Is there an optimum range of airtightness for a building?

Air transport control has been recognized as critical to the proper functioning of buildings. Airflow is related to all facets of environmental control because it influences transport of heat and moisture and affects indoor environment as well as the durability of the building enclosure. To a lesser degree, we also recognize that contamination of wall cavities in building assemblies by organic materials from inside or outside provides both the nutrients and the inoculation potential for mold growth. Moisture carried by air may also increase the rate of emission of volatile organic compounds from these materials. While keeping rain out of building enclosures is a primary consideration in design, controlling airflow through the building enclosure comes a close second in importance to allow environmental control within buildings. Yet, an increase in the airtightness comes with a cost as well as an increased risk of moisture entrapment in case of any failure, and this, in turn, relates to the type of the building.