WRB (Weather-Resistive Barrier)

A WRB (weather-resistive barrier) is a material installed behind exterior cladding to prevent liquid water from reaching the structural sheathing and framing, while allowing water vapor to pass through to the exterior — required by IRC R703.2 on all wood-frame exterior walls.

In Detail

Weather-Resistive Barriers in Construction

A WRB is a critical component of the exterior wall assembly that prevents bulk water from entering the wall cavity. IRC Section R703.2 requires a WRB on all exterior walls where cladding (siding) is applied over sheathing. The WRB goes between the structural sheathing and the cladding.

Common WRB Products

  • House wraps: Tyvek HomeWrap, Typar, etc. — non-woven polyolefin sheets wrapped around the building and stapled to sheathing
  • Integrated WRB sheathing: ZIP System — the WRB is built into the sheathing panel itself
  • Fluid-applied WRB: Henry BlueSkin, Prosoco R-Guard — liquid membranes rolled or sprayed onto sheathing
  • Building paper: #15 or #30 asphalt felt — the traditional WRB, still code-compliant

Key Performance Properties

  • Water resistance: Must resist liquid water penetration from wind-driven rain
  • Vapor permeability: Must allow water vapor to pass through (dry to the exterior)
  • UV resistance: Must withstand UV exposure during construction (90–180 days depending on product)
  • Durability: Must last the life of the cladding (30–50+ years)

Related Terms

Moisture Content

Moisture content (MC) is the percentage of water weight relative to the oven-dry weight of wood — it controls dimensional stability, fastener performance, and susceptibility to decay, making it one of the most important properties in lumber selection and installation.

Related Materials

ZIP System Sheathing

ZIP System sheathing is a structural panel with an integrated water-resistive barrier (WRB) and air barrier built into the panel face, eliminating the need for house wrap. Manufactured by Huber Engineered Woods, it combines structural sheathing and weather protection in a single step.

OSB (Oriented Strand Board)

Oriented strand board (OSB) is an engineered wood panel made from compressed wood strands bonded with waterproof resin. It is the most widely used structural sheathing panel in North American residential construction, offering uniform strength properties and lower cost than plywood.
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