Area Increase Interpretation - IBC 2018

[Johnny O]

HERE ARE THE FACTS:

AREA CALCULATIONS:
1,674 SF - EXISTING CONDITIONED B BUSINESS
4,366 SF - EXISTING CONDITIONED F-1 FACTORY
10,038 SF - NEW CONDITIONED S-1 STORAGE
1,420 SF - NEW UNCONDITIONED COVERED STORAGE
17,498 SF - TOTAL

BUILDING OCCUPANCY CLASSIFICATION:
MIXED OCCUPANCY
GROUP B, (SECTION 304.1) - 1,674 SF
GROUP F- 1 (SECTION 306.2) - 4,366 SF
GROUP S-1, (SECTION 311.2) - 9,950 SF

CONSTRUCTION TYPE:
TYPE IIB, NON-COMBUSTIBLE (UN-SPRINKLERED, UNPROTECTED), (SECTION 601)

ALLOWABLE HEIGHTS AND AREAS:
SECTION 503.1 REFERS TO SECTIONS 504 AND 506 FOR BUILDING HEIGHT, NUMBER OF STORIES, AND AREA.
HEIGHT B, F, S 55’ (TABLE 504.3)
NUMBER OF STORES B, F-1, S-1 2 STORIES MOST RESTRICTIVE (TABLE 504.4)
AREA ARE B, F-1, S-1. 15,500 SF MOST RESTRICTIVE (TABLE 506.2)
AREA INCREASE (SECTION 506.3.3)
If=(F/P-.25)W/30 (CALCULATED w IS 52, 30 MAX)
If=(632.125/632.125-.25)30/30 = .75 = 75%
INCREASE 15,500+(15,500X.75) = 27,125 SF
ACTUAL BUILDING HEIGHT = 23'
ACTUAL BUILDING NUMBER OF STORIES = 1
ACTUAL BUILDING AREA = 17,498

BUILDING OFFICIAL SAYS:
"1) To proceed building an addition exceeding 15,500 (F1) most stringent of the mixed uses without a fire sprinkler and fire alarm system, a 3 hour fire wall will be required between the F1 and S1 occupancies with 3-hour rated doors, self closing in accordance with Section 707.3.10 of the IBC, 2018 Edition. This item needs clarification.
2) If you decide to sprinkler and alarm the building, a sprinkler and fire alarm package is required to be submitted to an approved third party for review and approval. This must be done prior to the installation of these systems. Separate permits are required."

QUESTION:
Doesn't the area increase apply to the max un-sprinklered area from 15,500 to 27,125? My Owner doesn't want to install a sprinkler system and also doesn't want to separate the F-1 from the S-1 with a 3-hour fire wall.

 

[Johnny O]

Not critical to the question, but the S-1 is actually 11,458 SF

 

[steveray]

You are over both F1 and s1 sprinkler thresholds....or will be...Ch. 9 not 5....

[F] 903.2.4 Group F-1. An automatic sprinkler system
shall be provided throughout all buildings containing a
Group F-1 occupancy where one of the following conditions
exists:
1. A Group F-1 fire area exceeds 12,000 square feet
(1115 m2).

[F] 903.2.9 Group S-1. An automatic sprinkler system
shall be provided throughout all buildings containing a
Group S-1 occupancy where one of the following conditions
exists:
1. A Group S-1 fire area exceeds 12,000 square feet
(1115 m2).

You might be able to use fire barriers not fire walls, but not sure that matters...

 

[TheCommish]

Area increases come 3 ways, increase construction type, open perimeter of the building, sprinkler installation.
If the owner does not want to sprinkler, they are short sited, sprinkling allows for a number of trade offs.

The other choices for not sprinkling, build smaller building, don't build the building.

 

[RLGA]

It is frustrating when the people at the building department who are responsible for plan reviews cannot get their terminology correct. It is not a "fire wall" that the plans examiner was referring to, but a "fire barrier" between fire areas. The plans examiner's reference to Section 707.3.10 for fire area separation with fire barriers makes this clear.

Separate the Group S-1 from the rest of the building with a 3-hour fire barrier (much easier and cheaper to do than a fire wall) to stay under the sprinkler thresholds for Groups F-1 and S-1. You can still use the nonseparated occupancies calculation method to show allowable area compliance--using the separated occupancies method will only get you an additional 1,000 to 2,400 square feet, depending on how much each occupancy is increased.

However, I agree with TheCommish, that not installing a sprinkler system is short-sighted. In the long run, adding a sprinkler system will save them money by reducing insurance premium rates (https://nfsa.org/wp-content/uploads/2019/07/Fire-Sprinklers-Save-Lives-and-Money-paper.pdf). Depending on the insurance company, the ROI will likely not be very long.

 

[Tim Mailloux]

do you have any mezzanines? While they dont add to the building area I am pretty sure they do contribute to the fire area