Question on IBC 705.8 -- Allowable Area for Openings [specifically for California Building Codes]

[B_olantis]

I've got a situation where we're trying to get a SFH built above a parking area. The SFH is ~1650 sq ft, same for the parking area below it at ground level. One side of the garage/SFH combo is proposed to face an ADU also on the property [3.5' gap from assumed property line between the two], and on that side both the ADU and the SFH will have at least 1-hour fire exterior fire rated walls. Two other sides will face an existing property line at ~8' minimum spacing. The other side will face the street and is 15' back. The SFH will be designated a group R-3. The 1st story will be built from non-combustibles (8" thick solid concrete walls, concrete ceiling/2nd story floor)

From CBC Table 705.8 [https://codes.iccsafe.org/s/CABC202...-protection-features/CABC2022P1-Ch07-Sec705.8], it states that for FSD of >5 ft and <10 ft, "

1. f. The area of unprotected and protected openings shall not be limited for Group R-3 occupancies, with a fire separation distance of 5 feet or greater.

"


We wanted to have some of the walls be open in the 1st floor parking garage (i.e., no door, no window, just open air). The questions are:

a) Is an "unprotected" opening defined as something with a non-fire rated window or door -- or can it just be an open space in the wall?
b) If it has >50% open area per definition above, will it still meet requirements based on the the proposed fire separation distance?
c) I saw the private parking garage exemption (note j:

1. "j. The area of openings in a building containing only a Group U occupancy private garage or carport with a fire separation distance of 5 feet or greater shall not be limited.",

but reading up on "https://codes.iccsafe.org/s/CABC2022P1/chapter-4-special-detailed-requirements-based-on-occupancy-and-use/CABC2022P1-Ch04-Sec406.3#:~:text=Private garages and carports shall be classified as Group U,93 m2) in area." states that it is limited to 1000 sq ft of area (but then has a note saying "Exception: The area of a private garage accessory to Group R-3 one- or two-family dwellings shall not be greater than 3,000 square feet in area." -- if the garage is all by itself on the 1st floor, is it "accessory" to? Or does this not matter, since it meets the setbacks per subnote "f"?

 

[RLGA]

I'm confused. You state there is a 3.5-foot gap between each building and the assumed property line, which is a 3.5-foot fire separation distance. So, why are you trying to use provisions for fire separation distances of 5 to 10 feet?

 

[steveray]

I'm confused. You state there is a 3.5-foot gap between each building and the assumed property line, which is a 3.5-foot fire separation distance. So, why are you trying to use provisions for fire separation distances of 5 to 10 feet?

Maybe this? I was confused and didn't want to weigh in on Cali stuff...

Two other sides will face an existing property line at ~8' minimum spacing. The other side will face the street and is 15' back.

 

[Yankee Chronicler]

We wanted to have some of the walls be open in the 1st floor parking garage (i.e., no door, no window, just open air). The questions are:

a) Is an "unprotected" opening defined as something with a non-fire rated window or door -- or can it just be an open space in the wall?
b) If it has >50% open area per definition above, will it still meet requirements based on the the proposed fire separation distance?
c) I saw the private parking garage exemption (note j:

1. "j. The area of openings in a building containing only a Group U occupancy private garage or carport with a fire separation distance of 5 feet or greater shall not be limited.",

but reading up on "https://codes.iccsafe.org/s/CABC2022P1/chapter-4-special-detailed-requirements-based-on-occupancy-and-use/CABC2022P1-Ch04-Sec406.3#:~:text=Private garages and carports shall be classified as Group U,93 m2) in area." states that it is limited to 1000 sq ft of area (but then has a note saying "Exception: The area of a private garage accessory to Group R-3 one- or two-family dwellings shall not be greater than 3,000 square feet in area." -- if the garage is all by itself on the 1st floor, is it "accessory" to? Or does this not matter, since it meets the setbacks per subnote "f"?

I'm also not from California, but I'm going to suggest looking closely at definitions. To my simply mind, a dwelling unit on stilts is a dwelling unit on stilts, not a 2-story structure with a "garage" on the lower level. In commercial work, of course, there are open parking structures and enclosed parking structures, but I don't think those definitions come over to the residential code.

Suppose you rate the floor-ceiling assembly separating the parking from the dwelling unit, and rate the supporting columns. If you don't have any "walls," does that affect the analysis? The dwelling unit is in a protected box.

 

[B_olantis]

I'm confused. You state there is a 3.5-foot gap between each building and the assumed property line, which is a 3.5-foot fire separation distance. So, why are you trying to use provisions for fire separation distances of 5 to 10 feet?

I was under the assumption the % opening area is on a wall-by-wall basis, if the property line gap is different (say backyard vs side yards setbacks? is that normally not the case? The walls I’m trying to apply unlimited opening to it to are at least 8’ from the fenceline. Any weigh-in if the unprotected opening can mean open-air? (CA or elsewhere?)

 

[RLGA]

I was under the assumption the % opening area is on a wall-by-wall basis, if the property line gap is different (say backyard vs side yards setbacks? is that normally not the case? The walls I’m trying to apply unlimited opening to it to are at least 8’ from the fenceline. Any weigh-in if the unprotected opening can mean open-air? (CA or elsewhere?)

Okay, but you did not clearly state that those were the only walls (you stated, "We wanted to have some of the walls be open in the 1st floor parking garage," but did not identify which ones).

Openings are openings, and if they are not fire-protection-rated, they are considered "unprotected."

Per footnote "f" of Table 705.8, I would say that unlimited unprotected openings are permitted where the fire separation distance is 5 feet or greater. You could have up to 15% unprotected openings on the walls with a fire separation distance of 3.5 feet (assuming the buildings are sprinklered).