<![CDATA[Traditional Malay buildings in riverine settings reflect long-term adaptation to hot-humid tropical conditions. However, the relationship between their architectural and spatial characteristics and measured thermal conditions remains insufficiently examined, particularly in traditional palaces. This study evaluates the adaptive thermal acceptability of measured conditions at Istana Gunung Sahilan, Riau, Indonesia, in relation to its passive tropical design characteristics. A single-building case study combined architectural analysis with quantitative field measurements. Architectural observation, photographic documentation, and three-dimensional modelling identified features related to solar and rainfall protection, natural ventilation, and transitional and raised-floor spaces. Air temperature, relative humidity, and air velocity were measured sequentially at 23 points across two floors during four observation periods on a single cloudy day. Point 1, located outdoors in an unobstructed area, served as the outdoor reference. The 22 indoor points were assessed using the ASHRAE Standard 55 adaptive framework, with instantaneous outdoor air temperature used as an approximate model input. Operative temperatures increased from 24.7–28.0°C at 11:00 to 28.9–30.5°C at 15:00. All indoor points met the 80% acceptability range throughout the survey. Within the narrower 90% range, acceptable points decreased from 100% at 11:00 and 13:00 to 90.9% at 14:00 and 50% at 15:00. Locations with measurable airflow were generally more likely to remain within the narrower range during warmer periods, although airflow was unevenly distributed. The findings indicate an association between spatial configuration, air movement, and model-based adaptive thermal acceptability, highlighting the relevance of opening distribution and connections between interior and transitional spaces. As measurements covered only one cloudy day and no occupant surveys were conducted, the results represent a preliminary assessment of measured conditions rather than actual occupant comfort or performance across different weather conditions.]]>
