We had a "preliminary review" chat with the building official yesterday. We did not get into the details of what we are proposing, but got a read on how our proposal would be evaluated. My observations:
- They intend to apply IBC critieria only, as you suggested they would. The official seems to be unaware of the differences in NFPA 101 regarding separation ratings for specific occupancies. I don't think he cares.
- He will evaluate our proposed design in comparison to other approved reference designs. I got the impression that he was primarily thinking what I might find on the UL listing of wall assemblies. We looked broader than that for a good comparison.
- We still intend to submit the design that is most recently listed above. We reference the designs posted by Georgia-Pacific in their Gypsum Assemblies Library. http://www.buildgp.com/GypsumA...es.aspx?ShowAll=True We believe that our design falls within the range of the 3 wood stud, 2-hour rated designs they list. We also reference Harmathy’s 10 Rules of Fire Resistance Rating. Specifically to make the point that adding layers to the wall can only help (Rule #1) and that because the embedded steel pole is at least 1/2" behind the Type X gypsum, it will not meaningfully affect the wall performance (Rule #5). We added the 3/8" gypsum in the middle to give some way to contain the mineral insulation... otherwise it seems like a mess.
It might be presumptive of me, but as a registered engineer, I am assuming that I'm qualified to make these judgments, and don't plan to ask for a 3rd-party review. That's our story.
We expect to submit today, and should find out in the next two weeks whether the BO is on board.
Thanks for your help!