Mezuza on Each Doorpost

Question: We have doors between our lounge and dining room, and I am unsure which side to affix the mezuza to. Can I affix one to each side?

Answer: The Tur (OC 34:1) and the Shulchan Aruch (OC 34:2) write that one who wears ‘Rashi tefillin’ and ‘Rabbeinu Tam tefillin’ should wear them together. Unlike wearing tefillin with five parshiyos, doing so does not pose an issue of bal tosif. One should have in mind that only one pair are kosher tefillin, while the other pair are ‘no more than straps.’ The Magen Avraham (34:2) notes that this only applies as only one set is considered to be kosher. One wearing two sets of the same tefillin, however, would certainly be transgressing bal tosif.

R' Yaakov Ettlinger (Binyan Tzion 99) compares placing two mezuzos on opposite doorposts to wearing two pairs of tefillin simultaneously. As only one doorpost can be the correct place for a mezuza, placing one on the other doorpost is akin to wearing the ‘wrong tefillin’. Likewise, R’ Yaakov Emden (Sheilas Yaavetz 1:70) writes that when there is a safek which side to affix the mezuza to, one should affix one to each side. However, the Maharam Schick (YD 287) disagrees, arguing that as both mezuzos are kosher, this is not the same as wearing two different pairs of tefillin.

R’ Ovadia Yosef (Yabia Omer OC 6:2) brings both opinions though does not offer a clear psak. Nonetheless, R’ Yitzchak Yaakov Weiss (Minchas Yitzchak 1:9) sides with the Maharam Schick. He quotes R’ Avraham Dovid Wahrman (Daas Kedoshim 286:25) who notes that it is unheard of to place two mezuzos on one doorway (see Chelkas Yaakov YD 162). Likewise, R’ Shmuel Wosner (Shevet Halevi 2:152) writes that one must not affix two mezuzos, though writes that when one cannot ascertain which is the main room, one can simply choose which side to affix it to.

Nonetheless, R' Moshe Feinstein (Igros Moshe YD 1:176) dismisses this, writing that if there is no door on the doorway and one cannot ascertain which is the main room, the doorway may be exempt from a mezuza. Likewise, he rejects the option of affixing two mezuzos.

In conclusion, one must not affix two mezuzos to one doorway. Rather, one should consult with a Rav as to the correct place to affix it.