Analysis of European Legislation on Indoor Climate and Air Quality

Throughout 2024, the European Union has carried out a comprehensive review of the regulatory frameworks for the built environment and atmospheric air quality. This process has resulted in two landmark legal acts: Directive (EU) 2024/1275 of the European Parliament and of the Council on the energy performance of buildings (hereinafter EPBD) and Directive (EU) 2024/2881 on ambient air quality and cleaner air for Europe (hereinafter the Air Quality Directive). Together, these directives mark a fundamental shift from a predominantly theoretical approach to building operation and environmental protection towards an explicitly data-driven reality, where continuous documentation, technical monitoring, and legal accountability are central. For building owners, managers, and industrial operators, this means a massive expansion of technical infrastructure requirements, including the installation of data loggers and building automation and control systems (BACS), as well as a significant tightening of the legal risks associated with non-compliance.  

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The regulatory framework for indoor climate monitoring in EPBD 2024/1275

EPBD 2024/1275 represents a recast of the previous building directive with the aim of accelerating the renovation wave in Europe and achieving the goal of a decarbonised building stock by 2050 at the latest. One of the most innovative aspects of the new directive is the formal recognition of Indoor Environmental Quality (IEQ) as an inseparable component of a building's energy performance. Legislators have recognised that the pursuit of energy efficiency must not come at the expense of users' health and well-being, which has led to stringent requirements for the installation of monitoring systems. 

Article 13 and the extension of requirements for building automation and control systems (BACS)

The core of the new monitoring requirements is found in Article 13 of the EPBD, which concerns technical building systems. The directive lowers the threshold for when a building must be obligatorily equipped with building automation and control systems (BACS). While the requirement was previously primarily aimed at very large installations, a gradual phase-in is now being introduced for smaller systems. 

For non-residential buildings, Article 13, paragraph 9, sets two primary thresholds based on the nominal useful output of the installation for heating, air conditioning, or combined ventilation. The nominal useful output is calculated as the sum of all heat- or cold-producing units in the building, including heat pumps, boilers, and refrigeration units.  

For building owners with installations above $70kW$ , this means that by the end of 2029 at the latest, they must have installed systems that not only control the installation but continuously monitor and log data. For installations above $290kW$ , the deadline has already passed or is imminent in national implementations, which underscores the speed of the green transition. 

Technical specifications for data logging: 15-minute interval and history

The directive and associated technical standards (including EN ISO 52120-1) define the functional requirements for these monitoring systems. For a system to be considered compliant with the legislation, it must possess specific data collection and analysis capabilities.

The legislation calls for continuous monitoring with a maximum sampling interval of 15 minutes. This requirement is fundamental for identifying inefficiencies in real-time and ensuring that indoor climate parameters such as temperature, humidity, and CO2-concentration do not deviate from healthy limits for short periods, which would otherwise be hidden in hourly averages. At the same time, there is an explicit requirement for at least one year of historical data storage. This historical database is crucial for the building owner for several reasons:

1. Seasonal variations: It allows for the analysis of the building's behaviour under different climatic conditions throughout an entire calendar year.

2. Efficiency control: It enables benchmarking of actual energy savings over time against projected values.

3. Documentation requirement: It forms the technical foundation for proving that the indoor climate has been healthy and compliant with regulations in case of complaints or lawsuits.

For parameters such as temperature, a sensor precision of ±0.5∘C, and for relative humidity $\pm 3\%RH$, is required. The systems must also have built-in alarm functions that automatically notify administrators if the recommended limits from the World Health Organization (WHO) are exceeded.

Indoor Environmental Quality (IEQ) and sensor requirements

EPBD 2024/1275 introduces, for the first time, a clear definition of indoor environmental quality in Article 2, no. 66. It is defined as the result of an assessment of the conditions inside a building that affect the health and well-being of users, based on parameters such as temperature, humidity, ventilation rate, and the presence of pollutants.

According to Article 13, paragraph 10, building automation systems must be capable of monitoring indoor environmental quality by 29 May 2026 at the latest. 

Zero Emission Buildings

For Zero Emission Buildings (ZEB), the requirements are even stricter; here, measuring and control devices for monitoring and regulating indoor air quality must be installed. For existing buildings, this requirement comes into force for major renovation works, if technically and economically feasible. This creates a direct incentive for building owners to integrate advanced IEQ sensors (CO2, PM2.5, VOC) into their monitoring strategy.  

The new Air Quality Directive 2024/2881 and Article 28

While the EPBD regulates technology inside buildings, the new Air Quality Directive (2024/2881) addresses the air we breathe in general and the legal consequences of pollution. The directive is a recast of previous rules and aims to bring EU air quality standards into closer alignment with WHO recommendations by 2030 at the latest, with a vision of zero pollution by 2050. 

The direct right to compensation for health damage

The most significant innovation in the Air Quality Directive is Article 28, which deals with compensation for damages to human health. The article unequivocally states that Member States must ensure that natural persons who suffer health damage as a result of a breach of national rules implementing the directive's most central articles (Articles 19 and 20) have the right to claim and obtain compensation for this damage.

This represents a paradigm shift in European environmental law, as it gives citizens and employees direct legal recourse against authorities' omissions. For a compensation claim to be valid, the infringement must have occurred intentionally or through negligence on the part of the competent authorities. This typically applies in situations where authorities have failed to develop adequate air quality plans or have neglected to implement necessary measures to reduce pollution levels below the established limit values.

Documentation requirements and burden of proof distribution

One of the biggest obstacles for citizens in environmental damage cases has historically been the technical and scientific requirements for proving causality. Article 28 directly addresses this by easing the burden of proof for the claimant to ensure effective access to judicial review.

The legislation operates with a shared documentation obligation and a presumption rule:

1. Role of the claimant: The citizen or employee must present relevant scientific evidence or data that creates a presumption that the violation of air quality standards has contributed to their health damage. Here, data from local monitoring stations or even indoor climate data from building systems can serve as supporting documentation.

2. Role of the authorities (Reversed burden of proof): Once the claimant has made a prima facie case for causation, the documentation obligation shifts to the competent authorities. They must disprove the causal link or document that they have fulfilled all their obligations under the directive.

3. Access to evidence: Member States are obliged to ensure that citizens have access to the data and information held by the authorities that are necessary to assess a claim for compensation.

This structure means that the lack of valid data is a massive risk for the party bearing the documentation obligation. If an authority or operator cannot present unbroken time series of air quality data, they will find it extremely difficult to meet the burden of proof and reject a compensation claim.

Definition of "Air" and scope of application of Article 28

For building owners and employers, it is crucial to understand the precise demarcation of Article 28 of the Air Quality Directive. According to Article 4, point 1, "air" (or ambient air) is defined as outdoor air in the troposphere, with the exception of workplaces where specific health and safety regulations apply and where the public does not have normal access.

This immediately means:

• Indoor climate in private residences: Falls as a starting point outside the scope of Article 28 of the Air Quality Directive, but is regulated by the EPBD's requirements for healthy standards.

• Workplaces: Are exempt under Article 4 because they are covered by occupational health and safety legislation (e.g. Directive 89/654/EEC). However, if an employee is exposed to illegal outdoor air on their way to work or in outdoor work areas, Article 28 applies.

• Indirect link: Even though Article 28 targets authorities, it puts pressure on all building owners and employers to document their own "defense". If the outdoor air in a zone is illegal, and a building owner cannot document that their indoor filtration and ventilation are working correctly (via EPBD loggers), they can become involved in complex liability distributions.

Synergy between EPBD and the Air Quality Directive for building owners

For the professional building owner, the two directives are not isolated silos, but two sides of the same coin. The EPBD provides the technical tools (data loggers, sensors, BACS), while the Air Quality Directive provides the legal consequences for lack of monitoring. 

The data logger as a legal shield and sword

The requirement for 15-minute sampling and 1 year of history in the EPBD serves as an indispensable documentation tool.

• As a shield: If an employee or tenant files a lawsuit for health damage due to poor indoor climate, the owner can use the logged data to prove that the ventilation has operated optimally, that CO2 levels have been below the limit values, and that humidity has been controlled. Without this data, the owner will be in a vulnerable position in a legal system that increasingly emphasizes citizens' right to a healthy environment.

• As a sword: If a building owner can document that their indoor air quality follows the harmful patterns from the outdoor atmosphere (for which the authorities are responsible), this data can be used to support a claim against the authorities under Article 28. This enables a precise identification of where the pollution originates and who has neglected their documentation and action obligations. 

Responsibility and whistleblowing

The Air Quality Directive also requires Member States to lay down penalties that are effective, proportionate and dissuasive. The severity of the infringement and its impact on the population, including sensitive groups, must be taken into account. This, combined with whistleblower protection, means that employees have significantly improved opportunities to force building owners and authorities to comply with regulations by pointing out deficiencies in the logged data.

Overview of implementation deadlines and milestones

For building owners, it is critical to keep track of the various deadlines to avoid legal repercussions and loss of property value.  

What is still unclear and upcoming?

Although the frameworks have been established, there are still a number of unresolved technical and legal elements that building owners should monitor in the coming years.

Technical implementing acts

The Commission is to adopt a number of implementing acts to fill in the technical details. For the Air Quality Directive, this concerns specific details about modelling programs and geographical representativeness, which are expected in mid-2026. For the EPBD, the most critical outstanding issues are: 

• Interoperability (Art. 16): Rules on how data should be exchanged in an open format are expected by December 2025 at the latest.

• GWP calculation framework (Art. 7): A common EU model for calculating the global warming potential of buildings throughout their life cycle is expected by the end of 2025 at the latest.

• SRI (Smart Readiness Indicator): The final rules for mandatory application of smart readiness indicators for systems above $290kW$ are expected in June 2027.

National definitions of "Adequate Indoor Climate"

The directive allows Member States some leeway to define precisely what "appropriate standards" for the indoor climate are. In Denmark, we await updates to the Building Regulations, which will specify the numerical values for ventilation and pollutants that BACS systems must log against.

Legal practice for compensation cases

The question of whether private building owners and employers can become "co-defendants" in cases of external air pollution is still unresolved in legal practice. Although Article 28 of the Air Quality Directive is aimed at authorities, the trend in the EU Court of Justice indicates an expansion of liability for any actor who has a duty of documentation and neglects it.  

Implications for building operations and strategic recommendations

The combined requirements of the EPBD and the Air Quality Directive necessitate a proactive strategy from building owners and administrators.

Data as the new basis for property value

The ability to document a healthy indoor climate through high-frequency, valid data logs will become a crucial parameter for property value and rental potential. Buildings that cannot present historical data for CO2, humidity, and temperature (and eventually particles), will be considered a legal and financial risk.

From reactive to proactive maintenance

Installation of systems that meet the requirements for installations above $70kW$, enables a shift from reactive to proactive operation. By analyzing trends in the logged data, failures in ventilation systems or insulation can be detected before they result in harmful health conditions or unnecessary energy consumption. This supports both operational economy and legal compliance.

Action plan for building owners

1. Technical audit: Review all properties to assess the total nominal power of HVAC systems. Identify systems between $70kW$ and $290kW$ to plan for BACS installation before the 2029 deadline.

2. Standardization of Data Logging: Ensure that all new and upgraded systems are configured for a sampling interval of a maximum of 15 minutes and have a robust backup solution that guarantees at least one year of history.

3. Interoperability in procurement: When tendering for new building management systems, ensure that they support open data formats in accordance with EPBD Article 16, so that you are not locked into a specific supplier.

4. Integration of IEQ sensors: Consider including particle sensors (PM2.5) and VOC meters in the main occupied spaces. This is not just a technical upgrade, but crucial evidence in future occupational health and compensation cases.

5. Legal preparedness: Establish procedures for quick release of air quality data to tenants and authorities to counter the presumption rules in Article 28 of the Air Quality Directive. 

Conclusion

Europe is facing a technological and legal transformation of the built environment. The adoption of EPBD 2024/1275 and Air Quality Directive 2024/2881 has created a reality where building operation has become synonymous with data management and health documentation. For installations above $70kW$ the data logger is no longer an option, but a legal requirement to ensure continuous monitoring at 15-minute intervals and one year of history. At the same time, Article 28 of the Air Quality Directive has provided citizens and employees with a powerful legal tool to seek compensation if they are exposed to unhealthy environments.

Building owners who act now by upgrading their technical infrastructure and ensuring valid data protocols will not only comply with legislation and avoid sanctions, but will also position themselves strongly in a market where healthy buildings are a fundamental prerequisite for both social and economic sustainability. The regulatory wave has set a new standard: The air we breathe must now be proven clean – all the time, every 15 minutes, year after year.

In-depth technical and legal perspective on data logging

To understand the full scope of requirements for data loggers and their role in the new European order, it is necessary to delve deeper into the functional expectations for Building Automation and Control Systems (BACS) and their interaction with the rights enshrined in the directives.

Continuous electronic monitoring: More than just data collection

EPBD Article 13, paragraph 11, introduces a requirement for "continuous electronic monitoring" for new residential buildings and buildings undergoing major renovations, from May 29, 2026. This is not merely a passive data logging requirement. The system must have the intelligence to measure the efficiency of installations and notify building owners or administrators in case of significant variation, or when maintenance is due.

For building owners with installations above $70kW$ this effectively means that the data logger must act as a "self-monitoring watchdog". If a ventilation motor decreases in performance or a filter becomes blocked, the system must register this within the 15-minute interval and generate an alarm. If the owner ignores these alarms and it leads to an unhealthy indoor climate, the one-year historical log will serve as ultimate proof of negligence in a compensation case under Article 28 of the Air Quality Directive or national occupational health law.

Distribution of documentation duty across ownership types

Who bears the duty of documentation depends on the building's use and contractual relationships:

• Public buildings: Here, the authority bears both the responsibility as building owner (EPBD) and the responsibility for air quality management (AQD). The authority has an absolute duty of documentation and is the direct target for Article 28 claims.

• Commercial properties for rent: The building owner is obliged to provide BACS data to the tenant (employer) in accordance with EPBD Article 16. The employer then has the duty of documentation towards their employees. If the owner does not provide data, or if the system (BACS) does not comply with the $70kW$-requirement, the owner can be held liable for the tenant's subsequent legal losses.

• Industrial operators: These actors are subject to Article 28 of the Air Quality Directive as potential "polluters at the source". Their monitoring systems must be able to document that their emissions do not unlawfully contribute to ambient air quality, otherwise they risk lawsuits with a relaxed burden of proof.

Scientific context: Measurement parameters and their significance

The logging of the indoor climate must cover a spectrum of parameters, each with health relevance. Below are the primary parameters that modern data loggers under EPBD are expected to cover:

1. Particles (PM2.5 and PM10): Fine particles are identified in the Air Quality Directive as one of the biggest threats to public health, with a requirement to halve the permitted levels by 2030. Logging of indoor particles is crucial to prove whether ventilation adequately filters external pollution.

Maintaining a 15-minute sampling interval ensures that the system can react to rapid changes, for example, when a meeting room fills up or an industrial process starts.

Legal analysis of Article 28 and employee rights

The Air Quality Directive's Article 28 is fundamentally rooted in the principle of "access to effective remedies" in the Charter of Fundamental Rights.

The employee as claimant

Although Article 28 focuses on ambient air, it has significant implications for employees. If an employee falls ill due to air pollution originating from an area where authorities have exceeded limit values, the directive grants them the right to sue the authority directly.

In practice, the employee will be able to:

• Use data from the building's data loggers to show that pollution exists indoors at the same levels as outdoors, proving infiltration.

• Benefit from a relaxed burden of proof, where the authority must disprove the correlation if the employee can make a plausible case.

• Demand full compensation for medical expenses, lost earnings, and in some cases, non-economic damages.

Limitation periods and legal certainty

Member States must set limitation periods for claims for damages that are reasonable and do not make it practically impossible to obtain compensation. The period must typically not be shorter than 5 years and must not begin to run before the infringement has ceased and the injured party knows (or ought to know) that there is damage and an infringement. This creates long-term liability for authorities and indirectly for building owners, further emphasizing the need for historical data storage for at least one year as an absolute minimum and preferably longer as a precautionary measure.

Global Warming Potential (GWP) and future requirements

An overlooked but critical deadline for building owners is found in EPBD Article 7. This introduces requirements for calculating a building's Global Warming Potential (GWP) throughout its life cycle.

This means that the building owner must be able to document not only the operation but also the environmental impact of building materials. This is related to indoor climate monitoring, because low-GWP materials can sometimes emit other types of VOCs that the system must be able to detect and log. 

Conclusion and action-oriented summary

With the 2024 legislation, the use of data loggers for the indoor climate has gone from being a technical niche to a central requirement at the intersection of energy policy, health law, and liability.

Key deadlines for the building owner

December 31, 2024: Ensure all large systems ($>290kW$) have BACS with indoor climate monitoring.

May 29, 2026: Have your data protocols ready for 15-minute sampling and one year of history to meet national transposition. 

1December 1, 2026: Be prepared for citizens' new rights to compensation under the Air Quality Directive.

December 31, 2029: Implement the installation of data loggers and control systems in all buildings with systems above $70kW$. 

The legislation is clear: Data is your best friend and your biggest risk. By investing in robust data logging systems now, building owners can ensure their property value, protect user health, and navigate safely in the new European legal landscape. The ambiguities that still exist in the form of national standards and delegated acts should not lead to inaction, as the overall objectives and minimum technical requirements of the directives are already established and binding.

Sources:

• EPBD 2024/1275
• Air Quality Directive 2024/2881