This paper describes a new general method for building simulation programs which is intended to be used for the modelling of complex facades The term complex facades is used to designate facades with venetian blinds prismatic layers light re-directing surfaces etc In all these cases the facade properties have a complex angular dependence In addition to this such facades very often have non-airtight layers and/or Imperfect components (e g non-ideal sharp edges non-flat surfaces) Therefore building planners often had to neglect some of the innovative features and to use work-arounds in order to approximate the properties of complex facades in building simulation programs A well-defined methodology for these cases was missing This paper presents such a general methodology The main advantage of the new method is that it only uses measureable quantities of the transparent or translucent part of the facade as a whole This is the main difference in comparison with state of the art modelling based on the characteristics of the individual subcomponents which is often impossible due to non-existing heat- and/or light-transfer models within the complex facade It is shown that the new method can significantly increase the accuracy of heating/cooling loads and room temperatures (C) 2010 Elsevier B V All rights reserved