This article presents the ＇grey box＇ models used to represent building envelopes based on the entry of a limited number (ten or so) of parameters per thermal zone. These parameters correspond to the geometric data as well as the thermal characteristics of buildings (i.e., areas of walls, heat losses, etc.). These ＇grey boxes＇ are implemented in the CLIM 2000 environment for ＇multi thermal zones＇ models in the residential sector. The technical features, applications and limitations of these models are presented on the basis of software comparisons and experimental measurements. (C) 2000 Elsevier Science S.A. All rights reserved.