Office buildings in central Chile normally show higher cooling than heating energy demand.Overheating is a frequent problem in this type of buildings in cities like Valparaso and Santiago.Santiago (33S) presents a Mediterranean climate, with a high thermal temperature oscillationbetween day and night throughout the year. Valparaso -with a temperate climate influenced by thePacific Ocean- shows lower temperature compared with Santiago. On the other hand, latelly, officebuilding have been incorporating double skins facades in ofiice buildings without previous studies todetermine if this is an appropriated strategy for these cities.This paper shows the thermal performance of a multistory office building with a double skin facade inSantiago and Valparaso, comparing it with an identical building without this type of facade. Thermalperformance was studied with TAS software. Results show that double skin is not necessarily aneffective strategy for energy efficiency. A non appropriate design and/or a non proper operation ofdouble skin facades may generate over ventilation, overheating and a high cooling energy demand in office buildings in mentioned cities. Cooling nocturnal natural ventilation in office buildings (withoutdouble skin), combined with solar protection are effective strategies for energy efficiency in office buildings.