Case:The defendant (=def) rented an apartment from the plaintiff (=pl). Pl is suing def for not paying rent in full. Def counters that since the heat in the apartment was not working for much of the winter, despite pl’s half-hearted efforts to fix it, and since there were other shortcomings in the apartment, they should not have to pay in full.

Ruling:The Shulchan Aruch (Choshen Mishpat 312:7) rules that if a rented house fell, the renter can reduce the rent corresponding to the time it was down. The Rama (ad loc.) says the same is true if it burns down and that if all the houses in the area burn down, it is a "plague of the region" and the rent is reduced. The Rama’s opinion is unclear because he seems to distinguish between one house burning down and many burning down, but it seems that in both cases a reduction in rent is called for. The S’ma (312:34) and the Taz demonstrate that the Rama cited an opposing opinion (that is missing from our texts) that usually rent is not reduced, after which he added that if it happened to many houses, all agree it is reduced. The Netivot Hamishpat (312:13) says that if the renter agreed to pay in advance, the rent is not reduced, and that is why it has to add that if several houses were burnt, there is a reduction. It emerges that in a case that the house became dysfunctional for part of the time, there is a machloket whether he has to pay in full. The machloket revolves around the question whether one who rents real estate is like the property’s owner for that time. If he is, then just like any other landowner, when something happens to the property, the owner loses.
The aforementioned machloket would seem to apply to cases where the apartment continued to function but on a lower level. However, the Rambam (Sechirut 5:1) and Shulchan Aruch (CM 310:1) rule that if one rented an animal and it got sick so that it worked inefficiently, he has to pay in full. The Ra’avad and Rashba (Bava Metzia 78a) disagree. Most poskim accept the Rambam’s opinion that the renter has to pay in full. However, here there are other reasons to accept def’s claim.
The Rambam’s logic to distinguish between an animal that died in the middle of the rental and a sick animal is that when there is no clear change in the animal, just that it is presently less efficient, we attribute the loss to the misfortune of the renter (P’nei Moshe II:32). However, in this case, many of the apartment’s deficiencies were present at the time of the rental. Therefore, it was not def’s misfortune but pl’s lack of responsibility in not providing a fully functional apartment (see Netivot Hamishpat 310:1). The fact that pl was responsible to fix the deficiencies also changes two things. His responsibility means that when the need for fixing arose, it was pl’s misfortune as well. Also, if he did not fix problems in a timely fashion, he breached the contract in a manner that requires compensation.
Beit din ascertained that pl was negligent in his handling of the situation and assessed a sum to reduce from the rental fee.