One of the most basic rules of eiruvei hatzerot is that the residents of the courtyard must be partners in food so that they can be viewed as a single household, permitting them to carry in the courtyard and back and forth from their homes to the courtyard. In order to accomplish this, the food must be placed in one of the houses that opens to the hatzer (courtyard). The Mishna on our daf teaches that there are some structures in the hatzer that are not viewed as dwelling places, and therefore the eiruv cannot be placed in them. For example, the bet sha’ar – the gatehouse to the courtyard – is not considered a place where people live, so the eiruv cannot be placed there. Following that logic, the Mishna also teaches that if someone were to live in the gatehouse, he would not be considered a resident of the courtyard, and would therefore not play a role in the establishment of the eiruv.
Rav Yehuda, the son of Rav Shmuel bar Sheilat, said: Any place with regard to which the Sages said that one who resides there does not render it prohibited for the other residents of the courtyard to carry, one who places his eiruv there, his is not a valid eiruv, except for a gatehouse that belongs to an individual. If a structure is used as a passageway by only one person, he does not render it prohibited for the other residents of the courtyard, and an eiruv placed there is a valid eiruv.
This rule is, apparently, based on the understanding that if only one family uses the gatehouse and it is not open to public access, it is considered part of their home, and would, therefore, meet the criterion of being a place where people live.
The Jerusalem Talmud discusses this question, and reaches the opposite conclusion. According to the Yerushalmi, a bet sha’ar d’yahid (gatehouse that belongs to an individual) is not considered a dwelling place at all and cannot be used to house the eiruv, while a normal bet sha’ar that is open to the public meets the requirement to be a place where people live, so the eiruv can be put there and someone living in it is considered a resident of the courtyard. The logic of the Yerushalmi seems to be that a private gatehouse is considered insignificant and has no halakhic significance. If someone lives there, he will, at best, be considered a member of that household. The public gatehouse, on the other hand, is a significant structure that must be considered.