The aim of the Norwegian research centre on Zero Emission Buildings(ZEB) is to develop competetive products and solutions of buildings with zero emission of greenhouse gases related to their production, operation and demolition. However, to develope solutions and concepts for zero emission buildings it is first necessarry to develop a sound definition of ZEB (for single buildings, and also cluster of buildings). During the first 3 years of the centres running, significant work have been done to adress different issues related to the ZEB-definition, among them defining CO2 factors for various energy wares. Work done in the International Energy Agency…