By law, mezuzahs are attached to the door jambs of all rooms of a Jewish home or place of work, if this room is related only to a Jew or his family. (i.e., in a communal apartment, a mezuzah is not hung in public areas, and at work, a mezuzah is hung, for example, on the jamb of a personal account).
The exception is the bathroom, toilet and non–residential premises, such as an attic or a warehouse – there is no need to install a mezuzah. If you have only one mezuzah, it is better to attach it at the main entrance to the house.
Do not install a mezuzah at the entrance to a temporary dwelling – that is, one where a person is going to live for less than 30 days.
A mezuzah is not attached at the entrance to a living room if its area is less than 3.68 sq. m
. Whether a mezuzah should be attached at such an entrance where there are no jambs and lintels or on a door of a different shape or type other than a casement, you should ask a rabbi.