Pursuant to California Civil Code _ 1941, landlords have a duty to maintain residential property in a condition "fit for human occupation." Landlords must not let conditions exist that render the property "untenantable." Such conditions may include lack of weather protection, broken windows, doors, or locks, plumbing or gas problems, lack of hot or cold water, electrical problems, or unclean, unsanitary conditions. (Parallel duties may also exist under the rental agreement and the common law.)
If a landlord fails to remedy an untenantable condition, the tenant may undertake repairs and deduct the cost from the rent, but only under certain conditions.
Initially, the tenant must give the landlord "reasonable" notice that an untenantable condition exists and that it requires fixing. Although this notice may be oral, it should be in writing. Thirty (30) days is presumed to be a "reasonable" amount of time, however it can be much less depending on the type and severity of the condition.
After the notice period expires and the landlord fails to correct the condition, the tenant can vacate the property with no further obligation or the tenant may repair the condition and deduct the cost of the repair from the next month's rental payment.
There are two significant limitations to the right to "repair and deduct": (1) the tenant can deduct a maximum of one month's rent and (2) a tenant can only utilize this procedure two times in any 12-month period.