Why prescriptive requirements are no longer enough: how performance-based IAQ requirements can transform ventilation design, inspection and operation under the evolving EPBD framework.
Valérie Leprince, Cerema | LinkedIn profile
Jelle Laverge, University of Ghent | LinkedIn profile
Gaëlle Guyot, Cerema | LinkedIn profile
(Note: Opinions in the articles are of the authors only and do not necessarily reflect the opinion of the European Union)
Energy performance requirements in buildings have progressively evolved from prescriptive rules toward performance-based approaches, enabling the assessment of actual outcomes both at the design stage (through simulation) and in operation. In contrast, the evaluation of indoor air quality (IAQ) and ventilation systems across Europe still largely relies on static compliance criteria, contributing to a persistent gap between expected and real indoor environmental quality.
The recast of the Energy Performance of Buildings Directive (EPBD) calls for a more integrated vision of building performance, addressing both energy use and indoor environmental quality. This evolution implies that IAQ management systems should follow a similar transition, moving from prescriptive requirements toward performance-based approaches that span the whole building life cycle—from design and commissioning to inspection and operation.
Such a shift is particularly critical for ventilation systems with variable airflow rates, including demand-controlled and hybrid systems, where design flow rates alone cannot reflect real conditions of use. In these cases, performance must be assessed through a combination of simulation-based design approaches and in situ indicators, such as CO₂ levels and other IAQ metrics, to ensure that ventilation effectively responds to occupancy and maintains adequate air quality.
This article argues that aligning national regulations and standards with the EPBD framework requires embedding performance-based IAQ criteria throughout design methodologies, inspection practices and operational monitoring. This is a necessary step to close the performance gap and to deliver buildings that achieve both energy efficiency and healthy indoor environments in practice.
Over the past decade, the building sector has embraced the concept of smart buildings as a cornerstone of the energy transition. Advanced control systems, connected devices and data-driven optimisation have significantly improved the ability to manage energy use in buildings. However, this rapid ‘smartisation’ has also revealed a fundamental limitation: smartness does not necessarily guarantee performance from the perspective of occupants.
A building can be highly automated, optimised for energy consumption and compliant with regulatory energy performance requirements, yet still fail to provide adequate indoor environmental quality (IEQ). This gap highlights a key issue: building performance has too often been defined through technical compliance and from an energy perspective rather than human outcomes.
The transition toward human-centred buildings requires redefining performance in terms of occupants’ needs. In this context, IAQ becomes a central indicator, as it directly affects health, cognitive performance and overall well-being. Ventilation systems, long treated as secondary technical components, are therefore emerging as critical infrastructure for delivering real building performance and need to support the shift toward smartness. In this context, the concept of smart ventilation has been emerging and is recognised as a promising technical solution for energy savings while promoting IAQ (Durier et al., 2018; Guyot et al., 2018a; Mortari et al., 2025a, 2025b).
The recast of the Energy Performance of Buildings Directive (EPBD) reflects this evolution. By integrating indoor environmental quality considerations alongside energy performance, it establishes a framework that goes beyond smartness as a purely technological concept. Instead, it promotes a vision of buildings that are not only efficient and connected but also responsive to human needs.
However, achieving this vision requires a fundamental shift in how ventilation systems and IAQ management are designed, assessed and regulated.
Despite major advances in IAQ science, current regulatory frameworks across Europe still largely rely on prescriptive approaches (Guyot et al., 2025, 2019, p. 39, 2018b). Ventilation requirements are typically defined through fixed airflow rates per person or per floor area, depending on building type and use. While these rules provide simplicity and enforceability, they are largely derived from a combination of energy efficiency considerations and assumptions related to perceived air quality rather than a comprehensive assessment of indoor air quality outcomes. As such, they represent a highly simplified approximation of complex indoor environments and often fail to address the full scope of IAQ challenges, including pollutant exposure, moisture control and associated health impacts.
As highlighted in recent research, indoor air quality is not determined solely by airflow rates. It results from dynamic interactions between pollutant sources, building characteristics, occupant behaviour and system operation. Activities such as cooking, cleaning or occupancy patterns can lead to highly variable exposure conditions that cannot be captured by static design values.
Moreover, existing standards often provide limited guidance on how to account for different pollutants, emission scenarios or exposure pathways. Even when alternative approaches are proposed—such as pollutant-based design methods (EN 16798-1)—the lack of practical implementation guidance restricts their use in real projects.
This situation has led to a paradox: while the scientific understanding of IAQ has significantly progressed, regulatory and standardisation frameworks have not fully integrated these advances. As a result, many buildings comply with ventilation requirements but still fail to ensure satisfactory indoor air quality in practice.
The contrast with energy performance is striking. Over the past decades, energy regulations have progressively transitioned toward performance-based approaches. Today, energy performance is routinely assessed through dynamic simulation at the design stage.
This evolution has enabled a much more robust evaluation of building performance, accounting for climate conditions and system interactions. Importantly, it has also created a shared framework across Europe, allowing comparability and continuous improvement.
IAQ has not followed the same trajectory. While tools and methodologies for performance-based IAQ assessment exist, their integration into regulations and standards remains limited. This creates a structural imbalance: buildings are designed and evaluated with high precision for energy use but with relatively coarse assumptions for indoor air quality.
The EPBD recast explicitly aims to address this imbalance by promoting a more integrated approach to building performance. However, translating this ambition into practice requires extending the performance-based paradigm to IAQ management.
A performance-based approach to IAQ design shifts the focus from prescribed inputs (e.g. airflow rates) to desired outcomes (e.g. pollutant exposure levels, health impacts or comfort indicators). This approach relies heavily on simulation to capture the dynamic nature of indoor environments (Guyot et al., 2025; Poirier et al., 2021).
Advanced modelling tools, including multi-zone airflow and pollutant transport models, allow designers to evaluate different ventilation strategies under realistic conditions. These tools can account for:
Such simulations enable the comparison of design options based on their actual performance, rather than simplified assumptions.
Figure 1. Schematic diagram illustrating a performance-based approach for ventilation at the design stage of a building, from (Poirier et al., 2021).
Figure 2 – Example of simulation-based IAQ performance assessment for three ventilation systems. The exhaust-only and balanced systems offer the same total airflow (Poirier et al., 2021).
One of the key advances in performance-based IAQ design is the use of exposure-based metrics. Instead of targeting a fixed ventilation rate, the objective becomes:
Metrics such as cumulative exposure, peak concentration or health-based indicators (e.g. DALYs) provide a more direct link between design decisions and their impact on occupants. The DALY approach also allows prioritisation of pollutants based on their actual health burden.
While performance-based design is essential, it is not sufficient on its own. A key lesson from both energy and IAQ performance is that building performance cannot be ensured at a single stage. It must be continuously assessed throughout the building life cycle.
This is particularly critical for smart ventilation systems with variable airflow rates, such as demand-controlled or hybrid systems. In these systems, airflow continuously adapts to occupancy, pollutant levels or environmental conditions. As a result, there is no single ‘design flow rate’ that can be verified during inspection.
Current inspection frameworks often rely on checking nominal airflow rates, system components or maintenance conditions. These approaches are not suited to variable-flow systems, where performance depends on control strategies and real-time operation.
For example, a demand-controlled ventilation system may deliver adequate IAQ under normal conditions but fail during peak occupancy if sensors are poorly calibrated or control algorithms are not properly configured.
To address these limitations, inspection practices must evolve toward performance-based verification. This can be achieved through two complementary approaches.
First, system-oriented verification focuses on the functioning of the ventilation system itself. This includes assessing system response under varying conditions, evaluating control strategies, verifying sensor accuracy and reliability, and measuring proxy variables that indicate correct operation. Such an approach also highlights the need for improved product and system certification frameworks to establish robust links between measurable parameters and actual IAQ performance.
Second, performance can be assessed through longer-term monitoring of indoor environmental quality indicators, including direct measurements of indoor contaminants. The increasing availability of sensors and digital technologies creates new opportunities to monitor IAQ in real time. These systems can provide continuous feedback on indoor conditions, enabling:
Indicators such as indoor CO₂ concentrations are useful to evaluate the responsiveness of ventilation systems to occupancy; however, they are not sufficient on their own to guarantee a healthy indoor environment. A broader set of IAQ indicators is therefore required.
Nevertheless, the deployment of monitoring systems must be accompanied by clear frameworks for data interpretation, quality assurance and privacy protection.
Figure 3 – Total exhaust ventilation airflow, building average relative humidity and building average CO₂ concentration for a single-family house equipped with humidity-based ventilation, from (Poirier et al., 2024).
The transition toward performance-based IAQ approaches cannot be achieved without a fundamental evolution of both European standards and national regulatory frameworks. While the recast EPBD establishes the political mandate by requiring the assessment of indoor environmental quality and strengthening provisions on system inspection and monitoring, it does not, on its own, provide the technical tools needed for implementation. These must be delivered through standards and translated into enforceable national regulations.
To enable Member States to develop performance-based regulation, standards must move beyond prescribing ventilation rates and instead provide a structured framework for IAQ assessment. In particular, EN 16798-1 should evolve to define:
Critically, this framework must include default IAQ indicators and threshold values that can be directly used by Member States in regulation, while still allowing adaptation to national contexts.
Equally important is the way these indicators are defined. Requirements must be expressed in a way that is meaningful. For example, stating that indoor CO₂ concentration should remain below 1000 ppm is insufficient if not associated with a clear metric such as ‘average concentration during occupied periods’ or ‘90% of occupied time’. In dwellings, the location (bedroom, living room, or average of all rooms) must be specified as well. Without such definitions, requirements cannot be consistently assessed or enforced.
In this context, EN 16798-1 should act as a toolbox for performance-based IAQ regulation, providing not only target values but also the structure needed to define robust and measurable requirements.
A shift toward performance-based design also requires significant improvements in the supporting calculation methods and input data.
Simulation plays a central role in assessing IAQ performance at the design stage, yet its practical implementation remains limited by the lack of standardised assumptions and guidance. To address this, EN 16798-1 should provide:
The work performed in the IEA-EBC Annex 86 has provided this knowledge.
In parallel, calculation methods must evolve to better reflect real building behaviour. In particular, EN 16798-7 should further integrate multi-zone airflow and pollutant transport modelling, allowing a more accurate representation of pollutant distribution within buildings and the impact of ventilation strategies.
Without these elements, performance-based design remains difficult to implement in practice, limiting its uptake beyond research and expert applications.
The EPBD now makes the inspection of all technical building systems and the consideration of indoor environmental quality a central requirement. However, existing inspection standards are not fully adapted to smart IAQ management systems, particularly those relying on demand control or natural and hybrid operation.
EN 16798-17 should therefore evolve to support the inspection of these systems through:
This evolution is essential to ensure that inspection frameworks remain relevant in a context where system performance depends on real-time adaptation rather than fixed operating points.
While standards provide the technical foundation, Member States are responsible for translating these into regulatory requirements. This implies a shift from prescriptive rules toward clearly defined IAQ performance objectives, applicable both at the design stage and during operation.
In practice, this requires that national regulations:
The EPBD creates the obligation to address IEQ and to strengthen inspection and monitoring practices. It is now the role of national frameworks to operationalise these requirements, using the tools provided by standards.
The transition from smart to human-centred buildings requires a fundamental shift from compliance-based approaches to verified performance outcomes. Ventilation systems must no longer be assessed solely against design flow rates, but on their ability to deliver healthy indoor environments in real conditions of use. The EPBD provides a strong framework to drive this evolution by integrating energy performance and indoor environmental quality. However, its success depends on the capacity of standards and national regulations to operationalise performance-based IAQ approaches. Extending the logic already applied to energy performance is essential to close the gap between smart technologies and the actual needs of building occupants.
Durier, F., Carrié, R., Sherman, M., 2018. What is smart ventilation? VIP 38. Air Infiltration and Ventilation Centre (AIVC).
Guyot, G., Leprince, V., Poirier, B., Kolarik, J., 2025. State-of-the-art on the use of performance-based approaches for residential ventilation in 2024. REHVA Journal.
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Guyot, G., Walker, I.S., Sherman, M., Linares, P., Garcia Ortega, S., Caillou, S., 2019. A review of performance-based approaches to residential smart ventilation. VIP 39. Air Infiltration and Ventilation Centre (AIVC).
Guyot, G., Walker, I.S., Sherman, M.H., 2018b. Performance-based approaches in standards and regulations for smart ventilation in residential buildings: a summary review. International Journal of Ventilation, pp. 1–17. https://doi.org/10.1080/14733315.2018.1435025
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Mortari, D., Wang, Y., Guyot, G., Plagmann, M., Mendes, N., 2025b. Smart Ventilation in Residential Buildings. TN 74.
Poirier, B., Guyot, G., Woloszyn, M., 2024. Uncertainty quantification: For an IAQ and energy performance assessment method for smart ventilation strategies. Building and Environment, 266, article 112115. https://doi.org/10.1016/j.buildenv.2024.112115
Poirier, B., Guyot, G., Woloszyn, M., Geoffroy, H., Ondarts, M., Gonze, E., 2021. Development of an assessment methodology for IAQ ventilation performance in residential buildings: an investigation of relevant performance indicators. Journal of Building Engineering, 43, article 103140. https://doi.org/10.1016/j.jobe.2021.103140
