70. By When the Mezuzah Must be Placed

11:20 A cellar door set in the ground does not require a mezuzah. This is because a doorpost must be upright to require a mezuzah.

11:21 A person who rents a house outside of Israel has 30 days to affix the mezuzah. This is because it is not considered a permanent dwelling until he has resided there for 30 days.