Section C402.1/Building Envelope Requirements (2018 Edition)
IECC 2018 Section C402 covers prescriptive envelope insulation and fenestration requirements for the 2018 code cycle.
The building thermal envelope must meet the insulation and fenestration requirements of Tables C402.1.3 and C402.1.4 based on climate zone. Opaque envelope assemblies (walls, roofs, floors) must meet the minimum R-values or maximum U-factors from the tables. The 2018 IECC allows compliance through insulation R-value, assembly U-factor, or component performance rating. Fenestration must meet maximum U-factor and SHGC values from Table C402.4. A continuous air barrier is required per C402.5.
Key differences from IECC 2021 and 2024
The 2018 IECC has less stringent insulation requirements than the 2021 edition in several climate zones. Roof insulation R-values were increased in the 2021 edition. Fenestration U-factor and SHGC limits were tightened in 2021 and again in 2024. The 2018 edition does not include the additional efficiency package options (C406) that became more restrictive in later editions. Air barrier requirements exist in 2018 but were strengthened in 2021.
What plan reviewers look for
Plan reviewers check the energy code compliance form for the correct edition. They verify wall, roof, and floor insulation values against the 2018 tables. They check fenestration U-factor and SHGC on the window schedule. They verify the air barrier is identified on wall sections. They confirm the climate zone determination.