[The case presented is a complex one that has several elements to it. We have chosen to focus primarily on one element.]
Case:


Ruling: There is a machloket about how to relate to work that a kablan/ uman (craftsman, who is paid by the job, not by time) does and the payment due to him (Bava Kama 98b). One opinion views it as the worker working directly for the owner and automatically creating an obligation according to their agreement. The other opinion views the kablan as accumulating quasi-ownership in the object (uman koneh b’shevach kli = ukbsk), corresponding to the value of the improvements, and selling his part in the object to the owner for his wages due.
The Divrei Geonim (82:4) discusses a case where a kablan made improvements in fabric that his friend was preparing for a nobleman, but before he could return the object to his friend, the nobleman burnt the clothes in anger. He says that whether or not the kablan deserves to be paid for his work depends on whether ukbsk, as in this case the worker’s quasi-acquisition was destroyed. Since poskim are undecided on that matter (see Shach, Choshen Mishpat 306:30) the worker cannot extract payment from his friend out of doubt when he is not able to return the object, even if it was not his fault.
However, there are several opinions that hold that the machloket of ukbsk applies only to cases where the worker himself damaged the object after making improvements or to the matter of the worker having a lien on the object to receive his fees. According to the view that limits the machloket, both opinions regarding whether ukbsk agree that the worker acquires rights to his pay, which remain even if something (beyond the worker’s control) happens to the object (see Shach, CM 126:76). Some distinguish between cases where the object was destroyed in the midst of the work, in which case he does not yet deserve his pay, and where the work is completed and thus pay was due (S’ma 335:8; K’tzot Hachoshen 305:2).
Nevertheless def can rely on the opinions that pl does not deserve the money, so that money cannot be extracted from him. The matter is clearer in this case, where pl was aware that construction exceeded the permit and he should have thus made a condition that he demands to be paid even if the work is suspended or destroyed.
[The author of this ruling does not deal with the significant question of whether ukbsk applies to work done to land, as opposed to movable objects.]