Fortunately CA is very tenant friendly, and they have a couple of implied covenants that go with every lease - these CANNOT be waived in the lease.
1. Implied warranty of habitability:
Civil Code 1941.1 - http://www.leginfo.ca.gov/cgi-bin/displaycode?section=civ&group=01001-02000&file=1940-1954.1
2. implied warranty of quiet enjoyment CC 1927:
So basically if the home is in such a condition that it is not safe, is not clean, or is not in a condition such that the tenant can have quiet enjoyment of the property, then it constitutes a "constructive eviction".
If the landlord is in breach of these covenants, the tenant is constructively evicted and may remain in possession and stop rental payments in proportion to the impairment of use and enjoyment of the premises.If the tenant is actually or constructively evicted from the premises as a result of events not caused by the tenant, such as partial condemnation or lack of access to the premises the tenant’s rental obligations terminate if (and only if) the tenant vacates the premises - it is similar to a breach; since the landlord breached his part of the contract, the tenant need perform theirs.
In order to help avoid any liability (ie one needs adequate proof that the unit is uninhabitable) it is best to take pictures, have witnesses, etc. Another good thing that can really help is to call the local health inspector, or for criminal events, the local police department, so the incident is document.
Here is general information for future reference
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