How do I know which side of the door frame the mezuzah goes on? Rule number one: Mezuzos go on the right side as you go deeper into the house.
Picture yourself in a small apartment. If you are standing in the living room you go through a small hallway to get either to the bedroom or to the bathroom. Which side of the hallway does the mezuzah of the small hallway go on? The simple answer is that we put it on the right side going into the living room from outside the apartment, and on the right side of the hallway going to the bedroom and on the right side of the bedroom door itself. This is so whether or not there is a door to the hallway. Often people put the hallway mezuzah on the right side going into the hallway from the bedroom. This is incorrect. First I will explain what they are thinking and then I will explain the actual halacha. They think that since the living room is a proper room (בית דירא ממש), and the hallway only has a semi official room status (בית שער). They further reason that a mezuzah always goes on the right side from the room that is not obligated in mezuzah for its own sake, but rather because it is an entrance way into a room that is obligated in mezuzah. Although there are cases that this halacha would apply to, for example, a hallway between two rooms that both have access to the outside, and one of those rooms is a regular living space and the other is a hallway, it would not apply in our case. The reason that our case is different is that the first rule of mezuzah placement is that the mezuzah always goes on the right side as you go deeper into the house. As long as a room is deeper into the house you put it on the right. This means that if you start outside the house and walk to the room that is the farthest from the outside, or deepest into the house, you will always put the mezuzah on the right side of the door going inward. This rule only works when it is clear which way is going deeper into the house. If there are doors to the outside from the living room and from the bedroom, then we have to think about which way is going deeper into the house. Generally, we follow the Aruch Hashulchan who explains that when there are multiple doors from the outside going into a house, the main door should be considered the starting point of the house and all determinations of what is deeper into the house should be based on that starting point. Otherwise, he points out, nobody could ever figure out what side to put their mezuzos on. If we imagine a situation where there is a living room, hallway, and bedroom and the bedroom has a door to the outside, most likely, the door from the living room will be the starting point since it is used more often as an entrance from the outside. Once we can consider a particular door as the house’s starting point, than we will apply the rule that the mezuzah always goes on the right side as you go deeper into the house. In our actual case, where there is no doorway to the outside from the bedroom, it is very easy to see that the right side going into the hallway from the living room is deeper into the house.
Does it make a difference if the entrance to the hallway has a door?
Since the bedroom is deeper into the house, it makes no difference if the entrance to the hallway has a door. Let’s say the bedroom has a door to the outside and you can’t determine which door is the main entrance to the apartment because in your estimate you use both entrances equally, then it would make a difference if the hallway has a door. Now that you have two equally used entrances from the outside which direction is deeper into the house, from the living room door or from the bedroom door. If the hallway between the two rooms has a door we would use the direction that the door opens up into to determine which side the mezuzah should be placed on. The Talmud teaches that when it isn’t possible to determine which way goes deeper into the house because there are two main doors from the outside that are in more or less equal usage, then we go by which way the door swings into. Doors swing into rooms, so if the door swings into the living room side, the mezuzah will go on the right side into the living room and if it swings into the bedroom side, the mezuzah will go on the right side going into the bedroom.