As you design a building envelope, it can be easy to focus on getting the insulation right.  After all, the International Building Code goes to great lengths to require specific R-values and U-factors.  And while the thermal control layer is certainly important, the building code is less specific about the other major control layers: the water resistive barrier (WRB), the air barrier, and the vapor control layer.  Water, air, and vapor are harder to quantify than heat, which is why the code spends less time discussing them.  But if your wall fails to control them, all the insulation in the world won’t help.

Fortunately, the folks at have compiled many helpful, free resources to give you guidance where the code is silent.  Visit the application pages on WRBs, air barriers, water vapor control, and thermal insulation for articles, research reports, step-by-step installation guides, and more.

Also, take a look at this quick video, part of a series where Joe Lstiburek, Ph.D., P.Eng, explores effective building envelope design:

For additional information, review the following articles, as well as the previous videos in this series:

Perfect Wall Articles

  1. Creating the ‘Perfect Wall’: Simplifying Water Vapor Retarder Requirements to Control Moisture
  2. Perfect Walls are Perfect, and Hybrid Walls Perfectly Good
  3. Wood Framed Wall Insulation Calculator Explained
  4. New Wall Design Calculator for Commercial Energy Code Compliance
  5. Energy Code Math Lesson: Why an R-25 Wall is Not Equal to a R-20+5ci
  6. Continuous Insulation Solves Energy Code Math Problem

Video Series

  1. Fear Building Envelopes No More with This Website & Videos
  2. Video: Thermodynamics Simplified Heat Flows from Warm to Cold
  3. Video: Moisture Flow Drives Water Induced Problems
  4. Video: How the 'Perfect Wall' Solves Environmental Diversity
  5. Video: How Important Is Your WRB?
  6. Video: A Reliably Perfect Wall Anywhere
  7. Video: The Best Wall We Know How to Make 
  8. Video: How to Insulate with Steel Studs
  9. Video: Thermal Bridging and Steel Studs
  10. Video: Better Residential Energy Performance with Continuous Insulation
  11. Video: How to (Not) Ruin a Perfectly Good Wall
  12. Video: Tar Paper and Continuous Insulation? No Problem!
  13. Video: Do CI and WRBs Go Together?
  14. Video: Assess Your 'Perfect Wall' Using Control Layers