Vapor Retarder

A comprehensive assessment of the state-of-the-art of water vapor control for modern, code-compliant, light-frame wall assemblies. The primary goal of this effort is to evaluate and reconcile existing building science knowledge and practices. An important secondary goal is to support the development of practical and comprehensive water vapor control requirements or recommendations that may be used as a basis to reach various audiences and serve multiple purposes, including building industry education and building code development.

Concerns regarding moisture control performance can affect walls of any thickness, with or without the added protection of exterior continuous insulation. One purpose of this Research Report is to present data to evaluate and substantiate an appropriate application of continuous insulation in an R20+5 assembly (e.g., R20 cavity insulation plus R-5 continuous insulation on the exterior).