It is a requirement for risers going thru multiple stories to use flexible fire stopping?
Fire stopping caulks and mastics (plus other methods) are only required when passing through fire resistive enclosures. Generally, risers are installed inside the stairs enclosure, so only the cross main branching out will require fire stopping caulk (assuming that particular stairs enclosure is required to be fire resistive by code).
Thank you for the answer. But my main concern is to know if it has to be flexible. I’m on a seismic area.
I am thinking that you have answered the question yourself. Will a static firestop work in a dynamic (moving) joint? NO. A seismic joint or firestop will require a flexible system. You will need a system that has been tested with movement (dynamic).
Hilti and 3M claim some models of their fire stopping caulks to be "flexible". I have never used them, so I don't know if they are really frangible enough to not warrant installing flexible couplings on both sides of the wall/slab.
Locally, some contractors prefer to patch the hole with cement or concrete and install flexible couplings, since it is a lot cheaper than buying a listed/approved fire stopping material.
You need to use the proper firestop method for the opening and item going through the penetration.
Cannot answer the earthquake question, I am thinking NO, flexiable firestop material not required
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