Energy code
The energy code: the framing's U-factor and the glass's SHGC.
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The energy code
- IECC edition
- 2015, 2018, 2021 or 2024: the one your jurisdiction adopted.
- Climate zone
- From the IECC climate zone table, by county, such as 5B.
- Energy source
- The sheet or spec, for the report.
- Glass for the energy check
- Only used before you add glass types: low-E, clear or triple.
U-factor
Each elevation's framing is checked on the manufacturer's published total-product U at the NFRC rating size, with your glass when it's published for it (or read along the framing's published values for other glass, marked interpolated). It's compared with the code's fixed-glazing limit. When it misses, the page lists the nearest framing that both meets the limit and carries the wind.
SHGC
The glass's solar heat gain coefficient is checked against the code's limit, with no overhang credit (a projection factor under 0.2). The 2015 and 2018 IECC split the limit by orientation: set Faces on the elevation, or the stricter south, east and west limit is used. The 2021 and 2024 editions split it by fixed and operable glazing; fixed is used.
The check uses the center-of-glass SHGC. The whole product's, on the NFRC label, is lower, so a pass here holds, and a miss here may still pass on the label. A calculated SHGC on a unit with two coatings can read low, so it's shown as CHECK: use the maker's value.
The code tables were read from published summaries. Confirm the limit against the code and amendments your jurisdiction adopted; compliance is the project's NFRC label certificate at submittal.