California’s Green Building Standards Code (CALGreen), Title 24, Part 11, cut the commercial building threshold for mandatory embodied carbon compliance from 100,000 square feet to 50,000 square feet on January 1, 2026, roughly doubling the number of projects that must document material emissions to get a permit. The change arrives alongside two other shifts practitioners need to track together. The California Air Resources Board (CARB) hit the first reporting deadline under California’s Climate Corporate Data Accountability Act (SB 253) on August 10, 2026, and the international standard governing how Environmental Product Declarations (EPDs) get built and verified, ISO 14025, was rewritten for the first time in nearly 20 years in late June. Specifiers who lean on EPDs to satisfy CALGreen’s prescriptive pathway now face a wider regulatory net and a changed set of rules for the documents that fill it.
California’s net widens
CALGreen’s embodied carbon mandatory measures took effect July 1, 2024, requiring non-residential buildings over 100,000 square feet and K-12 school buildings over 50,000 square feet to demonstrate reduced embodied carbon through one of three pathways. A project can document reuse of at least 45% of an existing structure and enclosure, run a whole building life cycle assessment showing at least 10% lower global warming potential than a code baseline, or take the prescriptive route and specify products, primarily concrete, steel, glass and mineral wool, backed by Type III EPDs with global warming potential no higher than 175% of the industry average for that product category, per CALGreen Table 5.409.3. Hospitals under the jurisdiction of the Office of Statewide Health Planning and Development and most residential projects remain exempt. The California Building Standards Commission administers the code and adopted the 2025 CALGreen cycle, effective January 1, 2026, which lowered the commercial threshold to 50,000 square feet.
The practical effect is a much larger population of mid-size commercial projects, office buildings, warehouses, retail centers, now facing a compliance obligation that previously applied only to the largest developments. Ben Stapleton, chief executive of the US Green Building Council of California, has argued the mandate’s real leverage is on the supply side: California’s market size pushes manufacturers to produce lower carbon products that then become available nationally. Emily English, sustainability director at the contractor BnBuilders, described the on-the-ground reality in blunter terms, calling the added documentation “another piece of paper to review” and “another hurdle to keeping things moving,” a framing likely to resonate with project teams now clearing the lower threshold for the first time this year.
The Scope 3 question sitting behind both
Embodied carbon reporting does not exist in a vacuum from corporate climate disclosure, and California just hit its first deadline there too. The California Air Resources Board finalized initial regulations implementing California’s Climate Corporate Data Accountability Act (SB 253) and its companion climate-related financial risk law (SB 261) on February 26, 2026. The first-year reporting deadline under SB 253, applicable to companies with more than $1 billion in global annual revenue doing business in California, fell on August 10, 2026, just one week before publication of this article, and covered only Scope 1 and Scope 2 emissions. Scope 3, the category that would capture purchased construction materials for building owners, developers and product manufacturers alike, has no reporting deadline yet. CARB has said it will run a separate rulemaking later in 2026 to set Scope 3 requirements and deadlines starting in 2027, and SB 261 enforcement is currently paused by a Ninth Circuit injunction, making its disclosures voluntary in the meantime.
That timeline matters for embodied carbon specifically because Scope 3 accounting, once it arrives, will lean on the same EPD infrastructure that CALGreen already requires for prescriptive compliance. A revised ISO standard that changes how EPDs are verified and what independence they must demonstrate is not just a technical footnote for program operators. It is the data layer that Scope 3 rules will eventually sit on top of.
What to watch
Specifiers working prescriptive CALGreen compliance on projects between 50,000 and 100,000 square feet should confirm with manufacturers whether cited EPDs were issued under the prior ISO 14025 edition or the revised one, and ask program operators directly whether re-verification is expected, since neither EPD International nor EPD Australasia has set a public transition deadline. Sustainability officers at companies approaching the SB 253 revenue threshold should treat the August 10, 2026 Scope 1 and Scope 2 filing as a dry run, not a finish line, and start mapping construction and materials spend into Scope 3 Category 1 now, ahead of CARB’s forthcoming rulemaking. Building departments in California processing 2025 CALGreen cycle permits should expect more embodied carbon submittals across a wider range of project sizes than in any prior cycle, and should budget review time accordingly. The common thread across all three is the same: the paperwork behind embodied carbon claims is getting more scrutiny, not less, and the standards writing that paperwork are changing under practitioners’ feet.