Question
In a previous article you wrote that if one neighbor built an apartment on the unused space in his building with the approval of the other neighbors but without their monetary participation, when the neighbors subsequently contribute towards the cost of building in the dead space, they are not entitled to charge him rent for using the property in the years prior to their payment. This is a very common situation and often it takes years until the neighbors pay and in the interim building costs often change significantly, as they did this year in Israel due to the war. If the neighbors cannot charge rent for the prior years, perhaps the reason is that the one who built is the owner of the apartment he built and when the neighbors pay him, they are then buying a portion of the apartment which their neighbor built. If that is the proper understanding of your ruling then the price that the neighbors must pay should be the cost to build the room at the time the neighbors pay and not how much it actually cost the one who built. Is that correct?
Answer
The fact that the one who built is not obligated to pay rent does not prove that the apartment belonged to him until the neighbors paid him. The reason is that perhaps the correct rationale is that since the one who built, built for the neighbors, when the neighbors fail to pay him for his expenses, he is just allowed to withhold payment for use of their property as a legal weapon to force the neighbors to pay what they owe him for building. Nonetheless, all the neighbors always own the apartment. We have to seek further to decide this issue.
One case where this issue is discussed by the Rishonim concerns a wall between two neighbors. The Mishna (BB 5A) rules that each neighbor can force the other to participate in constructing a wall that is four amos (about two meters) high between the two properties. The Mishna says that if one of the neighbors (A) wishes to build even higher, he may build but he cannot force his neighbor B to participate in the addition. However, if B who did not pay subsequently builds on his own property in a manner that utilizes the higher wall, he must pay his share of the amount his neighbor spent on the additional height.
The Rishonim (Tosafos ibid, Nimukei Yosef BB 3A and many others) question why, when B makes use of the additional height, he needs to pay anything. They argue that in the initial stage when A spent the money to build, he did so for himself to ensure that B will not be able to see into his property. Therefore, for the original building B should not owe anything.
At the second stage when B makes use of the higher wall, he should also not be liable because his benefit did not cause A any additional expense. This seems to be a situation of ze nehene veze lo choseir-B's benefit did not cause a loss for A. Thus, B should not be liable at that stage either.
Tosafos gives two answers why B has to pay for the benefit he derived. These answers are not relevant to our discussion. However, what is important for us is that according to Tosafos, when A builds, we view him as building for himself. It is only later when B begins using A's wall, that he can be charged for using A's wall.
The Nimukei Yosef (BB 3A) has a totally different approach. (The Ketsos 158, 6 agrees and gives a detailed explanation of this approach.) He argues that when A built, he did so with the intention that B will eventually use the wall and pay for his share. Therefore, when A built, he built both for himself and for B. Thus, when B began using the additional height of the wall, he accepted A's offer and he acquired his part of the wall retroactively from the time the wall was built.
The Ketsos explains that if one follows the approach of the Nimukei Yosef the question of Tosafos does not begin because B never uses A's wall. Rather, when he uses the wall, he acquires partial ownership of A's wall retroactively.
The Chazon Ish (BB 3, 1) discusses the issue of how much B has to pay A according to the Nimukei Yosef if the cost of building the wall changed between the time when A built and the time B began using the wall. He rules that since B acquires ownership retroactive from the time A built the wall, he must pay according to the price at the time A built regardless of any price fluctuation.
We note that the rationale of the Chazon Ish is very clear. A offered to sell a share in the wall at the time he built the additional height onto the jointly-owned four amos high wall and B later accepted that offer. Moreover, according to the Nimukei Yosef this is the better alternative for A since otherwise B could just use A's wall without paying anything because he could claim that his benefit does not cause A any loss. Note that the Nimukei Yosef does not agree with the answers of Tosafos. Thus, there is no way that A can charge a higher price due to the rise in the cost of building the wall.
The important principle that we can derive from this discussion is that when one makes an acquisition which is effective retroactively, the price is the price at the time that the sale took effect legally and not the price when the seller's offer was accepted. (Of course, this is not typical because generally sales do not take effect retroactively.)
Turning to your situation, in the previous article we studied the Gemara (BM 117A) that discusses a two-story house that collapsed and the owner of the upper floor wished to rebuild and the owner of the downstairs did not yet want to rebuild. We saw that the owner of the upper floor may rebuild the downstairs and live there until he is reimbursed by his downstairs neighbor. We learned that the only reason he may live there without paying the owner of the downstairs rent for his use of the downstairs is because the downstairs owner did not yet pay for the cost of building his floor. Furthermore, we saw that Tosafos ruled that if the downstairs burns down before its owner pays for the cost to build his floor, he does not owe anything to the upstairs owner who built it.
From these rulings it is apparent that when the upstairs owner builds, he does so with the intention that the downstairs owner will eventually reimburse him for the building and when the downstairs owner actually reimburses him, he acquires his rebuilt floor retroactively. The fact that when the owner pays he acquires it retroactively is clear because if he only acquires it after he pays there is no issue concerning the payment of rent for the use of the downstairs by the upstairs owner who built it. If the upstairs owner owns the first floor until he is paid for his expenses he would not owe anyone rent. Moreover, we see from the fact that in case the downstairs burns down that the downstairs owner owes nothing, that until he actually pays for the building the upstairs owner does not own the floor at all.
Therefore, it is clear in this case that paying for the improvement serves to retroactively acquire it for the owner of the place that was improved.
Moreover, generally when one improves another person's property, he does so with the intent that he will be paid by the property owner who will retroactively acquire the improvement when he pays what he owes. That is why the Ra'avad ruled (cited by Rosh BM 8, 23 and explained by the Chazon Ish BB 2, 6 and others) that the reason one who built a structure on someone's vacant property may live there and not pay rent is because the property owner did not yet pay him for his building.
Another proof that in general when one improves another person's property the price he is entitled to is the price at the time of building, is a general ruling of the Rambam and SA (CM 375, 9) that if the one who improved the property cannot prove how much it cost him to build he must swear to the amount. If the determinant is the cost at the time of payment, it is irrelevant how much it cost to build.
Thus, we have seen that when one improves another person's property, he does so with intent to be paid later by the property owner who will then acquire his improvement retroactively. Also, we have seen that the price that the owner must pay if he acquires an improvement retroactively is the cost at the time it was built and not the cost at the time that the owner pays for it.
Since in your situation when you built the apartment, you built it on the vacant space that belonged to all the apartment owners, you improved a commonly-owned property. Therefore, when the other apartment owners pay you, they retroactively acquire their share of what you built. Therefore, even if prices rose in the interim you are only entitled to be paid according to your cost to build the apartment.
We note that it is probably in your best interest that it works this way because if you were the owner of the apartment until the neighbors paid you, when you calculate how much they have to pay you would have to deduct the depreciation in the value of what you built due to time and wear and tear. Also, you would have to pay rent for use of the land (not the apartment) until they paid as the Rosh rules (BK 2, 6) in the case where a person built on the land that belonged to orphans.
