Office buildings in Santiago and Valparaíso, Chile normally show higher cooling than heating energy demand. Overheating and high cooling energy consumption are recurrent problems in this type of buildings in the mentioned city during summer periods. Santiago (33°S) presents a Mediterranean climate, with a high temperature oscillation between day and night during summer. Valparaíso, by the coast of Santiago Valparaíso -with a temperate climate influenced by the Pacific Ocean-shows lower temperature compared with Santiago. On the other hand, office buildings of the country have been incorporating some design patterns of certain developed countries, without considering the particular climate of Chile. In fact, double skins façade have been lately used in this type of buildings without previous studies in order to know if it is an appropriated strategy for Chilean climates. No studies have been made to identify physical phenomena that regulate their behaviour in the country. This paper shows the thermal performance of an office building with a double skin facade in Santiago and Valparaíso, comparing it with an identical building in which this type of facade is not used. Simulations showed that double skin is not necessarily an effective strategy for energy efficiency. When using other strategies like the solar protection, nocturnal ventilation in office buildings without double skin, energy efficiency may be reached, tending to zero energy cooling demand.