Everyone is talking about air tightness but only a few people know the meaning and the facts about complete building sealing:
The sense of a complete building sealing system is, to protect your home against bad weather, dampness and heat-loss.
Warm, dry and energy efficient are some of the main criterias for buildings today.
The best insulated building is worthless without a proper sealed building envelope, which mostly consists of various solutions to secure the building structure against wind, driving rain, dampness and heat-loss.
Mostly a breathable barrier protects the building on the outside, like for example a roof underlay. This layer prevents the ingress of
dampness and driving rain. The same function is covered by having the external walls properly plastered.
On the internal side, the most buildings require a so called vapour control barrier.
This barrier prevents that damp warm air, coming from the room, get acces into the building structure.
The vapour control barrier has another function too - to protect the building against draughts and heat-loss, caused by unregulated
air infiltration. This fact is mostly called "Air Tightness", but please don´t forget the equally important fact of vapour control. Especially fibrous and fluffy insulation materials like mineral
wool, cellulose or spray foam have to be protected against the risk of condensation, because they will not insulate in case they get damp.
Internal plaster is airtight but has only a limited capacity to act as a vapour control layer.
The easy principle for a proper building sealing means for the most buildings:
The external sealing should be weatherproof but breathable whilst the internal sealing has to be airtight & vapour inhibiting.