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The external envelope of a building should be as airtight as possible and this doesn’t only apply to Passive Houses.
Therefore, in accordance with construction technology regulations, a good level of airtightness is generally required today, and rightly so. This applies even more for a comfortable Passive House.
|Due to insufficiently airtight building components, warm and
moist air can flow from the inside towards the outside and thus
lead to condensation on colder parts of the construction. Most
building damage occurs in this way. This can be remedied by
careful airtight construction.
Regarding energy saving construction, airtightness isn’t a pastime, it is vital for the prevention of moisture penetration in building components. As the illustration shows, air flowing out from leaks transports substantial amounts of moisture into the construction. As the air cools on the way out, the water in the air condenses and remains inside the construction.
Airtightness should not be confused with thermal insulation. Both are important for the building envelope, but they must be implemented independently of each other:
Airtightness is an important requirement for energy-saving construction, but it is not the most important one (as sometimes misrepresented by popular publications - good insulation is the most essential requirement).
Airtightness should not be confused with diffusion impermeability either: for example, oiled paper is airtight but diffusion permeable. Ordinary interior plaster (gypsum plaster, lime plaster, render, or fibre reinforced loam render) is also sufficiently airtight while being diffusion permeable at the same time.
For a quality assured Passive House (certificat of the PHI) an airtightness with a very low remaining leakage is required:
The n50 value has to be not higher than 0.6 h-1. This is a quite demanding requirement, but experience has shown
It's a bad idea to think, that you'll gain anything from alleviating the airtightness requirements. The only result will be, that yo'll get higher risks for bad performance. On the other side, it's not much an effort to learn how to deign and to build really airtight.