When a roach problem crosses into a legal violation
Yes. A serious cockroach infestation can be a habitability violation in California when the landlord fails to address it. State law requires rentals to be kept free of vermin, and cockroaches qualify.
California's habitability standard (Civil Code Section 1941.1) lists a building being "free from... rodents, and vermin" as part of what makes a home livable. A stray roach now and then may not rise to a legal violation, but a real, ongoing infestation — especially one the landlord was told about and did not properly treat — can breach the implied warranty of habitability, the automatic promise that your home will be fit to live in.
Because roaches spread through the walls and pipes of a building, these infestations are often the landlord's problem to solve, not the tenant's. If cockroaches have taken over your unit and your landlord will not deal with it, a free, confidential review can explain your options.
This is general information about California tenant rights, not legal advice. Every situation is different.