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Window U-factor + SHGC reference
Typical U-factor (thermal transmittance) and SHGC (solar heat gain coefficient) for common window types, with IECC climate-zone compliance ceilings.
Typical U-factor
0.3
SHGC: 0.35
IECC Zone 4 ceiling
0.32
PASS prescriptive
IECC residential prescriptive U-factor ceilings (windows)
- Zone 1: U ≤ NR, SHGC ≤ 0.25
- Zone 2: U ≤ 0.40, SHGC ≤ 0.25
- Zone 3: U ≤ 0.32, SHGC ≤ 0.25
- Zone 4 (except marine): U ≤ 0.32, SHGC ≤ 0.40
- Zone 5 + marine 4: U ≤ 0.30, SHGC ≤ NR
- Zone 6: U ≤ 0.30, SHGC ≤ NR
- Zones 7 + 8: U ≤ 0.27, SHGC ≤ NR
Values per IECC 2021 residential prescriptive (Table R402.1.3). Commercial prescriptive (ASHRAE 90.1) values differ; consult MEP engineer for project-specific compliance path.
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