Wind can create shifting positive

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Air transfer
The new codes include major changes regarding air transfer—not only because of a desire for increased energy efficiency, but also because air movement is often a large contributor to moisture migration.

Air has a natural tendency to move from high to low pressure (Figure 3). Sources of pressure differentials at a building envelope are diverse. For example:

and negative pressures on the enclosure;
stack effect can exist with differences in atmospheric pressure between the rcs data top and bottom of the building; and
fan pressure created by the HVAC system can also result in positive or negative pressure, depending on mechanical system design and operation.
Air carries moisture in the form of vapor, which can then encounter surfaces below the dewpoint and cause condensation. For air transfer to occur, there must be a path or a hole between two areas of differing pressure—either exterior to interior, or between varying interior conditions.