have a 1 hr rated storage room, designer has submitted a UL-U419 wall, typical 1 layer (each side) 5/8" type "X" Gypsum, no problem. For the ceiling he submitted a UL-P516 2 layers 5/8" bottom side of framing, not a problem. My question is is there a detail on how the two should join? walls extend all the way to the bottom of roof deck (typical metal building) and the ceiling is down about 5'. The two layers on the ceiling will join just one layer on the wall. They say there is not a detail. I have not found any reference to how this joint should be. Any thoughts?