Hi.
While doing Dorf 1 BL Alt I had a question about dead ends in lobby situations: Dorf's book says that if an "open" area is designed off a corridor, this area is considered circulation and therefore, its depth shouldn't exceed 20'. Otherwise it's considered a dead end.
How is this dimension measured? to the centerline of the door (as shown by dimension line "A" in the image? Does dimension "B" need to comply as well? is it to the furthest point in the lobby? I'm confused about this issue and I'm not even sure I'm being clear with my question. Has anyone seen any study notes or FAQ that could help me?