What would be more critical a fire rated wall to ceiling joint or a wall to wall joint? I would think it's the fire rated wall to ceiling joint since heat travels up and would concentrate in the upper area.
I would say equal
Might depend on the make up of the wall. If it has two layers of sheet rock, the joints should be staggered. So the vertical joint, in away does not matter/ or not as critical.
I would not place one over the other concerning critical performance. The most critical aspect is that all construction details of the individual certified joint designs are intended to be followed. The most critical fire containment barriers may require special inspector to verify compliance to the certified designs,
The certification of the joint systems are the basic standard used to investigate is ANSI/UL 2079, "Tests for Fire Resistance of Building Joint Systems." ANSI/UL 2079 defines four types of joint systems: floor-to-floor, wall-to-wall, floor-to-wall and head-of-wall. In addition, bottom-of-wall joint systems have been investigated using the general methods and conditions of acceptance specified for the four defined types of joint systems.
With that said, the conditions of acceptance for the wall to wall joints are different for wall to ceiling joints (head of wall).
All the joints are critical based on the conditions of use.
Excerpts from Joint Systems, XHBN - UL Product Spec
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