Unpermitted units, explained
An illegal rental unit is a living space that is rented out even though it was never approved or permitted for people to live in. It is sometimes called an unpermitted unit.
Common examples include a garage, basement, attic, or shed that was converted into a living space without proper permits; a unit added to a property without city approval; and extra units squeezed into a building beyond what is legally allowed. These spaces often lack things the building code requires for a legal home, such as proper exits, ceiling height, ventilation, heat, or safe wiring and plumbing.
A unit can be "illegal" because it was built or converted without permits, because it does not meet safety codes, or because the property is not zoned to allow another rental unit there.
Importantly, the fact that a unit is illegal is the landlord's problem to answer for — not a reason you lose your rights as a tenant. If you think you are renting an illegal unit, a free, confidential review can help you understand your protections.
This is general information about California tenant rights, not legal advice. Every situation is different.