Here's a twist on the 9/28/2021 post regarding 4 or 8 sprinkler residential calcs (link here):
Given an NFPA 13-2016 fully sprinklered wood framed apartment project, with residential sprinklers, and unsprinklered combustible concealed TJI spaces between floors, per Section 126.96.36.199.6 similar to this system:
Spaces between joists are blocked into 160 cubic feet using the same TJI material.
Spaces are not firestopped with a minimum ½” drywall on the sides of certain TJI’s into 160 cubic foot spaces.
Since the 2013 NFPA-13 came out, my understanding has been that unless we were to install ½” gypsum on the side of every few TJI’s to subdivide into 160 cubic foot spaces, an 8-sprinkler calculation is required in the occupied spaces above and below this assembly.
Some have argued that since it’s a 1-hour assembly, a 4 sprinkler calculation is fine since that’s greater than a 30 minute barrier (light hazard water supply duration) as discussed in 188.8.131.52.5.1 (B). However, Annex A184.108.40.206.5.1 seems support the 8 sprinkler calculation because the assembly is the qualifying non-sprinklered area.
However, in the above example, a portion of that assembly in itself provides a 30 minute barrier. It’s a 1 hour rated assembly but In this case, the bottom is 2 layers of Type X which in itself is greater than a 30 minute barrier.
I’m guessing that the top with tongue and groove sheeting and 1” of gypsum would also provide at least a 30 minute barrier.
Would the NFPA 13 sprinklered dwelling spaces above and below this (allowed) non-sprinklered floor/ceiling space require a 4 or 8 sprinkler calculation?
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3/23/2023 08:58:56 am
The way I ready the 13-2022 Edition, you are still required to provide the 8 sprinkler calculation but you would not have to extend that 8 sprinkler calculation (or other design method) to the adjacent areas that do not have unsprinklered areas (it would go back to the 4 sprinkler design)
Todd E Wyatt
3/23/2023 09:34:53 am
Determining the fire-resistance rating (FRR) of a tested assembly or individual components such as gypsum board should be based on the adopted Code (e.g. 2021 IBC). The FRR “of building elements, components or assemblies“ are determined by 703.2.1 Tested Assemblies or 703.2.2 Analytical Methods “without the use of automatic sprinklers or any other fire suppression system” or by 703.2.3 Approved Alternate Method.
Todd E Wyatt
3/23/2023 09:35:33 am
3/23/2023 09:44:15 am
This can be tricky as it can go either way really. My default answer would be that both areas above and below should have the extended design area based on A.220.127.116.11.1 that Dan posted above.
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