[bdowling]

It’s a simple breach of contract. A rental agreement basically states that the tenant will pay rent and the landlord will provide a habitable apartment. The most common breach occurs when the tenant doesn’t pay their rent. However, when the apartment isn’t habitable, it’s the landlord who is in breach. The damages in such a case are the cost of substitue comparable accommodations, even if that cost is higher than the rental amount. So the landlord may not have to provide substitute accommodations, but he would be liable for damages if he didn’t.

Edit: I may be biased by living in California where there is apparently an implied warranty of habitability.