I could not find a lot of information on Fire Walls and how they should be rated mainly because this topic gets easily mixed and confused with occupancy separation. After searching a while I encountered this article that helped me clear things out. https://specsandcodes.typepad.com/the_code_corner/fire-walls/
Here’s my summary:
If you have a building and need to separate different occupancies within, you use IBC Table 508.4 — this gives you the rating of the assembly you need to use (OK, I knew that)
BUT, if you have a building to which you are building an addition, and the construction type is not the same as the original??? We know that we need a fire wall between the two portions, but what should be the rating?
We turn to IBC Table 706.4 and first evaluate the occupancies we are separating (if many and different, use the most stringent one). Then we consider the construction type and evaluate if this gets us a reduction of the rating (because we have different construction types on each side, we choose the most stringent as well)
To clarify, fire walls could be used to separate two sections of a building as two separate buildings even if the construction type is the same.
Hope this helps someone else too :)
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