Western Europe Functionalism ideas are born of the need for scientific and technological progress in producing new materials and building technologies. Today energy efficiency has become one of the most important characteristics of any project, where functionalism reflects well-designed building components. Reducing energy consumption, improving energy efficiency and minimizing greenhouse emission in the building is vital for the planet's survival. This study intends to provide expertise in design and construction disciplines to use the idea concept of Fallingwater and Villa Savoye, functionalist-style buildings, from the golden era of functionalism. This evaluation can help a new generation of designers and architects to improve the passive energy efficiency and daylight of studied concepts, pragmatic and organic. As a case study, the authors simulated and evaluated the energy efficiency of two conventional architecture designs stated above. Energy efficiency and daylight simulation of these functionalist-style buildings were executed using the BIM-based Building Energy Simulation (BES) tool. The indoor temperature variation and the amount of illuminance for each zone were assessed. The result indicates that the main temperature variation (mean air and operative temperature) in both buildings is not suitable for living and some parts of the regularly occupied floor receive too much direct sunlight. Based on the results, some passive energy-saving measures such as improving building orientation, material and shape, window wall ratio (WWR), adding external shading device, window position, and size are suggested to help researchers in the AEC industry in the future reforming process.