Do walk-in closets need a mezuzah

Question

According to the Halacha, do walk-in closets need a mezuzah? Or no, since they are not regularly lived in are they exempt from having a mezuzah?

Answer 1

Star-K provides an in-depth answer to your question here along with footnotes.

Some takeaways as follows:

Size is a factor

A large walk-in closet is halachically considered to be a room if it is four amos wide and four amos deep, or larger. Four amos is equivalent to 6 feet according to Rav Chaim Noeh, 7 feet 1 inch according to Rav Moshe Feinstein, and 7 feet 7 inches according to the Chazon Ish. Rabbi Heinemann, shlit”a, paskens that one should not recite a bracha unless the closet is larger than 7 feet 1 inch by 7 feet 1 inch

Frequency of use

A room which has a floor area of less than 16 square amos is generally exempt from a mezuzah. However, the Chamudei Daniel is of the opinion that a room which is fully functional for its intended purpose is required to have a mezuzah, even if it has a floor area of less than 16 square amos. According to the Chamudei Daniel, a walk-in closet is required to have a mezuzah. Other Poskim disagree with the Chamudei Daniel, and the Chazon Ish is quoted as having said that one may be lenient and not concerned about the chumrah of the Chamudei Daniel.

It serves as a connecting room to a larger area

Reb Akiva Eiger suggests a different reason as to why this walk-in closet requires a mezuzah. He points out that the doorway of the walk-in closet connects two areas, the area of the walk-in closet and the area of the larger room to which the closet is attached. Even though the walk-in closet may have a floor area of less than 16 square amos, the room to which the closet is attached has a floor area of more than 16 square amos. Reb Akiva Eiger says that the doorway does not require a mezuzah due to the closet, but it does require one due to the larger room.

Conclusions

Therefore, for different reasons, the Chamudei Daniel and Reb Akiva Eiger both agree that the doorway of a walk-in closet with a floor area of less than 16 square amos requires a mezuzah. However, there is a significant difference between these opinions. According to the Chamudei Daniel, the mezuzah should be affixed to the doorpost on the right side when walking from the larger room into the closet, and it should be positioned slanting towards the closet. However, according to Reb Akiva Eiger, it is the larger room that necessitates the mezuzah which should be affixed on the right side when walking from the closet into the room (the left side when walking from the room into the closet); it should be positioned slanting towards the room.

Other Poskim disagree with Reb Akiva Eiger and pasken that the larger room does not necessitate a mezuzah on the doorway of the closet. Rabbi Heinemann, shlit”a, paskens that one should be choshesh for the opinion of Reb Akiva Eiger and affix a mezuzah without a bracha to the doorway of a walk-in closet with a floor area that is less than 16 square amos. The mezuzah should be attached to the left side when walking from the room into the closet. If the floor area of the walk-in closet is so small that one does not actually walk into it when retrieving objects from the closet, then the doorway of the closet does not require a mezuzah.