Tropical regions experience intense and highly variable solar radiation, often resulting in excessive indoor illuminance, uneven daylight distribution, and visual discomfort in high-rise residential buildings. This study investigates the daylighting performance of various external horizontal slat configurations as a shading strategy for east- and south-facing rooms in a typical high-rise apartment under both intermediate sky with sun and overcast sky conditions. Using IESVE simulations, ten shading device (SD) configurations (SD 1–SD 10) were evaluated for their impact on daylight illuminance and distribution uniformity. Results show that high-rise apartment room with a commonly used overhang provided poor daylighting quality, with excessive illuminance and low distribution uniformity. SD 10 and SD 9 achieved the best performance at 09:00 and 12:00, respectively, for east-facing rooms across design days, while SD 10 was optimal for south-facing rooms on both 21 March and 22 December. Under overcast sky conditions, SD 9 demonstrated superior performance. This study proposes a novel adaptive external shading device featuring adjustable horizontal slats that can be reconfigured throughout the day to respond to changing solar positions and sky conditions. This approach overcomes the limitations of fixed shading systems by adapting to dynamic tropical sky conditions, offering a practical solution for enhancing daylight quality in tropical high-rise apartments. The findings provide design guidance for the development of energy-efficient shading, climate-responsive shading systems tailored to tropical environments.

Tropical daylight provision is inherently coupled with intensive solar heat gains, particularly in south-facing rooms that experience pronounced seasonal variations in solar altitude and exposure across different times of the year. When appropriately designed, external shading devices can mitigate solar heat gains while maintaining adequate indoor daylight availability. This study investigates the daylighting and thermal performance of a representative south-facing apartment room equipped with combined horizontal and vertical slat-based shading devices using a controlled, comparative simulation framework under tropical climate conditions. Parametric simulations were conducted using IES-VE to evaluate multiple shading configurations with varying slat positions, depths, and combinations under representative sky conditions and seasonal design days. The results demonstrate that mid-height horizontal slat configurations reduced front-zone Estimated Indoor Illuminance (EII) by up to 54.9%, while enhancing daylight penetration into deeper areas under direct sunlight conditions. Bottom horizontal slats further improved daylight distribution by reflecting sunlight into deeper zones, producing peak increases in EII of up to 26.8% in the middle zone and 19.7% in the rear zone under direct solar conditions. The addition of vertical slats further improved thermal performance by limiting lateral solar exposure without significantly diminishing the daylight-redirecting effects of horizontal elements. Selected integrated shading configurations achieved maximum reductions in operative temperature of up to 2.5 °C during peak afternoon periods compared with the base case within the adopted evaluation framework. However, under intermediate sky conditions without direct solar contribution, the daylighting and thermal benefits of slat-based shading were substantially reduced. Based on these findings, the study proposes a movable external shading system with adjustable horizontal and vertical slats for south-facing apartment rooms, intended to respond to changing solar conditions across the evaluated design days. Overall, this study provides mechanism-oriented insights to support the development of climate-responsive façade strategies for tropical high-rise residential buildings, with the aim of improving daylight distribution and reducing cooling demand.