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IECC Windows and Doors Performance

Updated Apr 3, 2026

Establishes U-factor and solar heat gain requirements for windows, skylights, and doors.

IECC Section 5 addresses window and door thermal performance. Windows must meet U-factor (heat transfer rate) limits ranging from 0.23-0.62 depending on climate zone and window type. Solar Heat Gain Coefficient (SHGC) limits of 0.25-0.45 reduce cooling loads in sunny climates. Skylights must meet stricter U-factor requirements than vertical windows due to roof exposure. French doors and sliding glass doors must meet door U-factor requirements. Operable windows and doors that are properly installed and maintained provide better performance than air leakage paths.

TAGS

iecc energy-code windows doors

DETAILS

section

502

category

Envelope Requirements

code body

IECC

code year

2021

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