In Office buildings in Chile, cooling energy demand is higher than heating demand. The climate of the country show important differences between cities by the ocean and those of interior regions. Main cities of Central Chile are Santiago and Valparaiso, both located at around 33°S. Santiago presents a Mediterranean climate, with a high temperature oscillation between day and night during cooling period. Valparaiso, by the coast, shows lower temperature fluctuation compared with Santiago during identical period. In order to define design strategies for energy efficiency of office buildings in mentioned cities, a sensitivity study has been made, considering variables like window to wall ratio, type of windows (clear and selective glazing, including low e, single and double glazing), use and type of external solar protection (ESP) and use of nocturnal or diurnal ventilation. In opaque facades, thermal insulation is considered. In case of walls, in order to increase thermal inertia external insulation is assumed. The sensitivity analysis is developed considering a square building containing office rooms on all four orientations. This 10 story building has been specially proposed and designed for this analysis. Methodology considers an evaluation of heating and cooling demand of the building in both cities. For this purpose, simulation software under dynamic conditions has been used (TAS). The lowest cooling energy demand is reached when using the lowest window to wall ratio (20 %), with ESP in east, west and north oriented glazed areas. In fact, fully glazed facades in both cities are not recommended. Nocturnal ventilation was highly effective for decreasing cooling demand in both cities. In the case of Valparaiso, due to relatively low temperature during cooling period (maximum lower than 26 °C), diurnal ventilation for cooling purposes is also effective.