The International Organization for standardization (ISO), Technical Committee 163 "ThermalPerformance and Energy Use in the Built Environment" (ISO/TC 163) is dealing with development oftools that can be used to design and construct or retrofit energy efficient buildings and installations. Theoverall aim for this is to reduce our dependency of non-renewable resources and to reduce theemission of harmful substances to the air. Methods are needed for the evaluation of the energyperformance of complete buildings and parts of buildings or building installations. In order to arrive atenergy efficient buildings, materials and products that effectively contribute to the thermal performanceof the building and its installations must be used. Standards dealing with the design and evaluation ofmaterials, components and systems play an important role in arrive at this goal. ISO/TC 163 hasproduced and will produce sets of standards by reference to which performance requirements can beexpressed at various levels, from materials to complete buildings. A substantial part of this work isconducted through the subcommittee SC 2: Calculation methods, which is in brief presented in thispaper.