Overview of a simulation model for combined heat, air, moisture and pollutant transport (CHAMP) simulations is presented. Simulation models have become commonly used tools in many disciplines of engineering science. The developments in algorithms and numerical methods have made it possible to predict the performance of building envelope structures and whole buildings and to investigate the phenomena occurring inside the building systems to enhance our understanding of the built environment's behavior. However, the field of Indoor Air Quality is still lacking the reliable tools to predict and analyze the building components' behavior largely because of the lack of material properties and models that can make use of them in an integrated modeling environment. The building envelope simulation model (CHAMP-Envelope) development starts from thermodynamic principles including as many details as is practical and known in the state-of-the-art hygrothermal models. The capabilities of the current version of the building envelope simulation model are described. Applications and results from the simulation model are presented for a typical North-American wood frame wall exposed to indoor and outdoor climate. The model can also be used to predict pollutant transport from interior finishing and furnishing materials and systems as well as from exterior walls and from outdoor. The detailed model will be used in research to develop proven and validated simpler models and tools to be used by designers and integrated software. Future extensions of the model development include combining the model with whole building simulation models and creating a simulation environment that would allow designers and researchers to work with shared databases and input/output data structures.