Fire rating for exit stair wall

IBC indicate
713.4 Fire-resistance rating. Shaft enclosures shall have a fire-resistance rating of not less than 2 hours where connecting four stories or more, and not less than 1 hour where connecting less than four stories.
one of the PDD case studies is asking to pick a stair wall assembly for a 3 story building . the answer picked the 2-hour rating rather than 1 hour . would someone from BS explain why?
here is the scenario
" The owner of an existing pair of industrial buildings has hired an architect to design and document their conversion into an art museum. The site contains tax parcels 7 and 8 along Center Street. It is important to the project’s design goals that a single, large floor between each building through their demising walls is created. The architect has concluded the Design Development Phase and is proceeding with the Construction Documents phase.

The client has provided the following general information about the project to the architect:

  • The site consists of two separate industrial building parcels that were merged into a single lot by the previous owner
  • Total site area = 6,800 sq. ft
  • The site is currently zoned for Institutional uses, which allows as-of-right use as an art museum
  • Each existing building is composed of 3 floors
  • There is no existing elevator
  • Each floor is 16’-0” in height, and the total building height, measured from the ground floor, is 48’-0”
  • The entire building is planned for use as an Assembly (A) use within the Institutional (I) art museum
  • The facility will need to comply with the Americans with Disabilities Act (ADA)."

Hello @xurubi -

I agree that the code states that you have to follow 713.4 Fire-Resistance rating for shaft enclosures. The only reason that this structure would be counted as 4 stories according to 713.4 is if it has a basement. Once you have 4 stories as you noted the code changes and says that you need to have a 2 hour rated enclosure.

Perhaps @coachchrishopstock has a better interpretation of this question/code.

Thanks @coacheliserenwick , I agree with your interpretation!

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