The hygrothermal behaviour of the building envelope affects the overall performance of a building. Numerous tools exist for the simulation of the heat and moisture transfer in the building envelope and whole building simulation tools for energy calculations. However, working combinations of both models for practical application are just about to be developed. In this paper such a combined model, that takes into account moisture sources and sinks inside a room, input from the envelope due to capillary action, diffusion and vapour absorption and desorption as a response to the exterior and interior climate conditions as well as the well-known thermal parameters will be described. The new model is validated by performing a series of field experiments and the moisture buffering capacity of the building envelope is investigated. In the conclusions the possible range of future applications of hygrothermal building performance models is addressed and the needs for further research are identified. (c) 2004 Elsevier Ltd. All rights reserved.