The hardest part of building a resilient wall is managing moisture. If water gets inside the wall, all sorts of problems arise, including mold, rust, and structural degradation, depending on the materials used. It would be simple enough if moisture was only coming from one direction: just put a water resistive barrier (WRB) layer facing that direction and be done! But moisture comes from both sides. In the winter, warm, moist air on the inside heads towards the cool, dry air outside, and the opposite occurs in the summer. The most effective solution is to block moisture on one face of the wall, and promote drying through the other face. There are plenty of resources available on the water vapor control page that get into the technical aspects of this approach.
In the video below, Joe Lstiburek gives a quick overview of moisture transmission:
For additional information, review the following articles, as well as the previous videos in this series:
Perfect Wall Articles
- Creating the ‘Perfect Wall’: Simplifying Water Vapor Retarder Requirements to Control Moisture
- Perfect Walls are Perfect, and Hybrid Walls Perfectly Good
- Wood Framed Wall Insulation Calculator Explained
- New Wall Design Calculator for Commercial Energy Code Compliance
- Energy Code Math Lesson: Why an R-25 Wall is Not Equal to a R-20+5ci
- Continuous Insulation Solves Energy Code Math Problem
- Fear Building Envelopes No More with This Website & Videos
- Video: Thermodynamics Simplified Heat Flows from Warm to Cold
- Video: Moisture Flow Drives Water Induced Problems
- Video: How the 'Perfect Wall' Solves Environmental Diversity
- Video: How Important Is Your WRB?
- Video: A Reliably Perfect Wall Anywhere
- Video: The Best Wall We Know How to Make
- Video: How to Insulate with Steel Studs
- Video: Thermal Bridging and Steel Studs
- Video: Better Residential Energy Performance with Continuous Insulation
- Video: How to (Not) Ruin a Perfectly Good Wall
- Video: Tar Paper and Continuous Insulation? No Problem!
- Video: Do CI and WRBs Go Together?
- Video: Assess Your 'Perfect Wall' Using Control Layers