In the recent past new concepts for the building envelope have been developed with theunderlying wish to improve the energy performance of a building as well as comfortconditions in the inner spaces. Examples are: solar walls, high-tech window systems, doublefacades and integration of daylighting systems and of PV-panels. In this paper the doublefacade concept is discussed.This kind of facade is considered as a device to be used for pre-heating the ventilation airduring winter as well as for nocturnal cooling of the building during summer. The doublefacade concept includes different ventilation strategies as well as different ways ofinteraction between cavity and interior of the building and between cavity and exterior.Moreover, it is part and parcel of the indoor climate system and should be synchronised withthe air conditioning system.In order to make an evaluation of the overall energy performance of buildings with ventilateddouble facades, the energy performance of double facades is simulated and analysed on ayear round basis. Based on simulation output the efficiency with which ventilation air can bepreheated by the double faade is analysed. The effect of various parameters on the efficiencyare given, such as: the dimensions of the double faade and the control of the air flow in thecavity.