Ensuring an airtight seal

If the building envelope is not airtight (whether in renovated or new buildings), i.e. if it has localized leaks, then warm, humid air moves from the interior through the elements of the building envelope. As this air cools down on its way out, moisture can condense in the elements in question and mould can then develop.

In addition such localized leaks cause ventilation heat loss, which in turn impairs the insulation effect of the building envelope. The heat transferring surface of the building must therefore be implemented with a permanent airtight seal.

Continuous airtight level in a building (source: Schulze Darup)

Typical defects are: window and door interfaces, joints between building elements, junctions between masonry and lightweight structures, penetrations for building services and especially conduits and flush-mounted power points for electrical facilities.

Airtight and draught-proof implementation has the following advantages:

structural damage is avoided
the thermal insulation takes full effect
airborne sound insulation is effective
ventilation systems are effective
air quality is improved (due to the ventilation system required)

To check the airtight seal, the so-called "blower door test" is carried out, in which a pressure differential is created using a fan mounted in a blower door in-stalled to achieve an air seal. At a pressure differential of 50 pascal airflow is measured both at reduced and at increased pressure. The arithmetic mean of the two values is the measured n50 value.

Blower-door-test (source: Schulze Darup)