Ohalot, Chapter Twelve, Mishnah Five
Today’s mishnah deals with a house that has two stories, but is not completed. There are roof beams going across each ceiling, but there are gaps in between each beam that have not yet been filled in with the plaster.
1) [With regard to] the roof beams of a house and of the upper story which have no plaster ceiling upon them and are in a line, [the upper ones exactly above the lower]:
a) If there is uncleanness beneath one of them, all beneath that one becomes unclean.
b) If it is between a lower and an upper [beam] what is between them becomes unclean.
c) If it is above the upper [roof beams], what is directly above to the sky becomes unclean.
2) [In the case] where the upper [roof beams] were [over the gaps] between the lower [roof beams]:
a) If there is uncleanness beneath one of them, what is beneath all of them becomes unclean;
b) If above them, what is directly above to the sky becomes unclean.
Section one: In the first scenario, the upper roof beams are precisely above the lower ones. If there is uncleanness beneath one of the beams of the house, anything below it is impure because it forms an ohel. However, the beam also prevents the impurity from spreading to the area above it. And the impurity doesn’t spread to anywhere else in the house because there is nothing overshadowing the spaces in between the beams.
If the impurity is on top of the lower beam and below the upper beam, it remains in this area.
If it is above one of the upper beam then the impurity only travels upwards.
Section two: In this case the upper and lower roof beams are not lined up. Rather the upper beams are spaced right in between the lower beams.
If there is impurity underneath one of them, then it spreads to the area underneath all of them, as if there was only one roof. In other words, we look at the bottom beams as if they had been raised to a level equal to the lower beams.
If the impurity is found above any of the beams, it is not in any ohel, and therefore it only defiles that which is found directly above it.