2.50 kg or 2.50 tons? The flat-glass unit error in CALGreen 5.409.3

Open CALGreen's embodied-carbon prescriptive path — Table 5.409.3 — and run your eye down the material rows. Steel is in MT CO2e/MT. So is rebar. Then you hit flat glass: 2.50 kg CO2e/MT. One row, a different unit, and a number a thousand times too small to describe real glass.

Here's the thing: no flat-glass EPD on the market can pass that row as printed. Float glass carries well over a thousand kilograms of CO2e per metric ton — the Buy Clean benchmark alone sits at 1,430. A ceiling of 2.50 kilograms per ton isn't a stretch target; it's physically impossible. Read literally, the code fails every compliant product. The fix is a single unit: the row should read 2.50 MT CO2e/MT.

The row that can't be met as printed

Table 5.409.3 is the prescriptive path for product global warming potential (GWP). Each permanently installed product it lists needs a Type III environmental product declaration (EPD), and the product's declared GWP can't exceed the table value. For nonresidential projects, this path applies at 50,000 square feet or greater as of January 1, 2026.

Scan the units column and the flat-glass row is the odd one out.

Verified against the 2025 CALGreen (Part 11) code text, Table 5.409.3: hot-rolled structural steel sections read "1.77 | MT CO 2e/MT" and steel plate "2.61 | MT CO2e/MT," but flat glass reads "2.50 | kg CO2e/MT." Every metal row is in metric tons per metric ton; the glass row is printed in kilograms.

A plan checker who takes the printed unit at face value and compares it against a glazing EPD — which reports in the hundreds-to-thousands of kg CO2e per ton — will fail glass that actually complies. That's the foot-fault.

Where 2.50 actually comes from (our math)

The table's own footnote tells you the unit is wrong. Footnote 1 — the one slated for repeal — states the Table 5.409.3 limits are "based on 175 percent of Buy Clean California Act (BCCA) GWP values."

So go to the BCCA source. DGS publishes the flat-glass limit at 1,430 kg CO2e per metric ton of glass — that is 1.43 MT CO2e/MT (effective January 1, 2025, unfabricated product).

Now the arithmetic, which is ours: 1.43 × 1.75 = 2.50. The printed "2.50" is exactly 175 percent of the BCCA flat-glass limit expressed in metric tons per metric ton. The number is right; the unit label is off by a factor of 1,000. The real ceiling is 2.50 MT CO2e/MT — 2,500 kg CO2e per ton, not 2.5 kg.

One caution: don't reverse-engineer the rest of the table this way. The flat-glass match is clean because its BCCA limit hasn't moved, but other BCCA values have been lowered since, so not every row equals 175 percent of today's published numbers. Use this check for flat glass only.

The same error sits in the voluntary Table A5.409.3, where flat glass is listed at 2.15 (Tier 1) and 1.43 (Tier 2), also labeled "kg CO2e/MT" — values that line up with 150 percent and 100 percent of that same 1.43 MT/MT BCCA limit.

What's changing — and what isn't

The correction is already written. The final express terms for BSC 03/25 and DSA-SS 04/25 — the 2025 Intervening Cycle packages amending CALGreen Part 11 that went before the Building Standards Commission at its August 25–27, 2026 meeting — change the flat-glass unit in both tables from "kg CO2e/MT" to "MT CO2e/MT." BSC's stated rationale calls it a typo: correct the printed unit of value "from kg CO2e/MT to MT CO2e/MT." The same packages repeal Footnotes 1 and 2 under each table — footnote 1 being the one that states the 175-percent BCCA basis (150 percent in the voluntary Table A5.409.3) — because code users were misreading them as an instruction to multiply the table values.

Two things this is not. It isn't new law — the GWP ceilings don't move; only the printed unit is corrected. And it isn't in force yet: these are supplement changes slated to take effect July 1, 2027. (For why this 2027 cycle is so thin, see our AB 130 supplement preview.) Until the supplement publishes, confirm the recorded action with your jurisdiction rather than assuming the printed page is final.

How to keep compliant glazing from failing

• Read the flat-glass row as 2.50 MT CO2e/MT today. That's the only value the footnote math and the BCCA source support.
• Check the EPD's declared unit before you compare. A glass EPD may report kg CO2e per ton or per square meter — convert to the table's basis first.
• Put the unit on the WS-5 calculation sheet. Spelling out "MT CO2e/MT" next to the 2.50 keeps a reviewer from failing compliant glazing on a printing error. (It's the same decimal-and-unit trap as the WS-2 water worksheet — see 0.35, not 35.)
• When stakes are high, verify with your local jurisdiction which printing and which unit they're reviewing against.

What CrossBeam does with it

CrossBeam reads glazing submittals against the unit the code actually means — 2.50 MT CO2e/MT — so a compliant flat-glass EPD isn't failed on a printed typo. It flags the unit mismatch before it reaches a corrections letter, and tracks the BSC 03/25 correction so the right ceiling applies whether a project is reviewed under today's printing or the 2027 supplement.