Spread of Fire and Ply Diaphragm Continuity Through Intertenancy Wall

[Backcheckrage]

An architect brought up a really good point to one of my details.

The issue is they claim the fact that the plywood diaphragm continuous through the IT wall, then when a fire catches on one apartment, the plywood floor with catch fire and perpetuate fire through the ply diaphragm and fire will then enter the neighbouring apartment. They want to cut my ply sheathing between the two units, now I effectively have two separate buildings.

I feel this "spread of fire" issue is real... how do you get around this? I can't have little separate diaphragms on this buildings, what is the detail to keep fire from spreading across and respect diaphragm action at the same time?

 

[DETstru]

Is there not gypboard on the underside of the joists and gypcrete or some other cementitious coverage on the top of the plywood? I assume there is some sort of fire blocking between the joists at the head of the wall as well?

 

[Backcheckrage]

DETstru: Yes, there is double gyp to the underside of the floor framing. And we are thinking of doing a sand-cement mix of say 25mm to top off the floor (we can't get Gypcrete in my country). Is the cementitious topping the answer to protecting the plywood from igniting?

Regarding the shear transfer through the floor, I can't find literature which would suggest this is a fire-risk to the apartment on the other side of the IT wall. Anyone have experience with apartments and fire separation or know literature to explore these details?