Indoor Air. 2020;30:481-491. | 481 wileyonlinelibrary.com/journal/ina 1 | INTRODUC TI ON Volatile organic compounds (VOCs) are important gaseous pollutants, because many of them have known adverse effects on human health and comfort, ranging from mild irritation to acute toxicity and carcinogenicity. 1-4 Indoors, VOCs are the most prevalent air pollutants and also the most studied. Lowering indoor VOC concentrations can improve working productivity and reduce health effects. 5,6 Indoor VOC concentrations are influenced by different factors, such as building characteristics, occupants' behaviors, and environmental parameters. 7-10 Specifically in residential buildings where people spend 68% of their time, 11 known sources of VOCs Abstract Exposure to elevated levels of certain volatile organic compounds (VOCs) in households has been linked to deleterious health effects. This study presents the first largescale investigation of VOC levels in 169 energy-efficient dwellings in Switzerland. Through a combination of physical measurements and questionnaire surveys, we investigated the influence of diverse building characteristics on indoor VOCs. Among 74 detected compounds, carbonyls, alkanes, and alkenes were the most abundant. Median concentration levels of formaldehyde (14 μg/m 3 ), TVOC (212 μg/m 3 ), benzene (<0.1 μg/m 3 ), and toluene (22 μg/m 3 ) were below the upper exposure limits. Nonetheless, 90% and 50% of dwellings exceeded the chronic exposure limits for formaldehyde (9 μg/m 3 ) and TVOC (200 μg/m 3 ), respectively. There was a strong positive correlation among VOCs that likely originated from common sources. Dwellings built between 1950s and 1990s, and especially, those with attached garages had higher TVOC concentrations. Interior thermal retrofit of dwellings and absence of mechanical ventilation system were associated with elevated levels of formaldehyde, aromatics, and alkanes. Overall, energy-renovated homes had higher levels of certain VOCs compared with newly built homes. The results suggest that energy efficiency measures in dwellings should be accompanied by actions to mitigate VOC exposures as to avoid adverse health outcomes. K E Y W O R D S building characteristics, dwellings, energy efficiency, thermal retrofit, ventilation, volatile organic compounds