2015 IEBC 1012.1.1.2, IBC 508.4, and Fire Areas

[Fuls]

I have a project in Wisconsin, using IBC 2015 (with amendments), in an existing mixed S-1/B occupancy which is roughly 30,000 sq. ft., 1 story, unsprkinklered.
A proposal is to change a portion of the building (10,000 Sq. Ft.) to be separated and will include a change of use (to A-3). It isn't the full 10,000 sq. ft., but the separation would include all occupancies not otherwise separated.

IEBC 1012.1.1.2 - 2015 - makes it clear in the commentary that if separated by fire barriers per IBC 508.4, then only that portion needs to comply (with the various referenced sections). The commentary also includes the phrase "this shall also apply to exceeding IBC chapter 9 thresholds".

Here's the question:
1) IBC 508.4 requires only a 2-hour wall between the A-3 space and the S-1 space (worse case). IBC 707.3.10 would require a 3-hour barrier to be separate fire areas. If the 2-hour barrier is provided, does the A-3 space need to have a sprinkler installed, or not? The "Fire area" is more than 12,000 sq. ft. (per IBC 903), but the change-in-use area is separated per 508.4 and is less than 12,000 sq. ft. on its own. Intent is to avoid sprinklers.
2) If the barrier would be a 3-hour barrier, sprinklers would not be required for the work area. However, the commentary on IEBC 1012.1.1.2 makes it seem the higher-level barrier may not be needed.

 

[RLGA]

I would say the 3-hour separation per IBC Section 707.3.10 would be necessary to avoid a sprinkler system because IEBC Section 1012.1.1.2 does not designate which type of separation is required (occupancy separation per IBC Section 508.4 or fire area separation per IBC Section 707.3.10).

If you were to provide a 2-hour fire barrier per IBC Section 508.4, the fire area would still be greater than 12,000 sq. ft., but the IEBC would only require the Group A-3 portion to have the sprinkler system rather than the entire fire area per the last portion of IEBC Section 1012.1.1.2: "...that portion [meaning only the Group A-3 portion] shall comply with all of the requirements of Chapter 9 for the new occupancy classification [meaning it must be sprinklered because IBC Section 903.2.1.3 requires a sprinkler] and with the requirements of this chapter."

If you provide a 3-hour fire barrier per IBC Section 707.3.10, then the fire area is less than 12,000 sq. ft., and the Group A-3 sprinkler provisions of IBC Chapter 9 would not apply; thus, avoiding the need to sprinkle any portion of the building.