When an 'Atrium' is not a true atrium by Code

[George McGerd]

I am designing a large, 3-story high school (use group E), new-construction, 2018 IBC and 2018 NFPA 101 (LSC) are applicable. Obviously it will be fully-sprinklered IAW all applicable codes.

The building will feature a large, 3-story volume "space" located in the center, inside of which will be a communicating / convenience stair connecting all three stories. The stair will NOT serve as one of the required means of egress. The 3-story volume will be completely open to the first floor (level of exit discharge) but will be fully enclosed from the second and third stories by a glass curtainwall, designed a ‘smoke barrier’. There will be no operable windows or fenestration within the curtainwall smoke barrier. The only openings on the 2nd and 3rd stories will be doors for access leading directly to the communicating stairway, which will be automatically closing upon the detection of smoke.

Here are my assumptions:

1. Smoke control and protection requirements of IBC Section 909 will not be required since this ‘atrium’ doesn’t actually ‘connect’ any of the stories. By definition ‘connect’ means to be ‘open’ to or ‘communicate’ with another stories. The automatically closing doors do not serve to ‘connect’ the stories.

2. Smoke protection features required under the LSC ‘atriums’ Section 8.6.7 are NOT applicable because the volume is not considered a true ‘atrium’ by definition, due to the fact that the 2nd and 3rd stories are enclosed and separated from the remainder of those floors by the curtainwall smoke barrier.

3. Fire protection analysis required under LSC ‘atriums’ Section 8.6.7 is not applicable, same rationale as point 2 above.

4. The curtainwall smoke barrier enclosure does not have to be fire rated under IBC or LSC since the stories aren’t ‘connected’. Reference IBC 404.6, exception 4, and LSC 8.6.6(4)(a).

5. Sprinklers are not required to be placed at 6’-0” intervals alongside the curtainwall smoke barrier, as otherwise required by LSC due to it not being classified as a true ‘atrium,’ and as otherwise required by IBC 404.6.1.1, since I’m tapping exception 4 instead of exception 1.

Please shoot holes in my assumptions. Let me know if I’m overreaching on this one. I tend to try to do that sometimes.

Thanks !!!

 

[RLGA]

George:

I’m at a conference with very limited time, but I just want to point out that, at least from an IBC perspective, there are holes in your assumptions. When I get some time to respond in depth, I will identify those holes and the code citations to back them up.

 

[RLGA]

George:

The area should go to first in the IBC is Section 712 for vertical openings. Essentially, you have a space that penetrates three stories; therefore, you have to comply with one of the methods permitted by Section 712.1.

The method provided in Section 712.1.1 requires the use of a shaft enclosure around the opening, and, per Section 713, this means a 1-hour fire barrier in your case for the entire space through all floors. Since you do not want that, then this method is not applicable.

Section 712.1.2 is not applicable to your situation.

Section 712.1.3 is also not applicable, since you situation does not involve an escalator.

Sections 712.1.4, 712.1.5, and 712.1.6 are also not applicable, since the openings do not involve through penetrations, joints, or air transfer ducts/openings, respectively.

I’ll come back to Section 712.1.7.

Section 712.1.8 is not applicable since you situation does not involve a chimney.

Section 712.1.9 would only apply if the space connected two stories.

Section 712.1.10 does not apply since this is not a parking garage.

Section 712.1.11 would apply if the upper levels can be considered mezzanine and not stories, but based on your description, I assume the upper levels must be considered stories and not mezzanine.

Section 712.1.12 applies to exit access stairways and ramps per Section 1019, but based on your description, this also would not be applicable.

The remaining methods within this section are also not applicable based on the described use and classification of the space.

Thus, we are directed back to Section 712.1.7 for atriums as your only option, which requires compliance with Section 404. Therefore, by IBC definition, what you have is an atrium.

Section 404 establishes the requirements for atriums, thus everything must conform to these unless a specific section has an exception that applies. Smoke control is still required per Section 404.5 because it is an atrium since the atrium is through three stories. An atrium must be separated from the floors by a 1-hour fire barrier per Section 404.6; however, Exception 1 allows the use of glazing to provide a smoke partition (not a smoke barrier) with the installation of sprinklers spaced as directed along the glass partition on both sides if there are walking surfaces on both sides or only the room side if there is not a walking surface on the atrium side. Since you have three stories, you are permitted up to three stories to be open into the atrium without separation, but the volume of those three stories must be included in the smoke control design per Section 404.6, Exception 3.

 

[George McGerd]

RGLA, first, I greatly appreciate your feedback. This is a rather complex design from a code compliance perspective and I want to make sure I have my ducks in a row before I go in front of the AHJ for a preliminary / schematic review so I don't get shot down right out of the gate.

I didn't take too close of a look at Section 712, but as you mention in your analysis the only paragraph applicable to this design would be 712.1.7 for atriums. I agree that per the IBC definition this space is an atrium. However, under the LSC this space would be defined as a "communicating space" and not as an atrium (that's an aside because I think any potential holes in my theory stem from the IBC requirements)

As established by 712 (IBC) this space must comply with Section 404. However, I'm trying to tap a number of exceptions listed under 404 since, while my space does penetrate 3 stories, it technically doesn't "connect" the first story to any other story because I am providing the curtainwall smoke partition around the entire atrium, bottom starting at the top of the first story and running up to the roof (third story) to fully isolate this three story space from the second and third stories. The only argument that could be made for a connection is the pair of smoke doors located within the smoke partition at the second and third story levels which will be provided for access to the communicating stair (e.g. monumental staircase) ONLY. In my opinion, the smoke doors are not a true connection (they will automatically close upon detection of smoke) Based on my interpretation 'connection' means to be open to or 'communicate' with another story. (Anyone...please advise me here if you disagree, because my entire case rests upon acceptance of this definition of 'connection'.)

Section 404.5 - exception: In other than I-2 and I-1 condition 2, smoke control is not required for atriums that connect only two stories. Therefore, smoke control not required because technically I am not connecting the stories.

Section 404.6 - Atrium spaces shall separated from adjacent spaces by a 1-hour fire barrier - exception #4 states: A fire barrier is not required between the atrium and the adjoining spaces where the atrium is not required to be provided with a smoke control system. Therefore, the curtainwall partition does not also have to be fire rated because smoke control is not required, again because I am not connecting the stories.

If I were to use 404.6 exception 1 to get out of the fire rating, then I agree that I would be bound to provide the sprinklers alongside the glass at intervals not exceeding 6'-0" o.c. But, because I am tapping exception 4, I can shed the 1-hour fire barrier requirement w/o providing the sprinklers.

I LOVE to do this design with curtainwall acting as a smoke partition ONLY, but if push comes to shove, we can specify a 1-hr curtainwall. $$$$$$$ cha-ching.

Thank you,
George

 

[George McGerd]

Here's another potential argument the AHJ could use to 'ding' me. While I personally consider this space to be an atrium an not a 'penetration' I guess the argument could be made that it's penetrating 2 horizontal assemblies (e.g. floors) and therefore would be also subject to the requirements of Section 714 "Penetrations". I'm using type IB construction so my floors are fire rated to 2 hours (we're using composite deck on steel frame, sprayed w/ SFRM). Section 714.5 - penetrations thru horizontal assemblies: penetrations of a fire resistance rated floor not required to be enclosed in a shaft by section 712.1 shall be protected in accordance with 714.5.1 thru 714.5.4. Those sections don't specifically address the hourly rating of penetrations so I'd have to assume that the penetration would require the same fire rating of the construction being penetrated - i.e. 2-hours. YIKES. thoughts?

 

[RLGA]

RGLA, first, I greatly appreciate your feedback. This is a rather complex design from a code compliance perspective and I want to make sure I have my ducks in a row before I go in front of the AHJ for a preliminary / schematic review so I don't get shot down right out of the gate.

I didn't take too close of a look at Section 712, but as you mention in your analysis the only paragraph applicable to this design would be 712.1.7 for atriums. I agree that per the IBC definition this space is an atrium. However, under the LSC this space would be defined as a "communicating space" and not as an atrium (that's an aside because I think any potential holes in my theory stem from the IBC requirements)

As established by 712 (IBC) this space must comply with Section 404. However, I'm trying to tap a number of exceptions listed under 404 since, while my space does penetrate 3 stories, it technically doesn't "connect" the first story to any other story because I am providing the curtainwall smoke partition around the entire atrium, bottom starting at the top of the first story and running up to the roof (third story) to fully isolate this three story space from the second and third stories. The only argument that could be made for a connection is the pair of smoke doors located within the smoke partition at the second and third story levels which will be provided for access to the communicating stair (e.g. monumental staircase) ONLY. In my opinion, the smoke doors are not a true connection (they will automatically close upon detection of smoke) Based on my interpretation 'connection' means to be open to or 'communicate' with another story. (Anyone...please advise me here if you disagree, because my entire case rests upon acceptance of this definition of 'connection'.)

Section 404.5 - exception: In other than I-2 and I-1 condition 2, smoke control is not required for atriums that connect only two stories. Therefore, smoke control not required because technically I am not connecting the stories.

Section 404.6 - Atrium spaces shall separated from adjacent spaces by a 1-hour fire barrier - exception #4 states: A fire barrier is not required between the atrium and the adjoining spaces where the atrium is not required to be provided with a smoke control system. Therefore, the curtainwall partition does not also have to be fire rated because smoke control is not required, again because I am not connecting the stories.

If I were to use 404.6 exception 1 to get out of the fire rating, then I agree that I would be bound to provide the sprinklers alongside the glass at intervals not exceeding 6'-0" o.c. But, because I am tapping exception 4, I can shed the 1-hour fire barrier requirement w/o providing the sprinklers.

I LOVE to do this design with curtainwall acting as a smoke partition ONLY, but if push comes to shove, we can specify a 1-hr curtainwall. $$$$$$$ cha-ching.

Thank you,
George

You are connecting three stories, whether you have smoke partitions, smoke barriers, fire partitions, or fire barriers. The code gives you those options for separating that connective space from the individual stories. The best option is to call it an atrium, and smoke partitions are permitted, so there’s no argument there. However, smoke control is still required, regardless of how many of your three stories are separated from the atrium by the smoke partitions with fire sprinklers.

The only way to avoid the atrium requirements is to consider it a shaft, and since you’ve indicated that the floor systems are required to be 2-hour horizontal assemblies, then the walls of the shaft would need to be fire barriers also rated for 2 hours per Section 713.4.

 

[RLGA]

Here's another potential argument the AHJ could use to 'ding' me. While I personally consider this space to be an atrium an not a 'penetration' I guess the argument could be made that it's penetrating 2 horizontal assemblies (e.g. floors) and therefore would be also subject to the requirements of Section 714 "Penetrations". I'm using type IB construction so my floors are fire rated to 2 hours (we're using composite deck on steel frame, sprayed w/ SFRM). Section 714.5 - penetrations thru horizontal assemblies: penetrations of a fire resistance rated floor not required to be enclosed in a shaft by section 712.1 shall be protected in accordance with 714.5.1 thru 714.5.4. Those sections don't specifically address the hourly rating of penetrations so I'd have to assume that the penetration would require the same fire rating of the construction being penetrated - i.e. 2-hours. YIKES. thoughts?

In this instance, the connecting space would not be considered a penetration as referred to in Section 714, since it is not an item penetrating the floor, but rather a space; thus, it would be considered a shaft, as I discussed in my previous post.

 

[DontKnowMuch]

George,
Did you have any luck?