Assessment of LEVEL(S) Key Sustainability Indicators

Abstract

The growing global emphasis on sustainability science has catalyzed significant advancements in research and practice within this domain. Among the various initiatives, the European Union has introduced LEVEL(S), a comprehensive framework for assessing the sustainable performance of buildings. This system provides a standardized methodology for evaluating and reporting key aspects of building sustainability across Europe, leveraging a structured set of indicators to address performance throughout a building’s life cycle. This study conducts a thorough analysis of the key performance indicators (KPIs) within the LEVEL(S) framework. It highlights critical limitations, such as the absence of specific metrics, misalignment with existing regulations and standards, and the absence of clear thresholds needed to effectively evaluate the performance of each KPI. Through a rigorous analysis of these KPIs, this study explores the potential for developing an enhanced and more refined framework to address these challenges.

1. Introduction

The concept of measuring sustainability in architecture, which originated from the environmental awareness of the 1960s and 1970s, has significantly evolved. This period marked the emergence of modern sustainable architecture, shaped by the environmental movement and concerns over the depletion of natural resources [1]. Energy shortages and crises of the time highlighted the importance of minimizing energy loss in buildings, sparking interest in sustainable energy design [2,3].

By the 1990s, various sustainability standards and certifications were introduced, emphasizing the integration of engineering and architecture, with a focus on material integrity, system efficiency, and advanced technology [4].

In the 21st century, the global adoption of sustainable practices in architecture has gained momentum, with a significant rise in the number of buildings earning such protocols. In Europe, several systems assess and promote sustainability while reducing carbon emissions. For example, although widely adopted in North America, the leadership in energy and environmental design (LEED) system has also gained traction in parts of Europe [5,6,7]. Similarly, the building research establishment environmental assessment method (BREEAM), developed in the UK, is widely recognized as a leading sustainability assessment method across the continent [5,8].

Additionally, region-specific protocols play a critical role in advancing sustainable architecture. For example, the Passive House (Passivhaus) standard is particularly prominent in Germany and Austria [9,10], while ITACA and CasaClima are widely utilized in Italy and neighboring regions. The latter, in particular, is compulsory for new buildings and buildings that have undergone deep renovation work in the Trentino Alto Adige region.

Although the abovementioned protocols are becoming increasingly widespread, they employ a variety of methodologies and assessment processes that, due to their diversity, can often lead to confusion among users and stakeholders in the building sector, making it challenging to navigate and compare their requirements effectively. In this context, the European Union introduced a new framework in 2017 to serve as a guideline, called LEVEL(S), which was initially conceptualized in 2015 [11]. LEVEL(S) provides comprehensive sustainability indicators that assist in building projects evaluating and enhancing their performance. Within the framework of the energy performance of building directive (EPBD), LEVEL(S) serves as a European standard for assessing and reporting the sustainability performance of buildings throughout their life cycle [12]. Since the EPBD identifies LEVEL(S) as a tool that enables the measurement of building performance, the definition of metrics and thresholds becomes crucial. The primary objective of this development is to standardize sustainability measurements across the European Union by defining a set of metrics and a comprehensive suite of indicators. Specifically, the framework includes 16 common indicators distributed among 6 macro-objectives within the LEVEL(S) structure. It is important to clarify that this study introduces the term “metrics”, since in LEVEL(S), the indicators can be measured in multiple ways, referred to precisely as metrics. While LEVEL(S) merely cites certain metrics as control parameters in the design process, it does not provide specific calculation methods or thresholds. Consequently, our analysis will primarily focus on the more clearly defined KPIs and then will highlight the main gaps. This approach lays the foundation for a comprehensive and robust evaluation system for future research. Implementing LEVEL(S) is vital to advancing sustainable construction practices, and its continuous refinement could play a key role in driving progress in this field. Consequently, ongoing LEVEL(S) framework research is crucial for its continued development and optimization.

In this context, this study aims to analyze the KPIs and thresholds delineated in LEVEL(S), drawing directly from official documents (user manuals) available on the European Union’s official website. In addition, this study will identify when metrics or thresholds are missing or inconsistent with the commonly accepted literature. Both the existing KPIs and the missing or inconsistent thresholds will be used to evaluate the advantages and limitations of this framework.

This study is structured as follows: it begins by introducing various rating systems and protocols employed in Europe, supported by a literature review to assess the strengths and weaknesses of the LEVEL(S) framework compared to other global rating systems. Then, LEVEL(S) is analyzed in detail, focusing on its KPIs and areas where improvements are needed. The assessment analyzes and addresses the following three main shortcomings: (i) the lack of clearly defined metrics; (ii) missing thresholds; (iii) misalignment with widely accepted regulations, standards, or other relevant references. Finally, the document includes a comprehensive summary table for each macro-objective within the LEVEL(S) framework and a detailed review of the key findings.

Figure 1 below illustrates the methodology and objectives of this study.

2. LEVEL(S)-State of the Art: Strengths, Weaknesses, and Main Areas of Improvement

Firstly, it is important to note that, despite the LEVEL(S) framework being launched several years ago, the scientific literature on this topic remains limited. The main studies, which delineate the key distinctions between LEVEL(S) and other rating systems along with evaluating areas for enhancement and assessment of LEVEL(S)’s strengths and weaknesses, have been thoroughly analyzed and summarized below. The advantages will be discussed first, followed by weaknesses.

In more detail, LEVEL(S) exhibits robust alignment with the European Green Deal, bolstering key EU policy initiatives such as the Circular Economy Action Plans of 2017 and 2021 [13] as well as the renovation wave initiative, emerging as a circular tool for accelerating the renovation of the EU building stock and enhancing sector-wide energy efficiency [13]. According to Marchi et al., who evaluate green building rating systems (GBRSs), LEVEL(S) provides a suite of clear, cohesive indicators. These indicators align building energy performance metrics with the strategic objectives outlined in the EU’s 2020 Circular Economy Action Plan (CEAP), demonstrating LEVEL(S)’s strong compatibility with these policy goals. Additionally, its open-source nature facilitates seamless integration with other GBRSs, enhancing its adaptability and effectiveness in promoting sustainable building practices [14].

A key advantage of the LEVEL(S) framework is its robust incorporation of life cycle thinking (LCT) and circular economy principles, setting it apart from other green building rating systems (GBRSs) such as BREEAM, LEED, DGNB, CASBEE, and WELL. Unlike many of these systems, LEVEL(S) adopts a holistic perspective, addressing the entire life cycle of a building—from design and production to construction, use, maintenance, demolition, and disposal. While methodologies like those of BREEAM and DGNB also incorporate life cycle considerations, LEVEL(S) emphasizes ensuring continuity across all phases of a building’s lifespan [15]. By prioritizing adherence to sustainability principles during the critical early stages of design, production, and construction, LEVEL(S) establishes a foundation for long-term performance and enduring environmental benefits [16].

Similarly, Kanafani et al. have highlighted that LEVEL(S) not only addresses critical dimensions such as environmental performance, health, comfort, cost, value, and risk but also ensures that its life cycle assessment (LCA) rules are aligned with national and NGO-led initiatives and programs. This strategic alignment promotes greater harmonization across various rating protocols, reinforcing LEVEL(S) as a comprehensive and adaptable framework for sustainable building practices [17]. Moreover, LEVEL(S) is notable for incorporating design elements that facilitate adaptability, renovation, deconstruction, reuse, and recycling [18]. Developed to establish a harmonized system, LEVEL(S) empowers European policymakers and stakeholders by offering a transparent, consistent, and accessible framework for evaluating sustainability in the construction sector [19].

Some other works [13,20] highlighted a further strength of the LEVEL(S) framework: its structure. This is subdivided into three distinct levels of project construction and allows for seamless alignment with various project stages. It supports both qualitative and quantitative evaluations, beginning with Level 1 (conceptualization), progressing to Level 2 (design and construction), and culminating in Level 3 (post-completion performance), which assesses as-built and in-use performance. This staged approach ensures a thorough assessment throughout the project life cycle.

Besides the strengths mentioned above, some weaknesses have also been highlighted in the literature. In more detail, a 2021 study [14] critically evaluated green building rating systems (GBRSs) such as LEED, BREEAM, GREEN STAR, and LEVEL(S), identifying several key limitations. One major issue is that each system uses regional metrics, creating a potential misperception among stakeholders and underscoring the need for standardized metrics. Additionally, these systems, including LEVEL(S), lack sufficient focus on social and economic issues, raising concerns about affordability and the potential for greenwashing, where sustainability becomes more of a marketing tool than a genuine practice. The study also noted that regional variations in certification and weighting systems complicate the sustainability assessment process, especially for non-experts [14]. As a newer framework, LEVEL(S) may face similar challenges due to the absence of a standardized assessment method, limited integration with other GBRSs, and an inadequate consideration of social and economic factors.

The key weakness of the LEVEL(S) framework lies in its limited integration with widely recognized global sustainability protocols. In particular, Ferrari et al. specifically pointed out the lack of a comprehensive analysis of how LEVEL(S) aligns with these systems. They emphasized the importance of assessing its compatibility with international standards and enhancing transparency regarding parameters, tools, and underlying assumptions [15].

A 2023 study by De Wolf et al. also identified significant gaps, particularly in its practical application within professional contexts. Their research highlighted the need for a more comprehensive analysis of end-user requirements, particularly concerning whole life cycle (WLC) assessment tools and data sources. They also pointed out the insufficiency of current life cycle assessment (LCA) tools and databases, particularly in terms of design, functionality, and integration with professional workflows such as building information modeling (BIM) [13]. According to the official documentation [11], one barrier to LEVEL(S) application is the complexity of the calculation methods and the access to a helpful tool.

Moreover, a further critical gap lies in integrating the ISO 52000 [21] series and the standards developed under mandate 4806, which require adherence to specific calculation methods. This gap highlights the need for harmonization in applying energy efficiency standards worldwide and across the EU, particularly regarding methodologies, scopes, and performance metrics [22,23]. As a result, there is a lack of harmonization of these methods across different member states, leading to inconsistencies in the final assessment. Similarly, other research [20] has shown that the complexity of EU documents within the LEVEL(S) framework makes extracting and applying relevant information difficult. In fact, even if LEVEL(S) provided some calculation tools, the following three main issues persist: the framework’s complexity, the need for accurate data to perform a calculation, and the difficulty of the calculation methods. These findings highlight the importance of expertise in navigating these challenges effectively.

In agreement with these findings, Kanafani et al. highlighted the complexity of such guidance, noting that LEVEL(S) combines key elements from various existing standards, but this approach results in a multi-source amalgam that lacks clearly defined benchmarks [17].

Considering the above-described literature review,

Table 1. LEVEL(S) SWOT analysis.

Strengths	Weaknesses
➣ LEVEL(S) exhibits robust alignment with the European Green Deal, bolstering key EU policy initiatives; ➣ It is recognized as a circular tool for accelerating the renovation of the EU building stock; ➣ Its open-source nature facilitates seamless integration with other GBRSs; ➣ It establishes a foundation for long-term performance and enduring environmental benefits; ➣ Its structure, subdivided into three distinct levels of project construction, allows for seamless alignment with various project stages.	➣ LEVELS uses its own metrics, creating a potential misperception among stakeholders; ➣ It lacks sufficient focus on social and economic issues; ➣ Limited integration with other GBRSs; ➣ Difficult practical application within professional contexts; ➣ It lacks a comprehensive analysis of end-user requirements, particularly concerning whole life cycle (WLC) assessment; ➣ It lacks some metrics and specific thresholds.
Opportunities	Threats
➣ Assessing LEVEL(S) compatibility with international standards and enhancing transparency regarding parameters, tools, and underlying assumptions could strongly increase the potentiality of the tool; ➣ The definition of clear thresholds for every metric could make LEVEL(S) an effective tool to precisely quantify (and improve) the actual sustainability of buildings within a unified EU framework.	➣ Unlike established rating systems such as LEED or BREEAM, LEVEL(S) does not provide an official labeling mechanism or certification “plate” that can be used for public communication or commercial valorization. This absence could limit its adoption as stakeholders do not benefit from a visible, standardized sustainability recognition that could enhance the assets’ market value or reputational appeal. ➣ Lack of easy to calculate metrics for every indicator limits the possibility to obtain comprehensive evaluations, thus precluding the reliability of the tool.

presents a SWOT analysis.

3. KPIs Analysis: Methods and Tools to Measure the Indicators

As briefly introduced, LEVEL(S) relies on a set of quantifiable indicators [11,16,24,25,26,27,28,29,30,31,32,33,34,35,36,37], categorized into six macro-objectives, as outlined in

Table 2. LEVEL(S) macro-objectives indicators [11,16,24,25,26,27,28,29,30,31,32,33,34,35,36,37,39].

Macro-Objective	Indicator
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. Acoustics 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

[15]. According to the user manuals, evaluation about these indicators should consider a period of 50 years [38].

This section evaluates the KPIs of LEVEL(S), including their associated metrics, defined units of assessment, and the thresholds proposed by LEVEL(S) and identified in the existing literature. Additionally, a comprehensive table detailing each of the six macro-objectives of the framework is presented. This table outlines the corresponding indicators and specifies the relevant metrics and units of measurement for each indicator, providing a clear and systematic overview for stakeholders to assess and implement. Finally, a table is proposed that identifies key gaps for each macro-objective. No further assessment is necessary when all required information is available, as indicated by a green tick in the table. Conversely, the absence of essential information requires further inquiry, denoted by a red cross.

3.1. Greenhouse Gas and Air Pollutant Emissions Along a Building’s Life Cycle

The first macro-objective is based on two main indicators: use stage energy performance and life cycle global warming potential. The first one and its related metrics are measured in kilowatt-hours per square meter per year (kWh/m²/year). As detailed in

Table 3. LEVEL(S) macro-objective indicators for the first macro-objective, greenhouse gas and air pollutant emissions along a building’s life cycle [11].

Indicator	Metrics	Unit
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 CO2e/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)

, essential metrics for assessing a building’s energy utilization encompass the energy demands for heating, cooling, ventilation, hot water, and lighting. These are quantified in kilowatt-hours per year (kWh/year), providing a comprehensive measure of the total energy consumption through the building’s operational phase. The threshold used for this indicator varies based on several parameters, including the climate zone and the type of building (such as residential or office buildings). This indicator aims to reduce energy consumption and encourage the integration of renewable energy.

The benchmark in terms of primary energy consumption has been defined in LEVEL(S) for office and residential buildings, according to four different climate zones (

Table 4. The thresholds for total primary energy use per square meter per year for both office and residential buildings [11].

EU Climatic Zone	Office Buildings	Residential Buildings
Mediterranean	80–90 kWh/m2	50–65 kWh/m2
Oceanic	85–100 kWh/m2	50–65 kWh/m2
Continental	85–100 kWh/m2	50–70 kWh/m2
Nordic	85–100 kWh/m2	65–90 kWh/m2

) [11]. These benchmarks serve as guidelines for the minimum energy performance, advocating for a significant reduction in non-renewable energy use and an increase in on-site or nearby renewable energy production, in line with the EU’s broader sustainability and energy efficiency goals [11].

However, it should be noted that the reported values are slightly different from the thresholds proposed during the drafting stages of the draft of the last Energy Performance of Buildings Directive (EPBD) recast [40]. Although such values were ultimately omitted from the final version of the Directive, leaving their specific definition to each member state [41], they can still be considered representative.

The second indicator, life cycle global warming potential, is quantified in kilograms of CO₂ equivalent per square meter per year (kg CO₂e/m²/year). Standards such as EN 15978 [42] systematically delineate performance criteria across various stages of a building’s life cycle, encompassing the product stage, construction, usage, and demolition phase. The LEVEL(S) study underscores the critical alignment of these life cycle stages with precise performance criteria, providing comprehensive guidelines and benchmarks for assessing life cycle global warming potential. However, the user manuals fail to specify the applicable benchmarks for each life cycle stage [26].

Consequently, as the LEVEL(S) study clarifies, while the document classifies life cycle stages, it omits detailed thresholds and necessitates the derivation of thresholds for life cycle global warming potential from alternative pertinent sources. This study reveals that the second LEVEL(S) indicator explicitly defines metrics for evaluating life cycle global warming potential. However, assessing the alignment of content with cited standards and regulations is challenging as the absence of established thresholds for life cycle stages complicates direct comparisons with other regulations and standards. This often results in potential inconsistencies. Consequently, instances where alignment cannot be assessed are marked with a red cross in

Table 5. Identification of the main weaknesses related to missing metrics, undefined thresholds, or incongruence with the regulations and standards of the KPIs suggested by LEVEL(S).

Macro-Objective	Indicator	Metrics Definitions	Threshold Definitions	Alignment with Standards/Regulations
1. Greenhouse gas and air pollutant emissions along a building’s life cycle	1.1. Use stage energy performance	✓	✓	✓
	1.2. Life cycle GWP	✓	✗	✗

below. This table concisely summarizes these aspects for both indicators.

The first macro-objective exhibits potential for significant enhancement. Specifically, the use stage energy performance indicator requires refinement in its total energy consumption range thresholds. Furthermore, there is a notable absence of clearly defined performance thresholds for the life cycle GWP indicator for each stage of a building’s life cycle. The absence of these defined thresholds leads to unresolved discrepancies with other regulations and standards.

3.2. Resource-Efficient and Circular Material Life Cycles

The second macro-objective embraces four different KPIs, as summarized below.

For the first, bill of quantities, materials, and lifespans, LEVEL(S) specifies specific units for each metric. This indicator underscores the importance of accurately estimating the quantity of materials used in construction. At this stage, when estimating the quantity of materials, considering the lifespans of various materials is crucial for reducing waste and enhancing resource efficiency. Thus, in this KPI it is pivotal to establish a connection between the bill of quantities (BoQs) and the environmental product declaration (EPD) or life cycle inventories (LCIs) to calculate carbon footprints and assess other environmental impacts. The LEVEL(S) sustainable framework generally has no sustainability targets or performance criteria for the recycled accounts or lifespans of materials. Nevertheless, it adheres to relevant guidelines and specific standards [35]. In such respect, the procedure related to such an indicator makes the user aware of the quantity of materials used and their cost.

Table 6. LEVEL(S) macro-objective indicators for the second macro-objective: resource-efficient and circular material life cycles [35].

Indicator	Metrics	Unit
2.1. Bill of quantities, materials, and lifespans	Total quantity of materials used	Tons and % split for ten predefined material fractions
	Quantities of materials used split by building aspect	Tons and % split for shell, core, and external elements
	Cost of materials used	€ and % for shell, core and external elements
	Normalized total material	kg/m2
	Normalized total Cost	€/m2
2.2. Construction and demolition waste	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

[35] presents the metrics related to the bill of quantities, materials, and lifespans, along with their relevant units.

Considering the second indicator, construction and demolition waste (CDW) and materials, a metric for waste quantity is defined as kg/m². The LEVEL(S) framework sets a target of 70% for the reuse, recycling, and material recovery of non-hazardous CDW [36]. The lack of a clear definition for the threshold in the literature review renders it challenging to evaluate the content’s compliance with the referenced standards and regulations. For the third indicator, design for adaptability and renovation, the adaptability score is used as the metric. The maximum score is set at 100. The adaptability score is calculated using key design parameters such as the internal space distribution, building servicing, and façade structure. To determine the score, each design aspect’s score is multiplied by its weighting factor and these are summed to achieve a total out of 100. This indicator assigns scores to encourage construction which is adaptable to future needs, aims to avoid demolition, and seeks to reduce waste [27]. Consequently, without defined thresholds from other studies, evaluating the content’s alignment with the cited standards and regulations becomes impossible.

The fourth indicator, design for deconstruction, reuse, and recycling, does not have a defined metric in the official LEVEL(S) document; moreover, no primary threshold is specified for this indicator. However, the circularity score, ranging from 0 to 100 percent, serves as a guideline for identifying the most suitable end-of-life options for building components. This range can be regarded as a de facto threshold, promoting achieving a higher circularity coefficient [24]. In exploring the alignment with other regulations and standards, this study examines potential inconsistencies through an alternative threshold framework. It specifies that a buildings’ minimum design service life should be measured in years [43]. Consequently, the thresholds derived from literature studies significantly differ from the circularity scores, which are calculated as percentages, as outlined by LEVEL(S).

The second macro-objective, resource-efficient, and circular material life cycles encompasses four indicators and presents a range of assessments, as shown in

Table 7. Identification of the main weaknesses related to missing metrics, undefined thresholds, or incongruence with regulations and standards of the KPIs suggested by LEVEL(S).

Macro-Objective	Indicator	Metrics Definitions	Threshold Definitions	Alignment with Standards/Regulations
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	✗	✓	✗

. The bill of quantities, materials, and lifespans requires the establishment of clear and precise thresholds. Assessment of this indicator can be efficiently conducted using the Excel-based LEVEL(S) bill of quantities (BoQs) template or building information modeling (BIM) software to compile the BoQs. Nevertheless, in cases where other protocols and regulations fail to specify these BoQs definitions, it is impossible to assess content alignment with the cited standards and regulations. For the construction and demolition waste and materials indicator, the specification of metrics and thresholds is unnecessary as targets are already defined within the LEVEL(S) framework. However, the lack of defined thresholds in other studies compared to the LEVEL(S) framework precludes any assessment of content alignment with the cited standards and regulations. The design for adaptability and renovation indicator is represented by a red cross, which signifies the absence of defined thresholds in other studies compared to the LEVEL(S) framework. Consequently, this deficiency renders the assessment of content alignment with the cited standards and regulations impossible. Furthermore, the design for deconstruction, reuse, and recycling indicator presents significant challenges due to the lack of established metrics and the variability in the definitions of thresholds within the LEVEL(S) framework and other studies.

3.3. Efficient Use of Water Resources

This macro-objective encompasses a comprehensive evaluation of a single indicator using multiple metrics, quantified in three units. These units include total water consumption per occupant, efficiency of sanitary devices and fittings, and irrigation water needs for vegetated areas, as detailed in

Table 8. LEVEL(S) macro-objective indicators for the third macro-objective: efficient use of water resources [34].

Indicator	Metrics	Unit
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	-

below [34].

Total water consumption per occupant during the building’s use phase is measured in m³ per occupant per year, enabling comparisons across buildings of varying sizes and occupancy rates. The assessment of water-efficient sanitary devices and fittings considers various performance metrics for different sanitary options, such as flow rates for taps and showerheads in liters per minute and toilet flush volumes in liters per flush. Furthermore, the water scarcity metric is also mentioned and assessed using the water exploitation index (WEI+), which calculates the ratio of the net quantity of water extracted from a specific river basin, encompassing four main extraction types related to agriculture, electricity, production, manufacturing, and public water supply, to the average renewable freshwater resources available in that basin during a defined period.

Recommendations for rainwater harvesting and greywater reuse emphasize systems that rely on gravity or siphonic action for optional efficiency. The irrigation water requirements for vegetated areas are determined by the minimum water needed to compensate for evapotranspiration losses, factoring in plant species, vegetation density, local climate conditions, and irrigation system efficiency, and are measured in liters per day.

Lastly, the indicator enhances the use of water metering and submetering across different building sections. This practice facilitates efficient water management and helps identify potential leaks and areas needing improvement, thereby enhancing overall sustainability.

The metrics outlined above are not universally mandatory for inclusion in project reports as the LEVEL(S) document does not explicitly mandate their use. However, they are recommended for consideration within a project’s design concept to enhance the reporting format’s comprehensiveness [34].

LEVEL(S) provides a simplified tool for evaluating this indicator, along with a benchmark for residential buildings in

Table 9. Ranges of performance reported under the LEVEL(S) official document [34].

Type of Product	Most Efficient	Least Efficient	General Range of Performance	General Improvement Potential
WC suite	1.5 L/flush	9.0 L/flush	2.95–6.0 L/flush	Factor of 2
Bath tube	11 L	360 L	80–185 L	Factor of 2.3
Shower controls	4.0 L/flush	8.0 L/flush	4.0–8.0 L/min	Factor of 2
Shower handsets	4.0 L/flush	50.0 L/flush	6.0–12.0 L/min	Factor of 2
Wash basin tap	1.3 L/flush	150.5 L/flush	4.0–12.0 L/min	Factor of 3
Kitchen sink tap	1.3 L/flush	106.4 L/flush	4.0–12.0 L/min	Factor of 3

, available on the European water label website (http://www.europeanwaterlabel.eu/ (accessed on 9 April 2025)). This label outlines performance ranges for taps, showers, bathtubs, urinals, and toilets.

It must be noted that the LEVEL(S) document indicates that the above-reported benchmarks may differ across countries due to distinct geographical and methodological conditions [34]. Thus, evaluating content alignment with the cited standards and regulations is feasible.

Considering the above-reported analysis in

Table 10. Identification of the main weaknesses related to missing metrics, undefined thresholds, or incongruence with regulations and standards of the KPIs suggested by LEVEL(S).

Macro-Objective	Indicator	Metrics Definitions	Threshold Definitions	Assessing Content Alignment with Cited Standards and Regulations
3. Efficient use of water resources	3.1. Use stage water consumption	✓	✓	✓

, specific metrics and thresholds can clearly delineate water consumption during the use stage.

3.4. Healthy and Comfortable Spaces

The fourth macro-objective can be measured using four indicators and several metrics, as summarized in

Table 11. LEVEL(S) macro-objective indicators for the fourth macro-objective: healthy and comfortable spaces [28].

Indicator	Metrics	Unit
4.1. Indoor air quality	Ventilation Rate (airflow)	L/s/m2
	Total Volatile Organic Compounds (TVOCs)	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 Particulate Matter < 10 µg	µg/m3
4.2. Time outside of thermal comfort range	PMV	% 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

below.

The first KPI, indoor air quality, is described by ten metrics, which are explained in the following sections. In this regard, LEVEL(S) specifies the minimum airflow rates by referencing EN 16798-1 [44], as indicated in

Table 12. Suggested ventilation air flow rates for an office (from Table B10 of EN 16798-1 [44]) [28].

Category	Total Design Ventilation Air Flow Rate for the Room
	L/(s per Person)	L/(s m2)
I	20	2
II	14	1.4
III	8	0.8
IV	5.5	0.55

and

Table 13. Suggested ventilation air flow rates for a residential building (from Table B11 of EN 16798-1 [44]) [28].

Category	Total Ventilation Including Air Infiltration		Supply Air Flow per Person	Supply Air Flow Based on Perceived IAQ for Adopted Persons
	L/(s.m2)	Ach	L/(s per Person)	qp I/(s per Person)	qB I/(s.m2)
I	0.49	0.7	10	3.5	0.25
II	0.42	0.6	7	2.5	0.15
III	0.35	0.5	4	1.5	0.1
IV	0.23	0.4

. In Table 13, q_B is measured in I/(s.m²), where q_B represents the building or base airflow rate and q_p denotes the airflow rate per person. Regarding the measurement of total VOCs, LEVEL(S) suggests a limit of 500 µg/m³, also in agreement with the WELL standard [28]. Although formaldehyde is a volatile organic compound (VOC), due to its significant health risks, it is typically reported separately in LEVEL(S) to underscore its importance. The threshold for this carcinogenic compound is set at 27 parts per billion (ppb), considering again the WELL standard. Additionally, in the LEVEL(S) document, the threshold for benzene is set at an annual average concentration of 5 µg/m³ [28]. It should be noted that LEVEL(S) also follows best practices based on EN 13799 [45] to properly design ventilation systems. It includes specifications for air filtration on intakes in areas with poor urban air quality [46].

Table 14. Informative thresholds for materials with low and very low pollution levels [46].

Pollutant	Emissions from Building Materials
	Low Polluting Thresholds	Very Low Polluting Thresholds
Total volatile organic compounds (TVOCs)	<0.2 mg/m2h	<0.1 mg/m2h
Formaldehyde	<0.05 mg/m2h	<0.02 mg/m2h
Ammonia	<0.03 mg/m2h	<0.01 mg/m2h
Carcinogens (IARCs)	<0.005 mg/m2h	<0.002 mg/m2h
Odor emitting materials	Dissatisfaction < 15%	Dissatisfaction < 10%

mentions the main thresholds for materials with low and very low pollution levels.

Occupant comfort is closely linked to relative humidity levels. Excessively high humidity, exceeding 90%, can amplify the perceived severity of both hot and cold temperatures. On the other hand, a low humidity level, below 20%, may lead to discomfort by irritating the eyes, nose, and throat. Additionally, approximately 17% of the EU population, or about 80 million people, reside in homes plagued by damp conditions that foster mold growth. This mold presence is a nuisance and a serious health hazard, potentially triggering respiratory and allergenic issues [28].

The classification of volatile organic compounds (VOCs) as carcinogenic, mutagenic, or reproductive toxic (CMR VOCs) is reserved exclusively for compounds with carcinogenic, mutagenic, or reproductive toxicity properties. Due to the significant health risks associated with these substances, separate reporting is essential. For regulatory thresholds and specific guidelines on CMR VOCs, references should be made to standards such as EN 16516 [28,47].

The R-value is a metric used to assess the overall concentration of volatile organic compounds (VOCs) within a room or building, comparing it against established safe thresholds known as the lowest concentration of interest (LCI values). It is the principal metric for aligning emission levels with health-related EU standards. The user manual does not specify a threshold for this metric [28].

Radon is a radioactive gas from natural sources that can enter buildings and adversely affect human health. The WHO recommends maintaining indoor radon levels below 100 Bq/m³ to minimize health risks. Typical outdoor radon levels range from 5 to 15 Bq/m³. Radon primarily emanates from rocks and soil, and can accumulate especially in poorly ventilated areas like basement and ground floors [28].

PM10 and PM2.5 are the primary outdoor pollutants directly affecting indoor health. The specification of filters in intake ducts is the only method to control these pollutants indoors as they cannot be controlled at the source. In 2005, the WHO published values for outdoor air pollutant concentrations. For additional context, the WELL standard sets 15 µg/m³ limits for PM2.5 and 50 µg/m³ for PM10 [28].

The analysis of the collected information indicates that the LEVEL(S) framework offers a thorough evaluation of this indicator, making it an effective tool for building assessments. The thresholds defined by LEVEL(S) are derived from established protocols, such as the WELL standard, ensuring alignment and consistency across multiple standards and guidelines. As illustrated in the table above, the metrics and thresholds are clearly defined and align with other established standards.

Regarding the second indicator, time outside of the thermal comfort range, the unit of assessment is the percentage of time outside the defined maximum and minimum temperatures during the heating and cooling seasons. The reference temperatures are between 18 °C and 27 °C. The LEVEL(S) document specifies that the performance of a building should be assessed both with and without mechanical cooling and that the space or zone under consideration must account for more than 10% of the total useful area [25]. For thermal comfort analysis, two well-known models establish the thermal comfort conditions in air-conditioned and naturally ventilated buildings: the predicted mean vote (PMV) model and the adaptive model [48]. The PMV is measured based on the following four measurable quantities: air velocity, air temperature, mean radiant temperature, and relative humidity. Temperature ranges for thermal comfort are stipulated in EN 12251 [49] and EN 16798-1 [44], setting the original threshold for time spent outside of thermal comfort within these ranges. Consequently, EN 15251 [50], which outlines temperature ranges for thermal comfort, divides these into four categories. The second category from

Table 15. Informative thresholds between indoor thermal environment categories, the predicted percentage of dissatisfied (PPD), and acceptable (adaptive) indoor summer temperatures [51].

EN 15251 [50] Category	Fanger Method		Adaptive Method
	PPD(%)	PMV	Operative Temperature Variance (°C)
I	[6	−0.2[PMV[ + 0.2	62
II	[10	−0.5[PMV[ + 0.5	63
III	[15	−0.7[PMV[ + 0.7	64
IV	>15	PMV < −0.7 and PMV > 0.7

, used as the primary threshold, is specified as follows. These criteria are based on the Fanger comfort model (PMV and PPD) and the adaptive comfort model (operative temperature variance) [25]. For the thermal comfort range, defined models such as the predicted mean vote (PMV) and the adoptive model are available. There are no significant differences between studies regarding these models, and the thresholds defined by LEVEL(S) below can be used. The correlation between time outside the thermal comfort range and predicted mean vote (PMV) can be described as follows. PMV predicts occupant thermal sensation based on factors such as temperatures, humidity, and clothing, while time outside of the thermal comfort range measures how often temperatures fall outside the comfort range (18 °C to 27 °C). These topics are interconnected through the predicted percentage dissatisfied (PPD). While time outside the thermal comfort range shows the frequency and duration of potential discomfort, PMV and PPD quantify the impact on occupant comfort. This combined approach enables building designers to optimize both comfort and energy efficiency.

As evidenced by the preceding table, the indicator is comprehensively structured. Accordingly, there is no requirement to establish a unique metric or benchmark, nor is there a necessity to align with other standards, as these criteria are already satisfactorily met.

For the third indicator, lighting and visual comfort, the LEVEL(S) framework delineates a variety of metrics as detailed in Table 11. These metrics encompass various aspects of lighting, including intensity levels, spatial distribution, and contrast rendering. The framework specifies distinct metrics and the measurement units pertinent to different assessment areas. Some metrics employ a binary approach, indicating the presence or absence of certain functions. The primary aim of this indicator is to enhance occupant health and comfort through a comprehensive lighting and visual study. Consequently, incorporating quantitative and qualitative assessments that capture the experiences and feedback of the actual occupants is essential. Although Table 11 effectively enumerates several distinct metrics, the lack of established thresholds within the LEVEL(S) document complicates the evaluation of alignment with referenced standards and regulations. Consequently,

Table 16. Identification of the main weaknesses related to missing metrics, undefined thresholds, or incongruence with regulations and standards of the KPIs suggested by LEVEL(S).

Macro-Objective	Indicator	Metrics Definitions	Threshold Definitions	Alignment with Standards/Regulations
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. Acoustics and protection against noise	✓	✗	✗

denotes this limitation with a red cross.

Finally, regarding the fourth indicator, acoustic performance and protection against noise, the five main acoustics and noise protection design aspects are based on existing EN and ISO standards [33]:

• Façade insulation, D_2m,nT,w;
• Airborne sound insulation, R^′_w;
• Impact sound insulation, L^′_n,w;
• Service noise equipment, L_Aeq,nT;
• Room acoustics, A_eq

The related indicators help to understand how sound level measurements and acoustic analyses in an indoor environment can affect the occupants’ physical and mental well-being [52]. Clearly, various metrics associated with this indicator are quantified in decibels (dB). However, the absence of a defined threshold for this indicator means that it remains impossible to assess its consistency with other regulations and standards.

In general, it can be stated that the indicators of indoor air quality and time outside of the thermal comfort range have been comprehensively evaluated within the LEVEL(S) framework, avoiding the need for additional assessment. However, notable gaps remain in the last two indicators of the objective. Specifically, the lighting and visual comfort indicator requires defined thresholds to be established in the LEVEL(S) documentation. Furthermore, the absence of these benchmarks makes it impossible to assess the content’s alignment with other regulations and standards. The situation with the acoustic performance and protection against noise indicator mirrors that of the lighting indicator, with similar weaknesses.

3.5. Methods and Tools to Measure Adoption and Resilience to Climate Change

The fifth macro-objective is described by three KPIs and related metrics, as detailed in

Table 17. LEVEL(S) macro-objective indicators for the fifth macro-objective: methods and tools to measure adoption and resilience to climate change [29].

Indicator	Metrics	Unit
5.1. Protection of occupier health and thermal comfort	-	% 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

below.

For the first indicator, protection of occupier health and thermal comfort, the unit of assessment is the percentage of time out of range of the defined maximum temperatures during the cooling season. The reference temperatures are between 18 °C and 27 °C. The LEVEL(S) document specifies that the performance of a building should be assessed both with and without mechanical cooling and that the space or zone under consideration must account for more than 10% of the total useful area. In this indicator, relative to time outside of the thermal comfort range, the second indicator of healthy and comfortable spaces, it is important to highlight that the manual advocates using dynamic simulations. These simulations must be carried out using weather files for the specific location or region based on authoritative climate projections for 2030 and 2050 [29]. The LEVEL(S) framework fails to define specific metrics for the corresponding indicator. Furthermore, an analysis of the LEVEL(S) framework reveals that reference temperatures ranging between 18 °C and 27 °C could be established as a threshold. As compared to the LEVEL(S) framework, the absence of standardized thresholds in the existing literature renders the assessment of content alignment with cited standards and regulations unfeasible.

Regarding the indicator increased risk of extreme weather events, LEVEL(S) does not specify any threshold for an increased risk of extreme weather events; instead, it guides how to mitigate the impact of extreme weather [30]. This indicator focuses on the resilience of building structures and envelopes for withstanding extreme weather events. Moreover, the absence of a defined metric and the lack of a threshold definition in related studies renders the analysis of content alignment with cited standards and regulations impossible.

For the final indicator of the adoption and resilience to climate change, specific metrics exist for an increased risk of flood events. These metrics, along with their specified 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). For the upper stages of the LEVEL(S) framework, a performance-based unit of assessment is introduced, focusing on the modeling and simulation of the drainage system, where the units include runoff rates (l/S) for designed storms, retention capacity (m³), and discharge rates (l/S) at each outflow point. Based on specified rainfall data, this is designed to analyze the system’s response to maximum storm events. For this indicator, there is no specific threshold [29]. Furthermore, the absence of a clearly defined threshold in previous studies precludes a reliable analysis of content alignment with the cited standards and regulations.

According to the outcomes presented in

Table 18. Identification of the main weaknesses related to missing metrics, undefined thresholds, or incongruence with regulations and standards of the KPIs suggested by LEVEL(S).

Macro-Objective	Indicator	Metrics Definitions	Threshold Definitions	Alignment with Standards/Regulations
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	✓	✗	✗

, the first KPI, protection of occupier health and thermal comfort, requires the establishment of specific metrics; however, thresholds are already defined. The absence of clear thresholds in earlier studies leads to a zero percent alignment in content assessment. Similarly, the indicator for the increased risk of extreme weather events necessitates well-defined thresholds and metrics. Consequently, similar to the previous instance, content alignment analysis becomes unfeasible. Lastly, concerning the increased risk of flood events, issues with threshold consistency and regularity remain unresolved despite well-defined metrics. Although the metrics are clearly defined, the scenario regarding thresholds and regularity inconsistencies remains unchanged.

3.6. Methods and Tools to Measure Optimized Life Cycle Cost and Value

The objective includes two key indicators, as summarized below.

The first KPI, life cycle costs, as delineated in the LEVEL(S) document, does not have a threshold, but it does organize various metrics as detailed in

Table 19. LEVEL(S) macro-objective indicators for the sixth macro-objective: methods and tools to measure optimized life cycle cost and value [31].

Indicator	Metrics	Unit
6.1. Life cycle cost	Initial costs	€/m2y
	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

[31]. The document employs a standard unit of measurement: usable floor area per year (€/m²y) with costs projected or recorded annually over a 50-year reference period before being discounted to their net present value. This methodology is designed to boost the building management’s long-term sustainability and financial efficiency from a life cycle perspective [31]. Without a clearly defined LEVEL(S) threshold, assessing content alignment with the cited standards and regulations is impossible.

In the literature, optimizing life cycle cost and value involves evaluating the total cost of ownership of a product, system, or infrastructure over its lifespan while maximizing the derived value. This evaluation includes initial acquisition, operation, maintenance, and eventual disposal or decommissioning costs, balanced against the product’s benefits [53].

The value creation and risk exposure KPI is described by three metrics in the above table. The primary objective of this indicator is to evaluate the beneficial impacts of enhanced sustainability performance on a property’s financial valuation and risk rating. The assessment considers three distinct metrics, categorized as follows: Firstly, increased revenues from more stable investments suggest a growing interest from local markets in properties that maintain low void rates and are adaptable to future market conditions. This metric is assessed across all indicators of the LEVEL(S) framework through a straightforward ‘yes’ or ‘no’ response, following consultations with the client, and it has been agreed to incorporate this consideration into the financial valuation. Secondly, reduced operational overheads involve minimizing operational expenditure (OpEx) related to energy and water utilities and projected costs for maintenance, repair, and replacement. Lastly, reducing exposure to future risks is achieved by proactively anticipating potential impacts stemming from climate change. These latter two metrics are also assessed by a simple ‘yes’ or ‘no’ response following client consultations across all indicators of the LEVEL(S) framework [16].

According to the presented assessment in

Table 20. Identification of the main weaknesses related to missing metrics, undefined thresholds, or incongruence with regulations and standards of the KPIs suggested by LEVEL(S).

Macro-Objective	Indicator	Metrics Definitions	Threshold Definitions	Alignment with Standards/Regulations
6. Optimized life cycle cost and value	6.1. Life cycle cost	✓	✗	✗
	6.2. Value creation and risk exposure	✓	✗	✗

, the final macro-objective is not completely defined. For the first indicator, while metrics have been established, the thresholds have not been defined. This gap has hindered the ability of previous studies to assess content alignment with cited standards and regulations, consequently leaving regulatory inconsistencies unaddressed. Similarly, unresolved issues persist with the value creation and risk exposure indicator. Despite defined metrics, the lack of clear threshold definitions precludes a thorough analysis of content alignment with the cited standards and regulations.

4. Summary Overview and Conclusions

In this study, the LEVEL(S) framework, devised by the European Commission, was scrutinized to assess its role as a regional instrument within Europe. An initial analysis of the extant research highlighted the framework’s predominant strengths and weaknesses. The scarcity of scholarly articles on the subject resulted in limited scientific literature. However, a thorough examination of an extensive collection of documents from the European Union’s official website significantly augmented the research. The subsequent phase concentrated on the following three critical areas for improvement: identifying missing metrics for each indicator, clarifying undefined thresholds for each indicator, and resolving discrepancies between the established thresholds and the standards and regulations applied across various global rating systems.

According to the results obtained, it is possible to confirm that the LEVEL(S) framework is an important tool for guiding sustainable building design, offering a structured methodology for assessing environmental performance. However, a notable limitation of the framework is the lack of predefined thresholds for several key indicators, resulting in the difficulty of quantifying the level of a project’s actual performance against certain indicators. While LEVEL(S) provides a systematic approach to evaluation, it often leaves practitioners without clear benchmark values, requiring them to rely on external standards or project-specific targets. This absence of thresholds may lead to inconsistencies in interpretation and application, particularly when comparing performance across different projects.

Moreover, LEVEL(S) considers qualitative and quantitative metrics, ensuring that both measurable environmental impacts and broader sustainability considerations are accounted for. However, the flexibility in the assessment approach is further complicated by the multiple methods available to evaluate the same indicator. While this adaptability allows users to tailor assessments to their specific needs, it also means that different methods may focus on diverse aspects of the same sustainability dimension, potentially leading to discrepancies in results and limiting comparability.

Future developments of the framework should focus on addressing this gap by defining reference values or by integrating mechanisms to support practitioners in setting meaningful benchmarks aligned with broader sustainability goals.