Group U private garage building

[Sifu]

Given a single story, VB, NS building housing individual private garages, each < 1000sf². The layout is 11 bays across, back to back for a total of 22 bays. 2018 IBC 406.3.1 requires them to be classified a group U and to be separated from each other by 1-hr fire barriers. 707.5 requires the fire barriers to terminate at the underside of the roof sheathing, slab or deck above. There is no allowance I see to terminate them at a rated horizontal assembly in this case. I have a proposal to stop the fire barriers at a rated horizontal assembly, and proceed with draftstopping per 718.4 from the top of the fire barrier through the attic at every 3'000sf². So the garage bays are separated by fire barriers from each other, and by a horizontal assembly from the attic spaces above, but the fire barriers do not provide the continuity required of them by 707.5. It SEEMS like there is a path for this (I think I found it last time I faced this) but I can't find it now. Any thoughts?

 

[BN4537]

707.5 requires the fire barriers to terminate at the underside of the roof sheathing, slab or deck above.

I would classify the horizontal assembly as the floor or roof sheathing, slab or deck above. How would they build a horizontal assembly that isn't one of those?

 

[BN4537]

11.2.6 Unusable space.​

In 1-hour fire-resistance-rated floor/ceiling assemblies, the ceiling membrane is not required to be installed over unusable crawl spaces. In 1-hour fire-resistance-rated roof assemblies, the floor membrane is not required to be installed where unusable attic space occurs above.

So, I think you can call it a floor even if no floor membrane is installed.

 

[ICE]

I was going to answer but there isn't enough info.

 

[mtlogcabin]

What is the total sq footage? What is going to be in the private garages?

 

[Sifu]

4,920sf², detached garage buildings for R2 units. Concrete slab, 1-hr fire barrier walls, 1-hr horizontal roof/ceiling assembly. I did one of these some time ago, and to my credit I keep notes on what I do and the decisions I make, to my discredit, I didn't spell out how I came to the conclusion that this was ok. The one I looked at was done to an earlier code edition which has now changed, so I'm not sure how I concluded what I concluded. Looking at it today I tend to think they need the fire barrier continuity, but from a practical perspective I am having trouble seeing it. I have notes from my previous review expressly addressing this, just not my justification. I even guessed I came here for answers but I can't find a thread where it was addressed. I THINK I may have considered it good since each private garage is separated from the others by fire barriers, and from the attic by a horizontal assembly, but if so I glossed over the continuity issue, or not and I found a path.

It is all a little messy. This is the third version of the plan (first introduced to someone else +4 years ago), the first had separate fire walls due to '12 406.3.2, the second then changed it to a single fire wall due to area limitations with fire barriers based on the 2018 version of 406.3..1, , now presumably due to a value engineering process, this one has no fire walls with fire barriers except the in the attic, but they reduced the size to keep it under the limits.

 

[ICE]

2020 CBC. Your code may vary and seeing some of the section numbers quoted here by others indicates that I might be way off.

406.3 Private garages and carports. Private garages and carports shall comply with Sections 406.2 and 406.3, or they shall comply with Sections 406.2 and 406.4.

This is a private garage. Sections 406.2 and 406.3 apply to private garages and Sections 406.2 and 406.4 apply to public garages.

406.3.1 Classification. Private garages and carports shall be classified as Group U occupancies. Each private garage shall be not greater than 1,000 square feet (93 m2) in area. Multiple private garages are permitted in a building where each private garage is separated from the other private garages by 1-hour fire barriers in accordance with Section 707, or 1-hour horizontal assemblies in accordance with Section 711, or both.

Section 406.3.1 sends you to Section 707 or Section 711 or both.

707.1 General. Fire barriers installed as required elsewhere in this code or the California Fire Code shall comply with this section.

707.5 Continuity. Fire barriers shall extend from the top of the foundation or floor/ceiling assembly below to the underside of the floor or roof sheathing, slab or deck above and shall be securely attached thereto. Such fire barriers shall be continuous through concealed space, such as the space above a suspended ceiling. Joints and voids at intersections shall comply with Sections 707.8 and 707.9

Section 711 Floor and Roof Assemblies
711.1 General. Horizontal assemblies shall comply with Section 711.2. Non-fire-resistance-rated floor and roof assemblies shall comply with Section 711.3.

Section 707 has options based on what configuration is present. The fire barrier might terminate at a floor or roof sheathing, slab or deck above. In your case you have a roof sheathing and none of the others. Additionally, the fire barrier clearly shall extend through the attic space. Section 711 is mentioned as an option if the configuration present included a floor, slab or deck above as Section 711 is all about a horizontal assembly. I would expect the fire barrier at each garage that went from floor to roof sheathing.

 

[classicT]

SIFU, perhaps during your earlier review you were relying upon the following:

406.3.1 Classification​

Private garages and carports shall be classified as Group U occupancies. Each private garage shall be not greater than 1,000 square feet (93 m2) in area. Multiple private garages are permitted in a building where each private garage is separated from the other private garages by 1-hour fire barriers in accordance with Section 707, or 1-hour horizontal assemblies in accordance with Section 711, or both.​

From Section 406.3.1, the requirement for separation is from private garage to private garage. 406.3.1 would appear to allow for either fire barriers or horizontal assemblies to achieve this separation. From this logic, providing the 1-hr fire barriers b/w units with a 1-hr ceiling (horizontal assembly), the separation requirement of 406.3.1 seems to be met. This accomplishes the intent of preventing the spread of fire between individual garage units (i.e. compartmentalization).

However, as for Section 707.5, I would note that these are not fire partitions. As fire barriers, they need to extend through concealed spaces. Just as if these were fire barriers used to compartmentalize for fire area, they must extend through the concealed spaces in an attic or floor assembly.

 

[Sifu]

SIFU, perhaps during your earlier review you were relying upon the following:

406.3.1 Classification​

Private garages and carports shall be classified as Group U occupancies. Each private garage shall be not greater than 1,000 square feet (93 m2) in area. Multiple private garages are permitted in a building where each private garage is separated from the other private garages by 1-hour fire barriers in accordance with Section 707, or 1-hour horizontal assemblies in accordance with Section 711, or both.​

From Section 406.3.1, the requirement for separation is from private garage to private garage. 406.3.1 would appear to allow for either fire barriers or horizontal assemblies to achieve this separation. From this logic, providing the 1-hr fire barriers b/w units with a 1-hr ceiling (horizontal assembly), the separation requirement of 406.3.1 seems to be met. This accomplishes the intent of preventing the spread of fire between individual garage units (i.e. compartmentalization).

However, as for Section 707.5, I would note that these are not fire partitions. As fire barriers, they need to extend through concealed spaces. Just as if these were fire barriers used to compartmentalize for fire area, they must extend through the concealed spaces in an attic or floor assembly.

This is exactly my thinking. I believe I may have applied the separation but stopped short of the continuity. Since the previous code (2012) did not require fire barriers at every individual garage in lieu of fire walls at 3,000sf², a strategy this building originally employed, when they transitioned to the fire barrier strategy I may have missed it. Hard to accept, because it literally jumped off the page at me on this review, but #$% happens.

What I can't reconcile is that every single fire barrier would need to terminate at the roof sheathing, which is a sloped truss roof. Seems like all of these joints will present a heck of a problem in comparison to using the horizontal assembly. The result is 22 individual units with unprotected attic spaces with complete 1-hr separation or 22 units below the attic space all separated from each other, and 4 individual attic spaces separated from below by a 1-hr horizontal assembly but from each other only by draftstopping. I have no choice but to make the call, if there is a path I can't see I'm sure they will let me know.