FIELD NOTE · SUPPLEMENTAL SET
Unrated single pane: the U-factor Title 24 enters when no label arrives
ISSUEDJULY 11, 2026DRAWN BY THE NIGHTLY SWEEP
A fenestration unit arrives on site with a temporary label, and under Section 110.6(a)5 that label stays on the glass until the enforcement agency inspects it. Where a product carries no rating, the California Energy Code supplies numbers of its own out of Table 110.6-A and Table 110.6-B, set to be worse than a product anyone would specify on purpose. That substitution settles everything a glazing scope is later argued about. The label itself lists three numbers and certifies a fourth thing: U-factor under NFRC 100, solar heat gain coefficient and visible transmittance under NFRC 200, and compliance with the air leakage limit tested under NFRC 400 or ASTM E283.
Table 110.6-A is the substitution, printed: an unrated metal-frame single-pane operable window is entered at U-1.28, the fixed version of the same window at 1.19, and a metal frame with a thermal break carrying a double-pane unit at 0.66 operable and 0.55 fixed. None of those numbers measures the assembly standing in front of the inspector. The table is what the code enters when nobody produces a measurement.
The 2025 cycle put a floor under all of it on January 1, 2026, applying by permit application date under Section 100.0(a)2, and the floor is Section 120.7(d) of the 2025 Building Energy Efficiency Standards: vertical fenestration assemblies, area-weighted average U-factor, no greater than 0.47. In the 2022 standards that section was titled Mandatory Insulation Requirements and ran roof, wall and floor; the only glazing named in it was the opaque kind, spandrel panels and curtain wall held to 0.280 under 120.7(b)6. There was no requirement anywhere in the section for vision glass.
Section 140.0 requires a nonresidential building to satisfy the mandatory sections and then, separately, either the performance path in Section 140.1 or the prescriptive path in Section 140.2, and Section 141.0 imposes the same two-part structure on additions and alterations. The architect or the energy consultant picks which path the project runs, and the prescriptive one fixes the window's number while the performance one lets it trade against the rest of the building. Neither path reaches 120.7(d), which is to say no model carries the glass past 0.47. Two exceptions are written into Section 120.7 itself. The first is fenestration in a building meeting Part 7 of the California Building Code and the California Wildland-Urban Interface Code, where the building sits in a Fire Hazard Severity Zone or Wildland-Urban Interface Fire Area designated by the local enforcement agency. The second is a building used solely as a data center with a covered process load over 750 kW.
Unrated glass is assigned solar values the same way it is assigned U-factors. Table 110.6-B enters a metal-frame fixed single-pane clear unit at SHGC 0.83 and the double-pane clear version of it at 0.73. The prescriptive maximum standing against those is 0.26 area-weighted RSHGC for new curtain wall or storefront, 0.25 in Climate Zones 1 and 7, and 0.31 for altered fenestration in Climate Zones 6 through 10, 14 and 15 under Table 141.0-A.
One number in Table 140.3-B runs the other direction. It sets a minimum visible transmittance, 0.46 for curtain wall and storefront, which a dark selection runs into after the U-factor and the RSHGC have both been satisfied. Note 4 to Table 110.6-A closes the other loop, sending any assembly carrying window film that is not rated under NFRC 100 straight back to the defaults. Three of the five values below are SHGC as the label or the default table reports it, and two are RSHGC, the shade-corrected number the code regulates; on an unshaded opening the two are identical.
SOLAR GAIN, ASSIGNED AND ALLOWED (2025 ENERGY CODE) UNRATED SINGLE PANE, CLEAR (T110.6-B) 0.83 UNRATED DOUBLE PANE, CLEAR (T110.6-B) 0.73 WINDOW FILM BASELINE SHGC (T141.0-E-2) 0.35 ALTERED GLASS, SOCAL ZONES (T141.0-A) 0.31 NEW STOREFRONT, RSHGC (T140.3-B) 0.26
That is 8.7 to one, per square foot, between the storefront and the roof over it, and the roof answers to a separate part of the same code. A metal-framed wall in the same column is 0.060, and the opaque spandrel panels between the vision lites carry a mandatory 0.280 under Section 120.7(b).
The glass is not the loosest thing in the envelope, and the mass-wall rows of that column say so: light mass wall at 0.364, heavy mass wall at 0.690, both permitted to lose more per square foot than any window in the table. Roofs run roughly eight to eleven times tighter than the glass, and framed walls three to seven times. The glass sits mid-pack.
An unrated single-pane fixed window entered at 1.19 is 3.3 times what a new fixed window has to hit in the same zone, which is the distance between what is in the wall now and what the code will accept in it.
Whether a plan checker applies the 0.58 in 141.0(b)1E to a straight replacement, or the 0.47 the Section 141.0 preamble pulls in from the mandatory band, the code text does not settle. A bidder in front of that gap carries the tighter number or asks the plan checker before the takeoff goes out, because the question does not get easier once the order is placed.
Under all of it sits the code's own escape hatch: glass replaced in an existing sash and frame, or sashes replaced in an existing frame, are repairs under the note to Section 141.0(b)2A, and a repair only has to be at least equivalent to the original under Section 141.0(c). The line is drawn by what comes out of the wall, not by how much of it. Pull the frame and the Section 100.1 definitions make the work an alteration at any size, and only then do the 150 and 50 square-foot triggers start counting.
The competitor who replaces nothing at all is the film installer, whose alteration path runs through Exception 1 to Section 141.0(b)3A and whose standard design under Table 141.0-E-2 is U-0.40 and SHGC 0.35 without third-party verification of the existing conditions, or the Table 110.6-A and 110.6-B defaults with it.
Storefront, curtain wall and atrium roof systems are site-built fenestration in the code's own definition, so no sticker arrives with them. Section 10-111(a)1A requires a label certificate instead, under NFRC 700 for site-built products or NFRC 705 for the Component Modeling Approach, listing U-factor, SHGC and VT.
Section 110.6(a)6 attaches a deadline: before an occupancy permit is granted, site-built fenestration outside single-family buildings has to be certified against the acceptance requirements of Reference Nonresidential Appendix NA7, with the matching label certificate readily accessible at the project location. A missing certificate does not fail the glass; it holds the occupancy permit, and the building does not open until somebody produces the paper. The code puts that requirement at the project location, which is where the contractor who installed the units is standing and the office that wrote the specification is not.
The Statewide CASE Team, which writes the technical proposals the Energy Commission adopts, puts the alteration side more plainly still, reporting that the required U-factors for fenestration alterations have been unchanged since at least the 2013 code.
The prescriptive tightening did not happen. A floor arrived instead, set beneath prescriptive numbers that have not moved since 2022, in a section that had nothing to say about vision glass in either of the two prior cycles.
The next move is drafted and not adopted. The 2028 Final CASE Report on nonresidential fenestration, dated June 2026, proposes U-0.34 for fixed windows in Climate Zones 1 through 4 and 16, U-0.43 for operable windows in Climate Zones 1 through 5 and 9 through 16, and an alteration trigger at 100 percent replacement of any single fenestration type. None of that is law, and the numbers in it moved between the measure summary and the final report.
The 2025 Final CASE Report on the nonresidential envelope, the document the 0.47 came out of, set the number against products widely available in the market, with one exception it names: large-scale storefront assemblies using single-pane structural glazing, which would need thermally broken frames to reach it. That is a sentence about frames, written into a standards proposal years before the code took effect, and the label on site only reports what it produced. It gets read at inspection, and by then the frame is anchored and the glass is set.
Table 110.6-A is the substitution, printed: an unrated metal-frame single-pane operable window is entered at U-1.28, the fixed version of the same window at 1.19, and a metal frame with a thermal break carrying a double-pane unit at 0.66 operable and 0.55 fixed. None of those numbers measures the assembly standing in front of the inspector. The table is what the code enters when nobody produces a measurement.
The 2025 cycle put a floor under all of it on January 1, 2026, applying by permit application date under Section 100.0(a)2, and the floor is Section 120.7(d) of the 2025 Building Energy Efficiency Standards: vertical fenestration assemblies, area-weighted average U-factor, no greater than 0.47. In the 2022 standards that section was titled Mandatory Insulation Requirements and ran roof, wall and floor; the only glazing named in it was the opaque kind, spandrel panels and curtain wall held to 0.280 under 120.7(b)6. There was no requirement anywhere in the section for vision glass.
Section 140.0 requires a nonresidential building to satisfy the mandatory sections and then, separately, either the performance path in Section 140.1 or the prescriptive path in Section 140.2, and Section 141.0 imposes the same two-part structure on additions and alterations. The architect or the energy consultant picks which path the project runs, and the prescriptive one fixes the window's number while the performance one lets it trade against the rest of the building. Neither path reaches 120.7(d), which is to say no model carries the glass past 0.47. Two exceptions are written into Section 120.7 itself. The first is fenestration in a building meeting Part 7 of the California Building Code and the California Wildland-Urban Interface Code, where the building sits in a Fire Hazard Severity Zone or Wildland-Urban Interface Fire Area designated by the local enforcement agency. The second is a building used solely as a data center with a covered process load over 750 kW.
Clear single pane, entered at 0.83
The solar half of the label is governed by a quantity the code names and the label does not. Section 140.3(a)5C regulates relative solar heat gain coefficient rather than SHGC, meaning solar heat gain corrected for external shading. The two are the same number until the opening carries an overhang or exterior horizontal slats extending past each jamb by the depth of the projection, at which point the designer may take credit for the shade through Equation 140.3-A. The equation is optional either way.Unrated glass is assigned solar values the same way it is assigned U-factors. Table 110.6-B enters a metal-frame fixed single-pane clear unit at SHGC 0.83 and the double-pane clear version of it at 0.73. The prescriptive maximum standing against those is 0.26 area-weighted RSHGC for new curtain wall or storefront, 0.25 in Climate Zones 1 and 7, and 0.31 for altered fenestration in Climate Zones 6 through 10, 14 and 15 under Table 141.0-A.
One number in Table 140.3-B runs the other direction. It sets a minimum visible transmittance, 0.46 for curtain wall and storefront, which a dark selection runs into after the U-factor and the RSHGC have both been satisfied. Note 4 to Table 110.6-A closes the other loop, sending any assembly carrying window film that is not rated under NFRC 100 straight back to the defaults. Three of the five values below are SHGC as the label or the default table reports it, and two are RSHGC, the shade-corrected number the code regulates; on an unshaded opening the two are identical.
SOLAR GAIN, ASSIGNED AND ALLOWED (2025 ENERGY CODE) UNRATED SINGLE PANE, CLEAR (T110.6-B) 0.83 UNRATED DOUBLE PANE, CLEAR (T110.6-B) 0.73 WINDOW FILM BASELINE SHGC (T141.0-E-2) 0.35 ALTERED GLASS, SOCAL ZONES (T141.0-A) 0.31 NEW STOREFRONT, RSHGC (T140.3-B) 0.26
Storefront held at 0.41, the roof above it at 0.047
Climate Zone 6 is the zone the Energy Commission models on the Torrance weather file, per Reference Joint Appendix JA2, Table 2-1; the zone a project actually sits in is fixed by physical location under the California Climate Zone Descriptions, an address lookup rather than a city list. In that zone, Table 140.3-B holds a fixed window to a maximum U-factor of 0.36 and curtain wall or storefront to 0.41. The same table, the same column, holds a wood-framed roof to 0.047.That is 8.7 to one, per square foot, between the storefront and the roof over it, and the roof answers to a separate part of the same code. A metal-framed wall in the same column is 0.060, and the opaque spandrel panels between the vision lites carry a mandatory 0.280 under Section 120.7(b).
The glass is not the loosest thing in the envelope, and the mass-wall rows of that column say so: light mass wall at 0.364, heavy mass wall at 0.690, both permitted to lose more per square foot than any window in the table. Roofs run roughly eight to eleven times tighter than the glass, and framed walls three to seven times. The glass sits mid-pack.
An unrated single-pane fixed window entered at 1.19 is 3.3 times what a new fixed window has to hit in the same zone, which is the distance between what is in the wall now and what the code will accept in it.
Replaced glass, counted in square feet
Section 141.0(b)1E is new this cycle as well, and it decides whether a glazing scope is a project or a line item. Where more than 150 square feet of a building's vertical fenestration is replaced, the replaced units may not exceed U-0.58; where more than 50 square feet is added, the added fenestration goes to Section 120.7(d) at 0.47. On the prescriptive path, Table 141.0-A caps altered vertical fenestration at 0.47 in every Southern California climate zone.Whether a plan checker applies the 0.58 in 141.0(b)1E to a straight replacement, or the 0.47 the Section 141.0 preamble pulls in from the mandatory band, the code text does not settle. A bidder in front of that gap carries the tighter number or asks the plan checker before the takeoff goes out, because the question does not get easier once the order is placed.
Under all of it sits the code's own escape hatch: glass replaced in an existing sash and frame, or sashes replaced in an existing frame, are repairs under the note to Section 141.0(b)2A, and a repair only has to be at least equivalent to the original under Section 141.0(c). The line is drawn by what comes out of the wall, not by how much of it. Pull the frame and the Section 100.1 definitions make the work an alteration at any size, and only then do the 150 and 50 square-foot triggers start counting.
The competitor who replaces nothing at all is the film installer, whose alteration path runs through Exception 1 to Section 141.0(b)3A and whose standard design under Table 141.0-E-2 is U-0.40 and SHGC 0.35 without third-party verification of the existing conditions, or the Table 110.6-A and 110.6-B defaults with it.
Storefront, curtain wall and atrium roof systems are site-built fenestration in the code's own definition, so no sticker arrives with them. Section 10-111(a)1A requires a label certificate instead, under NFRC 700 for site-built products or NFRC 705 for the Component Modeling Approach, listing U-factor, SHGC and VT.
Section 110.6(a)6 attaches a deadline: before an occupancy permit is granted, site-built fenestration outside single-family buildings has to be certified against the acceptance requirements of Reference Nonresidential Appendix NA7, with the matching label certificate readily accessible at the project location. A missing certificate does not fail the glass; it holds the occupancy permit, and the building does not open until somebody produces the paper. The code puts that requirement at the project location, which is where the contractor who installed the units is standing and the office that wrote the specification is not.
Fixed windows at 0.36, three cycles running
The prescriptive window numbers have barely moved in three cycles: in the 2019 standards, effective January 1, 2020, the vertical fenestration values were uniform across all sixteen climate zones, fixed 0.36, operable 0.46, curtain wall or storefront 0.41. The 2022 standards, effective January 1, 2023, split fixed windows to 0.34 in Climate Zones 9 and 11 through 15 and storefront to 0.38 in Climate Zones 1 and 7; the 2025 standards, effective January 1, 2026, moved none of it, and every fenestration value in Table 140.3-B is identical to the 2022 edition.The Statewide CASE Team, which writes the technical proposals the Energy Commission adopts, puts the alteration side more plainly still, reporting that the required U-factors for fenestration alterations have been unchanged since at least the 2013 code.
The prescriptive tightening did not happen. A floor arrived instead, set beneath prescriptive numbers that have not moved since 2022, in a section that had nothing to say about vision glass in either of the two prior cycles.
The next move is drafted and not adopted. The 2028 Final CASE Report on nonresidential fenestration, dated June 2026, proposes U-0.34 for fixed windows in Climate Zones 1 through 4 and 16, U-0.43 for operable windows in Climate Zones 1 through 5 and 9 through 16, and an alteration trigger at 100 percent replacement of any single fenestration type. None of that is law, and the numbers in it moved between the measure summary and the final report.
The 2025 Final CASE Report on the nonresidential envelope, the document the 0.47 came out of, set the number against products widely available in the market, with one exception it names: large-scale storefront assemblies using single-pane structural glazing, which would need thermally broken frames to reach it. That is a sentence about frames, written into a standards proposal years before the code took effect, and the label on site only reports what it produced. It gets read at inspection, and by then the frame is anchored and the glass is set.