After Energy Performance of Buildings-directive (EPBD) came into operation within the European Union, Finland also began the work to adjust building codes matching the new directive. There was no regulation dealing with air tightness before, but when the building codes were changing, air tightness was taken into the codes. In the newest version of Energy Efficiency of buildings-code (the version of 2012, the earlier versions 2010 and 2008) the air leakage value is determined as follows: The air leakage value q50 is not allowed to be higher than 4 (m3/h*m2). The better value can be proven by measurements or by other types of procedures. If air tightness has not been proven by measurement or by other procedures, air leak rate 4 (m3/h*m2) must be used in energy efficiency calculations. The reference value used in evaluation of heat losses is q50 = 2 (m3/h*m2). In the new building code the levels of air tightness has been determined: As an example, for apartment houses and offices a good level is 1, 0 - 4, 0 (m3/h*m2) equal to n50 0, 5 - 1, 5 1/h. Changes in building codes have caused an emerging interest to measure and to improve air tightness in buildings. Also measuring of air tightness is now certified as a building thermographer has been certified. Also mentioned in the new building code is that the air tightness of a building can also be measured by using the ventilation system of the building.

In this paper, results and experiences of air tightness measurements of different buildings are presented using the own ventilation system of the building. The results have also been compared with the results of coincident blower-door measurements. Some suggestive calculations of the effect of air leaks for energy efficiency have also been made dealing with various levels of air tightness. Also the use of two-stage thermography in locating air leak patterns has been introduced. The use of the building's own ventilation system can be used in evaluating the level of air-tightness, but the results differ from the results achieved using the blower-door method. It is essential that a certain level has been set in the design phase and it is verified. The biggest problem is in existing building stock and theoretically the biggest potential to save energy is in existing buildings. There are some limitations especially when aiming to verify the specified air tightness level using the building`s own ventilation system and also when evaluating the actual energy losses caused by air tightness.