073 - Vapor Barriers Explained: Water, Air, and Moisture in Walls

Vapor barriers, air barriers, and water barriers each do a completely different job inside your wall assembly, and mixing them up is one of the most common mistakes on the ARE.

In this episode, we break down the three barrier types that protect your building envelope from moisture damage. You'll learn how weather resistive barriers and drainage planes keep bulk water out, and why air leakage actually carries far more moisture than vapor diffusion.

We walk through perm ratings, the three classes of vapor retarders, and the warm-side rule for vapor retarder placement by climate. We also cover rainscreen systems, the perfect wall concept, thermal bridging, blower door testing, and the moisture sandwich trap that causes mold and rot inside walls.

📝 Key topics covered:

Vapor barrier vs vapor retarder terminology

Weather resistive barriers and house wrap

Drainage planes and rainscreen assemblies

Window flashing and water intrusion

Air barrier material vs air barrier system

Blower door testing for air leakage

Perm ratings and vapor retarder classes

Vapor retarder placement by climate