Chapter 34 of the California Building Code addresses the issue of when code upgrades are triggered in existing buildings.
Section 3402 defines an existing building as a “structure erected prior to the date of adoption of the appropriate code, or one for which a legal building permit has been issued.”
Section 3403, 3404, and 3405 deal with additions, alterations and repairs of existing buildings in that “Additions, alterations or repairs may be made to any building or structure without requiring the existing building or structure to comply with all the requirements of this code, provided the addition, alteration or repair conforms to that required for a new building or structure.”
The basic premise of Chapter 34 is that if you touch it you need to bring it up to current code. If there is no work then there is no requirement to upgrade.