People spend a substantial proportion of their time in confined spaces. Approximately 90% of the day is spent at home, work or school, and in traveling [1], so much so that the definition of the “indoor generation” is spreading. In addition, with the advent of the COVID-19 pandemic, the entire world’s population has been forced to stay in confined spaces (especially at home) for long periods of time, which has provided the opportunity to rethink the design and operation of buildings to make them more liveable and efficient in relation to the needs of their users [2].

To improve buildings and their characteristics, the feedback provided directly by users is fundamental information to enable the technical and structural functions to be adapted to the well-being of users [3]. The post-occupancy evaluation (POE), which was introduced in the United States in the 1960s and then disseminated globally, fits perfectly into this context ^[4][5][6][4,5,6]. This assessment consists of a process of analyzing the characteristics and performance of buildings, carried out with particular attention to the perspective of the inhabitant/user of the building. The concept of the POE is that by asking users about their needs and experiences in the built environment, better spaces can be designed and used ^[7][8][7,8]. By building performance, researchwers mean the behavior of the building system, as a whole, when used by the end user, according to their needs [8]. By allowing a “post-dwelling” evaluation, following the actual use of the spaces by the final recipients of the building, the POE makes it possible to identify any discrepancies between the performances modeled in the design phase and those experienced by the occupants. This reveals whether this discrepancy is due to failures in the building design, construction, management or misuse, and it also identifies improvements that can be made. In this way, this approach combines the information collected through the monitoring of the structural and physical parameters that characterize the living spaces and the qualitative and quantitative indications collected through questionnaires, interviews and visits inside the buildings, directly involving the users [9]. All this makes the POE a useful tool for continuous improvement that is capable of providing useful information to all the actors involved in the life cycle of a building ^[10][11][10,11] and that is applicable to any type of building [12].

According to the authors of [13], the POE evaluates the performance of the analyzed environments according to three main types of aspects: functional, technical and behavioral. Functional performance elements relate to the functionality and level of efficiency of a building’s features, including accessibility, adequacy of spaces and facilities, and services, etc. Behavioral performance concerns the interaction between occupant activities and the physical environment provided. Finally, the elements of the technical performance—such as hygiene and the quality of the indoor environment—represent the factors that influence the comfort, health and productivity of the occupants.

The benefits that the POE guarantees, in the short, medium and long term, are as follows [5]:

• Short-term benefits include obtaining feedback from users about problems in buildings and in identifying solutions.
• Medium-term benefits include the feed-forward of the positive and negative lessons learned into the next building cycle.
• The long-term benefits are aimed at creating databases and at updating, upgrading and generating planning and design protocols and paradigms.

The concept of the POE has evolved considerably over time, adapting to different contexts and applying increasingly complex tools for the collection, processing and combination of qualitative and quantitative data. Therefore, the methodologies for POE are different and there are many ways to conduct it, which characterizes the great flexibility of this approach [14].

As people spend most of their time indoors, indoor environmental quality (IEQ) is one of the priority factors influencing the physiological and psychological health of occupants and results in changes in their habits, well-being, and their physical and cognitive productivity ^[15][16][15,16]. The National Institute for Occupational Safety and Health (NIOSH) describes the IEQ as the quality of a building’s environment, related to the health of occupants within it. IEQ encompasses the conditions inside a building (air quality, lighting, thermal conditions and ergonomics) and their effects on the occupants or residents.

As indicated in [17], parameters such as thermal, acoustic, light and air quality could—also taking into account individual factors (age, sex, etc.) [18]—strongly influence well-being and health, while also playing a role in the performance of the building, such as its energy consumption. Demonstrating the direct relationship between the IEQ parameters and occupants’ comfort has been the goal of many studies: ^{[16][19][20][21][22][23]}[16,19,20,21,22,23]. For this reason, the POE method is an ideal approach to analyze the interaction between the factors that make up the IEQ and the users of buildings.

In [24], articles that were published between 2000 and 2015 and that identified and classified many indicators to measure the IEQ dimension within the POE’s applications were analyzed. Using POE, each factor was analyzed from the following two aspects: (i) the values of this particular parameter in the environment were analyzed, and (ii) the perception that users have of this particular parameter was assessed [25].

The scientific literature appears to be very rich in articles that analyze the application of the POE approach to different reference contexts, demonstrating its effectiveness as a study tool and as a support for improving planning, management and behavior in a confined environment, both domestic and economic/productive/services.

Several reviews were also conducted, as summarized in Table 1, each focused on particular aspects assessed by the POE or on specific case studies. In [26] the literature on POE, with a particular focus on the origins, theories, benefits and approaches that make up POE, were reviewed by the authors. Similarly, in [27] the authors conducted a critical and exhaustive review of 146 POE projects since 2010 in order to obtain both a qualitative and quantitative benchmark on this issue. The review in [28] critically examined recent case studies of green building certification systems, such as Leadership in Energy and Environmental Design (LEED), Building Research Establishment Environmental Assessment Method (BREEAM), Green Mark and Green Star. In [29], an analysis of the POE tools to identify the methods applied for the evaluation and the metrics used to measure occupant satisfaction was conducted by the authors. The authors of [30] presented the state of the art on the links between IEQs and the well-being and comfort of occupants, with a particular focus on commercial and office buildings. In particular, the literature has analyzed indoor air quality, sick building syndrome, thermal comfort, acoustic comfort and visual comfort, with the aim of providing indications on some primary parameters that characterize the IEQ. The authors of [17] presented a review of the literature about indoor environmental quality (IEQ) and occupant comfort, identifying the most studied parameters. Similarly, review studies ^[24][31][24,31] identify the factors that distinguish each characteristic aspect of IEQs. In [15], the authors, in assessing the health and satisfaction of occupants in green buildings, also analyzed the design, aesthetics and ergonomics of buildings, which characterize the IEQ.

Considering previous work that has examined POE and the various perspectives for future development that have been described, the purpose of this articlentry was to review and compare the recent literature on the application of POE methodology to provide both a qualitative and a quantitative assessment of the main factors that make up the IEQ. Therefore, the specific focus of this entryreview was the application of one/several/all of IEQ’s variables in the POE methodology, by considering the papers that describe the integration of the IEQ into the POE evaluation.

The contribution to the related literature that this articlentry intends to offer is an analysis of the methods used internationally in POE methodology and of the determining factors in defining the IEQ. In addition, in the discussion some limitations of the current literature are identified to guide future research on this theme.

2. IEQ Parameters

The interaction between the IEQ and occupant satisfaction is very complex. Due to the numerous studies available (e.g., ^{[17][22][36][37][38][39]}[17,22,46,50,106,146]), it has been shown that the IEQ has a direct short- and long-term effect on the comfort, health and productivity of the occupants of buildings. Therefore, to analyze these aspects, the POE also contributes to the evaluation of all the possible factors [31]. As reported in [25], the factors that influenced IEQ and occupant satisfaction can be divided into physical factors (thermal comfort, indoor air quality, lighting and acoustic environment), which can be assessed by corresponding measurable parameters and non-physical factors (layout of space, privacy, cleanliness, facilities, and the view from the building) that are difficult to measure with tools. Most of the authors (88%) considered the IEQ parameters in the case studies described as supporting elements for understanding occupant satisfaction and for planning possible improvements. In some cases (21%), the IEQ factors were not taken into account. The authors of ^[40][147] compared the expected and actual energy performance of non-residential buildings and applied the POE to produce more accurate energy performance models. The authors of ^[41][81] used the POE to prioritize maintenance work to achieve the maximum occupant satisfaction. The authors of ^[42][68] aimed to improve the accuracy of buildings’ energy simulation, through the evaluation of occupant behaviors. The authors of ^[43][67] evaluated the functional performance of entrance spaces in apartments in the Kurdistan region of Iraq. With respect to the physical parameters, the analyzed authors described whether or not the evaluation of the POE was completed by in situ measurements, or whether the evaluation was carried out solely by qualitative assessments and judgments, provided by the users of the spaces investigated. In this case, there was a greater balance: 43% expected physical measurements, while 57% of the authors only made qualitative assessments. Some case studies that complemented the POE surveys with field measurements were as follows: ^[44][148], alongside the questionnaires, the authors also measured the temperature, relative humidity, noise, light, and CO2 concentrations in the case study of Universiti Teknologi PETRONAS’ new academic complex; the authors of ^[45][149] measured the brightness of highly glazed modern buildings, which require solar protection to ensure the visual and thermal comfort of the occupants; the authors of ^[46][150] detected the temperature and relative humidity trends in houses in the hot and humid tropical climate of Darwin; the authors of ^[47][151] measured the brightness in collective housing in Algeria; the authors of ^[48][152] measured different physical parameters (temperature, relative humidity, noise, light and CO2 concentrations) for a comparative study on green and conventional malls in Beijing, China; the authors of ^[49][61] focused on noise measurements to improve the acoustic performance of residential buildings in Turkey. Conversely, some authors only carried out qualitative evaluations, as follows: the authors of ^[50][135] analyzed the relationship between defects and occupant satisfaction and loyalty in build-then-sell houses; the authors of ^[51][86] assessed how maintenance features might affect occupant satisfaction; the authors of ^[52][71] analyzed the demand for space in the common areas of student residences in Iran; the authors of ^[53][153] applied the POE to understand how occupants perceive wood in built environments; the authors of ^[54][129] analyzed how the social dimension of physical space in educational contexts can explain a student’s academic achievement. Considering only the 157 articles that provided qualitative and/or quantitative assessments of IEQ’s physical parameters, Table 25 reports the frequency of analysis of the four categories proposed in [25]: thermal comfort, indoor air quality, lighting and acoustics. For each variable investigated, the main types of tools used for measurement were also reported, as support elements for the design of measurement campaigns, which are useful for the use of the POE methodology. All categories were considered by a significant number of authors. The thermohygrometric evaluation of environments was the most considered category (85%), in particular, by measuring the temperature, relative humidity and atmospheric pressure. The authors of ^[55][154] described the importance of thermal control for building occupants and facility managers. The authors of ^[56][155] described the case study of a LEED gold-rated university building, in which thermal comfort was analyzed as an IEQ factor. In ^[57][42], with a case study of university dormitories in China, they described residential satisfaction, which was also linked to thermal comfort. In ^[58][118], in evaluating the performance of an agri-food building in Italy, they measured the indoor heat levels in hot and cold seasons. In two studies, ^[16][59][16,156], the authors measured the thermal conditions in green office buildings in Jordan. In ^[60][157], evaluating 20 office buildings, they measured the lighting levels as a factor in visual comfort and workplace productivity. The authors of ^[61][158] analyzed the internal conditions of the Arts Tower (Sheffield, UK), also through light measurements. The authors of ^[62][159] analyzed the physical quantities of lighting in an open plan office to assess the layout of the environment and the effect on the occupants. The authors of ^[63][160] compared green office buildings with different levels of energy consumption intensity, using light measurement as a rating indicator. The authors of ^[64][161] analyzed the IEQ of platinum, green-certified office buildings in Malaysia, assessing thermal comfort, indoor air quality, acoustics, lighting, furnishings and cleanliness. The authors of ^[65][162], by monitoring the performance of four social housing units certified to the Code for Sustainable Homes level, measured CO₂ levels as a representative parameter of indoor air quality. Likewise, the authors of ^[66][115] applied CO₂ measurements as an air quality indicator to assess energy-certified buildings. The authors of ^[67][54] also used this indicator to assess the quality of office space at an Australian urban university. In ^[68][163], the authors verified occupants’ satisfaction with the indoor environment at work, through the qualitative assessment of indoor air quality. In ^[69][164], for the assessment of green office buildings, they measured many air pollutants, such as CO₂, PM2.5, CO and formaldehyde. The authors of ^[70][165], in a zero-carbon building, measured CO₂ and PM2.5 concentrations. Finally, noise was analyzed in 62% of the papers collected. The authors of ^[71][166] quantified several key factors influencing occupant satisfaction in higher education institutions in the USA and Lebanon, considering acoustic quality as one of them. The authors of ^[72][167] analyzed the environments of university buildings in Chongqing, China, through questionnaires and occupant measurements. The authors of ^[73][168] analyzed the office plan of the Land Rover/Ben Ainslie Racing (LR/BAR) team’s headquarters in Portsmouth, UK. A comparison was made between the measurements with the occupants’ perception of comfort with respect to the same parameters. The authors of ^[74][169] examined occupant satisfaction in three excellent BREEAM-certified buildings at Coventry University, in the UK. Qualitative assessments were carried out on the perceptions of the occupants, evaluating the thermal environment, indoor air quality, as well as the visual and acoustic environment. The authors of [11] analyzed satisfaction in the office buildings of the University of Southampton (UK), by measuring and evaluating the thermal, acoustic and air quality of the indoor environment.