In the past and still often today, building regulations and standards don't reflect the state-of-the art with respect to the performance assessment of buildings in terms of energy use and indoor climate. Because of the field of most of these regulations (transmission losses, energy demand for heating,...) and the typical used components, the assessment procedures were rather simple and not really a reflection of the physical behaviour (e.g. dynamic behaviour of buildings). Energy Performance (EP) standardisation and regulation is by an increasing number of countries considered as an attractive approach for achieving a more energy efficient built environment. Several countries have already enacted such EP based regulation (the Netherlands, France, ASHRAE approach in North America, ...), or are preparing one (Germany, Greece, the Flemish Region, ...). Moreover, a European Directive on the energy performance of buildings (EBPD) has been adopted in November 2002 with as deadline for implementation 2006.