HydroGap Drainable Housewrap

Weather barriers are materials intended to resist air and moisture that has penetrated
the cladding system. Standards and building codes refer to materials that resist liquid water as either water- or weather-resistive barriers (WRB). When combined with flashings, WRBs are part of a system of bulk water resistance often called the concealed drainage plane.

Any rigid sheathing, sheathing membrane, or flexible sheet good that resists bulk water can be combined with flashings to create the concealed drainage plane, or weather WRB). WRBs are typically flexible sheet goods (often house wraps and building paper that come in wide rolls) whose sole or primary purpose is resisting bulk water. WRBs can also be fluid-applied designed for roller or spray gun application.

WRBs may also perform as a primary component of air barrier systems. The vapor permeability of WRBs varies considerably; many are formulated with relatively high vapor permeability to promote evaporative or diffusive drying to the exterior of the building assembly.

Flexible sheet products qualifying for GreenSpec comply with ASTM E2556-10, “Standard Specification for Vapor Permeable Flexible Sheet Water-Resistive Barriers Intended for Mechanical Attachment” Type II Minimum Performance Requirements and are neither gross cross woven nor perforated. Liquid applied products comply with AC 212, "Acceptance Criteria for Water-Resistive Coatings used as Water-Resistive Barriers over Exterior Sheathing."

Weather barrier products listed here contribute to durability and/or reduce the potential for indoor air quality problems associated with moisture and mold.

Note that the vapor permeability of materials designated as the weather barrier can vary widely and the desirability of low or high or no vapor permeability is always in the context of the primary direction of wetting, the primary direction of drying, and the vapor permeability of all the other components in the assembly.

Also note that terminology for materials meant to manage moisture in exterior building enclosures varies widely, even among specifiers and code officials. Master Format language is unclear for this section, using terms such as vapor, air infiltration, and thermal variation in language that can only be described as cryptic. GreenSpec uses the term weather barrier to mean the system of materials achieving a continuous manage of liquid moisture, the dedicated drainage plane interior to the building cladding, often referred to as the WRB.