The floor slab is not required to be rated for our project, we only have to provide firestop at the curtainwall/slab edge condition per CBC 2019 section 714.5. The slab thickness is 6". Our curtain wall vertical mullion is spaced 48" o.c., but this Hilti design item 2B stated "locate mullions (vertical aluminum framing) min. 60 in. oc." Can we use this firestop design even our mullion is spaced tighter?
Hello Veng,
Thank you for your question. The code language we can reference here (which is the same in the IBC) is 2019 CBC Section 715.4.1 Exterior Curtain Wall/Nonfire-Resistance-Rated Floor Assembly Intersections, which states:
"Voids created at the intersection of exterior curtain wall assemblies and nonfire-resistance-rated floor or floor/ceiling assemblies shall be sealed with an approved material or system to retard the interior spread of fire and hot gases between stories." (https://up.codes/viewer/california/ibc-2018/chapter/7/fire-and-smoke-protection-features#715.4)
Note that this language does not require a tested and approved listing, but rather an "approved material or system" to fill the joint. While the final decision of whether or not a solution is code compliant will always be left to the discretion of the local Authority Having Jurisdiction, it is my opinion that utilizing HI/BPF 120-10 with a non-rated floor, although the mullion spacing requirements are not met, would be more than satisfactory per the code section pasted above. If needed, the Hilti Fire Protection Design Team can provide a non fire-rated custom detail in the form of a cold smoke seal for this specific condition. You can request this detail by visiting hilti.com/ej.
Please let me know if you have any additional questions.
Thank you,
Michael Duncan
Fire Protection Engineer
Hilti
Our slab has a two-hour requirement, but we do not meet the 60" min spacing between mullions. What implications does that have on us and are there ways to get around it? For reference we have selected HI/BPF 120-10.