On the Active Involvement of Occupants for Improving the Thermal Resilience of Buildings: An Opportunity Still Overlooked

Abstract

Climate change and extreme weather compromise building energy performance and Heating, Ventilation, and Air Conditioning (HVAC) systems, impacting occupant wellbeing and health. However, occupants can naturally adapt through their behaviors, representing a form of intrinsic resilience that enhances the building’s capacity to handle thermal extremes. This study explores the role of occupants in buildings’ thermal resilience; it begins by investigating passive and active strategies commonly discussed in the literature, then analyzes whether occupants are treated as passive or active subjects with adaptive capacity. Four databases were consulted, and 22 peer-reviewed papers were screened based on the following criteria: a clear definition of thermal resilient buildings, inclusion of at least one quantitative method for assessing whole-building resilience, original scientific contribution, and a focus on whole-building rather than component-level resilience. Analysis highlights that the intrinsic thermal resilience of occupants has received limited importance in current discourse on building resilience; in most studies (12 out of 22), occupants are treated as passive thermal loads, with no adaptive behavior considered. This study also suggests examining strategies traditionally used in energy efficiency and indoor comfort as a preliminary approach to encourage adaptive behaviors, and, above all, opens a discussion on integrating occupant behavior into resilience strategies.

1. Introduction

In recent years, as stated by reports from the United Nations Office for Disaster Risk Reduction (UNDRR), the frequency and severity of climate change-related extreme weather events, and related disasters, have been rising significantly [1,2]. Similarly, the Second Assessment Report of the Urban Climate Change Research Network (UCCRN) emphasizes that cities are notably susceptible to climate-related disasters due to the interconnectedness of urban infrastructure, population growth, and economic dynamics [3].

This urgency is reflected in global and regional policies, like the United Nations Sustainable Development Goals (notably Goal 11, which promotes resilient, sustainable and safe cities) [4], and in various European strategies addressing climate change and energy [5,6,7]. Among these, the Next Generation European Union (EU) initiative [8], integrated into Italy’s National Recovery and Resilience Plan (PNRR) [9], plays a key role in promoting sustainable development.

Scientific research has also intensified its focus on these challenges, particularly in developing strategies for mitigation and adaptation [10], incorporating innovative technologies [11,12], and adopting life cycle approaches to assess sustainability and resilience [13,14,15]. Moreover, there is growing awareness of the importance of engaging building occupants in enhancing the resilience of the built environment [16].

Resilience itself is a broad and multidisciplinary concept. Within the building sector, resilience—particularly thermal resilience—has garnered increasing attention as a means of countering rising temperatures and extreme weather events. Although this topic is still evolving, recent studies have begun making progress in this area [17,18,19].

Ultimately, climate change-driven events pose a significant threat to urban environments, not only by influencing buildings’ energy and environmental performances [20,21] (given that they account for about 40% of urban energy usage and emissions [22,23]) but also by impacting occupants’ health [24,25,26].

1.1. Struggles Brought by Climate Change-Related Extreme Weather Events to the Built Environment, Buildings and Their Occupants

Exposure to extreme weather occurrences related to ever-higher temperatures (such as heat waves) not only leads to thermal discomfort for people but also increases health risks, the probability of developing chronic diseases (e.g., respiratory, cardiovascular, hormonal, neurological, etc.), and mortality rates [27,28,29]. Furthermore, these extreme events may cause problems to medical infrastructure, reducing its capacity to respond effectively [27,30,31].

In line with these observations, in July 2023, the World Health Organization (WHO) European Regional Office, for the first time, declared climate and extreme weather-related disasters an emergency affecting public health in Europe [32]. This declaration underscores the severity of the issue.

Comparing the occurrences of climate change-related natural disasters to their impact on human life, measured by the number of deaths, in Europe, it was found that between 1970 and 2019, a total of 1672 natural disasters and 159,438 deaths were recorded. Natural disasters were mainly caused by floods (38%) and storms (32%). On the other hand, deaths were mainly due to extreme temperatures (93%) with a total of 148,109 lives lost over the 50 years [33].

The Mediterranean region is one of the European areas most frequently affected by high-temperature heat waves, resulting in a higher increase in deaths during these events [27].

Regarding annual mean temperatures, a review of the literature has shown how climate change has led to a steady growth in global mean temperatures over the past 60 years, reaching an increase of more than 1.5 °C [34].

Increasing global temperatures cause a decrease in thermal comfort for occupants and lead to a rise in buildings’ energy consumption, as cooling needs increase dramatically, while (conversely) energy demand for heating tends to drop, causing a shift in thermal energy demand in the direction of cooling rather than heating requirements [17,35].

It should also be considered that during periods of extreme heat and power failures (likely due to a sudden increase in energy demand), buildings that rely on Heating, Ventilation, and Air Conditioning (HVAC) systems may turn out to be unlivable, as indoor temperatures can escalate beyond levels tolerable for human comfort [36].

In addition, most buildings rely on constant external energy supply and on effective active systems to ensure safety and comfortable indoor conditions for their occupants. This circumstance makes buildings and their occupants more vulnerable to climate change and especially to extreme heat events [37]. In fact, as shown in Figure 1, which was created by the authors based on their understanding of the relevant published literature, extreme temperature events result in increased electricity demand. This, in turn, leads to an increase in outdoor air temperature with the consequent intensification of the Urban Heat Island (UHI) effect (further worsening the building’s environmental performance) [38]. At the same time, increased energy demand can lead to the occurrence of power outages [39], which, if persistent, can lead to additional overheating conditions inside buildings during the summer.

Figure 1. Effects of extreme heat events on buildings and well-being and health of the occupants.

Given the above, and as the world continues to warm, and heat waves grow longer, more frequent, and intense, it is essential to design thermally resilient buildings that can withstand these climate changes.

According to a definition found in the literature, thermally resilient buildings are buildings that are resilient to an increase year by year of the average temperatures and capable of ensuring indoor thermal safety and comfort for their occupants across their entire lifespan, especially in the course of climate change-related extreme heat events and/or failure of the building equipment caused by power outages [40].

To avoid this last inconvenience (i.e., power outages), buildings’ thermal resilience could be increased using passive measures, which unlike active solutions do not require any energy supply. Indeed, using passive design strategies for addressing climate change minimizes the need for intensive HVAC systems and promotes the development of thermally resilient buildings [41].

However, in addition to investigating highly efficient passive—as well as active—solutions, the authors believe it necessary to study the inherent thermal adaptive capacity of building occupants to changing environmental conditions as this can greatly influence the energy demand and consequently the degree of thermal resilience of buildings [37].

1.2. Strategies of Occupant Adaptation to Face Climate Change Impacts

According to the well-known and widely utilized Fanger’s model, indoor thermal comfort of people can be evaluated using the Predicted Mean Vote (PMV) and Predicted Percentage of Dissatisfied (PPD) indicators, which are only applicable in conditions where occupants are fully acclimatized to the indoor environment [42]. However, this model has limitations in the adaptive context because it assumes people are passive recipients of their thermal environment whereas in reality, they continuously interact with it. Indeed, Nicol and Humphreys, in the 1970s, proposed a dynamic interaction between occupants’ perception of thermal comfort and their adaptive behaviors within buildings. This interaction could explain the broader temperature range that individuals tolerate in real-world settings, surpassing the predictions made by conventional rational models such as PMV/PPD. Hence, people cannot be considered merely passive receptors of the thermal environment they occupy, but they constantly interact with it; therefore, “…if a change occurs that produces discomfort, people will tend to act to restore their comfort…”. Accordingly, to preserve their thermal comfort individuals can adopt three main types of approaches: behavioral, physiological, and psychological [37,43]. Factors of behavioral, physiological, and psychological adaptation have therefore been developed and incorporated into various adaptive heat balance models [44,45,46,47].

Regarding the behavioral strategies, there has been growing interest within the scientific community in understanding how occupants interact with and modify the environment to achieve comfortable conditions. A detailed list of possible behavioral strategies is given in Table 1.

Table 1. Examples of some adaptive behaviors that buildings’ occupants can employ to accomplish thermal comfort during heat waves [16,37,44,48,49,50,51].

Adaptive Behavior Category	Action to Be Performed
Person-related	Adjusting clothing layers Modifying diet Showering more often Refresh limbs (e.g., arms and feet) with cold water Use wet towels Change posture/location/orientation
Building-related	Use lighter bedclothes Opening/closing/adjusting windows and/or shadings and/or doors Switch on fans and/or Air Conditioners (ACs) Switch off unused/superfluous electric equipment
Activity-related	Postpone and/or reduce non-urgent physical activities Keep informed of weather forecasts (and any related alerts) Keep up to date with health protection guidelines

In this context, when aiming to categorize occupants’ thermal behavioral strategies, two major types of actions can be identified: (i) changing environmental conditions to achieve their thermal comfort; (ii) tuning their comfort temperature to align with environmental conditions [37].

Concerning the physiological approach, adjusting autonomic thermoregulatory responses enhances the body’s capacity to handle ongoing thermal stresses [52]. Heat acclimation is characterized by a decrease in core temperature at rest, a lowered heart rate in physical exertion under elevated temperatures, and an increased rate of sweat production. Repeated exposure to elevated temperatures that significantly disrupt homeostasis—manifested through increases in core body temperature, skin blood flow, and sweat production—promotes physiological adaptations. Ultimately, these adaptations contribute to a reduction in subsequent heat strain and enhance overall acceptance and resilience to heat [30]. Conversely, the body’s physiological reaction to cold exposure involves alterations in both core and skin temperature; in fact, the body reacts by increasing metabolic heat production and minimizing heat loss, via constriction of blood vessels in the skin and shivering thermogenesis. Under cold conditions, three main actions have been identified: habituation, metabolic adaptation, and clothing insulation modification. These involve increased thermogenesis and enhancement mechanisms for conserving body heat [53].

Finally, psychological adaptation refers to changes in perception, expectations, and attitude towards environmental temperature [54]. Notably, some studies have considered the psychological state in the assessment of occupants’ thermal well-being [55,56,57,58], reaching the conclusion that, usually, models dealing with adaptive heat balance cope with psychological adaptations in a qualitative way rather than quantitatively, restricting their precision and applicability [54]. It was also shown that thermal comfort is not just a physical occurrence but is also closely connected to psychological well-being [59]. However, these studies have limitations regarding the nationality and age of analyzed people, as well as a lack of consideration for diverse climatic regions [60,61,62,63,64,65].

It is therefore evident how the previously discussed adaptive strategies, along with technological measures, can contribute to improving the buildings’ thermal resilience. Occupants, in fact, through their behavioral adaptation, could adjust their thermal comfort requirements/expectations by accepting a wider range of indoor temperatures. This would lead to a reduction in peak power demand, thereby resulting in reduced power interruption hazard and thus avoiding and/or reducing the possibility of thermal discomfort occurrences and related health hazards [66,67,68]. However, although human physiology has a certain capacity to adapt to changing climates [69], this adaptability alone may not be sufficient to ensure thermal comfort, given the uncertainties of future climate conditions [35].

Despite increasing interest in thermally resilient buildings, no studies to date—at least to the best of the authors’ knowledge—have explicitly explored how the intrinsic resilience of occupants can be meaningfully integrated into the broader framework of thermally resilient buildings.

1.3. Scope and Aim of This Paper

This work situates the theme of occupants’ thermal behavioral adaptation and the strategies to promote it within the broader context of building thermal resilience to extreme temperature events. The physiological and psychological aspects are not considered in the present analysis.

The main aim is to explore the role of occupants in thermally resilient buildings, with a focus on how their adaptive behaviors are addressed in existing literature. Rather than a formal literature review, this study draws on the literature to support a broader reflection on how occupants’ intrinsic resilience is currently recognized and valued.

For the sake of clarity, it is worth noting that at this stage of the analysis, our aim is not to distinguish between heat-oriented and cold-oriented resilience. Therefore, the findings are intended to be broadly applicable to resilience in the face of both heat and cold extreme weather events.

Before presenting the methodology and materials, a brief overview of the most effective technical solutions from previous research is provided to better contextualize the role and potential of occupant behavior in enhancing buildings’ thermal resilience.

2. A Glance at the Technologies and Design Strategies to Improve Buildings’ Thermal Resilience and Reduce the Risk for Occupants

This section presents the main technical solutions identified in the literature to improve the thermal resilience of buildings, classified into two categories based on their energy use: passive and active (Table 2). In addition to a brief description, the table shows how the reported solutions enhance the thermal resilience of buildings. For the sake of clarity, passive solutions—marked with the letter “P”—operate without external power, making them especially useful during power outages. In contrast, active solutions—marked with letter the “A”—depend on power sources such as the electrical grid, batteries, or on-site backup systems [40].

Table 2. Design strategies and technologies previously studied by researchers for their potential to enhance the buildings’ resilience to rising temperatures and extreme heat events (Active = A; Passive = P).

Measure	Type	Description	How It Affects Thermal Resilience	Ref.
Orientation and Layout	P	Building orientation refers to how a building is positioned relative to the sun and wind, while building layout refers to how rooms and spaces are arranged inside the building.	By minimizing the direct afternoon solar radiation and maximizing natural ventilation through windows aligned with prevailing winds, the building stays cooler. Also, a compact layout with fewer external walls reduces the surfaces exposed to direct sunlight, which helps keep the building cooler.	[40]
			Then, both actions reduce discomfort and prevent overheating indoor spaces during hot weather and extreme heat events. Additionally, they allow the building to use less energy for air conditioning, thereby reducing the risk of system failures during heat waves.
Solar Shading	P	It refers to the use of devices such as louvers, blinds, and overhangs to regulate the amount of solar energy entering the building.	By controlling the amount of solar energy entering through windows and other openings, indoor temperatures are kept cooler and more stable. This measure reduces discomfort and prevents overheating indoor spaces during hot weather and extreme heat events. In addition, it allows the building to use less energy for cooling purposes, thereby reducing the risk of system failures during heat waves.	[70,71]
Window Solar Film	P	It refers to the use of thin layers of polyester, metallic, or ceramic material applied to the glass windows that help control the amount of solar energy passing through.	By preventing excessive solar energy from entering through windows, the building stays cooler. This action reduces discomfort and prevents the risk of overheating indoor spaces during hot weather and extreme heat events. Furthermore, it allows the building to use less energy for air conditioning, thereby lowering the risk of systems’ failure during heat waves.	[70]
Thermal Insulation	P	It consists in adding materials such as foam, fiberglass, or cellulose, which have low thermal conductivity, to the traditional layers of walls and roofs.	By reducing the heat flow through the envelope, internal temperatures fluctuate less than external ones. This means lower energy use for cooling, and thereby a reduced risk of system failures during heat waves. In addition, thermal insulation combined with thermal mass delays how quickly the heat penetrates inside (thermal lag). So, during a heat wave, the indoor temperature increase is slower than outside temperature rise. Insulation thus enhances comfort and energy efficiency by attenuating heat transfer through the building envelope.	[72]
Green Roof	P	It is a roofing system that integrates some or all of the following elements into the traditional roofing assembly: waterproof membrane, protection against root action, mechanical protection, drainage, accumulation, filter, growing medium (substrate), and vegetation.	Being constituted by multiple layers—including soil with specific characteristics and vegetation—which provide high insulation, thermal inertia, and thermal mass with respect to traditional roofs, this type of roofing system reduces the heat transfer through the building roof, resulting in less heat entering during summer (and less heat lost in winter). In addition, evapotranspiration from the soil and plant species helps cool outdoor air thus regulating the local microclimate and mitigating the urban heat island effect. Both reduce thermal stress on buildings and lower energy demands for cooling purposes, thereby reducing the risk of system failures during heat waves.	[73,74,75,76]
Cool Roof and Cool Wall	P	It consists in the application of special paints, membranes, and/or reflective tiles on the external surfaces of buildings’ roofs and/or walls typically characterized by white color.	By using materials with high solar reflectance and high thermal emissivity, which maximize the reflection of solar radiation and enhance the emission of absorbed heat, these types of surfaces result in low solar heat absorption. Therefore, they reduce the amount of heat entering buildings, helping to maintain lower indoor temperatures. This decreases heat stress on buildings and lowers energy demand for cooling, which in turn reduces the risk of system failures during heat waves.	[70,75,76,77]
Phase change materials (PCMs)	P	It refers to the use of organic or inorganic materials characterized by melting temperatures in the ambient temperature range. They are used by incorporating them into traditional building materials.	By absorbing and releasing heat, PCMs reduce fluctuations in internal temperatures, stabilizing the indoor environment. This both improves occupant comfort—by preventing rapid overheating during the day and rapid cooling at night—and reduce energy demand for active cooling systems.	[78]
Photovoltaic Solar Panels	A *	These are systems powered by renewable energy that convert solar radiation directly into electricity using solar cells.	By generating electricity on-site, these systems reduce dependence on the power grid. This is particularly important during heat waves, when the risk of power outages and blackouts increases. With greater energy self-sufficiency, buildings can continue to operate properly, ensuring that air conditioning systems remain functional and maintaining occupant comfort and safety.	[40]
Integrated Indoor Microclimate Management System	A	It is a complex system that uses a set of sensors, controllers, and software to monitor the microclimatic conditions inside the building (e.g., temperature, humidity, air exchange, air velocity, etc.).	By constantly monitoring indoor conditions and responding immediately to external climatic conditions changes, these systems help maintain indoor comfort and optimize energy use. This prevents energy waste and reduces energy demand during peak times, helping to prevent system overload or outage.	[79]

* Photovoltaic panels have been considered in this study as an active measure, as they require energy input for operation (through batteries), but unlike other active systems, such as HVAC, they also produce energy. Energy production offsets consumption during outages if paired with storage.

Other technical solutions—both passive and active—have been studied by researchers to increase the buildings’ thermal resilience, although require action by occupants, namely natural ventilation and use of ceiling fans.

As for natural ventilation, it improves the buildings’ thermal resilience by expelling indoor heat without the need for electricity (passive measure). This helps to maintain comfortable indoor temperatures, especially during heat waves or power outage, ensuring the building remains livable even when mechanical cooling systems fail [72]. Regarding ceiling fans, it is a low-power active device with rotating blades that move the air inside the room (active measure). By increasing air movement, it enhances the occupants’ perception of cooling by convection and sweat evaporation, thus improving comfort during heat events with minimal energy use [70].

It is acknowledged that, although passive measures can help mitigate the risk of hazardous conditions, they do not always ensure the safety and comfort of occupants. Therefore, to maintain safe and comfortable environments, it is essential to integrate active systems, backup power sources, as well as energy storage solutions to provide adequate heating and cooling [40]. Additionally, it is recognized that no single strategy can simultaneously enhance the overall thermal performance of the building, improve conditions in the most overheated areas, and ensure day-to-day consistency. Therefore, implementing a combination of strategies is crucial [72].

After summarizing the main technical solutions studied to date by researchers to enhance the thermal resilience of buildings, the following section presents an overview of the methodology and materials used to conduct the research of the present work.

3. Methodology and Materials

By examining how current literature on the buildings’ thermal resilience integrates occupants’ thermal behavioral adaptation, and by investigating the relevance attributed to their intrinsic resilience, the authors analyzed a selection of scientific articles chosen based on criteria they defined.

To inform the conceptual analysis, the authors consulted major scientific databases, including ScienceDirect, Web of Science, Scopus, and Research Gate, to identify relevant literature on climate resilience in buildings. The authors focused on studies published up to and including 2025, written in English, that provide a clear definition of thermally resilient buildings and include at least one quantitative method for assessing resilience at the whole-building level. To guide reflection on the topic, the authors chose to include original contributions published in peer-reviewed scientific journals. Conference papers—despite often presenting emerging ideas—were excluded, as the authors aimed to base this preliminary exploration on fully developed studies rather than work in progress, which is more commonly found in conference papers. Review articles were excluded to avoid information redundancy. The selection emphasized studies addressing whole-building thermal resilience rather than individual components. As a result, the authors identified 22 pivotal articles [21,24,35,36,40,49,50,67,68,69,70,72,78,80,81,82,83,84,85,86,87,88] that support their conceptual investigation. Before presenting their findings, a brief overview of the key characteristics of these studies is provided to support the understanding of the study.

The articles selected in the research span the period from 2019 to 2025 and are published in a variety of scientific journals, as shown in Figure 2. The largest proportion are published in the journal Building and Environment (10 out of 22), followed by Energy and Buildings (4 out of 22) and the Journal of Building Engineering (3 out of 22).

Figure 2. International scientific journals in which the research papers examined in this study are published.

Additionally, the studies encompass a diverse range of countries across North and South America, Europe, Asia, and Oceania, reflecting a variety of climatic conditions worldwide. This diversity is highlighted in Figure 3, which visually maps the different geographical regions where the pertinent case studies were conducted. At present, no works carried out by African countries have been identified, possibly due to limited data availability or publication access.

Figure 3. Geographic dispersion of the literature research papers examined in this study.

Furthermore, the analyzed literature sample can be grouped into three main categories based on the primary objective of each article. Some studies focus primarily on introducing methodologies to measure buildings’ thermal resilience (categorized here as “Metric”), while others assess the effectiveness of specific actions and/or strategies to enhance resilience (categorized here as “Strategies to improve resilience”). A third group (categorized here as “Other”) encompasses (i) exploring the integration between the concepts of sustainability and resilience in buildings, and (ii) specific insights concerning the thermal resilience of buildings. Table 3 displays the distribution of articles across these three categories.

Table 3. Primary objective pursued in the research articles selected in this study.

Main Goal	No. of Reviewed Articles
Metric	10
Strategies to improve resilience	9
Other	3

As observed, most of the articles analyzed (45%) primarily focus on introducing thermal resilience assessment methods for buildings, followed by those that aim to analyze strategies for improving the thermal resilience of buildings (41%).

In addition, the topic of the thermal resilience of buildings is treated in relation to different types of climatic events. Specifically, the literature sample examined covers nine types of events against which thermal resilience is considered (Table 4).

Table 4. Distribution of selected articles by the type of event against which thermal resilience is considered.

Type of Event Against Which Resilience Is Considered	Number of Articles	Main Goals
Extreme hot events	8	Metric, strategies to improve resilience, others
Extreme hot/cold events coincident with power outages	3	Metric, strategies to improve resilience, others
Extreme hot events coincident with power outages	2	Strategies to improve resilience
Extreme hot/cold events	1	Metric, others
Extreme cold events (snowstorm) coincident with power outage	1	Metric
Hot weather	3	Metric, strategies to improve resilience
Hot weather coincident with power outage	2	Metric, strategies to improve resilience
Cold weather coincident with power outage	1	Metric
Hot/cold weather	1	Metric

As can be observed, most of the studies (15 out of 22) focus on extreme hot events and hot weather, both with and without power outages. Five studies examine combinations of hot/cold extreme events with and without power outages and cold/hot weather without power outage. Less frequent (only 2) are studies on extreme cold weather and cold weather. Therefore, the attention is primarily on the thermal resilience of buildings in response to extreme hot events (such as heat waves) and hot weather.

The selected literature was examined to explore whether and how the occupants’ thermal behavioral adaptation is accounted for in the research on thermally resilient buildings.

It is therefore important to note that the analyzed articles also consider the most vulnerable (fragile) individuals among the different types of occupants. More specifically, this group can be divided into two subgroups: low-income individuals (as in the case of residential social housing) and elderly individuals. The latter can, in turn, be further subdivided into three categories: (1) individuals who require continuous medical and nursing support due to chronic illness or physical/cognitive impairment (e.g., occupants of long-term care buildings); (2) older adults who need some assistance with daily activities such as bathing, dressing, medication management, and meal preparation (e.g., residents of assisted living facilities); and (3) independent or semi-independent elderly individuals who live in standard residential apartment settings without the level of support provided in assisted living or long-term care facilities.

4. Results

The results highlighted that in most studies (12 out of 22; 55%) occupants are regarded as passive thermal load sources, i.e., as subjects who do not adjust their environment. Adaptive behavior, meaning occupants are considered as reactive subjects who engage in all available adaptive behaviors in response to the environment, is only considered in some cases; however, this is less than half of the studies (8 out of 22; 36%) (see Figure 4).

Figure 4. How occupants are regarded in the studies examined.

This outcome therefore indicates that the intrinsic resilience of occupants is still given limited importance when discussing buildings’ thermal resilience—at least within the portion of the literature examined.

As indicated in the graph, for two studies it was not possible to confirm that the analysis includes occupants’ adaptive behaviors. This is the case of the work carried out by [50] and by [36]. In both these works, the adaptive behaviors of occupants are mentioned by the authors, and they state to consider shading and ventilation in their analysis, which are two systems that support adaptive thermal comfort. Nonetheless, no details are provided about whether or how occupants interact with these systems. In other words, it’s not specified, for example, that occupants can operate or adjust the shading or ventilation.

Based on this initial finding, the authors aimed to determine whether there is a correlation between the occupants’ roles and the types of buildings studied. In other words, they wanted to see if certain occupant roles are more common in specific building types. This analysis is based on the idea that occupant adaptive behavior is strongly influenced by the building’s physical context and use—for example, a person living in a house can open windows, while an office worker may have little to no control over the indoor environment.

A synopsis of all the investigated studies is provided in Table 5, which offers readers per each study reviewed the category of building(s) analyzed, how the occupants are considered by the researchers, and the specific occupant actions considered. A more detailed description of the types of building(s) considered in the studies, as well as the considerations given to the occupants, along with some article details (authors, title, year of publication, and country of the case-study) is provided in the Supplementary Materials.

Table 5. Category of building analyzed, the way in which the occupants are considered by the researchers, and the specific occupant actions analyzed.

Building Category Under-Analysis	How Are the Occupants Considered?			Considered Adaptive Behaviors
	Passive	Reactive	Passive or Reactive?
Single-family residential building	4	1	-	Shading control
Multi-family residential building	2	4	1	Natural ventilation, AC use, shading control, fan use, thermostat setting
Office building	3	-	1	-
Long-term building (including elderly-occupied residential apartments)	1	2	-	Natural ventilation, shading control, and fan use, controller settings
Building domain	2	1	-	Natural ventilation, shading control, clothing change, and relocating to other parts of the building (or outdoors)
Total number of articles	12	8	2	-

As it can be seen, the identified buildings include both residential and non-residential structures and, in more detail, they can be grouped into four main categories: (1) single-family residential buildings, (2) multi-family residential buildings, (3) long-term care buildings (such as nursing homes and assisted living facilities), and (4) office buildings. In cases when the study considered several categories of buildings the authors assigned the category named “building domain”.

When examining building categories versus occupant roles in more detail, some ambiguity exists in the analyzed studies. In other words, for the same category of building some studies consider the occupants as passive subjects, while others view them as reactive. This highlights that a unified, shared approach has yet to be established, and that research in this area is still proceeding in a somewhat fragmented manner.

Furthermore, as clearly illustrated in Figure 5, perspectives on occupant roles remain divided: 6 out of 22 studies classify occupants as passive subjects, whereas 5 view them as active agents, pointing out that there is no prevailing view to date, at least as far as residential buildings are concerned. In contrast, although only a few studies focus on non-residential buildings, occupants in these cases are predominantly treated as passive subjects.

Figure 5. Distribution of selected articles by type of building investigated and way of interpreting occupants.

Taking into consideration adaptive behavior typically means considering that occupants adjust their actions dynamically in response to the environment—for example, opening windows, adjusting blinds, changing thermostat setpoints, or manually turning the AC on or off based on personal comfort or changing conditions, etc.

Table 6 summarizes studies treating occupants as reactive agents, detailing how these adaptive behaviors are modeled and the specific occupant actions analyzed.

Table 6. Articles from the literature examined in this study in which the occupants’ behavioral adaptation to heat is considered (reactive occupants).

Authors	How Is the Adaptive Behavior of the Occupants Considered? (Original Text Is Reported in Italic)	Considered Adaptive Behaviors
Baniassadi et al. [78]	The authors mention the possibility for the occupants of the modelled building archetypes to control interior blinds, which would imply that occupants might manually adjust (open or close) interior shadings in response to environmental conditions to improve comfort and energy efficiency by controlling solar heat gain and daylight. This control reflects real occupant behavior rather than a fixed schedule. …occupant controlled internal blinds… Conversely, there is a sentence that suggests that heat behavioral adaptation of occupants is not taken into consideration for air-conditioning (AC) system: …for the rest of the year, AC was available and triggered at demand by thermostat (Table 1) and occupancy schedules (Figure 2)… Indeed, this sentence indicates that the AC system would turn on only when needed based on two conditions: when the temperature detected by the thermostat goes outside a set range and when the building or space is occupied; in other words, it assumed fixed comfort thresholds rather than human adaptive behaviors.	Shading control
Samuelson et al. [24]	The authors, during extreme conditions of the power outage scenario, assumed occupants will open windows as needed without restrictions …we made an adjustment to the ventilation control in the model, in order to allow the occupants to open the windows during our power outage period. In the baseline model window operation schedule allows occupants to open windows if the outdoor air is cooler than indoors between 6 a.m. and 10 p.m., limited by the outdoor temperature of 26.6 °C and indoor temperature of 25.5 °C. For the power outage scenario, because of the extreme conditions, we removed all limits to ventilation and let the occupants open windows as needed… A scenario where occupants are in physical or psychological condition which prevents them from opening windows has also been considered. Conversely, there is a sentence that suggests that heat behavioral adaptation of occupants is not taken into consideration always for AC system: …the thermostat setpoints are 20 and 24 C for heating and cooling, with no humidity control. The HVAC is available 24-h throughout the year and runs in response to the occupancy schedule and thermostat demand… Indeed, this sentence indicates that the HVAC system turns on based on two conditions: when the temperature detected by the thermostat goes outside a set range and when the building or space is occupied; in other words, it assumed fixed comfort thresholds rather than human adaptive behaviors.	Natural ventilation
López-García et al. [82]	The authors do explicitly account for different occupant adaptive behavior patterns in their case studies. Indeed, in listing the characteristics of selected case studies, refer to two different user adaptive behavior patterns: one including the use of AC for the period from 0.00 to 8.00 without night ventilation, and one including the use of night ventilation without AC use.	Natural ventilation and AC use
Sheng et al. [70]	The authors do explicitly account for the adaptive behavior of the occupants since it is stated that the occupants can control the temperature setpoint in their bedrooms through the ceiling fan. For example, they assumed that when the ceiling fans are in operation, the cooling setpoint can be increased (to 28 °C) when the space is occupied. …in our study, we assume that indoor air speed increases from the baseline value of 0.137 m/s to 0.8 m/s when the installed ceiling fans operate, and the cooling setpoint can be raised to 28 °C when occupied… In addition, occupant adaptive behavior is explicitly included by modeling realistic actions like shading control and window opening/closing according to indoor and outdoor temperatures and seasonal conditions. …the interior shade measure was modeled assuming rational use by residents—in summer, the shade is deployed during the day and open during the night to reduce daytime solar heat gain and allow night cooling; in winter, it is the opposite, the shade is open during the day and closed during the night to increase daytime solar heat gain and reduce nighttime heat loss from the bedrooms… …the natural ventilation measure was modeled assuming the residents open windows when the indoor air temperature is higher than outdoors during heat waves… During the cold event without power, we assume the residents close windows to stay warm… The study incorporates dynamic, situation-aware occupant behaviors rather than assuming fixed or static conditions.	Natural ventilation, shading control, nd fan use
Borghero et al. [68]	The authors do explicitly incorporate occupant behavior into simulations distinguishing between two types of occupant behaviors: Fixed Behavior: Assumes occupants follow a predetermined schedule for natural ventilation, such as opening windows at specific times. Aware Behavior: Assumes occupants make real-time decisions based on indoor and outdoor conditions, such as opening windows when external temperatures are lower than indoor temperatures. Specifically, the authors considered five scenarios: natural ventilation—fixed (NATVENT-F), natural ventilation—aware (NATVENT-A), mechanical ventilation (MECVENT), air conditioning—fixed (AC—F), and air conditioning—aware (AC—A). The fixed scenarios incorporate the adaptive behavior of the occupants to some extent but with limitations. The aware scenarios do account for adaptive occupant behavior in a meaningful way.	Natural ventilation, shading control, fan and AC use/thermostat setting
Hong et al. [40]	The authors recognize occupants’ behavioral strategies as important strategies—in addition to passive and active solutions and backup power and energy storage technologies—to improve the thermal resilience of buildings especially for buildings that are, e.g., naturally ventilated. However, the discussion on occupant behavior in response to extreme events is mostly qualitative: some adaptive behaviors (i.e., operable windows, moveable shading devices, clothing, and relocating to other parts of the building or outdoors) are cited and it is suggested on the one hand to design buildings with systems that allow occupants to help themselves and on the other hand to promote education and training of occupants in order to make them aware of what should act and how they should act during extreme events.	Natural ventilation, shading control, clothing change, and relocating to other parts of the building (or outdoors) (although it is treated only in qualitative terms)
Younes et al. [69]	The authors developed a control strategy that automatically controls natural ventilation (with motorized windows), mechanical ventilation (through the use of a ceiling fan), and air conditioning (HVAC), which guarantees the maintenance of optimal internal thermal environment with minimal energy consumption. …with the implementation of the proposed method, the operational mode ensures thermoneutral conditions for elderly occupants without requiring their input… Since the strategy does not require any input from the occupants, these latter are considered as passive beneficiaries rather than active participants shaping indoor conditions through adaptive behaviors. However, it seems worth noticing that the heat physiological adaptation of the occupants under analysis, namely elderly individuals, is considered since the control strategy developed uses predictive thermoregulatory and thermal sensation models to simulate the occupants’ responses. Nonetheless, the occupants are given the ability to modify the controller’s settings to accommodate individual preferences and behaviors (offering personalized setpoint temperatures and adapting based on individual preferences and behaviors …to accommodate individual differences in thermal sensation among elderly occupants in this study, they were given the ability to alter the controller’s settings…	Controller’s settings
Tomrukcu and Ashrafian [35]	The authors consider occupant adaptive behavior to some extent through their use of an adaptive thermal comfort model, which inherently assumes behavioral adjustments (like changing clothing, opening windows, or using fans) in response to environmental conditions—especially in naturally ventilated spaces …an analysis of an adaptive thermal comfort model is conducted, focusing on a specific room, such as the bedroom, where only natural ventilation is employed… The focus on a naturally ventilated room further supports this, as it positions occupants as active agents in managing their comfort by adjusting airflow.	Natural ventilation

As can be observed, the frequency of specific adaptive behaviors reported across the eight studies that consider occupants as reactive subjects varies. Specifically, natural ventilation is mentioned in 5 out of 8 studies, shading control in 3, fan use in 2, air conditioning use in 2, and settings control (e.g., thermostat adjustments) in 2 studies. In this summary, the authors do not consider the actions mentioned in the Hong et al. study, as the behavioral adaptation is addressed only in qualitative terms.

5. Discussion

In this section, the authors discuss the results of their analysis of the role of occupants in research on thermally resilient buildings. They also suggest examining strategies traditionally used in energy efficiency and indoor comfort as a preliminary approach to identifying appropriate strategies for encouraging occupants to put their intrinsic resilience into practice.

5.1. On the Role of Occupants in Research on Thermally Resilient Buildings

Our interest in building occupants stems from the understanding that a building’s performance is influenced not only by its design, installed systems, and the local climate, but also by the behavior of the people who live in or use it.

It is important to recognize occupants’ intrinsic ability to adapt through their actions and behaviors. In building performance research, occupants are typically conceptualized as either passive or reactive sources of thermal load.

As previously discussed, it is therefore essential to understand how to incentivize occupants to fully exercise their own intrinsic resilience. In the following a brief discussion on how to encourage occupants to adopt adaptive behaviors.

What emerged from the analysis is that little attention is still given to how human behaviors, such as clothing choices and changes, acclimatization, and the use of local cooling strategies (fans, portable air conditioners), can affect buildings’ thermal resilience. Greater emphasis is placed on the “building-plant” system when it comes to strategies to improve building thermal resilience. In other words, the intrinsic resilience of occupants, i.e., the occupant behavioral adaptation, is still given limited importance when discussing building thermal resilience—at least within the portion of the literature examined. In addition, between the two common ways of interpreting occupants, i.e., passive or reactive subjects, there is still no prevailing view to date, at least as far as residential buildings are concerned. Ultimately, even when adaptive behaviors are included in studies, they typically focus on a limited set of occupant actions, namely opening/closing windows, adjusting blinds, and turning fans on or off. Other adaptive behaviors such as modifying clothing or activity levels generally are not addressed.

These outcomes highlight a clear gap in current research on thermally resilient buildings. Addressing this gap is essential, as integrating behavioral adaptation with technical resilience measures—often designed without fully accounting for occupant behavior—can improve understanding of building performance under extreme (heat) conditions and lead to more accurate predictions and better-informed design and retrofit decisions.

5.2. On the Strategies to Encourage Virtuous Behaviors by the Occupants to Make Buildings More Resilient

It cannot be overlooked that encouraging adaptive behavior generally leads to more cost-efficient management of the indoor thermal conditions. Therefore, raising awareness about this potential could be an effective strategy to motivate them.

Nonetheless, in search of possible strategies to encourage occupants to adopt adaptive behaviors, the authors propose to examine the literature that has dealt with the relationship between energy saving in buildings—for the purposes of thermal comfort for occupants—and occupant behavior. Specifically, in the following they propose a brief review on how such behavior has traditionally been addressed in terms of energy efficiency and indoor comfort with the aim to identify possible common ground between these well-established approaches and resilience-oriented strategies. This proposal is grounded in the assumption that there is a connection between energy-efficiency behaviors and buildings’ thermal resilience. Specifically, behaviors that reduce reliance on mechanical cooling (e.g., by lowering energy consumption for air conditioning) decrease the strain on energy systems during extreme heat events. This, in turn, reduces the risk of system failures and enhances the building’s resilience to heat waves.

Historically, attention paid to the presence of occupants inside buildings has been aimed primarily at obtaining information needed to evaluate energy use and indoor comfort through Building Energy Performance Simulation (BEPS) software. For this purpose, the technique shared by several authors is the use of questionnaires to assess buildings characteristics and occupants’ behaviors (in terms of specific actions) which directly impact energy consumption to define parameters like the following: people presence and occupancy rates, and correlated heat gains (e.g., hourly/daily/seasonal occupancy hours,); techniques of adaptive behavior (e.g., clothing adjustment); ventilation rates (e.g., opening windows frequency, shading operation); and domestic appliance equipment, to deduce indoor heat gains and electrical/thermal loads (e.g., average number of domestic appliances and time of use, thermostat/HVAC control/adjusting, electrical devices/lighting switch on/off) [89,90,91].

Regarding the interaction between energy conservation and comfort, according to a study related to lighting performance (which is an aspect that is easy to act on in terms of interaction with occupants) optimizing user-centered applications by coupling them with post-occupancy automatic measurements (such as, through sensor fusion and integration) holds significant potential for enhancing comfort and achieving energy savings [92].

It is generically acknowledged that action influencing energy use related to heating, cooling, electricity, and lighting has to be considered [93]; indeed, results from the literature show that changes in building occupants’ behaviors could result in 10–40% overall energy savings [90]. However, it is pointed out how obtaining a precise estimate regarding the actual contribution provided by the actions implemented in terms of achievable energy savings remains challenging, since various personal factors (psychological and/or physiological) that have an important bearing on occupants’ behavior, and more closely related to comfort, are difficult to predict and/or influence (primarily due to the complex nature of users’ actual behaviors).

Another perspective with which to look at the interaction between occupants and buildings is one that goes beyond the single action/behavior to be taken but looks more broadly at strategies to spur occupants (and especially younger generations) to adopt more energy and environmentally friendly behaviors. Also, in this case, it is suggested to use on site measurements and questionnaires to get information on occupants’ behavior aimed at improving knowledge and/or use ad hoc leverage/incentives [94]. As for possible specific methods to influence occupants in adopting more sustainable and resilient behaviors, based on outcomes from literature, three strategies could be suggested: eco-feedback (a system that offers building occupants insights into their past and present energy usage—usually expressed in kWh or CO₂ emissions), social interaction (a comparison and/or occupants ranking within an established system that enables occupants to compare their energy consumption profiles), and gamification (an interactive experience that leverages/incentivizes processes of observational learning and incorporates information about individual behaviors) [93]. Gamification in particular represents the most innovative and young-people-friendly technique. In fact, results of a study aimed at evaluating the influence of gamification methods on occupants’ energy behavioral transitions show how significant energy savings (between 60% and 80%) could be achieved in residential, higher education and office buildings, while the effect on other public buildings (such as hospitals and healthcare centers) is very limited. The study also examined the effectivity of various gamification design items in optimizing use of resources and energy usage through different implementation techniques, highlighting the following percentages of achievable energy consumption savings based on the different adopted technique: Internet of Things (IoT) and Graphical User Interface (GUI)—up to 40%; Information and Communication Technologies (ICT)—between 15% and 30%; App—up to 20%; Human–Machine Interface (HMI)—up to 15%; Web-based—up to 10%; and Software—up to 8% [95]. The adoption of such techniques, relying on reward-based strategies, could help in enhancing resilience adaptive actions, especially during extreme weather-related events like power outages. By getting immediate positive feedback or tangible benefit people are more motivated to adopt these adaptive actions. Furthermore, challenges that could affect the effectiveness of these actions, such as privacy concerns, can be overcome by using blockchain-based systems for the exchange of information and/or IoT-based feedback.

To summarize, in general it is possible to make a distinction between two main types of interaction between occupant behavior and environmental energy performance of buildings: (i) the possible specific actions that occupants can take in order to improve both indoor comfort and energy performance of buildings, and (ii) the possible approaches/methods by which occupants can be informed and incentivized to engage in more energy and environmentally friendly behaviors.

As for point (i), the context seems to be more defined; and it was indeed possible to identify the main actions to be taken to improve the energy and comfort performance of a building, as shown in Supplementary Materials.

While, relative to point (ii) making occupants more informed and aware of the energy impact that the dynamics of the interaction between personal behavior and energy expenditure turns out to be a fundamentally important aspect; in fact, this serves as a prerequisite to incentivize occupants to adopt specific behaviors that are more energy sustainable, while ensuring that comfort conditions are guaranteed. Although the topic is of relevant interest and much debated in literature, there does not yet seem to be a shared approach/strategy regarding these two issues. However, based on the literature review conducted for this study, two strategies can be referred to: eco-feedback as an effective method for influencing and promoting resilient behavioral knowledge, and gamification as an innovative opportunity to encourage behavioral transitions towards resilient actions.

The reflections presented above on how occupant behavior has typically been examined in relation to energy efficiency and indoor comfort in buildings may serve as a foundation for identifying areas of overlap between these established frameworks and specific thermal resilience-focused approaches.

6. Conclusions

The overall contribution of this study is to initiate a focused discussion on incorporating the intrinsic resilience of occupants—specifically their adaptive behaviors in response to extreme temperature events—into the broader discourse on the thermal resilience of buildings.

6.1. Summary and Main Findings

First, this study investigated the extent to which occupants’ thermal adaptive behaviors are considered alongside traditional technological solutions as part of the strategy to enhance the thermal resilience of buildings. To this end, this study examined a focused selection of the literature.

The analysis revealed a significant gap: the intrinsic resilience of occupants, i.e., the occupant behavioral adaptation, is still underrepresented in current research, in fact less than 50% of the studies consider adaptive behaviors. Instead, current research primarily emphasizes technological innovations within the “building-plant” system (e.g., HVAC systems, materials, and structural enhancements), rather than on occupant-related strategies. Based on this result, a question does arise: may an “occupant-enabled resilience” be assumed as a new paradigm that challenges traditional PMV/PPD models?

Additionally, no prevailing perspective on occupant roles (passive vs. reactive) has emerged, especially in the context of residential buildings. When considered, occupant behaviors are often limited to window operation, blind adjustment, and fan use, while other adaptive actions like clothing or activity changes are largely ignored.

Second, this study questioned how to encourage occupants to adopt virtuous behaviors that enhance buildings’ thermal resilience. As a preliminary approach, it proposed reviewing effective strategies from energy efficiency and indoor comfort research to identify transferable methods. Eco-feedback and gamification emerged as promising methods to motivate occupant behavior changes, offering a valuable and actionable starting point for thermal resilience-focused strategies.

6.2. Limitations of the Study and Future Developments of Research

This research seeks to support the transition toward carbon-neutral buildings and highlights ways they can be modified to cope with future climate conditions. However, it must be acknowledged that to enable occupants to practice their intrinsic resilience, buildings should be designed to support occupants’ capacity to adapt to a broader range of thermal conditions. Therefore, more research exploring how buildings can be designed to support these adaptive behaviors needs to be performed.

Regarding the limitations of this study, note that only the literature singled out through the established keywords and eligibility criteria was considered. As a result, the findings and conclusions apply solely to the studies captured by these specific criteria. Future research should broaden the literature base to achieve a more comprehensive understanding. To this end, starting from the selection of 22 papers (that represent the reference in this conceptual work), three possible criteria for future iterations might be considering articles that cite those assumed as a reference in the conceptual work; using keywords most frequently present in the reference articles; and focusing on words that are recurrent in the titles of the reference articles. The advanced investigation of the so-identified studies posits two questions. The first question is how to evaluate the integration of occupant adaptive behavior into resilience studies. In this regard, one hypothesis might be to count the adaptive behaviors implemented during the study over the total listed in Table 1, also introducing a tentative weighting factor for each behavior. Alternatively, a threshold-based scoring system based on the number of behaviors adopted might offer another viable method. In addition, the number of possible interactions considered between adaptive behaviors with passive/active building strategies should be accounted for. In this regard, it should be noted that enabling adaptive behaviors may reduce the use of active systems such as advanced Building Management Systems (BMS); this would reduce energy consumption, make some systems partially independent from the energy supply, thus less vulnerable during power outages, and ensure a greater occupant acceptance of the environmental indoor conditions. The second question is how effective occupant actions are especially with reference to the occupants’ adaptation to extreme weather events. Currently, there are no established methods that allow technicians to systematically evaluate the impact of occupant behavior in such assessments. Therefore, further research is needed. For instance, comparing the energy performance of a building managed by traditional sensors (e.g., thermostats) with that of a building managed through the adaptive capabilities of the user could provide meaningful insights and inform suggestions. In this regard, to compare performance, metrics such as energy savings and occupant comfort levels could be used.

From a modeling perspective, in order to comprehensively evaluate thermal resilience, it needs to start thinking about how to integrate the adaptive behavior into building energy simulation models, such Energy Plus.

On the other hand, the implementation of case studies to test gamification and eco-feedback in thermally resilient buildings could serve as empirical validation with a view to propose guidelines and/or policy recommendations for integrating occupant education, in terms of adaptive behaviors, into standardized building codes.

As a future research direction, we also highlight the importance of integrating established behavioral change theories—such as the Theory of Planned Behavior and Social Cognitive Theory, which explain how people decide to engage in certain behaviors [96]—into the development and testing of effective strategies. In this context, examining how physiological (e.g., heat acclimation) and psychological (e.g., mood states) factors interact with behaviors would be valuable to strengthen the holistic view of occupant resilience.