I was renting an apartment for 5 years. About six months into our stay, I contacted the landlord and said that I believe there is mold in our ac vents and my children and I are getting sick. He sent over a handyman who sprayed some Lysol into the vent and told us to run the fan. I thought that was ridiculous, and realized what I was dealing with. I continued to wash the filters every couple of weeks but I knew there was mold. I suffer from allergies and my son (at the time we moved in he was a year old) was diagnosed with allergies shortly after moving in. I had respiratory issues throughout our stay. My son suffered from asthma and eczema the entire stay, with visits to Terem on occasion for severe asthma episodes. Because we both suffer seasonal allergies, and my son also has many food allergies, we did not know just how much the mold was contributing to the illnesses. We decided to break our lease. I hired a mold expert who not only confirmed mold in the walls, but said there was dangerous mold in the ac. About a week after moving to a new mold-free apartment, for the first time in five years my son slept peacefully through the night, breathing through his nose. No more mouth breathing and loud sleep-apnea-type snoring. A few months and his eczema is all cleared up. I have not needed to use my nasal sprays for months now. All allergies, seasonal and food, still remain, but no more mold. What is the Halacha with regard to the five years spent we paid rent for an uninhabitable mold environment that caused illness? Obviously, it took moving out to realize that the mold was the main factor and it had never been taken care of properly.
Before answering your question let us backtrack to the situation while you lived in the apartment and examine what you could have done.
Obviously mold, especially if it can cause illness, is a serious issue. You say you noticed the mold after six months and you asked the owner to fix the problem which he failed to do.
The first point to note is that it is the responsibility of the owner to ensure that his apartment is mold free whether the problem existed before you moved in or only started after you moved in. This is true both in Torah law and in secular law. (Secular law is sometimes important because it may create a custom and custom prevails in Torah law.) The Torah law is that any repair which the tenant cannot repair by himself is the responsibility of the owner. Moreover, if it is customary for the owner to fix the problem, even if the repair does not require a craftsman, the owner is required to do the repair. Similarly, Israeli law states, “It is the owner’s responsibility to repair any damages which materially prevent or inhibit the use of the rental unit.”
The second point is that if the owner did not remedy the situation you had the prerogative to break your contract and leave, which is what you did in the end. However, you could have done so from the moment the owner refused to remedy the problem. This is true whether he could fix the problem or he couldn’t. For example, the Maharam Padua (response 39) ruled that if the government forbade lending with interest, then one who rented a store which had a license which enabled its occupant to lend with interest could break the contract, even though there was nothing that the owner could do to rectify the problem. Certainly, if it was in the power of the owner to rectify the problem and he refused, as it was in your situation, you were allowed to vacate. This is stated by the Ra’anach (res. 38): “One is only obligated to pay rent for a house that is free of damages that are the responsibility of the owner.”
The third point is that you had the prerogative to force the owner to fix the mold problem. If one makes a contract he is required to ensure that the contract remains in effect. Thus, if one sells a defective but fixable item the Ulam Hamishpot (232, 5) rules that the seller must repair the item if the customer so desires, and he cannot refuse to fix it and return money. This is especially true by a rental since the Nesivos (312, 5) rules that an owner has a personal obligation to provide his renter with a usable property. We should note that the owner’s liability is limited to the amount of rent that he receives based on the contract. (There is a dispute if it is limited to the rent remaining until the termination of the contract or includes the entire rent the renter had to pay under the terms of the contract.) Moreover, if the owner would have refused to rectify the problem himself, you could have taken matters into your own hands and hired a company to fix the problem using future rent to fund the cost of fixing the problem.
However, you failed to make use of the remedies that were available to you for five years, and your question is if you are entitled to a partial reimbursement for the rent you paid.
The Mishna (Bava Metsiya 78 A) rules that if one rented a donkey and the donkey became blind one does not receive any reimbursement for the fact that it is much more difficult to use the donkey. Similarly, the Nesivos rules (310, 2) that if one rented a property and during the rental period the army required the occupant to quarter soldiers in the house, if the renter could still use the property he must pay rent in full. Only if the property became unusable is the renter entitled to cease paying rent for the time the soldiers were quartered in the house he rented.
Similarly, the Maharam of Padua, in the case of a store, ruled that if the property was usable for all of the original uses that it was rented for, the renter must pay in full. However, if the renter cannot fully utilize the rental then he is entitled to a reduction for the time the property was partially unusable. However, he adds that if there was no hope that the property would be fixed then the renter must choose to vacate and if he fails to do so he is not entitled to a reduction in rent.
In conclusion: You could have forced the owner to repair the property or you could have left. However, having failed to do either, you are not entitled to any reimbursement for the rent that you paid.