In general, a home of partners is obligated to have a Mezuzah. Thus, even if a home is occupied [owner/rented] by many people who share joint ownership or rent, it is obligated to have a Mezuzah on its doorposts. However, this only applies if all of the tenants are Jewish. However, if one of the tenants is a non-Jew, then it is exempt from having a Mezuzah. Thus, if one of the occupants of a home or room is a non-Jew, such as a home or room that is jointly owned or rented by a Jew and non-Jew, it is exempt from having a Mezuzah. [Some Poskim, however, conclude that one is to place a Mezuzah without a blessing, and so should practically be followed especially if the owner of the home is Jewish and it is simply rented to a Jew and gentile tenants. The above exemption only applies if the gentile actually lives in the home. If, however, the Gentile does not live in the home, then it is obligated in a Mezuzah while the Jew is living there, even if the gentile is one of the owners of the home.]
Does the gentile maid’s room in one’s home require a Mezuzah?
The reason: The reason for this is because 1) Part of it is owned by a non-Jew and is thus exempt from having a Mezuzah. 2) It may be dangerous, as the Non-Jew may suspect that the Jew is doing witchcraft on him. [Shach 286:6] 3) We learn that partners are also obligated in Mezuzah from the words “To increase your days” which is not applicable to non-Jews being that they do not fulfill the Torah, and thus are not deserving of long days. [Taz 286:2; Levush 286:1] The Shach ibid negates this latter reason.
Other Poskim: Some Poskim rule that the room is obligated in a Mezuzah even if it is jointly owned by a Jew and gentile. [Rashba Chulin 136a, brought in Biur Hagra ibid; Beis Yosef 286 in Bedek Habayis that we rule like Rashba; Rashal in Yam Shel Shlomo Chulin 135b in explanation of Rashba ibid; See Pischeiy Shearim 286:39; Pischeiy Mezuzos [Chazan] 286:16 that so is ruling of Michaber ibid unlike Rama and Mordechai]