Mishnayos Oholos Perek 6 Mishnah 4

[In the case of] a wall between two houses and there is uncleanness within it, The house nearer to the uncleanness is unclean, And the house nearer to the clean part is clean. If [the uncleanness] is in the middle, both are unclean. If there is uncleanness in one of the [houses] and there are vessels in [the thickness of] the wall: Those in the half nearer the uncleanness are unclean, Those in the half nearer the clean [house] are clean, And those in the middle are unclean. [With regard to the] plaster-work between the house and the upper story, and there is uncleanness in it: If it is in the lower half, the house [below] is unclean and the upper story is clean If it is in the upper half, the upper story is unclean and the house is clean: If it is in the middle, both are unclean. If there is uncleanness in either [the house or the upper story] and there are vessels inside the plaster-work, Those in the half nearer the uncleanness are unclean, And those in the half nearer the clean [space] are clean. If they are in the middle, they are unclean. Rabbi Judah says: all the plaster-work is considered as part of the upper story.

כֹּתֶל שֶׁבֵּין שְׁנֵי בָתִּים וְהַטֻּמְאָה בְתוֹכוֹ, בַּיִת הַקָּרוֹב לַטֻּמְאָה, טָמֵא. וְהַקָּרוֹב לַטָּהֳרָה, טָהוֹר. מֶחֱצָה לְמֶחֱצָה, שְׁנֵיהֶם טְמֵאִין. טֻמְאָה בְאַחַד מֵהֶן וְכֵלִים בַּכֹּתֶל, מֵחֶצְיוֹ וּכְלַפֵּי טֻמְאָה, טְמֵאִין. מֵחֶצְיוֹ וּכְלַפֵּי טָהֳרָה, טְהוֹרִין. מֶחֱצָה לְמֶחֱצָה, הֲרֵי הֵן טְמֵאִין. מַעֲזִיבָה שֶׁבֵּין הַבַּיִת לָעֲלִיָּה, טֻמְאָה בְתוֹכָהּ, מֵחֶצְיָהּ וּלְמַטָּן, הַבַּיִת טָמֵא וַעֲלִיָּה טְהוֹרָה. מֵחֶצְיָהּ וּלְמַעְלָן, הָעֲלִיָּה טְמֵאָה וְהַבַּיִת טָהוֹר. מֶחֱצָה לְמֶחֱצָה, שְׁנֵיהֶן טְמֵאִין. טֻמְאָה בְאַחַד מֵהֶן וְכֵלִים בַּמַּעֲזִיבָה, מֵחֶצְיָהּ וּכְלַפֵּי טֻמְאָה, טְמֵאִין. מֵחֶצְיָהּ וּכְלַפֵּי טָהֳרָה, טְהוֹרִין. מֶחֱצָה לְמֶחֱצָה, הֲרֵי הֵן טְמֵאִין. רַבִּי יְהוּדָה אוֹמֵר, כָּל הַמַּעֲזִיבָה לָעֲלִיָּה: