This study aims to investigate the energy-saving potentials and design approaches to move the small and medium office buildings in Bangkok neighborhood areas to become the Net-Zero Energy Building (NZEB). The envelope designs, such as increasing the material’s thermal resistance, adding shading devices, and using high energy-efficient systems, together with the electricity production from the photovoltaic cell, are applied in the studied buildings. According to the energy simulation results, with the implementation of current design techniques, the annual energy consumption of office buildings cannot reach the NZEB. However, these design approaches can enforce the maximum building’s energy-saving capability at 88 kWh/m2 that is nearly the Economic Building (ECON). The maximum energy reduction occurs when improving the high thermal performance of the building’s envelope and using high energy-efficient systems. To achieve this challenging target. Future studies should account for more energy-efficient systems as well as the building’s operation schedule.