Notes research carried out over the last five years in the EMPA sponsored by the Swiss Federal Ministry for Environmental Protection. The aim of the investigation is to elaborate appropriate guidelines for the construction of the building envelope and to develop appropiate guidelines for the construction of the building envelope and to develop appropriate calculation methods for ventilation heat losses. Discusses the main approaches of the various investigations. Gives a brief outline of the individual stages of the research in the EMPA in recent years. Provides and discusses the most important results to date and concludes by outlining the next stages in the research activities concerning ventilation heat loss.