Airtightness Systems


 There are two points in time of measurement: 

  • Measurement on completion (in use)
  • Measurement at phases in construction

The test of a building’s air-tightness is carried out in so-called ‘blower-door measuring procedures’. If this measurement is carried out in good time during construction it is possible to detect any leaks and still correct these easily. After all deficiencies have been corrected and the building completed, a final measurement takes place when the building is in use. 

This is how it works:

The blower-door measurement detects how much air volume in a building is exchanged per hour at a certain difference in pressure. 

In order to build up this difference in pressure a telescopic frame is positioned in an open window or a door leading outside which is then covered with a film.

In an opening in the film is a fan. The fan’s rotation is regulated so that a defined pressure between outdoors and indoors is reached. To retain this pressure the fan needs to convey an air volume current as high as that escaping through leaks in the building.

During build-up of this difference in pressure (low pressure in the house) it is easy to find leaky spots in the building’s skin. There is literally a draught through every crack. Further aids in detection of leakage are smoke dispensers (in over pressure), airflow anemometers and thermography.

For the degree of air-tightness, the n50 value, specific mandatory threshold values must be observed. The average value is indicated as measured value in the record.


Blower-door measurement is a standardized procedure for testing the air-tightness of a building’s skin. The n50 value (air exchange rate) shows how often the air in the building being measured is exchanged within one hour. The threshold values are controlled by national standards or in the specification for subsidies for residential buildings but can also be demanded by the planner. Both apartments and whole buildings are measured.For buildings without mechanical ventilation (with window ventilation) an n50 value below 3.0 per hour is usually specified, and for domestic ventilation below 1.5 per hour. For passive houses a rate of air exchange of below 0.61 per hour is specified. These values are taken from OIB RL6 and DIN 4108-7. Please be sure to check the threshold values required for your housing subsidies.