421. What Features Obligate a House in a Mezuzah

Tefillin, Mezuzah v’Sefer Torah 6:1

A house requires ten things to obligate its resident in a mezuzah. If any one of these is lacking, a mezuzah is not required. They are: (1) the area must be at least four cubits by four cubits (about six feet by six feet); (2) it must have two doorposts; (3) it must have a lintel; (4) it must have a roof; (5) it must have doors; (6) the entrance must be at least ten handbreadths high (about 30 inches); (7) it must not be sanctified; (8) it must be designed for human habitation; (9) it must be a respectable dwelling; (10) it must be designed for permanent residence.

Tefillin, Mezuzah v’Sefer Torah 6:2

A dwelling that is smaller than four cubits by four cubits does not require a mezuzah. If the area is the equivalent of sixteen square cubits it requires a mezuzah even if it is round, a pentagon, and certainly if it is rectangular.