Moisture Management in Wall Assemblies

Intermediate Level

Building science behind wall moisture management: WRBs, vapor barriers, rain screens, and proper sequencing to prevent rot and mold.

Materials Needed

ZIP System Sheathing
OSB (Oriented Strand Board)
CDX Plywood

Note

Never install vapor barriers on both sides of a wall — traps moisture and guarantees rot.

Note

ZIP System combines structural panel and WRB in one product, eliminating housewrap seam failures.

The Four Functions of a Wall

Every wall must manage structural load, thermal transfer, air movement, and moisture. Moisture management is the most common failure point.

Rain Control

The WRB is the primary rain control layer. Continuity at every seam and penetration is critical. In high-exposure areas, a rain screen gap provides drainage and drying.

Air Sealing

Air leakage carries 100× more moisture than vapor diffusion. Focus: bottom plates, top plates, penetrations, and sheathing seams.