Tractate Oholot - Chapter 10 - Mishnah 3 אהלות פרק י׳ משנה ג׳

If part of the uncleanness is in the house and part directly [below] the hatchway, the house becomes unclean, and what is directly [above] the uncleanness becomes unclean, the words of Meir. Rabbi Judah says: the house becomes unclean but what is directly [above] the uncleanness remains clean. Rabbi Yose says: if there is sufficient of the uncleanness for it to be divided so that [one part] defiles the house and [the other part] defiles what is directly [above] the uncleanness, [both spaces] become unclean; if not, the house becomes unclean but what is directly [above] the uncleanness remains clean.