IECC R402 — Building Thermal Envelope (Residential)

Updated Mar 25, 2026

Insulation R-values and fenestration U-factors by climate zone for residential buildings.

IECC 2024: Zone 1: ceiling R-30, wall R-13, window U-0.40. Zone 3: ceiling R-38, wall R-20 or 13+5ci, window U-0.32. Zone 4: ceiling R-49, wall R-20 or 13+5ci, window U-0.30. Zone 6: ceiling R-49, wall R-20+5ci or 13+10ci, window U-0.30. Air barrier ≤3 ACH50 Zones 3-8.

TAGS

IECC insulation R-value climate-zone energy-code

DETAILS

code year

2024

code system

IECC

code section

R402

SOURCES

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

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