Mishnah Oholot 12:5: The beams of the house and the upper story which do not have plaster on them and they are aligned, if there was impurity underneath one of them, underneath it is impure. [If it was] between the lower and the upper one, between them is impure. If it was on top of the upper one, opposite it up to the firmament is impure. If the upper ones were as if between the lower ones and there was impurity under one of them, underneath all of them is impure. If it was on top of them, opposite it up to the firmament is impure.

קוֹרוֹת הַבַּיִת וְהָעֲלִיָּה שֶׁאֵין עֲלֵיהֶן מַעֲזִיבָה וְהֵן מְכֻוָּנוֹת, טֻמְאָה תַחַת אַחַת מֵהֶן, תַּחְתֶּיהָ טָמֵא. בֵּין הַתַּחְתּוֹנָה לָעֶלְיוֹנָה, בֵּינֵיהֶן טָמֵא. עַל גַּבֵּי הָעֶלְיוֹנָה, כְּנֶגְדּוֹ עַד הָרָקִיעַ טָמֵא. הָיוּ הָעֶלְיוֹנוֹת כְּבֵין הַתַּחְתּוֹנוֹת, טֻמְאָה תַחַת אַחַת מֵהֶן, תַּחַת כֻּלָּם טָמֵא. עַל גַּבֵּיהֶן, כְּנֶגְדּוֹ עַד הָרָקִיעַ טָמֵא:

Mishnah Oholot 12:6: If a beam was placed from one wall to another wall and there was impurity underneath it, if it had a handbreadth's space, it spreads the impurity underneath all of it. If not, the impurity pierces and goes up, pierces and goes down. How large must its perimeter be for it to have a handbreadth's space? When it is round, its perimeter must be three handbreadths. When it is square, four because the square is larger than the circle by a quarter.

קוֹרָה שֶׁהִיא נְתוּנָה מִכֹּתֶל לְכֹתֶל וְטֻמְאָה תַחְתֶּיהָ, אִם יֶשׁ בָּהּ פּוֹתֵחַ טֶפַח, מְבִיאָה אֶת הַטֻּמְאָה תַחַת כֻּלָּהּ. וְאִם לָאו, טֻמְאָה בוֹקַעַת וְעוֹלָה, בּוֹקַעַת וְיוֹרָדֶת. כַּמָּה יִהְיֶה בְהֶקֵּפָהּ וִיהֵא בָהּ פּוֹתֵחַ טֶפַח. בִּזְמַן שֶׁהִיא עֲגֻלָּה, הֶקֵּפָהּ שְׁלשָׁה טְפָחִים. בִּזְמַן שֶׁהִיא מְרֻבַּעַת, אַרְבָּעָה, שֶׁהַמְרֻבָּע יָתֵר עַל הֶעָגוֹל רְבִיעַ: