Indoor Environmental Quality Factors Research Articles

Argumentation for Impact of Indoor Environmental Quality on Users’ Performance: Online Self-assessment Questionnaire.

When constructing a building, it is easy to forget that the success or failure of any project may rest on its indoor environmental quality (IEQ). Healthy and comfortable employees are often more productive especially considering that people spend 90% of their time indoors (LEED V4, 2014). The aim of this paper is to find out Indoor environmental quality factors that office building users are concerned with the most and to figure out which factors are having the greatest effect on their performance and satisfaction. The data analyzed and discussed in this paper was collected using an online self-assessment questionnaire. Self-assessment questionnaire is considered a method of applying post occupancy evaluation for a building, reliability of this approach is being relevant to everyday office work and can deal with descriptive, qualitative and subjective characteristics. Responses of 118 office occupants in Egypt showed that 32.7% voted for thermal comfort as the indoor environmental quality factor having the highest effect over their work performance. When asked about sources of dissatisfaction in the office environment, Problems related to visual comfort earned 36.1 % of the overall dissatisfaction sources, these problems were presented in the lack of having a window, window area is too small, insufficient daylighting, poor lighting levels, glare on computer screens, and lack of outdoor natural views within the workspace.

Clustering of Dutch school children based on their preferences and needs of the IEQ in classrooms

BackgroundIt is well-known that indoor environmental quality (IEQ) in classrooms can have an effect on school children's comfort, health and performance. Unfortunately, information about the school children's perception of IEQ factors in their classrooms is still insufficient. The objective of this study was to better understand school children's IEQ preferences and needs in classrooms. MethodsPerceptions, preferences, and needs regarding the IEQ in classrooms were collected by a questionnaire from 1145 school children (9–12 years) in 21 primary schools (54 classrooms) in the Netherlands. Descriptive analysis, correlation analysis, principal component analysis and two-step cluster analysis were used to analyse the data. ResultsUsing two-step cluster analysis, this study identified six clusters (profiles) of children based on their comfort perceptions and the importance of environmental factors. Among them, four clusters of children had specific concerns related to the IEQ factors: the ‘Sound concerned cluster’, the ‘Smell and Sound concerned cluster’, the ‘Thermal and Draught concerned cluster’, and the ‘Light concerned cluster’. However, the other two clusters of children did not show a specific concern, the ‘All concerned cluster’ was concerned about all IEQ factors in the classroom, while the ‘Nothing concerned cluster’ did not show any concern. ConclusionThis study allows for a better understanding of the preferences and needs of primary school children from their own perspective and provides a foundation for future studies to improve both the IEQ in classrooms and school children's comfort and health.

Indoor Environmental Quality performance of mixed-mode ventilated shopping malls in hot-humid climatic region

Studies have revealed important roles quality indoor environment plays on human health and productivity; consequently, its influence on certain shopping behavior has also been well spelt out. In other to keep up with the demand for quality indoor environment, new trend has been evolving in the design of Malaysian shopping malls. From fully air-conditioned to newly designed ones that integrate passive ventilation strategies; and as such operating under mixed-mode ventilation system. These passive ventilation strategies are implemented to reduce energy consumption and also to improve the indoor environment within the mall’s indoor space. However, the potentials of these designs in terms of their indoor environmental quality (IEQ) performance have not been studied nor have their advantages been revealed. In this study, occupants’ thermal perception and IEQ performance was investigated in two mixed-mode ventilated malls selected based on their design concept (‘open’ and ‘enclosed’). Both subjective and objective measurements were carried out in accordance with the ASHRAE performance measurement protocol for commercial buildings. Five IEQ factors (indoor air temperature, operative temperature, relative humidity, air speed, and carbon dioxide concentration level) were evaluated in the two malls. The results revealed that both malls fell below the ASHRAE comfort requirement but majority of the occupants still found the indoor thermal performance acceptable despite the high indoor air temperature recorded. For both malls, high air speed and low humidity level were recorded. However, higher air movement was still preferred by the occupants while the recorded mean carbon dioxide (CO2) concentration was within the recommended level. The ‘open’ concept mixed-mode ventilated mall proved superior compared to the ‘enclosed’ concept by providing a more thermally tolerance indoor environment for its occupants. Generally, results from this study contribute to the knowledge on the advantages of adopting sustainable designs in commercial buildings for improving the indoor environment as well as the health and general well-being of the occupants. The study will open more opportunities for future IEQ studies to be carried out in hot-humid climatic regions.

The Effects of Indoor Environment towards Middle–Income Group in Re-engineered Affordable Housing Scheme in Malaysia

The innovation of housing has evolved due to several issues such as the affordability and the sustainability of housing. Several housing designs were introduced to meet the affordable housing standard price for the middle-income group, particularly in the urban area. However, it is a challenge for the developers to provide affordable housing within the current market price with the element of sustainability. The developers use the concept of high rise building form and located near the public amenities to accommodate the users’ needs as well as to gain profits. Despite the rising demands, there is a limited study that focuses on the performance of the buildings, specifically on the indoor environmental quality (IEQ) of the affordable housing. This paper aims to assess the affordable housing performance by identifying the residents’ satisfaction level towards IEQ and the importance of the IEQ factors as well as their health condition. A questionnaire survey is one of the methods used in this study. The findings showed that the IEQ of affordable housing in Malaysia has resulted in the decrease of health towards the residents, with some dissatisfaction towards the IEQ. The insight from the residents can be used as an indicator to improve the IEQ as well as the building performance and to create a better affordable housing in Malaysia.

Residents' Satisfaction Towards the Indoor Environmental Quality of Re-engineered Affordable Housing Scheme in Malaysia

Malaysia is currently focusing on providing affordable housing all over the country, as part of the plan to tackle the problem of the rising costs of house ownership due to reasons such as the economic crisis and land limitations. However, a limited number of methodical studies have been conducted on residents’ feedback on the indoor environment of affordable housing. Indoor Environmental Quality (IEQ) is an important aspect of occupants’ wellbeing, as it affects their health and productivity. Therefore, evaluating residents’ feedback on IEQ is an important step in gauging building performance and conditions. In addition, the health and productivity of residents needs to be evaluated in order to identify the effect of IEQ on them. A questionnaire survey was used to achieve the study objectives and to gain access to the respondents’ views and feedback. The pilot questionnaire study was conducted at two housing apartments in Kuala Lumpur, Malaysia, and the data collected were evaluated and analyzed using SPSS software. The outcome of this pilot study is significant, as it shows the residents’ dissatisfaction level towards IEQ factors such as noise, glare and privacy, and other aspects of IEQ that are important, such as ventilation. Additionally, it has been found that the IEQ of the residents does affect their health and productivity. It is anticipated that the outcome of this study will serve as an indicator of building performance improvements needed to achieve a better indoor environment quality for affordable housing in Malaysia.

THE INDOOR ENVIRONMENTAL QUALITY PERFORMANCE OF GREEN LOW-INCOME SINGLE-FAMILY HOUSING

There is little empirical evidence in the literature about the indoor environmental quality performance of residential buildings in general and of social housing in particular. To address this problem, this study used a mixed-method approach to evaluate the indoor environmental quality performance of 17 green low-income single attached family houses in Brandon, Manitoba, Canada. Questionnaires were administered to occupants to assess their snapshot and long-term satisfaction with the indoor environment. In addition, snapshot measurements were carried out to evaluate the indoor environmental quality factors of thermal comfort, indoor air quality, lighting and acoustics. Occupants' snapshot satisfaction was categorized into two groups (i.e. satisfied/comfortable or dissatisfied/uncomfortable) and compared with snapshot measurements. The results showed the measured IEQ parameters were well below recommended threshold levels. Further, occupants with higher snapshot satisfaction were generally exposed to relatively lower levels of indoor pollutants. A statistically significant difference was found in PM10 level only between the snapshot satisfied and snapshot dissatisfied groups of occupants. Apparent sound transmission classes were below the standard reference value of 50, suggesting potential problems in noise attenuation within different spaces in each apartment and between apartments. The findings of this study could help governments implement green shadowing for public-housing and also renovate existing houses using the same principles.

Occupant productivity and indoor environment quality: A case of GSAS

Abstract Purpose The purpose of the paper is to establish links between Indoor Environment Quality (IEQ) factors that affect occupant productivity and Global Sustainability Assessment System (GSAS) building rating system. The paper analyses the current state of GSAS using a desktop study, survey and brainstorming session organised in a workshop with GSAS Certified Green Professionals (CGP). Methodology/design/approach The study was conducted in three steps. First, a comprehensive literature review was conducted to identify IEQ factors that influence occupant productivity in offices. The second step was a desktop analysis of current GSAS building rating system to identify criteria and submittals that may help to increase occupant productivity. It was followed by a facilitated workshop of GSAS CGPs that included a survey and a brainstorming session to highlight the current state of GSAS rated building performances on occupant productivity. The workshop was attended by 41 CGPs in Doha, Qatar. Findings The paper highlighted that GSAS needs to be updated to increase occupant productivity in GSAS rated buildings. A periodic post-occupancy survey in GSAS buildings should be mandated to ensure better occupant productivity. The paper also presented various methods to make GSAS rated buildings more occupant-friendly. Originality/value This study is the first study to analyse green building guidelines in the context of occupant productivity, especially in Qatar.

Differences in teachers’ satisfaction with indoor environmental quality and their well-being in new, renovated and non-renovated schools

Most studies on buildings’ renovations in relation to indoor environmental quality (IEQ) and occupants’ well-being have focused on offices, while those investigating schools focused on students rather than teachers. Most of these studies limited their assessment of well-being to occupants’ satisfaction with IEQ factors, overlooking essential aspects related to psychological, social and physical well-being. This article presents results of a research conducted in 32 schools in Manitoba, Canada, to assess teachers’ IEQ satisfaction and well-being in new, renovated and non-renovated schools. The research involved adapting and refining an IEQ satisfaction survey and developing and refining three new surveys to assess teachers’ psychological, social and physical well-being. The results of the refined surveys showed statistically significant differences in teachers’ satisfaction with IEQ factors between the new and renovated schools on one hand and the non-renovated ones on the other. However, no statistically significant differences were found in teachers’ psychological, social and physical well-being perceptions between all pairs of the three school categories analysed. Association analyses suggested a potential indirect impact of schools’ renovations on teachers’ well-being via their satisfaction with IEQ. The results of this study should aid school managers in making strategic decisions about the maintenance of their existing schools.

Occupants' indoor environmental quality satisfaction factors as measures of school teachers' well-being

Most studies that investigated the impact of buildings' indoor environmental quality (IEQ) focused on office buildings, with those studying schools focusing on the impact on students' well-being rather than teachers'. Additionally, most of these studies limited their assessment of well-being to occupants' satisfaction with IEQ factors (e.g. thermal comfort and lighting), overlooking essential aspects related to psychological, social, and physical well-being. This paper presents results of a study conducted in 32 schools in Manitoba, Canada, to investigate the extent to which occupants' IEQ satisfaction factors can be used as measures of teachers psychological, social, and physical well-being. The study involved adapting, deploying and refining an existing IEQ satisfaction survey; and developing, deploying, refining and validating three new surveys to evaluate teachers' psychological, social and physical well-being in schools. Three existing validated well-being surveys in the literature for assessing generic psychological, social and physical well-being were also deployed with the other surveys to teachers in the 32 schools. The association analyses between these different surveys found ventilation and thermal comfort to be the most significant measure of teachers' physical well-being with moderately positive correlations, while lighting and acoustics and privacy were insignificant measures of well-being, thus reinforcing the need to distinguish between occupants' IEQ satisfaction and their well-being in future research. The newly developed well-being surveys include some factors not found in the existing generic well-being surveys and are therefore likely to produce the most representative assessment of teachers' well-being for detailed IEQ impact investigation.

Influence of Indoor Environmental Quality on Work Productivity in Green Office Buildings: a Review

Indoor Environment Quality (IEQ) of offices is able to change occupants' behaviour by representing various conditions. The IEQ depends on factors such as lighting, noise, thermal quality, and air quality which directly or indirectly influence the occupants' behaviour and work productivity. To improve and support the work productivity of occupants, it is significant to consider occupants' physical condition, well-being and psychological facets which are affected by IEQ. Consequently, it is essential to understand initially the most effective IEQ factors that impact on occupants' behaviour and the overall satisfaction. Occupant's satisfaction can be improved by elimination or minimization factors that cause any discomfort, illness or dissatisfaction. However, most research on IEQ and occupant satisfaction are focused on conventional commercial and office buildings. There is a lack of research evaluating the performance and IEQ levels of new green buildings, in relation to work productivity. Thus, the current study reviews peer-reviewed journal articles and dissertations to find crucial factor influences on IEQ and work productivity in green offices. The results showed that increasing the quality of IEQ factors will most likely enhance occupant's productivity, which directly brings benefits for companies. Through a critical literature review, the study found that Indoor Air Quality (IAQ) is the most influential, which is vital for enhancing work productivity and it can boost occupants' satisfaction. Moreover, occupants' personal control over thermal condition shows the huge effect on enhancing work productivity. The results showed that there is a lack of a comprehensive study to rank the IEQ factors which effect on work productivity.

Assessing Staff Satisfaction with Indoor Environmental Quality in Assisted Living Facilities

This study contributed to knowledge of indoor environmental quality (IEQ) in assisted living facilities (ALFs) by examining staff satisfaction with the work environment, perceived productivity, and attitudes toward environmental sustainability in the workplace. An ALF Staff IEQ Survey was administered to staff ( N = 94) at 12 ALFs, which were newly constructed or renovated within the last 10 years. Staff who participated in the survey were divided into three age groups (young, middle–aged, and older) and two categories of responsibilities (medical and nonmedical). The questionnaire was designed to incorporate the Occupant IEQ Survey (Center for the Built Environment, 2013) and the Leadership in Energy and Environmental Design (LEED) rating criteria. It comprised six IEQ categories: space layout, thermal comfort, air quality, lighting and views, acoustic quality, and facility cleanliness and maintenance. Spearman's rank–order correlation coefficient, Kruskal–Wallis, and Mann–Whitney U tests were used for data analysis. Results identified 23 IEQ factors in all IEQ categories that significantly contributed to staff productivity. Six IEQ factors in four IEQ categories (space layout, thermal comfort, lighting, and facility cleanliness) were significantly related to staff environmental attitudes. In addition, 12 IEQ factors within five IEQ categories (except lighting quality) were found to have notable differences by age discrepancy, whereas five IEQ factors of air quality and facility cleanliness were significantly different for medical and nonmedical staff. The findings of this study provide designers with prioritized demands and preferences for decision making in terms of improving the work environment for the health and well–being of ALF staff. By incorporating the paradigms of evidence–based design (EBD), human–centered design (HCD), and sustainable design (SD), this study proposes a new triadic framework to transition from the current resident–centered model in elder care to a multistakeholder–focused model.

Perceived indoor environmental quality of classrooms and outcomes: a study of a higher education institution in India

ABSTRACTThe objective of this study was to assess students’ perceptions of the dimensions of the indoor environment of classrooms in a higher education institute in terms of spatial, thermal, visual, indoor air quality (IAQ) and acoustical parameters. This study attempted to determine the factors that influenced the perceived indoor environmental quality (PIEQ) and explored the relation between the perceived importance of indoor environmental quality (PI-IEQ) and academic satisfaction, academic ambience, academic performance and brand name/image of the institution. A field study of indoor environmental quality (IEQ) of 25 classrooms in the National Institute of Technology, Tiruchirappalli, India, was conducted and responses from 1295 students were obtained (N = 1295). Structural equation modelling was employed for data analysis. The research identified the six IEQ factors that influenced PIEQ as adaptive opportunities, furniture, daylight, acoustics, IAQ and thermal aspects. PIEQ had a positive influence on a classroom being perceived as conducive for learning. It was observed that PI-IEQ had the most significant and positive influence on academic ambience. The second most positive influence was on academic satisfaction. PI-IEQ had a positive influence on the brand name/image of the institute and on the academic performance.

Cooling capacity and acoustic performance of radiant slab systems with free-hanging acoustical clouds

Radiant slab systems have the potential to achieve significant energy savings, yet, when applied in the ceiling (e.g., thermally activated building system) the exposed concrete may also create acoustical challenges due to the high reflectivity of the hard surface. Balancing all of the building indoor environmental quality factors is important in the design of an effective workspace for the occupants, and so we need to consider the interactions between thermal and acoustic comfort. We assessed the cooling capacity in a hydronic test chamber and the sound absorption in a reverberation chamber to study the effects, for an office room, of different coverage areas of free-hanging acoustical clouds below a radiant chilled ceiling. The cooling experiments showed that for 47% cloud coverage of the ceiling area, we measured only an 11% reduction in cooling capacity caused by the blockage of radiant exchange between the ceiling and the room. The acoustical results showed that if the cloud covered 30% of the ceiling in a private office or 50% in an open plan office, acceptable sound absorption at the ceiling was achieved. We showed that good acoustic quality can be achieved with only a minor reduction of cooling capacity.

Thermal Environment and Thermal Sensations of Occupants of Nursing Homes: A Field Study

A demographic shift is underway in Australia; the number of people aged 65 and over is rapidly increasing. Regulations have been implemented to enhance the quality of care being provided in nursing homes; however, in the aged care sector there is little by way of guidance addressing design and performance issues in regards to Indoor Environmental Quality (IEQ), and there is still uncertainty as to the perceptions of residents on specific IEQ factors. The objectives of this study are to determine: how accredited facilities are performing in regards to thermal comfort conditions; how indoor environmental factors can be assessed in a non-intrusive way; and how occupants perceive their thermal environment. Air temperature and relative humidity were monitored over ten months in six nursing homes located in southeast NSW using 305 loggers. Subjective perception of the thermal environment was gathered from 157 residents, 31 family members and 64 staff who completed a questionnaire at the same time that local environmental parameters were monitored. Results show how accredited nursing homes performed in regards to thermal comfort, along with a detailed description of the non-intrusive methodology adopted to assess IEQ factors. Subjective responses of occupants, along with adaptive behaviour strategies employed by participants to counter unsatisfactory thermal conditions, were also examined. This study has practical implications for the aged care sector and provides quantitative evidence on how nursing homes should be designed and operated to enhance satisfaction and well-being of occupants.

The New NABERS Indoor Environment tool – the Next Frontier for Australian Buildings

In our ambition to improve the environmental performance of office buildings, it is easy to lose sight of their real purpose – to accommodate people. To understand the future of sustainable buildings, it is important to recognise that services such as HVAC and lighting are provided to create suitably comfortable conditions for staff to be productive.Providing a good quality indoor environment has been shown to increase staff productivity from improved comfort, health and wellbeing. Productive staff are essential for creating competitive businesses. The Property Council of Australia has estimated for offices that a 1% improvement in productivity would be equivalent to the whole energy cost of a building or, nationally $2 billion annually. The indoor environment quality (IEQ) of an office is complex and determined by many factors, including the layout of the space, lighting, air quality, thermal conditions and noise levels. These are influenced by the building characteristics, maintenance practices, tenant equipment and behaviour. The new NABERS Indoor Environment (IE) tool measures these IEQ factors and compares their performance against a set of benchmarks that reflect industry standards, scientific research and current market performance of office buildings. NABERS IE converts this complex information into a score on a six star scale – providing a direct measure of the overall IEQ for the office. This star rating provides a common language which can assist in coordinating multiple parties in setting goals, evaluating performance and recognising market achievements in occupant comfort and wellbeing.A high NABERS IE rating will help attract and retain tenants with excellence in indoor air quality and thermal comfort identified by tenants as significantly more important than other building attributes [14]. While for businesses, a high NABERS IE tenancy rating will identify you as an employer of choice – helping you to attract and retain staff.

Indoor environmental quality and occupants’ productivity

Purpose The purpose of this paper is to determine the relationship between indoor environmental quality (IEQ) and occupants’ productivity improvements in green buildings in order to propose probable enhancements of national green certification criteria. Design/methodology/approach Survey approach was selected under quantitative phenomenon. Hence, questionnaire survey was selected as a primary data collection technique. It was linked to semi-structured interviews to validate survey results. The survey data were analysed by using nonparametric statistical analysis techniques, such as significance testing and Spearman’s correlation. Statistical Package for the Social Science (SPSS) v.20 statistical analysis software was used in data analysis. Findings Seven factors were identified as significant factors which showed statistically significant monotonic correlation to major IEQ dimensions. Among those, air quality and acoustical partitioning factors confirmed a statistically significant weak positive monotonic correlation, whilst system control showed strongly positive monotonic correlation to occupants’ productivity in green buildings. Practical implications The findings can be practically implied as a basis to review the existing evaluation criteria of IEQ in national green certification system to propose probable enhancements. Originality/value The significant IEQ factors influencing occupants’ productivity were determined as the focal point of this research. Accordingly, new provisions were proposed to enhance the national green certification criteria.

Occupant Expectations on the Main IEQ Factors at Workspace: The Studies of Private Preschool Buildings

This study explores the relationship between the perceived performance of specific IEQ factors and occupants’ overall satisfaction with their workspace. The Indoor Environmental Quality (IEQ) in buildings is one of the most important factors affecting the physical development of children. The early education is compulsory and escalated numbers of 4-6 years children has boosted the numbers of private preschool. Frequently its operate in premises that have been fully refurbished, either in housing schemes, commercial buildings or institutional buildings. This has invited the questions on the building capability to provide a good environment to the children during the learning activities. Malaysia still lacks studies on the modification of the quality of the internal environment for private kindergartens. Post-Occupancy Evaluation (POE) is one method that has been used satisfactorily in the study and effect of IEQ in kindergartens. This research focuses on identifying occupant satisfaction towards IEQ in selected refurbished pre-school or kindergarten buildings. The objectives of the study are to iden-tify and determine the IEQ through feedback from building users. The study collected data on overall satisfaction and overall design importance through building inspection and questionnaires, the data obtained was analyzed to become a benchmark for the studies. 240 kindergartens in the whole country were selected for the study of IEQ.

A quantitative evaluation of indoor environmental quality in refurbished kindergarten buildings: A Malaysian case study

In Malaysia, the coverage of kindergarten education has improved dramatically in recent times, although many kindergartens are located in buildings that were not originally designed for that purpose. Indoor Environmental Quality (IEQ) is considered to be one of the most important factors affecting the physical development of children. Hence, it is essential to evaluate the indoor conditions of those kindergartens which are based in buildings that have been refurbished and adapted from their original purpose. It is posited that such refurbished environments provide sub-optimal IEQ for kindergarten use, which is reflected in user perception and satisfaction. This study presents the results of the IEQ investigations conducted in refurbished kindergarten buildings in Malaysia with the focus on identifying occupants' satisfaction with the various IEQ factors. The researchers aim to utilize the results of this work to develop a benchmark for analogous studies. 240 refurbished kindergarten buildings in Malaysia were studied to evaluate occupants' perceptions and levels of satisfaction. The results indicate that the occupants found Air Movement, Ventilation, and Freshness to be of a poor quality due to the high occupancy density. Noise was the least satisfactory IEQ factor due to the closeness of the kindergartens to main roads (external noise), as well as the small size of classrooms (internal noise). It was found that Colour and Attractiveness are the most important IEQ factors from the occupants' viewpoint. This study provides a practical benchmark for the conversion of buildings' usage.

Linear, Non-Linear and Alternative Algorithms in the Correlation of IEQ Factors with Global Comfort: A Case Study

Indoor environmental quality (IEQ) factors usually considered in engineering studies, i.e., thermal, acoustical, visual comfort and indoor air quality are individually associated with the occupant satisfaction level on the basis of well-established relationships. On the other hand, the full understanding of how single IEQ factors contribute and interact to determine the overall occupant satisfaction (global comfort) is currently an open field of research. The lack of a shared approach in treating the subject depends on many aspects: absence of established protocols for the collection of subjective and objective measurements, the amount of variables to consider and in general the complexity of the technical issues involved. This case study is aimed to perform a comparison between some of the models available, studying the results of a survey conducted with objective and subjective method on a classroom within University of Roma TRE premises. Different models are fitted on the same measured values, allowing comparison between different weighting schemes between IEQ categories obtained with different methods. The critical issues, like differences in the weighting scheme obtained with different IEQ models and the variability of the weighting scheme with respect to the time of exposure of the users in the building, identified during this small scale comfort assessment study, provide the basis for a survey activity on a larger scale, basis for the development of an improved IEQ assessment method.

Indoor environmental quality in school buildings, and the health and wellbeing of students

Poor indoor environmental quality (IEQ) in classrooms may be a risk for health symptoms and cause absence from school. We conducted a comprehensive study in order to assess the connection between IEQ in Finnish elementary school buildings and the health and academic performance of sixth grade students. The specific aim of the present paper was to study the school- or grade-level prevalence of symptoms in relation to IEQ. The school- or grade-level (i.e. group level) prevalence of self-reported symptoms and perceived IEQ was studied using data collected by a health questionnaire comprising 37 questions. The health questionnaire was sent to all 6th grade students in a stratified random sample of 355 elementary schools in Finland. Indoor environmental conditions were assessed with measurements of ventilation rate and thermal conditions of classrooms in a subsample of 56 schools. Altogether 297 elementary schools participated in the health questionnaire study and a total of 4248 questionnaires were returned (estimated response rate 62.6%). The most common weekly symptoms in the spring semester were fatigue (7.7%), stuffy nose (7.3%), and headache (5.5%). However, both mean prevalence values for different symptoms among all 6th grade students and group-level prevalence values for specific symptoms varied considerably. On the group level, the prevalence values most frequently found above 95% CI (calculated for N=15) were wheezing, cough with wheezing, and fever over 37°C. The most frequently reported IEQ factors causing daily inconvenience in classrooms were noise (11.0%) and stuffy air/poor indoor air quality (IAQ) (7.0%), which were also found most frequently above 95% CI on the group level (calculated for N=15), together with self-reported high indoor temperature and dust or dirtiness. Self-reported daily stuffiness/poor IAQ was significantly correlated with measured mean temperatures and ventilation rates in classrooms. High prevalence of students' self-reported stuffiness/poor IAQ may indicate high indoor temperature or low ventilation rate in classrooms. Also high group level prevalence of other IEQ factors and certain symptoms may be indicative of IEQ problems that should be further studied. The results of this study can be used as a reference for assessing the questionnaire-based prevalence of self-reported symptoms among 6th graders, and their association with IEQ in classrooms. For such assessment, the number of students responding to the questionnaire must be carefully considered, also bearing in mind that prevalence values are symptom specific.