Long-Term Indoor Hygrothermal Performance at Room Level in Occupied Residential Apartments Under a Hot Arid Coastal Climate: Implications for Sustainable Building Performance

Indoor hygrothermal conditions in occupied residential apartments are influenced by occupant behavior, room functions, and building characteristics. This study investigates long-term indoor hygrothermal performance at room level in two vertically adjacent occupied residential apartments in Jeddah, Saudi Arabia, under a hot-arid coastal climate. The monitored spaces comprised the master bedroom and living room in each apartment. Indoor air temperature and relative humidity were continuously monitored over 33 months, and the data were standardized to 30 min intervals for analysis. Dew point temperature was recalculated from the measured air temperature and relative humidity. For indoor air temperature, differences between corresponding rooms in the two apartments were modest, whereas bedroom–living room differences were larger. The paired monthly mean temperature was higher in the living room than in the master bedroom by 2.24 °C in the lower apartment and 2.63 °C in the upper apartment. Relative humidity did not follow the same spatial pattern, whereas dew point provided additional insight by revealing a distinct moisture-related condition in the lower living room, which recorded the highest mean dew point and the greatest month-to-month variability. The findings demonstrate that apartment-level averages alone do not fully represent room-level indoor hygrothermal performance. Room-level patterns also differed across air temperature, relative humidity, and dew point. Considering indoor air temperature, relative humidity, and dew point together provided a more comprehensive assessment of indoor hygrothermal performance. This study provides long-term field data on room-level indoor hygrothermal conditions in occupied apartments and supports more representative approaches to sustainable building-performance assessment in hot-arid climates.