Shifting from Prescriptive to Performance-Based Approaches in Residential Ventilation Design

Interview with Jelle Laverge and Núria Casquero-Modrego by Lada Hensen Centnerová

Núria Casquero-Modrego is an architect and construction engineer trained at UC Berkeley and the Polytechnic University of Catalonia (UPC). She is currently a researcher at Lawrence Berkeley National Laboratory (LBNL), where she focuses on the intersection of the built environment, indoor environmental quality, and occupant health. Her research aims to enhance both the energy performance and non-energy impacts of residential buildings, particularly through retrofits that prioritize health outcomes. She contributes to national and international initiatives, including the IEA EBC programme, ASHRAE, ISIAQ and UNEP. Previously, she worked on the SinBerBEST Project at UC Berkeley, led UC Berkeley’s 3rd-place team in the 2017 U.S. DOE Solar Decathlon, and served on the Polytechnic University of Catalonia (UPC) faculty. She also co-founded TC ESTUDI Arquitectura in Barcelona, specializing in energy retrofitting, and affordable housing.

LHC: What do you personally see as the biggest added value of the Annex 86 [1] ?

JL: For me, the key added value of the Annex is that it allowed us to establish a set of essential building blocks that collectively support a performance‑based assessment approach to indoor air quality (IAQ) management in residential buildings. This is exactly the direction we believe the field needs to take. It is not about introducing a single new simulation tool or a single new metric - what we need is a complete ecosystem that enables informed, holistic decision‑making.

NCM: For decades, our focus in housing research and policy has been on energy efficiency - primarily as a way to reduce costs. Today, however, homeowners are increasingly aware of the importance of health and well‑being. We are at a moment of transition: from looking at energy performance in isolation to adopting a broader perspective that also considers how buildings and their occupants are affected by extreme weather events, power disruptions, and other emerging challenges.

LHC: Jelle, you just said, it is not only about metrics, but you developed new metrics in this project, right?

JL: Yes and no. We mostly continued the development of already existing metrics. An important example is the DALY (disability-adjusted life year) metric, which is a metric that has been used by WHO (World Health Organization) since the 90s and we were able to further develop this method and apply it to indoor air. We were able to translate this theory into something that is useful for practice. We introduced the harm intensity [2], which is expresses the additional harm (in DALY) per unit of exposure (in mg/m³). This makes it easy to convert contaminant concentrations in dwellings to expected harm.

NCM: The follow-up to Annex 86 takes this one step further. Instead of developing new metrics, the goal is to establish a global framework to consistently estimate indoor air quality impacts in residential buildings, with harm intensity serving as a starting point.

LHC: Which contaminant typically found in dwellings has the highest harm intensity?

JL: That’s an easy one. By an order of magnitude, It’s PM (particular matter). All PM together have about 10 times higher harm intensity than any other pollutant, and between coarser particles and PM 2.5, PM 2.5 contributes the most by far. See Figure 1.

Figure 1. Harm caused by Contaminants of Concern in houses in the Global North. Percentage contribution for total harm. From [1], page 9.

LHC: Is there another metric that you improved or further developed?

JL: Yes, resilience.

We drew inspiration from the field of thermal comfort, where the concept of thermal resilience is well established, and adapted this idea to create an IAQ resilience metric. Resilience, in this context, helps designers, regulators, and other stakeholders understand how robust a building or system is when faced with unexpected or extreme conditions - such as a power outage or during a heatwave.

Our IAQ resilience framework is built around three key components:

·         Absorptivity: How long the building can maintain acceptable indoor air conditions after a disruptive event.

·         Shock impact: The extent to which indoor air quality deteriorates during that event.

·         Recovery: Once the event is over, how quickly the system can bring indoor conditions back within acceptable levels.

NCM: This type of assessment is becoming increasingly important in a world where uncertainty is the norm. Here in California, where I work, we face not only extreme heat events but also severe wildfire seasons. Power disruptions are common, and outdoor air can become highly polluted in a matter of hours. Understanding IAQ resilience is therefore critical - it helps us design buildings that can protect occupants even when electricity is unavailable or when outdoor air becomes hazardous due to wildfire smoke.

LHC: What would you like to do with this metric further?

JL: We believe that resilience should become a standard performance indicator - assessed during design just as routinely as we currently evaluate the required share of renewable energy to reduce the load on the electrical grid.

NCM: Here, I think the next step is to link this resilience framework with the work on quantifying health impacts. From there, implementation becomes essential. We need to test the metric in real buildings across different climates, assess the associated occupant health impacts (or Harm), and ultimately integrate IAQ resilience into design standards so it becomes part of how building performance is routinely evaluated.

LHC: Annex 86 was also about smart ventilation. What do you mean by smart ventilation systems anno 2026?

JL: In Annex 86 we explicitly chose not to limit our work to smart ventilation alone. Instead, we introduced the broader concept of IAQ management, which allows us to consider a wide range of technologies and strategies that can contribute to better indoor air quality in residential buildings. Our focus was therefore on smart IAQ management, not solely on smart ventilation systems.

For the ventilation component, we adopted the definition of smart ventilation developed by the AIVC (Air Infiltration and Ventilation Centre). According to this definition, a smart ventilation system is one that can adjust ventilation rates both in time and location - responding dynamically to the needs of the specific moment and the specific space within the building. This flexibility is essential if we want ventilation to perform effectively while balancing energy use, comfort, and air quality.

LHC: I assume that one of important results of this Annex is Pandora database [3] . Could you explain it?

JL: It is a database of source strengths for indoor air pollutants in residential buildings, based on an extensive review of the scientific literature. What I find even more valuable, however, are the tools we developed to process that information. These tools can generate statistical profiles that help you understand what the likely pollutant sources are for the specific type of building you are analysing.

The database provides modelers with realistic and well-founded input data, enabling more reliable estimates of occupant exposure. It is also designed to work in parallel with a second database that aggregates measured indoor pollutant concentrations. Together, these resources help bridge the gap between emissions data and actual indoor air quality outcomes, offering a much more robust basis for both modelling and decision-making. See Figure 2.

Figure 2. Overview of source data included in Pandora database. From [1], page 32

LHC: Based on the Pandora database, what is the biggest threat to indoor environment in residential buildings? People and their activities, emission form materials or outdoor air?

JL: From the perspective of impact on health, emissions from indoor materials are likely the least significant of the three major indoor pollution sources in most everyday situations. In a typical home, activities such as cooking or burning candles tend to have a much greater immediate impact on indoor air quality than emissions from materials.

However, and this is very important, in cases where bad (combinations of) materials or bad installation methods are used, their impact on occupants’ health can be substantial. Unlike short-term activities, problematic material emissions can be continuous and long-lasting, which means even relatively low emission rates can lead to prolonged exposure. So while they may not be the dominant source in most homes, they should not be underestimated when assessing potential health risks.

NCM: I would also add that extreme weather events are changing the picture. Wildfires or heatwaves can rapidly increase indoor contaminant levels, so we need to better understand the health impacts during these events and evaluate how effectively buildings protect occupants, specially ventilation systems. That’s why developing global datasets is so important, as they help us capture how indoor air may change during these types of events.

LHC: Another part of the Annex 86 was about smart materials. Could you explain what you mean by smart material for indoor air quality management?

JL: In general, if pollutants in the air come into contact with smart materials for IAQ management, they are either dissolved, absorbed, or they change/decrease their concentration.

LHC: Could you give an example of a such material?

JL: A well‑known example - one that has been studied for many years - is titanium dioxide (TiO₂). Under exposure to ultraviolet (UV) light, TiO₂ can catalytically decompose volatile organic compounds (VOCs) into smaller molecules. Under ideal conditions, these reactions produce carbon dioxide and water, although in practice they can also generate intermediate or by‑product compounds.

When surfaces are coated with TiO₂ and sufficient UV radiation is present in the room, the material can function as a sink for VOCs by continuously breaking them down through photocatalytic reactions.

LHC: And how long does this work?

JL: As long as there is UV and the access of the VOC’s to the TiO2 is not blocked, it will keep working.

The main focus in our project was on MOFS (Metal-organic frameworks). These are nano size materials that are created specifically to absorb particular pollutants very efficiently. For example, if you compare them to activated carbon, which is a very often used absorbent, they can absorb up to an order of magnitude more formaldehyde and they are easier to regenerate.

You can use this type of material on the surface in buildings. If there are low ambient concentrations of formaldehyde, this could be sufficient to keep absorbing formaldehyde for many years. Or you can use it on the filter medium of an air cleaner and then actively remove the pollutant from the space. MOF’s in general are very interesting materials with lots of potential applications in HVAC systems. Pioneers in MOF development won the Nobel Prize in Chemistry 2025.

LHC: So it is not used in practice yet?

NCM: One of the outputs of the Annex 86 was that we created a prototype air cleaner with a MOFs enhanced filter, but it’s not commercially available. Having said that, in the following Annex I know there is an intention to continue research in this area. Smart materials can help to reduce the problem indoors in the future. See Figure 3.

Figure 3. An example of MOF filter for VOC absorption. From [1], page 61

LHC: Another result of this Annex is that you developed a performance based approach for assessing smart ventilation. Is this going to be implemented in standards?

JL: Well, we’re working on that very intensively at the moment. A new proposed standard for the design of ventilation in residential buildings - EN 15665 - is under review. Many experts are pushing to shift the current prescriptive approach, which focuses on requirements such as fixed air‑change rates, toward a truly performance‑based framework.

This is similar to what we do in thermal comfort standards. They don’t prescribe how many Watt of heat you need to install but what temperature you have to maintain. That’s it. We believe the same approach should be used for IAQ. Design ventilation systems based on their performance in terms of IAQ parameters like there are assessed for example in TAIL, which is an assessing framework discussed in your previous interview [4].

LHC: You already mentioned a following Annex. What do you want to concentrate on?

JL: Initially the project wants to continue developing smart ventilation concepts with a stronger health‑oriented perspective, in collaboration more closely with industry to bring this approach into practice. Achieving this requires performance‑based standards. It also requires a standardized methodology for collecting indoor air contaminant data, so that researchers and ventilation system designers can work with consistent, comparable information. I believe that mitigation solutions and strategies will be one of the key themes moving forward.

This also ties into the latest version of the EPBD and the EN 16798-7 standard, which outlines how airflow calculations should be performed in buildings. At the moment, these methodologies still rely heavily on single-zone and quasi-steady-state assumptions. Yet we have been working with multi-zone dynamic simulation models for nearly 30 years, and we are eager to see these more advanced approaches reflected in future standards.

From my perspective, it is clear that the way we design ventilation systems for residential buildings needs to evolve. As I mentioned earlier, we should shift to performance-based standards that evaluate how systems actually maintain indoor air quality, rather than prescribing fixed design rules. The technology to do this already exists - and homeowners deserve to benefit from it.

Sources

[1]     J. Laverge et al., “IEA-EBC Annex 86: D3 - Methods and tools for the rating of IAQ management strategies,” 2025. [Online]. Available: https://annex86.iea-ebc.org/Data/publications/IEA EBC_Annex 86_D3.pdf

[2]     G. Morantes, B. Jones, C. Molina, and M. H. Sherman, “Harm from Residential Indoor Air Contaminants,” Environ. Sci. Technol., vol. 58, no. 1, pp. 242–257, Jan. 2024, https://www.doi.org/10.1021/acs.est.3c07374

[3]     G. Rojas and M. Abadie, “D2 - An open registry for the rating of IAQ management strategies,” 2025. [Online]. Available: https://annex86.iea-ebc.org/Data/publications/IEA EBC_Annex 86_D2.pdf

[4]     P. Wargocki and C. Mandin, “TAIL: Open-source rating scheme to evaluate the quality of the indoor environment,” REHVA J., vol. 63, no. 2, pp. 68–72, 2026, [Online]. Available: https://www.rehva.eu/rehva-journal/chapter/tail-open-source-rating-scheme-to-evaluate-the-quality-of-the-indoor-environment