Mishnah Oholot 14:3: A reed which is above an opening, even if it is one hundred cubits high, it spreads impurity in any size, says Rabbi Yehoshua, but Rabbi Yochanan ben Nuri says, it should not be treated more stringently than the protrusion.

קָנֶה שֶׁעַל גַּבֵּי הַפֶּתַח, אֲפִלּוּ גָבֹהַּ מֵאָה אַמָּה, מֵבִיא אֶת הַטֻּמְאָה כָל שֶׁהוּא, דִּבְרֵי רַבִּי יְהוֹשֻׁעַ. רַבִּי יוֹחָנָן בֶּן נוּרִי אוֹמֵר, אַל יַחְמוֹר זֶה מִן הַזִּיז:

Mishnah Oholot 14:4: A protrusion which surrounds the whole house and extends into the opening three fingers, if there is impurity in the house, vessels underneath it are impure. If the impurity were beneath it, Rabbi Eliezer declares the whole house impure, but Rabbi Yehoshua declares [it] pure, and similarly with a courtyard that is surrounded by a colonnade.

זִיז שֶׁהוּא סוֹבֵב אֶת כָּל הַבַּיִת וְאוֹכֵל בַּפֶּתַח שָׁלשׁ אֶצְבָּעוֹת, טֻמְאָה בַבַּיִת, כֵּלִים שֶׁתַּחְתָּיו טְמֵאִים. טֻמְאָה תַחְתָּיו, רַבִּי אֱלִיעֶזֶר מְטַמֵּא אֶת הַבַּיִת, וְרַבִּי יְהוֹשֻׁעַ מְטַהֵר. וְכֵן בְּחָצֵר שֶׁהִיא מֻקֶּפֶת אַכְסַדְרָה: