(a)

1. (1) Amendments, additions, and deletions to the California Building Standards Code, including, but not limited to, green building standards, adopted by a city, county, or city and county pursuant to Section 18941.5 or pursuant to Section 17958.7, together with all applicable portions of the California Building Standards Code, shall become effective 180 days after publication of the California Building Standards Code by the commission, or at a later date after publication established by the commission.
2. (2) The publication date established by the commission shall be no earlier than the date the California Building Standards Code is available for purchase by the public.

(c) Notwithstanding subdivision (b), and commencing October 1, 2025, to June 1, 2031, inclusive, a city or county shall not establish more restrictive building standards, including, but not limited to, green building standards, that are applicable to residential units, unless one of the following conditions is met:

1. (1) The changes or modifications are substantially equivalent to changes or modifications that were previously filed by the governing body of the city or county and were in effect as of September 30, 2025.
2. (2) The commission deems those changes or modifications necessary as emergency standards to protect health and safety.
3. (3) The changes or modifications relate to home hardening.
4. (4) The building standards relate to home hardening and are proposed for adoption by a fire protection district pursuant to Section 13869.7.
5. (5) The changes or modifications are necessary to implement a local code amendment that is adopted to align with a general plan approved on or before June 10, 2025, and that permits mixed-fuel residential construction consistent with federal law while also incentivizing all-electric construction as part of an adopted greenhouse gas emissions reduction strategy.