Overview
Building codes require that water vapor retarders be provided on the interior side of walls (warm in winter side) for mixed and cold climates to control water vapor diffusion and potential for condensation or moisture accumulation within assemblies during the winter. However, these rules of thumb have become outdated with newer building materials, insulation materials, and energy code insulation requirements. Thus, building codes are in a long overdue process of being updated. The guidance provided in the DESIGN RESOURCES section is based on the latest successful building code improvements that will come forward in the 2021 editions of the IBC and IRC.
DESIGN RESOURCES: Use the following resources to evaluate the water vapor control performance and drying potential of walls using FPIS. Be prepared to revise your insulation strategy determined in STEP 1 to achieve optimal moisture performance while also meeting or exceeding the energy code requirements for wall insulation.
- Online Wall Thermal and Moisture Design Tool
- Model Moisture Control Guidelines
- Research Basis of the Wall Calculator and Model Guidelines (also published as part of ASTM STP 1599).
- Educational Presentation
For additional information on water vapor control and related moisture control topics, refer to our Water Vapor Control and Residential Walls pages.