Shared wall
Short definitionThe single panel shared by two adjacent rooms. One panel is used instead of two separate walls, and its thickness is chosen for the colder room.
If two rooms are the same height, a single panel goes between them. This cuts both the panel quantity and the heat gain: the other side of a shared wall is another cold room, not outside air.
If the rooms are different heights, a shared panel cannot be used. Each room gets its own wall and the two panels stand back to back.