I've only got the 2016 building codes on me, but there don't seem to be major changes in the relevant 2019 building codes according to what information I've been able to find.
Section 402.5 (Chapter 4) of the California Mechanical Code states:
Each bathroom shall be mechanically ventilated in accordance with Division 4.5 of the California Green Building Standards Code (CALGreen).
Section 4.506.1 of the 2016 CALGreen measures state that:
Each bathroom shall be mechanically ventilated and shall comply with the following:
- Fans shall be ENERGY STAR compliant and be ducted to terminate outside the building.
- Unless functioning as a component of a whole house ventilation system, fans must be controlled by a humidity control.
I'm living in a relatively old building, and the restroom has a high vaulted ceiling and no mechanical venting. As a result, the restroom regularly gets moldy, and my landlord has been dragging their feet on fixing this. I suspect it would violate Section 17920.3 of the health and safety code, but I'm not certain:
Visible mold growth, as determined by a health officer or a code enforcement officer, as defined in Section 829.5 of the Penal Code, excluding the presence of mold that is minor and found on surfaces that can accumulate moisture as part of their properly functioning and intended use.
I've yet to ask about mechanical venting (which would almost certainly prevent the mold problem once it's been cleaned) because I'm not sure there's any obligation for this to be provided given that the apartment is old.