Individual Encasement in type V-A Construction

[nealderidder]

Good morning all.

I'm working on some details for a four-story wood frame project. Commercial use on the first floor and three stories of R-2 above. Walls/Floors/Roof all one hour rated assemblies but then there's the tricky bit with 704.3 (2019 CBC) which requires individual encasement. The exception is oddly worded but seems to mean that I only need to provide this 1 HR "encasement" on the "exposed" sides.

In the attached (STEEL BM Type V-A) - does the top of the W24 qualify as "unexposed" and thus meets the exception? Do you think this detail will fly? I don't see rated assemblies anywhere that show this condition. All the listed assemblies for steel beams are with steel/concrete floor decks.

These steel beams are only on the 1FL (wanted to keep the 1FL commercial space column free) and they support secondary wood beams. I think I'm off the hook for individual encasement for the wood beams (see WD BM Type V-A attached) since they aren't "primary frame" and are protected by the floor assembly per 704.4.2. Would you agree?

Thank you!

 

[nealderidder]

I don't think I've ever posted here and gotten zero responses... Does no one have any thought on this?

 

[steveray]

Technically....probably not "unexposed" I believe that is supposed to be exterior sides or primary frame elements....and the commentary is not much for help...

 

[Paul Sweet]

It looks reasonable to me, but I'm not in California. The gypsum board around the beam might be exposed to the weather for a while, so it would be good to use rated gypsum sheathing instead of plain type X.

 

[Christine]

Your detail steel beam Type V-A looks reasonable. You would need the double layer of gypsum each side of the steel beam if the projection of the bottom of the beam is more than 6" below the ceiling per the requirements for concealed spaces. If less than or equal to 6" projection, you do not need to run the double gyp up each side of the beam, just show solid blocking each side of the beam. You can also reference GA's Fire resistance design manual. The section on concealed spaces is in 718.5 of the 2015 IBC, the last version that I worked with.