Fire Barriers and Supporting Construction

IBC 2006/2009
2B or 3B Construction
3-Story, B occupancy
Fully Sprinklered
Exit Enclosures for stairs/shafts for elevators, other shafts

Let me start by saying I don't do much 3-story office buildings, however, after a code review, I have a few questions.

The section on fire barriers (707.5.1, 2009 ed) clearly states supporting construction shall have equivalent hourly ratings as the fire barrier with exceptions noted. In my case, you have a 1 HR exit enclosure (or shaft) that is permitted to be one-hour and is not listed under the the exceptions in 707.5.1, which leads to my questions.

1. Do I now have to go to a 2A or 3A building by virtue of the fire barrier support?
2. Can I use the fire sprinkler substitution per 601 d for compliance?
3. If yes to item 2, then a few issues arise. The project has an atrium (3 stories) so this would seem to eliminate that option.
4. If the atrium was eliminated, we often use the sprinkler to eliminate the area of refuge and stair width requirements for accessibility, does the 1 HR substitution void this exception as well? Appears to be all inclusive when using that as a substitution.

Thanks.

Glen
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