HSC §18938.5: (a) Only those building standards approved by the commission, and that are effective at the local level at the time an application for a building permit is submitted, shall apply to the plans and spec

(a) Only those building standards approved by the commission, and that are effective at the local level at the time an application for a building permit is submitted, shall apply to the plans and specifications for, and to the construction performed under, that building permit. (b) (1) A local ordinance adding or modifying building standards for residential occupancies, which are published in the California Building Standards Code, shall apply only to an application for a building permit submitted after the effective date of the ordinance and to the plans and specifications for, and the construction performed under, that permit. (2) Paragraph (1) shall not apply to any of the following: (A) A city or county that has been subject to an emergency proclaimed pursuant to the California Emergency Services Act (Chapter 7 (commencing with Section 8550) of Division 1 of Title 2 of the Government Code). (B) A permit that is subsequently deemed expired because the building or work authorized by the permit is not commenced within 12 months from the date of the permit or the permittee has abandoned the work authorized by the permit. (C) A permit that is subsequently deemed suspended or revoked because the building official has, in writing, suspended or revoked the permit due to its issuance in error or on the basis of incorrect information supplied. (c) No model code made applicable to any additional occupancy shall apply to any project that has been submitted for a building permit prior to the effective date of that model code. (d) Notwithstanding subdivisions (a) to (c), inclusive, the state and local building standards in effect at the time an application for a building permit is submitted, for a residential dwelling based on a model home design approved under those standards, shall apply to all future residential dwellings based on that approved model home design in the same jurisdiction, unless the model home design substantially changes at a later date or 10 years have passed since the building permit for the model home design was approved by the jurisdiction, whichever comes first.