Baba Metzia 10:1-2

Baba Metzia 10:1

If a house and an upper level belonging to two different people collapses, they divide the lumber, the stones and the mortar, and they examine the ruins to determine which party’s portion of the property was at fault. If one of them recognizes some of his own stones, he may take them but they count towards his share of what they divide.

Baba Metzia 10:2

Regarding a house and an upper level belonging to two different people, if the upper level was partially broken through into the house (i.e., there’s a hole in their joint floor/ceiling) and the owner of the house doesn’t want to fix it, then the owner of the upper level can come down and live in the house until the repair is made. Rabbi Yosi says that the lower party is only responsible for his own ceiling and the upper party is responsible for his own flooring.