IECC C402 — Building Thermal Envelope (Commercial)

Updated Mar 25, 2026

Commercial envelope: insulation R-values, window U-factors, SHGC, air leakage by climate zone.

IECC 2024 Commercial: C402.1 prescriptive. Walls: CZ1=R-13, CZ4=R-13+R-7.5ci, CZ6=R-13+R-12.5ci. Roofs: CZ1=R-25ci, CZ4=R-30ci. Windows: CZ1=U-0.50, CZ4=U-0.36, CZ6=U-0.32. Air barrier: <0.40 cfm/sf at 75Pa. Continuous insulation eliminates thermal bridges. Vestibules required CZ3-8.

TAGS

IECC energy-code insulation R-value U-factor commercial

DETAILS

code year

2024

code section

C402

SOURCES

🔗https://codes.iccsafe.org/content/IECC2021P1

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