table 1. Identifying gaps in metric definitions and threshold establishments within the LEVEL(S) framework. The presence of a metric or threshold is indicated by a green tick (✓), while its absence is shown with a red cross (🗶).

Macro-Objective	Indicator	LEVEL(S) Threshold	LEVEL(S) Metric
1. Greenhouse gas and air pollutant emissions along a building’s life cycle	1.1. Use stage energy performance	✓	✓
	1.2. Life Cycle Global Warming Potential	🗶	✓
2. Resource-efficient and circular materials life cycles	2.1. Bill of quantities, materials, and lifespans	🗶	✓
	2.2. Construction and demolition waste and materials	✓	✓
	2.3. Design for adaptability and renovation	✓	✓
	2.4. Design for deconstruction, reuse, and recycling	✓	🗶
3. Efficient use of water resources	3.1. Use stage water consumption	✓	✓
4. Healthy and comfortable spaces	4.1. Indoor air quality	✓	✓
	4.2. Time outside of thermal comfort range	🗶	✓
	4.3. Lighting and visual comfort	🗶	✓
	4.4. Acoustic and protection against noise	🗶	✓
5. Adaption and resilience to climate change	5.1. Protection of occupier health and thermal comfort	✓	🗶
	5.2. Increased risk of extreme weather events	🗶	🗶
	5.3. Increased risk of flood events	🗶	✓
6. Optimized life cycle cost and value	6.1. Life cycle cost	🗶	✓
	6.2. Value creation and risk exposure	🗶	✓

), and the red crosses indicate the identified gaps related to each indicator.

The present study addresses these shortcomings through an exhaustive evaluation of the pertinent literature.

4. Threshold and Metric Analysis: Methods and Tools to Measure the Indicators

This study is crucial for introducing the term “metrics” as it applies to LEVEL(S), where indicators can be measured in various ways, here, specifically referred to as metrics. While LEVEL(S) identifies certain metrics as control parameters for some indicators during the design process, it does not provide explicit calculation methods or define specific thresholds for these indicators.

LEVEL(S) macro-objectives indicators [18,25,26,27,28,29,30,31,32,33,34,35,36,37,38,39,41] are shown in

Table A1. LEVEL(S) macro-objectives and indicators [18,25,26,27,28,29,30,31,32,33,34,35,36,37,38,39,41].

Macro-Objective	Indicator	Metrics	Unit
1. Greenhouse gas and air pollutant emissions along a building’s life cycle	1.1. Use stage energy performance	Heating	(kWh/m2/year)
		Cooling
		Ventilation
		Domestic hot water
		Lighting
	1.2. Life cycle global warming potential	GWP-fossil	(kg CO2 e/m2/year)
		GWP-biogenic
		GWP-GhGs (fossil + biogenic)
		GWP-land use and land use change
		GWP-overall (fossil + biogenic + land use and land use change)
2. Resource-efficient and circular materials life cycles	2.1. Bill of quantities, materials, and lifespans	Total quantity of materials used	(Tonnes and %)
		Quantities of materials used split by building aspect	(Tonnes and %)
		Cost of Materials used	(€ and %)
		Normalized total materials	(kg/m2)
		Normalized total cost	(€/${\mathrm{m}}^2$)
	2.2. Construction and demolition waste and materials	Quantity of waste	(kg/m2)
	2.3. Design for adaptability and renovation	Adaptability score	-
	2.4. Design for deconstruction, reuse, and recycling	-	(Dimensionless scoring of the circularity potential of a building)
3. Efficient use of water resources	3.1. Use stage water consumption	Total water consumption per occupant	m3/person
		Water-efficient sanitary devices and fittings	l/flush
		Water Scarcity Indicator (WEI+)	-
		Rainwater harvesting and greywater reuse potential	-
		Irrigation water needs for vegetated areas	l/day
		Water metering and Submetering	-
4. Healthy and comfortable spaces	4.1. Indoor air quality	Ventilation Rate (airflow)	(l/s/${\mathrm{m}}^2$)
		Total Volatile Organic Compounds (VOCs)	(µg/m3)
		Formaldehyde	µg/m3
		Benzene	µg/m3
		Relative Humidity	%
		CMR VOCs	(µg/m3)
		R-Value	(Decimal Ratio)
		Radon	Bq/m3
		Particulate Matter < 2.5 µg	(µg/m3)
		Particulate Matter < 10 µg	(µg/m3)
	4.2. Time outside of thermal comfort range	PMV	(Percentage of time)
		PPD
	4.3. Lighting and visual comfort	Daylight Factor (DF)	(%)
		Spatial Daylight Autonomy (sDA)	(%)
		Daylight Glare Probability (DGP)	-
		Task Illuminance	lux
		Luminance	Candela
		Surface reflectance, shape, and color	% reflectance
		Melanopic irradiance/ equivalent daylight illuminance	-
		Visual hierarchy	-
		Luminance Distribution	-
		Brightness Contrast	-
		Illuminance Uniformity	%
		Intensity	Y/N
		Color Properties (incl. CCT, Saturation, Hue, CRI)	Y/N
		Color rendering	-
		Color consistency	-
		Correlated Color Temperature	K
	4.4. Acoustic and protection against noise	Façade Sound Insulation	decibels (dB)
		Airborne Sound Insulation
		Impact Sound Insulation
		Service Equipment Noise
		Room Acoustics
5. Adaption and resilience to climate change	5.1. Protection of occupier health and thermal comfort	-	(Percentage of time)
	5.2. Increased risk of extreme weather events	-	-
	5.3. Increased risk of flood events	Rainfall data	mm per unit time
		Total plot area	m2
		Total green space created	m2 or % of the total plot area
		Total stormwater retention capacity onsite	m3
		Runoff Rates	l/s
		Retention Capacity	m3
Discharge Rates	l/s	Discharge Rates	l/s
6. Optimized life cycle cost and value	6.1. Life Cycle Cost	Initial costs	(€/m2/yr)
		Annual costs
		Periodic costs
		Global costs by life cycle stage
	6.2. Value creation and risk exposure	Increased revenues from more stable investments	€
		Reduced operational overheads
		Reduced exposure to future risk

VfOCs classified as Carcinogenic, Mutagenic, or toxic for Reproduction according to Regulation (EC) No 1272/2008; Yes/No represents a binary or Boolean type of response.

in Appendix A. It can be observed that some indicators, such as Design for adaptability and renovation, Design for deconstruction, reuse, and recycling, and the Increased risk of extreme weather events, lack a specified unit of measurement or defined metrics. In contrast, other indicators, such as Bill of quantities, Material lifespans, Indoor air quality, and Acoustic protection against noise, have numerous metrics with clearly defined units. This mix of limited and abundant metrics, as outlined by LEVEL(S), suggests a need to explore additional protocols.

Metrics used for evaluating sustainability indicators can generally be classified into two primary categories: Quantitative and qualitative. In certain instances, qualitative metrics function primarily as control mechanisms and are not associated with defined thresholds.

The indicator Use Stage Energy Performance (refer to Table A1, Appendix A) is assessed using a quantitative metric that encompasses parameters, such as heating, cooling, ventilation, and other energy-related aspects. Similarly, Life Cycle Global Warming Potential is amenable to quantitative evaluation due to the availability of standardized, measurable data. Indicators, such as Bill of Quantities, Material Use, and Component Lifespan, are also well-defined through quantitative metrics and standardized units. Construction and Demolition Waste can be measured by the volume or weight of waste produced and is, therefore, evaluated through quantifiable means.

In contrast, Design for Adoptability and Renovation lacks defined units and is non-dimensional; consequently, it is most appropriately categorized as a qualitative indicator.

Use Stage Water Consumption represents a clearly quantifiable indicator, as does Indoor Air Quality, which can be assessed through various measurable parameters, including ventilation airflow rate and pollutant concentrations.

Time Outside of Thermal Comfort Range is evaluated using established quantitative metrics, specifically Predicted Mean Vote (PMV) and Predicted Percentage of Dissatisfied (PPD), both of which are discussed in detail in subsequent sections.

Indicators, such as Lighting and Visual Comfort and Acoustic Performance and Noise Protection can also be assessed using multiple defined metrics, as outlined in Table A1 of Appendix A.

The indicator Protection of Occupant Health and Thermal Comfort is typically quantified based on the percentage of time conditions remaining within defined comfort thresholds, reinforcing its classification as a quantitative metric.

Conversely, the indicator Increased Risk of Extreme Weather Events currently lacks standardized metrics or units, rendering it unclassifiable within a strictly quantitative or qualitative framework. However, for specific sub-categories, such as Risk of Flooding, measurable parameters exist, allowing for a quantitative assessment.

Finally, indicators related to Life Cycle Cost, Value Creation, and Risk Exposure, all grounded in economic evaluation, are inherently quantitative, as they rely on measurable financial data.

Section 4.1, Section 4.2, Section 4.3, Section 4.4, Section 4.5 and Section 4.6 discuss an assessment of LEVEL(S) Key Performance Indicators (KPIs) and their defined units of assessment, as well as the eventual thresholds proposed by LEVEL(S) and those identified in the literature. Additionally, an evaluation is conducted to determine the appropriate threshold and assess comprehensive metrics.

4.1. First Macro-Objective: Greenhouse Gas and Air Pollutant Emissions Along a Building’s Life Cycle

The first indicator, use stage energy performance, is expressed in kilowatt-hours per square meter per year (kWh/m²/year). Benchmark values for this indicator vary according to multiple factors, including climate zone, building type (e.g., residential or office), and the degree of on-site renewable energy generation. This indicator aims to encourage the integration of renewable energy sources and reduce energy consumption. LEVEL(S) suggested the thresholds for total annual primary energy use per square meter for both residential and office buildings in different climatic zones, as described in the previous study of the present authors [21]. For residential buildings, single-family houses are considered. These benchmarks act as reference points for minimum energy performance, promoting substantial reduction in non-renewable energy consumption while encouraging greater reliance on on-site or nearby renewable energy generation, in alignement with the EU’s overarching sustainability and energy efficiency objectives [18].

Nonetheless, during the drafting of the most recent recast of the Energy Performance of Buildings Directive (EPBD) [42], slightly different values were initially proposed but were ultimately excluded from the final text, with their precise definition left to the discretion of individual member states [43]. Nevertheless, the values identified can still be considered representative of current strategies, as reported in

Table 2. The thresholds from the last EPBD recast (primary energy) [42].

EU Climatic Zone	Office Buildings	Residential Buildings
Mediterranean	<70 kWh/m2y	<60 kWh/m2y
Oceanic	<85 kWh/m2y	<60 kWh/m2y
Continental	<85 kWh/m2y	<65 kWh/m2y
Nordic	<90 kWh/m2y	<75 kWh/m2y

.

Additionally, for the primary energy demand, a well-accepted best practice involves thresholds related to a Nearly Zero Energy Building (NZEB), which are defined in the NEB document in alignment with national, regional, and local conditions for both new buildings and renovations [20]. In

Table 3. The thresholds for NZEB according to different building types and climate zones [20,46].

Climate Zone	Building Type	NZEBs Benchmark		NZEB Targets (kWh/m2y)
		Net Primary Use (kWh/m2y)	Total Primary Use (kWh/m2y)
Mediterranean (e.g., Catania, Athens, Larnaca, Luga, Seville, Palermo)	Residential	40–55	85–100	35–100
	Non-residential	20–30	80–90	60–175
Oceanic (e.g., Paris, Amsterdam, Berlin, Brussels, Copenhagen)	Residential	15–30	50–65	15–70
	Non-residential	40–55	85–100	40–150
Continental (e.g., Budapest, Bratislava, Ljubljana, Milan, Vienna)	Residential	20–40	50–70	20–125
	Non-residential	40–55	85–100	25–125
Nordic (e.g., Stockholm, Helsinki, Riga, Gdansk, Tovarene)	Residential	40–65	65–90	65–95
	Non-residential	55–70	85–100	95–110

, member states have provided numerical indicators of primary energy use. Additionally, according to the last EPBD recast, member states are required to establish maximum national thresholds for the energy demand of zero-emission buildings or, at a minimum, achieve a 10% reduction from the NZEB standard [20]. In these tables, EPBD recast values and NZEB standards are prioritized because they establish EU-level baseline thresholds that steer the transition toward a highly energy efficient built environment; nevertheless, individual Member States may impose more stringent national or regional requirements [44,45].

Primary energy use varies by climate and building function, with Mediterranean regions consuming more due to cooling needs, while Nordic regions require more heating but less overall energy. Beyond climate, building shape, specifically the surface-to-volume (S/V) ratio, also affects thermal performance. A low S/V ratio is beneficial in both cold and hot climates, as it reduces heat loss and solar gain, while higher S/V ratios may support natural ventilation in tropical regions [47,48,49,50,51]. Among the three thresholds, LEVEL(s) and Table 2 and Table 3, the one from the latest EPBD recast (Table 2) shows a decrease in the ultimate threshold for primary energy use across different EU climate zones, indicating a trend towards stricter thresholds over time.

The second indicator, life cycle global warming potential, is assessed using the unit of kg CO₂ e/m²/year. Furthermore, applicable standards, such as EN 15978 [52], define performance criteria for various stages of a building’s life cycle, including the product stage, construction process, use stage, and demolition. Based on the LEVEL(S) study to establish specific performance criteria, it is necessary to consult the sections that outline detailed rules and benchmarks for assessing the Life Cycle Global Warming potential. LEVEL(S) does not define any thresholds, but it suggests conducting the LCA analysis over 50 years [27]. When evaluating this indicator, it is essential to consider the life cycle stages of a building, which encompass production, maintenance, cleaning, and replacement phases. The product and construction stage encompasses modules A1 through A5, while the use stage includes modules B1 through B5, and the end-of-life stage involves modules C1 through C4. In new construction projects, the assessment of embodied GHG emissions is conducted based on modules A1–A5, B1, B4, B5, and C1–C4. Modules B2 and B3 are excluded, as they pertain to maintenance and repair activities, which typically have a minimal carbon impact compared to other stages. For renovation projects, it is crucial to include all modules in the assessment. Consequently, in such projects, GHG emissions attributed to the materials used during the construction process are assigned to the use stage (B). Additionally, module D, which addresses the benefits derived from the reuse, recycling, or recovery of materials, remains optional in renovation scenarios.

Evaluating the embodied GHG emissions of a building involves a complex process that necessitates comprehensive data encompassing the construction products and their environmental impacts throughout the building’s lifecycle [20]. For instance, the NEB study highlights that the gross area, which encompasses the total floor area within the building envelope and external walls, is critical in calculating carbon emissions. However, the analysis often suffers from a lack of clarity regarding the scope and the building components considered. It remains ambiguous whether all construction phases and materials involved in the projects are fully accounted for. Moreover, the frequency with which various elements are replaced can significantly impact the results, yet this crucial information remains undocumented or inadequate. To accurately compute the overall Global Warming Potential (GWP) in large-scale projects, the methodology applied to the external wall system should be extended to all building elements and components. Core technical installations, including heating, cooling, electricity generation, and distribution systems, play a significant role in the preparation of the bill of quantities and profoundly influence the total GWP. Consequently, the cumulative GWP is derived by aggregating data from the building’s shell, core, and external works, presenting a substantial challenge in calculating the total GWP for the entire project. Furthermore, although results are commonly normalized based on the building area, the specific type of area considered (net or gross floor area, total building area, or conditioned space) is often not disclosed. The scope of the analysis and the components evaluated remain poorly defined; for instance, it is not always clear whether the assessment includes cradle-to-gate or cradle-to-grave phases. Additionally, the estimated lifespan of buildings varies significantly, ranging from 25 to 120 years, with buildings in different European locations yielding divergent mean values of embodied GHG emissions per unit of floor area. These elements collectively highlight the complexity of accurately estimating carbon emissions in building projects [20].

According to the NEB document, the production stage of a building accounts for a significant contribution to embodied GHG emissions, with an average of 300 kg CO₂ e/m². This stage, encompassing A1–A3 production, typically results in emissions ranging from 70 to 520 kg CO₂ e/m². The subsequent phase, B1–B4, which includes maintenance, cleaning, and replacement activities, also has a notable impact, with an average contribution of approximately 120 kg CO₂ e/m² over 50 years [20].

Studies on embodied carbon benchmarks in buildings suggest a reasonable classification for the magnitude and scope of estimates related to buildings’ embodied carbon footprints [53]. The literature often reports a wide range of values, highlighting variability that should be acknowledged and accounted for. Firstly, the primary embodied carbon (LCA stage A) for a building’s structure, foundation, and enclosure is typically less than 1000 kg CO₂ e/m²/year for various building types. This threshold can also be applied to new constructions [53]. Secondly, for low-rise residential buildings (less than 7 floors), it is reported that this figure is usually below 500 kg CO₂ e/m²/year, although the data are insufficient to state specific ranges confidently. Finally, for office buildings, the range of primary embodied carbon for the building structure, foundation, and enclosure falls between 200 and 500 kg CO₂ e/m²/year for 50% of the buildings [53].

Following this, for retrofit projects in various types of buildings, as well as in different regions and climate zones, carbon emissions typically range between 20–140 kg CO₂ e/m²/year. All the collected information could serve as the basis for a threshold system designed to evaluate embodied carbon emissions.

Table 4. Common indicators for the first macro-objective in the LEVEL(S) framework and leading international protocols. The absence of related indicators is indicated by a red (🗶).

Topic Treated by LEVEL(S)	CASBEE [54]	GREEN STAR [55]	BREEAM [56]	LEED [57]	ITACA [23]
Use stage energy performance	LR1.2 Natural Energy Utilization	🗶	ENE01 Reduction in energy use and carbon emission	Annual Energy use	Useful energy and non-renewable primary energy requirements during the life cycle Energy from renewable sources
	LR1.3 Efficiency in Building Service System		ENE 02b Energy monitoring
	LR1.4 Efficient Operation
	LR2.2 Reducing Usage of Non-renewable Resources
Life Cycle Global Warming Potential	LR3.1 Consideration of Global Warming	Construction Environmental Management	ENE 04 Low carbon design	Low Emitting Products	CO2 Equivalent emissions
	LR3.2 Consideration of Local Environment	Greenhouse Gas Emissions	MAT 01 Life cycle impacts
	LR3.3 Consideration of Surrounding Environment	Life Cycle Impacts

outlines the common indicators shared between the LEVEL(S) framework and prominent international protocols, along with their respective thresholds, that were applicable.

The CASBEE document is closely aligned with several indicators in the LEVEL(S) framework. Each indicator is associated with specific thresholds, defined by target levels designed to enhance energy efficiency. For instance, LR1.2, a subcategory under Load, emphasizes leveraging natural resources, such as wind and solar energy, to reduce energy consumption [54]. Emission performance is classified into five levels based on comparison with a reference value. Level 1 indicates poor performance, with emissions exceeding 125% of the reference value. Levels 2 to 4 represent progressively better outcomes, rating from slightly above to moderately below the reference value. Level 5 signifies superior carbon management, with emissions at or below 75% of the reference benchmark [54].

The GREEN STAR framework, developed by the Green Building Council of Australia (GBCA), establishes carbon emission benchmarks for new buildings that are comparable to those of the CASBEE protocol, but with a more focused scope. As in CASBEE, lower emissions correspond to higher sustainability ratings. For instance, buildings emitting 73 kg CO₂ e/m² annually receive a 4 Star rating, while those achieving 58 and 44 kg CO₂ e/m² qualify for 5- and 6 Star ratings, respectively. In addition to emissions, the framework evaluates key environmental performance indicators, including construction environmental management and life cycle impacts. Regarding energy efficiency, Green Star also establishes benchmarks for annual electricity use: standard practice is set at 98 kWh/m², with thresholds of 64, 49, and 24 kWh/m² corresponding to 4, 5, and 6 Star rating, respectively [55].

In contrast, BREEAM establishes specific energy consumption thresholds for operational performance. For example, buildings with energy consumption levels exceeding 8500 kWh/year for electricity and 67,000 kWh/year for other fuels are classified as significant consumers within the operational context. The BREEAM framework provides a detailed analysis of carbon emissions (kg CO₂ e/m²/year) and their associated credit allocations, but it does not define the threshold values [56].

ASHRAE Standard 90.1-2022 provides comprehensive guidance on energy consumption, including clearly defined thresholds for annual energy use across various building systems [53]. However, there is no mention of carbon emissions.

LEED, much like the BREEAM framework, also does not specify any thresholds either for carbon emissions (kg CO₂ e/m²/year) or energy use [23].

Lastly, the ITACA Protocol categorizes residential buildings based on primary energy demand for heating and domestic hot water (DHW), assigning ratings from A to G. This classification is detailed in the document, which is primarily available in Italian [55]. ITACA also does not specify any thresholds for carbon emission [23].

4.2. Second Macro-Objective: Resource-Efficient and Circular Material Life Cycles

In the LEVEL(S) framework, the first indicator under the second macro-objective covers the bill of quantities, materials, and lifespans, with specific units prescribed for each metric. This indicator highlights the crucial importance of precise material quantification in construction and the necessity of considering material lifespans to minimize waste and optimize resource efficiency. It is essential at this stage to link the Bill of Quantities (BoQs) and Environmental Product Declaration (EPD) or Life Cycle Inventories (LCIs). This linkage facilitates the calculation of carbon footprints and the evaluation of additional environmental impacts. Although the framework does not set explicit sustainability targets or performance criteria for material efficiency, carbon footprint reduction, or other environmental impacts, adherence to established guidelines and standards remains crucial [37]. Moreover, comparisons between the LEVEL(S) document and other scientific publications reveal that no defined thresholds exist for the bill of quantities, materials, and lifespans. Therefore, the absence of a defined domain precludes addressing the identified gap in threshold scarcity.

In the realm of construction and demolition waste (CDW) and materials, the LEVEL(S) framework mandates a target of 70% (by weight) for 2020, according to the reuse, recycling, and recovery of non-hazardous CDW [20,38]. Recovery rates for construction and demolition waste (CDW) vary significantly across EU Member States. To address this, it is essential to establish a baseline metric score, especially since the recovery rate exceeded 70% in several EU countries between 2018 and 2020. Nonetheless, there is a discernible upward trend among EU countries in approaching the stated threshold [58]. This standardized approach will help align national practices more effectively [20]. The baseline metric score is derived from Formula One, which includes two key variables. The first, the Generated CDW (CDW_G) sub-metric evaluation, is determined using the bill of materials and the quantities involved in a building-scale project. This process involves converting the inventory of materials, measured in kg or m³, into mass by using the density of the materials (kg/m³) to calculate the CDWG.

The second variable, the Recovered CDW (CDW_R) sub-metric, follows a similar approach but focuses specifically on materials such as concrete, XPS (Extruded Polystyrene, is a type of rigid foam insulation), and timber. The total recovered mass of CDW at the end of the building’s lifecycle is calculated by summing the individual masses of recovered concrete, recycled XPS insulation, and reused timber. Finally, the scoring metric, expressed as the ratio of CDW_R to CDW_G, is evaluated against a standard baseline metric of 70% [20].

$$\mathit{Baseline}\mathrm{ }\mathit{metric}\mathrm{ }\mathit{score}={\displaystyle \frac{\left[\left(\frac{{\mathrm{CDW}}_{\mathrm{R}}}{{\mathrm{CDW}}_{\mathrm{G}}}·100\right)\mathrm{ }-\mathrm{ }{\mathrm{T}}_{\mathrm{baseline}}\right]}{{\mathrm{T}}_{\mathrm{baseline}}}}·100$$

(1)

The LEVEL(S) user manual outlines the significance of various waste streams, namely Construction Waste (CW), Demolition Waste (DW), and Excavation Waste (EW), in detail (

Table 5. The thresholds for (CDW) are determined based on the influence of project type and location [38].

	Construction Waste (CW)	Demolition Waste (DW)	Excavation Waste (EW)
New construction in rural area	Normal levels (e.g., 48–135 kg/m2)	Low or zero. Nothing to demolish.	Can be high due to need to clear and level site, connect utilities and put foundations in place.
New construction in suburban area
New construction in urban area			Same as above, plus a high risk of contaminated soil.
Demolition and new construction in any area		Very high (e.g., 664–1637 kg/m2). Pre demolition audit highly recommended in all cases.	Can vary significantly depending on the differences between the old and the new building and factors such as basements and underground parking.
Renovation in any area	Low to normal levels (e.g., 20–326 kg/m2) but, depending on nature of renovation, this can be high.		Low or zero. Nothing to excavate normally.

). This classification takes into account the impact of both types of project and their locations, including rural, suburban, urban, and other specified areas [38].

Concurrently, the LEED certification system incorporates the standards and guidelines established by ASHRAE [57]. The document articulates specific thresholds for various indicators [59]. For instance, it specifies that the total volume of construction waste generated before the issuance of the final certificate of occupancy must not exceed 42 yd³ or 12,000 lbs per 10,000 ft² (approximately 53 m³ or 600 kg per 1000 m²) of new building floor area [60]. However, the information gathered clearly indicates that the thresholds for CDW outlined in the LEVEL(S) manual, coupled with the baseline metric score detailed in the NEB document, which is evaluated against a standard baseline metric of 70%, could establish a more robust threshold for CDW.

For the third indicator, which focuses on design for adaptability and renovation, no specific primary threshold is established. Nonetheless, this indicator promotes construction practices that are adaptable to future requirements and aims to minimize demolition and reduce waste by assessing corresponding scores [28]. The adaptability score, used as the primary metric within this indicator, is derived from key design parameters, including internal space distribution, building servicing, and façade structure. To compute this score, the individual scores of each design aspect are multiplied by their respective weighting factors, and the results are then aggregated to yield a total score out of 100 (the maximum achievable score). This scoring system is designed to promote construction practices that are adaptable to future requirements, minimize the need for demolition, and reduce waste [28].

Within the LEED certification system, distinct standards are established for the minimum design service life of buildings: temporary structures are capped at 10 years, medium-duration facilities, such as industrial buildings, at 25 years, and long-term constructions are expected to last at least 50 years [60]. Therefore, these benchmarks could serve as reference thresholds for this indicator.

For the fourth indicator, which addresses design for deconstruction, reuse, and recycling, no primary threshold has been specified. Nevertheless, circularity scores, ranging from 0 to 100 percent, guide identifying the most sustainable end-of-life practices for building components. These scores effectively establish a de facto threshold that encourages striving toward a higher circularity coefficient [25]. The LEVEL(S) document similarly outlines that circularity score values for elements, such as deconstruction, reuse, and recycling, range from 0 to 100 percent. In contrast, ASHRAE defines the minimum design service life of buildings in years. Taking into account the LEVEL(S) thresholds and integrating insights from various benchmarking approaches enhances our comprehensive understanding of sustainable building practices. However, for subsequent evaluations, the maximum circularity scores will be accepted at 100, as determined by the LEVEL(S) standard reference. Additionally, the circularity score could be defined as a metric for evaluating this indicator.

Table 6. Common indicators for the second macro-objective in the LEVEL(S) framework and leading international protocols. The absence of related indicators is indicated by a red (🗶).

Topic Treated by LEVEL(S)	CASBEE [54]	GREEN STAR [55]	BREEAM [56]	LEED [57]	ITACA [23]
Bill of quantities, materials, and lifespans	LR2.3 Avoiding the use of Materials with Pollutant Contents	Building Information	MAT 06 Material efficiency	🗶	Eco-friendly materials
		Responsible Building Materials
		Metering and Monitoring
Construction and demolition waste and materials	🗶	Construction and demolition waste	WST01 Construction waste management	Construction waste management	🗶
			WST03 Operational waste
Design for adaptability and renovation	Q2.3 Flexibility and Adaptability	Commitment to performance	MAT 05 Designing for durability and resilience	Durability Management Verification	🗶
	Q2.2 Durability and Reliability
Design for deconstruction, reuse and recycling	🗶	🗶	🗶	🗶	🗶

highlights the common indicators shared between the LEVEL(S) framework and leading international protocols, with explanations provided wherever thresholds are defined.

In the CASBEE framework, the deterioration resistance grade focuses on extending the period before major renovations are required under standard natural conditions and maintenance practices. Specifically, measures are implemented to prolong the interval until large-scale renovations become necessary over three generations (approximately 75–90 years). Additionally, under similar conditions, strategies are employed to extend the renovation cycle to two generations (approximately 50–60 years). The framework also defines specific thresholds for physical, functional, and social durability [54]. Durability is categorized into five levels based on the expected lifespan of materials or components. Level 1 represents the lowest durability, with an expected lifespan of 3 to 6 years. Level 2 ranges from 6 to 12 years, while Level 3 covers a moderate lifespan of 12 to 25 years. Level 4 reflects high durability, with components expected to last 25 to 50 years. Level 5 denotes the highest level of durability, with an expected lifespan of 50 to 100 years [54].

Unlike the CASBEE framework, the GREEN STAR document defines thresholds for construction and demolition (C&D) waste to support sustainable waste management. The criteria allocate three points for achieving 1.6–2.5 kg/m² of fitout area (defined as the internal floor area within a building that is subject to interior construction or refurbishment works), two points for 2.6–3.5 kg/m², and one point for 3.6–4.5 kg/m² [61].

LEED establishes defined thresholds for construction and demolition (C&D) waste to support sustainable building practices, much like the GREEN STAR framework. However, LEED permits a higher level of C&D waste compared to GREEN STAR. These differences are likely attributed to GREEN STAR’s stricter emphasis on total waste minimization, reflecting variations in assessment methodology and regional construction practices [62,63,64].

The LEED guidelines establish clear thresholds for construction and demolition waste, promoting sustainable building practices. Projects can earn credits based on the amount of waste generation. Generating less than 75 kg/m² awards one point, while reducing waste to below 50 kg/m² qualifies for two points. These criteria encourage efficient resource management and minimal environmental impact during the construction process [57].

The remaining protocols did not specify any threshold values for the indicated indicators.

4.3. Third Macro-Objective: Efficient Use of Water Resources

This macro-objective consists of a single indicator, which aims to measure water consumption per occupant per year, allowing for comparison between buildings of different sizes and occupancy rates. LEVEL(S) offers a streamlined instrument for assessing this indicator, complemented by a comprehensive benchmark table for residential buildings [21], which is accessible on the European Water Label website (http://www.europeanwaterlabel.eu, accessed 7 August 2025).

This resource outlines performance metrics for various fixtures, including taps, showers, bathtubs, urinals, and toilets, facilitating a deeper understanding and evaluation of water use efficiency. Nevertheless, the LEVEL(S) documentation indicates that benchmarks may differ among various countries, subject to distinct geographical and methodological conditions. This variability underscores the importance of contextual adoption in evaluating water use benchmarks [36].

Based on the relevant information, all necessary data about metrics and thresholds have been clearly identified, leaving no gap to be addressed. However, considering the diversity of climates and geographical conditions, more comprehensive regional data could be beneficial for further study.

The LEVEL(S) framework shares common indicators with other prominent protocols concerning the efficient use of water resources, macro-objectives, and their associated indicators, as illustrated in

Table 7. Common indicators for the third macro-objective in the LEVEL(S) framework and leading international protocols.

Topic Treated by LEVEL(S)	CASBEE [54]	GREEN STAR [55]	BREEAM [56]	LEED [57]	ITACA [23]
Use Stage Water Consumption	LR2.1 Water Resources	Potable Water	HEA09 Water quality	Rainwater management	Potable water
		Storm Water	WAT01 Water consumption	Total water use
			WAT02 Water monitoring	Efficient hot water distribution
			WAT03 Water leak detection and prevention
			WAT04 Water efficient equipment
			POL 03 Surface water run off

.

The CASBEE protocol specifies a minimum rainwater tank capacity of 80 L and establishes toilet water usage between 4 and 8 L, depending on the flushing or tank volume specifications [54]. However, the GREEN STAR document outlines water usage reduction benchmarks, ranging from 0 to 95% with points allocated in 10% increments [65]. Unlike the other two, BREEAM allocates water efficiency credits based on toilet flush volumes and shower flow rates, with stricter limits earning higher credits. Toilets using up to 6 L per flush can earn up to three credits, while those using 4.5 L can earn up to two credits. Showers must maintain a flow rate of 6 L per minute or less to quality as low water use [56].

LEED provides a more detailed assessment and establishes baseline water consumption for fixtures and fittings as shown in

Table 8. Water consumption for fixtures and fittings based on the LEED protocol [57].

Fixtures and Fittings	Water Consumption
Toilets	6 L per flush (lpf)
Urinals	3.8 (lpf)
Public lavatory faucets	1.9 L per min (lpm) at 415 kPa
Private lavatory faucets	8.3 L per min (lpm) at 415 kPa
Kitchen faucets	8.3 L per min (lpm) at 415 kPa
Showerheads	8.3 L per min (lpm) at 550 kPa per shower stall

.

Adopting a holistic approach, ITACA sets a standard daily potable water consumption of 120 L per inhabitant for residential buildings and sets an annual irrigation water requirement of 0.3 m³ per square meter of green area [23]. This highlights how various protocols employ distinct approaches to water management, shaped by specific regional conditions and priorities.

4.4. Fourth Macro-Objective: Healthy and Comfortable Spaces

In light of the comprehensive review conducted on the literature and the data collected for the previous study of the present authors [21], further information collection is deemed unnecessary. The initial two indicators, Indoor Air Quality and Time outside of the Thermal Comfort Range, have been exhaustively detailed, encompassing associated metrics and established thresholds. The corresponding data are systematically presented in a previous study by the present authors [21]. The data detail the three principal parameters for Air Quality metrics: ventilation rate, expressed in liters per second per square meter (l/s/m²); Total Volatile Organic Compounds (VOCs), quantified in micrograms per cubic meter (µg/m³); and the concentration of pollutants from external sources, measured by benzene levels, also in micrograms per cubic meter (µg/m³) [29]. Additionally, the second indicator is elucidated using Predicted Mean Vote (PMV) and Predicted Percentage Dissatisfied (PPD), as outlined in

Table 9. Informative thresholds between indoor thermal environment categories, the Predicted Percentage Dissatisfied (PPD), and acceptable (adaptive) indoor summer temperatures [66].

EN 15251 Category	Fanger Method		Adaptive Method
	PPD (%)	PMV	Operative Temperature Variance (°C)
I	≤6	−0.2 ≤ PMV ≤ +0.2	±2
II	≤10	−0.5 ≤ PMV ≤ +0.5	±3
III	≤15	−0.7 ≤ PMV ≤ +0.7	±4
IV	>15	PMV < −0.7 and PMV > 0.7

[26]. The threshold should relate to the percentage of time outside the comfort range. The LEVEL(S) framework defines a thermal comfort range between 18 and 27 °C, which may be interpreted as a performance threshold. However, it does not explicitly specify the percentage of time that indoor conditions are required to remain within this range.

For the third indicator, lighting and visual comfort, it is clear from Table A1 in Appendix A that there are various assessment parameters for calculating light. Each of these parameters measures different aspects of light and daylight, but they are all related to the overall assessment of lighting conditions. Based on a literature review from established protocols, including LEED and the EN 12464-1 standard [67], this analysis will focus on key daylight metrics such as Spatial Daylight Autonomy (sDA) and Useful Daylight Illuminance (UDI). These metrics will be thoroughly examined to enhance our understanding of various daylight parameters. Additionally, the LEVEL(S) document suggests using Spatial Daylight Autonomy (sDA) as the metric for daylight assessment. This dynamic metric is based on Typical Meteorological Year (TMY) data and is utilized in simulation programs to derive outcomes. The sDA measures the percentage of floor area that meets a specified daylight illuminance level for a specified fraction of operating h per year [68]. While the LEVEL(S) documents do not define a specific threshold [33], a threshold of 300 lux could be applied based on LEED certification standards [68]. The levels and quality of daylight play a crucial role in many aspects of human biology and psychology, as daylight resets our biological clocks daily [69,70,71,72]. Offering personal control over light conditions, advanced lighting controls represent a highly cost-effective strategy for reducing the energy consumption, carbon footprint, and operating costs of existing buildings, while simultaneously enhancing occupant satisfaction [73]. The minimum requirements can be retrieved from EN 12464-1, which specifies the thresholds for light and lighting in workplaces. Meanwhile, EN 17037 [74] offers detailed data and guidance on lighting levels, distribution, and daylighting. These standards aim to establish thresholds for achieving optimal visual comfort [33]. Further, the Useful Daylight Illuminance (UDI) range is between 100 and 2000 lux. This means that illuminance above 2000 lux may cause visual discomfort, while levels below 100 lux are insufficient for proper vision [73].

The fourth indicator, Acoustic Performance and Protection against Noise, targets the five principal aspects of acoustic and noise protection design, as defined by existing EN and ISO standards [34].

These aspects include façade insulation (D_2m,nT,w), airborne sound insulation (R^′_w), impact sound insulation (L^′_n,w), service noise from equipment (L_Aeq,nT), and room acoustics (A_eq). This indicator provides crucial insights into how sound level measurement and acoustic analysis within indoor environments impact the physical and mental well-being of occupants [75]. By addressing these key elements, the indicator enhances our understanding of environmental acoustics and their significance in designing occupant-friendly spaces.

However, based on the literature study,

Table 10. Sound classes for each parameter [77].

Class	Parameter
	D2m,nT,w [db]	R′w [db]	L′n,w [db]	LASmax [db(A)]	LAeq [db(A)]
I	<43	<56	<53	<25	<30
II	<40	<53	<58	<28	<33
III	<37	<50	<63	<32	<37
IV	<32	<45	<68	<37	<42

L_ASmax represents the Maximum A-Weighted, Slow-Time Weighted sound level; L_Aeq stands for Equivalent Continuous Sound Level, which is a measure used in acoustics to describe the average sound pressure level over a specified period.

, which defines the Sound Classes from I to IV, is used as a threshold system according to the Italian standard UNI 11367 [76]. In

Table 11. Sound classes for each parameter and various building uses [77].

Activities or Building Use	Parameter
	D2m,nT,w [db]	R′w [db]	L′n,w [db]	Lic [db(A)]	Lid [db(A)]
Hospital, clinics, and nursing	<45	<55	<58	<35	<25
Homes, dwellings, hotels, and inns	<40	<50	<63	<35	<35
Schools	<48	<50	<58	<35	<25
Offices, commercial, and recreational activities	<42	<50	<55	<35	<35

Sound pressure level from service equipment divided into those with continuous and discontinuous operation (L_ic, L_id).

, the defined range of acoustic performance parameters is presented, along with threshold classification for different types of buildings [77]. Therefore, this threshold can be used as the defined criterion.

Table 12. Façade sound insulation in dwellings, class limits [78].

Type of Space	Class A D2m,nT,50 [db]	Class B D2m,nT,50 [db]	Class C D2m,nT,50 [db]	Class D D2m,nT,50 [db]	Class E D2m,nT,50 [db]	Class F D2m,nT,50 [db]
In dwellings from outdoors; general suburban environment Lden = 55 db	<35	<31	<27	<23	<19	<15
In dwellings from outdoors; specific environment with sound sources characterized by Lden	<Lden-20	<Lden-24	<Lden-38	<Lden-32	<Lden-36	<Lden-40

L_den is the free field level for the general outdoor traffic sound as defined for the END; the typical background sound levels in this environment will be 40–50 dB in daytime; L_den is the free field level for the relevant outdoor sound sources as defined for the END. For a classification including the environment, the requirement must be increased in the same amount as the noise impact is higher than L_den = 55 db as is indicated in the third row.

provides an overview of the acoustic standards for façade sound insulation, by EU-wide regulations.

The established thresholds for sustainability protocols, highlighting common indicators shared between the respective protocols and the LEVEL(S) framework, are described below.

The CASBEE document outlines ventilation guidelines for different rooms, as shown in

Table 13. Ventilation guidelines for different rooms based on the CASBEE document [54].

Rooms	Ventilation Guidelines
Kitchen with a gas heat source (including exhaust hood)	The higher value between 30 KQ or 300 m3/h, where K represents the theoretical amount of exhaust gas and Q denotes the fuel consumption rate.
Kitchen with an electric heat source	300 m3/h
Bathroom	100 m3/h
Washroom	60 m3/h
Toilet	40 m3/h
Laundry area	60 m3/h

.

Taking a different approach, GREEN STAR establishes indoor air quality thresholds for Volatile Organic Compounds (VOCs) across various materials, including low-VOC paints, carpets, adhesives, and sealants. It also defines emission limits for key pollutants such as benzene, styrene, ozone, and particulate matter, ensuring comprehensive control of indoor air contaminants [79]. Regarding acoustics and noise protection, the internal noise levels should not deviate more than 5 dB from the designated satisfactory sound levels [80]. Daylight assessment is based on two key metrics: Daylight Factor (DF) and Daylight Autonomy (DA). DF requires at least 50% of the designated area to achieve a 2.0% factor under specified sky conditions, while DA mandates a minimum illuminance of 160 lux for 80% of occupied hours annually across 50% of the area [81].

The BREEAM protocol provides a more detailed acoustic assessment compared to GREEN STAR, defining performance standards for indoor ambient noise levels across designated spaces as shown in

Table 14. Performance standards for indoor ambient noise levels in the BREEAM protocol.

Function of Space	Indoor Ambient Noise Level (dB LAeqT)
General spaces (staffrooms, restrooms)	≤40
Single occupancy offices	≤0
Multiple occupancy offices	40–50
Meeting rooms	35–40
Reception areas	40–50
Spaces designed for speech, e.g., teaching, seminar, or lecture rooms	≤35
Concert hall, theatre, or auditoria	≤30
Informal café or canteen areas	≤50
Catering kitchens	≤50
Restaurant areas	40–55
Bars	40–45
Retail areas	50–55
Manual workshops	≤55
Sound recording studios	≤0
Laboratories	≤40
Sports halls and swimming pools	≤55
Library areas	40–50
Hotel bedrooms	<35

Measurement must be carried out when the space is unoccupied. Where ranges of noise levels are specified and privacy is not deemed by the final occupier to be an issue, it is acceptable to disregard the lower limit of the range and consider the noise level criteria to be lower than or equal to the upper limit of the range.

, establishing specific thresholds to maintain acoustic quality. L_AeqT or service noise from equipment pertains to the same acoustic and noise protection design considerations, which are guided by the relevant EN and ISO standards referenced in the LEVEL(S) user manual.

However, in terms of daylight, the BREEAM document primarily provides guidelines for controlling obtrusive light from exterior lighting installations and illuminated signage [56].

Daylight measurement in the LEED framework is assessed using Spatial Daylight Autonomy (sDA) and Annual Sunlight Exposure (ASE). The evaluation considers the average Spatial Daylight Autonomy (sDA) 300/50% value across regularly occupied areas, along with a minimum illuminance level of 300 lux for spaces equipped with view-preserving automatic glare-control devices [57].

Finally, considering the ITACA protocol, it establishes two airflow rate categories for mechanically ventilated environments based on the UNI EN 15251 standard [82]: 0.6 L/s.m² and 1.0 L/s.m² of floor area. In terms of daylight, the ITACA protocol evaluates natural light quality in primary occupied areas using the average daylight factor (FLDm), which is categorized into three performance levels: Insufficient (<2.0%), Good (<2.0%), and Excellent (<2.6%). Acoustic comfort is assessed according to the Italian standards UNI 11367 [76] and UNI 11532 [83], which define performance requirements for key acoustic parameters [23].

Table 15. Common indicators for the fourth macro-objective in the LEVEL(S) framework and leading international protocols. The absence of related indicators is indicated by a red (🗶).

Topic Treated by LEVEL(S)	CASBEE [54]	GREEN STAR [55]	BREEAM [56]	LEED [57]	ITACA [23]
Indoor air quality	Q1.4 Air Quality	Indoor Air Quality	HEA02 Indoor air quality	Enhanced Ventilation	Ventilation
Time outside of thermal comfort range	Q1.2 Thermal Comfort	🗶	🗶	Thermal comfort	🗶
Lighting and visual comfort	Q1.3 Lighting and Illumination	Lighting Comfort	HEA01 Visual comfort	Daylight and views	Visual Wellbeing
		Visual Comfort	ENE 03 External lighting
		Light Pollution
Acoustic and protection against noise	Q1.1 Noise and Acoustics	Acoustic Comfort	HEA05 Acoustic Performance	🗶	Acoustic Wellbeing
			POL 05 Reduction in noise pollution

shows the common indicators for the fourth macro-objective shared between the leading protocols and the LEVEL(S) framework.

4.5. Fifth Macro-Objective: Methods and Tools to Measure Adoption and Resilience to Climate Change

The first indicator, Protection of occupier health and thermal comfort, measures the percentage of time temperatures that exceed defined limits during the cooling seasons. The assessment considers a temperature range of 18 to 27 °C as the reference. According to the LEVEL(S) framework, building performance should be evaluated in scenarios both with and without mechanical cooling. Furthermore, the specific space or zone being assessed must constitute more than 10% of the building’s total useful area [30]. Additionally, the study highlights that, while both indicator 4.2, Time Outside of Thermal Comfort Range, and indicator 5.1, Protection of Occupier Health and Thermal Comfort, share a similar unit of assessment, they differ significantly in their focus and scope. Indicator 4.2 provides a year-round assessment covering both heating and cooling seasons, focusing on the building’s ability to maintain comfort across varying seasonal conditions.

In contrast, Indicator 5.1 narrows its focus to the cooling season alone, specifically addressing overheating risks as part of climate resilience planning. In essence, Indicator 4.2 evaluates comfort throughout the year, whereas Indicator 5.1 anticipates future temperature increases and prioritizes the building’s performance in mitigating overheating during warmer periods. Evidently, the LEVEL(S) framework defines reference temperatures for the Protection of Occupier Health and thermal comfort; however, other literature studies do not provide defined thresholds. Therefore, the reference temperatures could be used to assess the corresponding indicator. Based on the information gathered and the similarities identified between these two specific indicators, the metrics used for Indicator 4.2, Time Outside of Thermal Comfort Range, including the Predicted Mean Vote (PMV) and Predicted Percentage Dissatisfied (PPD), can also be effectively applied to Indicator 5.1, Protection of Occupier Health and Thermal Comfort, thereby addressing the gap related to metric deficiency.

LEVEL(S) does not define a specific threshold for the indicator Increased risk of extreme weather events. Instead, it provides guidance on mitigating the impacts of such an event [31]. This approach emphasizes the resilience of building structures and envelopes, focusing on their ability to withstand extreme weather conditions. The LEVEL(S) framework initially evaluates resilience through a qualitative assessment, guiding the early stages of analysis. In cases where practical measures to mitigate the occurrence of extreme weather events are unavailable, this indicator facilitates the design of buildings that minimize or prevent damage to the structure and safeguard occupants during such events. A more detailed, quantitative assessment is available in other stages of the framework, which incorporates Eurocode-based structural design standards to enhance resilience against challenges such as pluvial and fluvial flooding, windstorms, coastal flooding, droughts, heatwaves, hail, and snow [31]. For this indicator, it is not possible to define related metrics or thresholds.

For the final indicator of adoption and resilience to climate change, specific units exist for an increased risk of flood events, applicable only at the conceptual design stage, level 1. These units include inputs such as rainfall data (in mm per unit time), total plot area (m²), total green space created (m² or % of the total plot area), and total stormwater retention capacity onsite (m³). At the higher levels of the framework, a performance-based assessment approach is adopted, emphasizing the the modeling and simulation of the drainage system. The assessment units comprise Runoff Rates (Liters per second, l/s) for design storms, Retention Capacity (Cubic meters, m³), and Discharge Rates (l/s) at designed outlow points. This is designed to analyze the system’s response to maximum storm events based on specified rainfall data. For this indicator, there is no specific threshold; however, Sustainable Drainage Systems (SuDSs) represent a concept essential for providing guidelines to assess and control flood risk by managing stormwater at its source, thereby mitigating the overall risk of flooding. Therefore, the design team must be familiar with this approach [39].

The CASBEE document includes guidelines for maximum heating load in thermal insulation area zones under Energy-Saving Standards, expressed in W/m² [54]. However, GREEN STAR evaluates thermal comfort using two primary methodologies: the Predicted Mean Vote (PMV) method and the ASHRAE 55 Adaptive Comfort Model. It should maintain PMV levels between 61.0 or 60.5 for at least 98% of occupied hours annually [84]. Similarly, BREEAM and LEED also incorporate PPD and PMV metrics to assess thermal comfort, although each does so within its own distinct evaluation framework [57,84].

BREEAM defines an acceptable PMV range of −0.3 to +0.2 and typically considers PPD values between 3 and 10% as compliant [85]. However, LEED specifies a PMV range of −0.5 to +0.5, which corresponds to a PPD of less than 10% [86].

Table 16. Common indicators for the fifth macro-objective in the LEVEL(S) framework and leading international protocols. The absence of related indicators is indicated by a red (🗶).

Topic Treated by LEVEL(S)	CASBEE [54]	GREEN STAR [55]	BREEAM [56]	LEED [57]	ITACA [23]
Protection of occupier health and thermal comfort	LR1.1 Building Thermal Load	Thermal Comfort	HEA04 Thermal comfort	Thermal comfort	🗶
		Heat Island Effects
Increased risk of extreme weather events	🗶	Adoption and Resilience	LEE 01 Site selection	Site selection	Area design
			LEE 02 Ecological value of site and protection of ecological features	Heat island effect
			WST05 Adoption to climate change
Increased risk of flood events	🗶	🗶	LEE 01 Site selection	Site selection	Area design
			LEE 02 Ecological value of site and protection of ecological features	Heat island effect
			WST05 Adoption to climate change

shows the common indicators for the fifth macro-objective shared between the leading protocols and the LEVEL(S) framework. For certain indicators and protocols, as indicated in the table, no threshold values are specified.

4.6. Sixth Macro-Objective: Methods and Tools to Measure Optimized Life Cycle Cost and Value

Life cycle costs in the LEVEL(S) document do not have a specific main threshold; however, the document utilizes a common unit of measurement: usable floor area per year (€/m²/yr), with costs estimated or reported annually over the reference study period of 50 years, then discounted to their net present value. This approach aims to enhance the long-term sustainability and cost-effectiveness of building management from a life-cycle perspective [32]. As previously mentioned, the LEVEL(S) assessment lacks a scaling system. In the literature study, measuring the optimized life cycle cost and value involves assessing the total cost of ownership of a product, system, or infrastructure over its lifespan, while ensuring maximum value is derived from it. This assessment includes initial acquisition costs, operation, maintenance, and eventual disposal or decommissioning costs, all balanced against the value or benefits the product provides. Various methods and tools are utilized for this purpose. Firstly, Life Cycle Cost Analysis (LCCA) is defined as a crucial approach that promotes economic sustainability. It aids in decision-making by selecting the best alternative to enhance environmental and social sustainability. This is achieved by assessing costs across different phases of a building’s construction, such as operation, maintenance, and demolition [87]. Total Cost of Ownership (TCO) is a management accounting-oriented tool used for measuring and selecting suppliers. It considers not only the price but also the cost effects of the alternatives. TCO aims to calculate all costs associated with purchasing, deploying, using, and retiring a product or system [88].

While not quantifiable in standard units, value creation and risk exposure are linked to specific metrics within this indicator. Key metrics include increased revenues from more stable investments, reduced operational overhead, and minimized future risk exposure. These metrics are evaluated against all indicators of the LEVEL(S) framework using a simple ‘yes’ or ‘no’ response, following client consultations. It has been agreed that these considerations should be integrated into the financial valuation process. As indicated by the study, this indicator lacks a defined threshold [35]; however, there are methods available for its assessment. Value engineering represents a systematic approach designed to evaluate the functions of goods and services, aiming to achieve the essential functions required by the user at the minimum overall cost, without compromising the requisite quality or performance. Frequently, in the construction industry, value engineering (VE) is mistakenly equated with mere cost reduction efforts [89]. Then, cost–benefit analysis (CBA) in an environmental context is the process of economically evaluating policies and projects, especially those intended to enhance environmental services or actions that could impact the environment, occasionally in a negative way, as a side effect [90]. Thereafter, Life Cycle Assessment (LCA) serves as a critical tool for companies and organizations looking to identify and mitigate environmental challenges. It provides a comprehensive analysis of the environmental impacts that occur throughout every stage of a product’s lifespan, from its inception to its disposal [91]. However, in conclusion, based on studies and official documents from the LEVEL(S) framework, as well as other related research, there is no defined threshold for assessment in this matter. When discussing this macro-objective, the metrics serve solely as a means of control, independent of thresholds.

Table 17. Common indicators for the sixth macro-objective in the LEVEL(S) framework and leading international protocols. The absence of related indicators is indicated by a red (🗶).

Topic Treated by LEVEL(S)	CASBEE [54]	GREEN STAR [55]	BREEAM [56]	LEED [57]	ITACA [23]
Life cycle cost	🗶		MAN 02 Life cycle cost and service life planning	🗶	🗶
Value creation and risk exposure		Ecological Value

highlights common indicators between the LEVEL(S) framework and relevant protocols for optimizing life cycle cost and value. There are no clearly defined thresholds about the specified indicators.

4.7. Overview

In this section, a ranking scale is assigned to LEVEL(S) based on studies to establish different thresholds for each indicator.

Table 18. Identification of the main threshold of the KPIs suggested by LEVEL(S). A red cross indicates the absence of a metric or threshold (🗶).

	Identification of the Main Threshold of the Key Performance Indicators (KPIs) Suggested by LEVEL(S)
Indicator	Macro Objective	Metric	LEVEL(S) Threshold	New Threshold		Refs.
Use stage energy performance	Greenhouse gas and air pollutant emissions along a building’s life cycle			Office Buildings	Residential Buildings	[20,42]
		Energy based Metrics such as Heating, Cooling, Lighting, Ventilation	Table 4 of authors’ previous study [21]	Mediterranean < 70 kWh/m2y Oceanic < 85 kWh/m2y Continental < 85 kWh/m2y Nordic < 90 kWh/m2y	Mediterranean < 60 kWh/m2y Oceanic < 60 kWh/m2y Continental < 65 kWh/m2y Nordic < 75 kWh/m2y
Life cycle global warming potential		GWP Metrics	🗶	Residential: 500 kg CO2 e/m2 Building’s structure, Foundation, and Enclosure: less than 1000 kg CO2 e/m2 Office Buildings: Between 200 and 500 kg CO2 e/m2 A1–A3 production, 70 to 520 kg CO2 e/m2 B1–B4 maintenance, cleaning, and replacement activities, approximately 120 kg CO2 e/m2		[20,53]
Bill of quantities, materials, and lifespans	Resource-efficient and circular materials life cycles	Total Quantity of materials used	🗶	There is no specific performance criterion, indicator, or threshold
Construction and demolition waste and materials		Baseline metric score	70%, Table 5	🗶		LEVEL(S), [20]
Design for adaptability and renovation		Adaptability score	🗶	Temporary structures are capped at 10 years, Industrial buildings at 25 years, long-term constructions are expected to last at least 50 years		[60]
Design for deconstruction, reuse, and recycling		Circularity score	Maximum circularity score	🗶		LEVEL(S)
Use stage water consumption	Efficient use of water resources	Total water consumption per occupant	Table 9 of authors’ previous study [21]	🗶		LEVEL(S)
Indoor air quality	Healthy and comfortable spaces	Ventilation Rate (airflow)	Table 12, Table 13 and Table 14 of authors’ previous study [21]	🗶		LEVEL(S)
Time outside of Thermal comfort range		PMV, PPD	🗶	There is no specific performance criterion, indicator, or threshold
Lighting and visual comfort		Spatial Daylight Autonomy (sDA)	🗶	300 lux for sDA Between 100 and 2000 lux for UDI		[68,94]
Acoustic and protection against noise		Façade Sound Insulation	🗶	Table 10, Table 11 and Table 12		[77,78]
Protection of occupier health and thermal comfort	Adaption and resilience to climate change	PMV, PPD	The reference temperatures shall be between 18 and 27 °C	🗶		LEVEL(S)
Increased risk of extreme weather events		🗶	🗶	There is no specific performance criterion, indicator, or threshold
Increased risk of flood events		Rainfall data	🗶	There is no specific performance criterion, indicator, or threshold
Life cycle costs	Optimized life cycle cost and value	Cost Metrics	🗶	There is no specific performance criterion, indicator, or threshold
Value creation and risk exposure		Increased revenues from more stable investments	🗶	There is no specific performance criterion, indicator, or threshold

, based on the International and European Standards and Certification Systems, summarizes the thresholds for each indicator related to the LEVEL(S) framework. According to the official website of the European Union, different thresholds can be assigned to each indicator based on the International Organization (ISO) [92] and the European Committee for Standardization (CEN) [93].

5. Conclusions

In this study, the LEVEL(S) framework, developed by the European Commission, was critically analyzed to better understand its function as a regional sustainability assessment tool within Europe. The analysis began by summarizing the gaps identified in previous research, with particular attention to the specific shortcomings associated with each indicator in the framework.

A comprehensive assessment of the framework’s structure and its Key Performance Indicators (KPIs) was conducted to enhance the evaluation of this emerging methodology. Both quantitative and qualitative metrics were clearly defined and systematically analyzed to ensure a robust foundation for comparison. To further this effort, a comparative analysis was conducted using tabular data to assess the alignment of common indicators in the LEVEL(S) framework with those in prominent international sustainability assessment protocols, including CASBEE, GREEN STAR, BREEAM, LEED, and ITACA.

The research also incorporated a thorough review of official European Union documentation and the relevant academic literature, aimed at addressing the previously identified limitations of the framework. One of the key findings of this study was the lack of a clearly defined scaling system based on threshold values, which remains a critical shortcoming in the LEVEL(S) methodology. Unlike other global sustainability systems that rely on established scales, the LEVEL(S) framework lacks a standardized measurement system tailored to each indicator.

To address this gap, a threshold analysis was conducted. This involved a review of existing thresholds using a combination of literature sources, including EU publications, academic articles, and benchmarks from leading international protocols. The goal was to identify the most appropriate threshold for each indicator. The study ultimately proposed a set of thresholds and corresponding metrics for various indicators; however, it also recognized that not all indicators within the LEVEL(S) framework can be associated with fixed thresholds or quantifiable metrics. These cases are indicated with a cross-symbol in Table 18, which summarizes the main thresholds and their applicability.

As presented in Table 18, this study assigned metrics and thresholds to various indicators where feasible. For instance, thresholds for Use stage energy performance ranged from 60 to 75 kWh/m² y depending on climate, and the threshold for Life cycle global warning potential was set at 500 kg CO₂ e/m² for residential buildings. Construction and demolition waste was assigned a 70% recovery rate, while Design for Adaptability required a minimum lifespan of 50 years. Lighting and visual comfort were defined by a threshold of 100 to 2000 lux for useful daylight illuminance (UDI), and Protection of occupier health and thermal comfort was set between 18 and 27 °C. For certain indicators, particularly those shaded in gray, the scientific literature and the protocols or frameworks do not provide sufficient information to define a threshold. For these indicators, the threshold should, therefore, be established based on experimental measurements carried out on real case studies.

Further details for Water consumption, Indoor air quality, and Acoustic performance are also provided in the Table 18.

In conclusion, the study provides a well-documented foundation for the thresholds and metrics necessary for the further development and evaluation of the LEVEL(S) framework. It serves as a valuable resource for future research and practical implementation across sustainability assessment contexts in Europe. Practitioners and policymakers may adopt these metrics and thresholds for implementation in new projects or for the renovation of existing buildings, utilizing the most up-to-date threshold and assessment methodologies. However, challenges remain in applying these thresholds to diverse regions, each with its own specific climate and regional conditions. Moreover, defining appropriate scaling systems and assigning weights to each indicator represent further complexities that must be addressed in future work.