Windows, fans, and solar shadings during summer and heatwave: Occupant behavior and potential for improvement in heat-mitigation practices

• Largest French occupant behavior dataset in residential buildings during summer. • Analysis of behavior with windows, solar shading, fans, and their combinations. • Potential for improvement in heat-mitigation practices: 15–75 %, mainly in daytime. • Fan use much lower than other contexts, reflecting cultural differences. • Findings support realistic behavior models and awareness campaigns. Occupant behavior during summer and heatwaves has a strong impact on overheating in free-running residential buildings. Yet, the use of windows, solar shadings, and fans remains poorly studied. This study addresses this gap through the largest monitoring campaign of its kind in France on this topic, covering 76 dwellings across three regions in summer 2023. Window states, solar shading positions, fan use, and indoor and outdoor conditions were systematically monitored for four months. Behaviors were analyzed individually and in combination to better understand real behavior in this context and assess the adoption of heat-mitigation practices and their potential for improvement. Results reveal substantial diversity across dwellings and through summer periods. General tendencies are consistent with previous datasets from other countries and contexts, with two main differences. Fan use is over four times lower at similar indoor and outdoor conditions, likely reflecting cultural factors. Unlike air-conditioned buildings, no cutoff temperature is observed for night-time window opening, reflecting a distinct night cooling strategy. During heatwaves, adaptive behaviors are adopted, yet the potential for improvement averages 40 % and ranges from 15 % to 75 % across dwellings. The largest potential of improvement lies in closing windows during the day when outdoor temperatures exceed indoor ones, whereas heat-mitigation practices are more consistently adopted at night. These findings provide a foundation for developing needed, more realistic occupant behavior models for French residential context during summer and heatwave. These results provide guidance for future awareness campaigns promoting passive heat-mitigation practices of occupants, emphasizing their importance.