בבא מציעא י׳:א׳ - י׳:ב׳

הבית והעליה של שנים – the house belongs to one of them and the upper story belongs to the other.

שניהם חולקים – because it is not known that these stones are of the upper story and those are from the lower part.

ורואים אלו אבנים הראויות להשתבר – if the house was crushed from its foundations and fell below it, one can know that the lower stones were broken. But if the upper part of the wall fell there from it a lot, the upper [stones] broke, since they fell from a high place, and the lower ones [remained] whole, since they fell from a low place. And [from] the first part [of the Mishnah] where it is taught that both of them divide it, is speaking about when the wall fell at night and they removed/cleared away the stones immediately, and it is impossible to establish if it fell through pressure and the bottom ones broke, or through seizing an object violently to take possession [caused them] to fall and the upper ones were broken (Bava Metzia 116a).

מקצת אבניו – and they are whole.

נוטלן – such as the case that this one claims that with some of them (i.e. the stones), it is truth, and with some, he states that he doesn’t known, for since he admits to part [of it], he is liable for an oath according to the Torah, and he is unable to take an oath, and whomever is liable for an oath and is not able to take an oath must pay. But if he said concerning all of them that he did not know, he should take an oath that he did not know and divide them (i.e., the stones) equally with his fellow.

הבית והעליה – He who leases out the upper story that is on top of his house to his fellow and says to him: “the upper story that is on top of this house, I lease to you, and the upper story opened up [a hole] of four handbreadths by four handbreadths (according to Shmuel – Bava Metzia 116b) for now, if this one (i.e., the one who has been leased the upper story) needs to use the upper story, he must use half of it above and half of it below.

ואין בעל הבית רוצה לתקן – the upper story.

הרי בעל העליה יורד ודר למטה – completely [lives downstairs] , for he had prepared the house for the upper story. And we do not force him to live half above and half below.

מעזיבה – plaster of mud/clay that they place on the ceiling. Rabbi Yose holds (Bava Metzia 117a) that the concrete of stone chippings and clay serves to level the depressions, and it levels the depressions of the upper story floor. But the Rabbis hold that the concrete of stone chippings strengths the ceiling, and the strengthening of the ceiling is required to be done by the lower dweller. And the Halakha is according to the Sages.