IBC 2018 I-B, Business, High-rise separation from I-B, S-2 Parking Garage

[redbird11]

Hello,
I am looking at the separation between a I-B sprinklered, high-rise 26 feet away from a I-B, S-2 non-sprinklered public parking garage.

FIRE SEPARATION DISTANCE. The distance measured from the building face to one of the following:

1. The closest interior lot line.
2. To the centerline of a street, an alley or public way.
3. To an imaginary line between two buildings on the lot.

So the lots are not set at the moment and can likely be outlined as needed. So I'm looking at #3 and I have 26' from face of building to face of garage.

Table 602 10 ≤ X < 30 IB, S-2 has 1 hour rating with footnote c.
c. Open parking garages complying with Section 406 shall not be required to have a fire-resistance rating.
Confirmed compliance with 406.

Then for the building, if i have 16 feet to the imaginary lot line with B Occupancy the table has 1 with footnote c. However, the table also has footnote g.

g Where Table 705.8 permits nonbearing exterior walls with unlimited area of unprotected openings, the required fire-resistance rating for the exterior walls is 0 hours.

Table 705.8 - MAXIMUM AREA OF EXTERIOR WALL OPENINGS BASED ON FIRE SEPARATION DISTANCE AND DEGREE OF OPENING PROTECTION

705.8 15 to less than 20f, g, j - Unprotected, Sprinklered (UP, S)i - 75% Allowable Area

So does this mean that 25% of the solid exterior wall needs to be 1 hour rated but 75% of glazed openings are not required to be rated? I don't have a commentary for IBC 2018, maybe looking back to 2015 or 2012 commentary would help?

 

[RLGA]

So I'm assuming based on what you presented, that you plan to place an imaginary line 10 feet from the parking structure and 16 feet from the building, correct?

Assuming the above, then you're correct regarding the open parking garage. However, I don't think you're reading the exterior wall requirements for the other building exactly right if you want to use Footnote 'g' of Table 602.

Table 602 requires Type I-B buildings with a Group B occupancy to have 1-hour exterior walls when the fire separation distance is 10 feet to less than 30 feet. Footnote 'g' states that when a nonloadbearing exterior wall is allowed to have unlimited unprotected openings per Table 705.8, then the wall is not required to have a fire-resistance rating. Per Table 705.8, a wall with a fire separation distance of 16 feet is only permitted 25% of the wall area to have unprotected openings or 75% if the building is sprinklered. In either case, unlimited unprotected openings are not permitted, so Footnote 'g' is not applicable. You're correct in that it means that up to 75% of the wall area per story can have unprotected openings and that the remaining wall area (i.e., the solid wall area) must have a 1-hour rating (assuming the building is sprinklered). If the building is not sprinklered, then only 25% of the wall area is permitted to have unprotected openings and the remaining wall area is required to have a 1-hour rating. Or, you can have a mix of protected and unprotected openings, provided the sum of the ratios of actual to allowable for each does not exceed 1 (Section 705.8.4).

To have unlimited unprotected openings to get the benefit of Table 602, Footnote 'g,' the building will have to be sprinklered and the fire separation distance must be at least 20 feet. If there is no sprinkler system, then there is no way to take advantage of Footnote 'g' because you will need a fire separation distance of at least 30 feet.