The implementation of the Energy Performance of Buildings Directive (EPBD) has caused in most of the EU Member States more severe requirements for the energy demand of buildings. In order to meet these requirements, not only buildings components with better U-values and more efficient building systems have to be used, also the ventilation losses have to be reduced. A contribution to this necessary reduction is the improvement of the building envelope airtightness, mainly the airtightness of building components and joints. With the EPBD implementation or even before some of the countries have included minimum airtightness requirements in their building codes. According to an investigation at the end of 2007 in the ASIEPI project, several EU Member States have minimum requirements regarding the building envelope integrated in their building codes. These are: the Czech Republic, Germany, Denmark, the Netherlands, and Great Britain. Spain has partial requirements focussing on windows. The existing minimum requirements refer to new buildings (residential and non-residential).