Combining to Form a Minyan
Question
If five men are in one room and five men are in another room, but there is a door post that is dividing both groups of five, however, each group can see the other, are they still considered a minyan? According to the Shulhan Aruch
Answer
Shalom!
Thank you for your question.
The relevant Talmudic passages to this issue can be found in Pesachim 85b in the context of joining together for the purpose of eating the Passover offering, which are the same as for prayer, and more explicitly relating to prayer in Eruvin 92b. Also of interest is the Rashba in his responsa 1:96 who discusses the old fashioned elevated Bima where the chazzan would stand and whether it is a separate domain. He says that since everyone sees everyone else, everyone combines towards the minyan.
The answer to your question is that if they are two separate rooms they cannot join and be considered as one minyan, unless its one room and there happens to be a doorway in the middle of the room then they can join.
While all authorities agree that it is best for all 10 men to be in the same room, here are some of the rulings of the Shulchan Aruch as you have asked.
1. Those standing in the doorway do count towards the minyan (Mishna Berura 55:50)
2. Even somebody in the outside half of the doorway is counted toward the minyan (55:13)
3. The chazzan standing in a doorway with a few people on each side can count to join both groups into 10. (55:15)
Even those not in the room with the minyan may answer the congregational responses. (OC 55:20, Mishna Berura 55:61).