Abstract The aim of this research is to investigate the thermophysical behaviour of building envelope multi-layer components and assess the whole building–plant response. The investigation was carried out in two different phases. The first phase concerned the study of the dynamic response of building envelope multi-layer components, by providing an improved implementation of the present European Standard UNI EN ISO 13786:2008. The proposed method allows one to determine the transient thermophysical performance of opaque building components that are associated with a thermal zone maintained at constant or variable air temperature. The variable internal air temperature can be associated with experimental data. The second phase consisted of a transient analysis of the above thermal zone with a conditioning plant working. The building plant simulations were carried out by EnergyPlus software. The method proposed, based on European standards, is particularly useful in the perspective of the Certification of the Energy Performance of the building–plant system, required by the European Union. It can provide a useful tool for developing an abacus of different envelope multi-layer component performances in order to support design choices.