Landlords facing any claim of the breach of the warranty of habitability may have defenses available to the action by their tenant. Some defenses are provided by statute, where certain defenses and limitations on tenant actions and remedies are specifically enumerated.
Every lease agreement carries with it an implied warranty of habitability. That is, the landlord warrants to the tenant that the premises leased to the tenant for the purpose of habitation is in fact suitable for human habitation. This does not need to be written in your lease in order to be in effect; the implied warranty of habitability is implied in every lease agreement.