In connection with the requirements of energy saving and reducing greenhouse gas emissions, the current construction is characterized by high levels of airtightness of the building envelope. On the other hand, high levels of airtightness can be the cause of poor indoor air quality due to inadequate ventilation. Energy savings and ensuring the quality of the indoor environment are two confronting requirements of the current construction. The airtightness can be defined as a resistance of the construction to infiltration air. The building envelope should be airtight in order to prevent uncontrolled leak air. Air tightness of building envelopes is usually expressed in terms of total air exchange rate at pressure difference 50 Pa. This paper analyzes the airtightness of energy efficient buildings in terms of the construction system and building materials. The analysis are investigated both vertical and horizontal constructions. The basic data set consists of energy-efficient buildings built in the years 2004-2014 in the Czech Republic