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The 2021 IECC Assemblies tool is designed to help builders select foundation, wall, and roof construction assemblies that meet 2021 International Energy Conservation Code (IECC) and 2021 International Residential Code (IRC) requirements for both thermal efficiency and condensation control. The tool addresses each of the IECC climate zones individually and includes:

Building Assemblies: Drawings showing section views of building assemblies that safely meet the 2021 envelope requirements are provided in PNG and PDF formats. A variety of construction types are represented for each climate zone. Window installation drawings focusing on flashing details for different wall types are also provided. All drawings are accompanied by a set of explanatory notes highlighting key details and indicating potential alternatives. Links to relevant Building America Solution Center guides are also given for each construction type.

Case Studies: Case studies of actual projects that have met the prescriptive 2021 requirements are presented.

While this tool focuses on prescriptive R-value requirements, the IECC and IRC offer multiple paths to compliance. Due to its simplicity, the prescriptive R-value path is often the most limiting approach. Some assembly types may comply more readily using the prescriptive U-factor approach or the UA Alternative. Other more flexible compliance alternatives are the Total Building Performance path and the Energy Rating Index Compliance Alternative.

The assemblies presented in this tool do not cover all possible options for meeting the 2021 envelope requirements, and the construction types are not intended as recommendations of the best options for each climate zone. Instead, they provide a variety of instructional examples that demonstrate some of the key principles in attaining thermal efficiency while controlling moisture concerns within the assembly.

All of the roof and wall assemblies have been vetted by hygrothermal modeling to assess moisture risk. When possible, wall assemblies were modeled using the Building Science Advisor tool.

To learn more about 2021 IECC climate zones, See the report “Guide to Determining Climate Zone by County: Building America and IECC 2021 Updates” for an explanation of the climate zones and tables of all U.S. counties and their climate zone designations. The data sets for these tables were developed by DOE and are publicly available. They can be accessed at

This tool was funded by the U.S. Department of Energy. It was created through collaboration between Pacific Northwest National Laboratory, Building Science Corporation, and Oak Ridge National Laboratory. Building Science Corporation provided the drawings. Oak Ridge National Laboratory developed the Building Science Advisor and provided hygrothermal modeling.