A weather resistive barrier (WRB) is an important element of high performance home construction. The WRB serves the critical function of shedding bulk water that inevitably penetrates all siding types, nonabsorbent, and are vapor permeable to promote drying of moisture that reaches them. A WRB may or not be an air barrier, depending on the material.
Because this a high performance Scope of Work, the WRB detailed here will be house wrap, which functions as both a drainage plane and an air barrier when it is properly taped at the seams.
NAHB Research Center