Passive cooling strategy is proven to be effective to resolve thermal discomfort. A study was conducted to study the effectiveness of natural ventilation combined with various building retrofit methods on improving the indoor thermal environment for terrace houses under hot-humid climates, especially by using roof cover. Natural ventilation was found to improve the room’s thermal condition, but still not enough to achieve thermal comfort. The use of roof cover did maintain consistency in surface temperature on roof tiles and reduced convective heat flux of approximately 70~80% in the attic and 88% in the room. The mean surface temperature for the top surface of roof tiles and air temperature in the attic during daytime was reduced to approximately 4.4 °C and 1.6 °C, respectively. Meanwhiles, the daytime mean air temperature in the room was reduced by approximately 1 °C. Due to the effectiveness of improving the thermal comfort in the house, roof cover with HDPE nets has the potential to be developed as a passive building retrofit method for houses with roof tiles in hot, humid climate regions.