Mixed Occupancy - Assembly allowable story height

[el cholo]

2009 IBC

Existing building is Type IIA - Fire Sprinklered

Mixed Use B/M Non-Separated

5 stories tall.

M is most restrictive, increase to minimum 5 floors per 504.2

We are going to do a office build-out on levels 4 & 5, problem is we will have large conference rooms (bigger than 750 sq ft) on level 4 & 5, which will have to be counted as A-3 Assembly space.

Trying to use it as an accessory occupancy per 508.2, I run into the problem that Type IIA for A3 group has a limit of 3 stories height, so per section 508.2.3 It's impossible because the floor we're building out is on level 4 & I'm not allowed to use any height increase with the sprinklers.

Next is separated occupancy per section 508.4, I need to separate the Assembly from Business with 1 hr assemblies vertically & horizontally. Section 508.4.3 says the allowable height needs to per Table 503, but this time it doesn't specifically say that we're not allowed to use the height increase with the sprinkler, so I'm assuming I can increase the height to 4 & able to put an Assembly space on that level???

Am I correct in my assessment, I can put a large Assembly space on level 4 in a Type IIA sprinklered building using the separated occupancies option? Can y'all let me know if I'm missing anything.

Thanks,

 

[RLGA]

Can you try using separated occupancies for the Group A-?

 

[Builder Bob]

Separated could run into problems with the supporting construction for the fire barriers....

 

[el cholo]

I believe separated occupancies is my only option, since Section 508.4.3 doesn't forbid the use of height increase for sprinklers.

Regarding supporting construction; I'm looking at Section 707.5.1, it says to go to section 704.3 for encasement if the walls are more than 2 stories high. In this case the wall is only 1 story, but it's on level 4, so not sure if this is considered more than 2 stories high?

 

[RLGA]

Separated could run into problems with the supporting construction for the fire barriers....

It shouldn't. If the building is Type IIA construction, then everything should be 1-hour construction, which is the same rating required for the separation with a sprinkler system.

 

[RLGA]

Regarding supporting construction; I'm looking at Section 707.5.1, it says to go to section 704.3 for encasement if the walls are more than 2 stories high. In this case the wall is only 1 story, but it's on level 4, so not sure if this is considered more than 2 stories high?

Section 704.3 would be required of your building regardless of whether or not it was supporting a fire barrier. However, I have a solution for you that may not require creating fire barriers around the Group A-3: treat then entire 4th story as a Group A-3. Thus, you would have a mix of separated and nonseparated occupancies, which is permitted. The entire 4th story would be nonseparated within the story (i.e. the Group A-3 is not separated from the adjacent Group B on the story); however, with the required 1-hour horizontal assemblies for the Type IIA construction can be used as the required separation from the 3rd and 5th stories.

 

[kilitact]

508.2.3 Allowable building area and height. The allowable building area and height of the building shall be based on the allowable building area and height for the main occupancy in accordance with Section 503.1. The height of each accessory occupancy shall not exceed the tabular values in Table 503, without increases in accordance with Section 504 for such accessory occupancies. The building area of the accessory occupancies shall be in accordance with Section 508.2.1.

The allowable building height and area is based on the main occupancy not the accessory use.

 

[RLGA]

508.2.3 Allowable building area and height. The allowable building area and height of the building shall be based on the allowable building area and height for the main occupancy in accordance with Section 503.1. The height of each accessory occupancy shall not exceed the tabular values in Table 503, without increases in accordance with Section 504 for such accessory occupancies. The building area of the accessory occupancies shall be in accordance with Section 508.2.1.The allowable building height and area is based on the main occupancy not the accessory use.

kilitact: The building height and area is based on the Group M per the OP. The issue is that a Group A-3 is only permitted up to the third story as an accessory occupancy and they want the Group A-3 on the fourth story. It would be permitted on the fourth story if considered as separated occupancies, which allows a sprinkler increase of one story.

 

[kilitact]

kilitact: The building height and area is based on the Group M per the OP. The issue is that a Group A-3 is only permitted up to the third story as an accessory occupancy and they want the Group A-3 on the fourth story. It would be permitted on the fourth story if considered as separated occupancies, which allows a sprinkler increase of one story.

RLGA,

Your correct in that the building height and area is based on the M/B. An accessory used A is not prohibited on the fourth floor.

 

[Builder Bob]

In the 2012 IBC, it would be prohibited

508.2 Accessory occupancies.

Accessory occupancies are those occupancies that are ancillary to the main occupancy of the building or portion thereof. Accessory occupancies shall comply with the provisions of Sections 508.2.1 through 508.2.4.

508.2.3 Allowable building area and height.

The allowable building area and height of the building shall be based on the allowable building area and height for the main occupancy in accordance with Section 503.1. The height of each accessory occupancy shall not exceed the tabular values in Table 503, without increases in accordance with Section 504 for such accessory occupancies. The building area of the accessory occupancies shall be in accordance with Section 508.2.1.

 

[kilitact]

In the 2012 IBC, it would be prohibited 508.2 Accessory occupancies.

Accessory occupancies are those occupancies that are ancillary to the main occupancy of the building or portion thereof. Accessory occupancies shall comply with the provisions of Sections 508.2.1 through 508.2.4.

508.2.3 Allowable building area and height.

The allowable building area and height of the building shall be based on the allowable building area and height for the main occupancy in accordance with Section 503.1. The height of each accessory occupancy shall not exceed the tabular values in Table 503, without increases in accordance with Section 504 for such accessory occupancies. The building area of the accessory occupancies shall be in accordance with Section 508.2.1.

Builder Bob,

The same wording is in the 2009. "The height of each accessory occupant shall not exceed...", this is specific to the the accessory use. The building area and height has noted in the first sentence of 508.2.3, gives design criteria for the entire building.

 

[el cholo]

Section 704.3 would be required of your building regardless of whether or not it was supporting a fire barrier. However, I have a solution for you that may not require creating fire barriers around the Group A-3: treat then entire 4th story as a Group A-3. Thus, you would have a mix of separated and nonseparated occupancies, which is permitted. The entire 4th story would be nonseparated within the story (i.e. the Group A-3 is not separated from the adjacent Group B on the story); however, with the required 1-hour horizontal assemblies for the Type IIA construction can be used as the required separation from the 3rd and 5th stories.

Making the whole 4th floor would increase the occupant load by too much for the existing stairs. Just FYI, the building right now is under construction, but it will be existing by the time we get to permit.

 

[el cholo]

Builder Bob,The same wording is in the 2009. "The height of each accessory occupant shall not exceed...", this is specific to the the accessory use. The building area and height has noted in the first sentence of 508.2.3, gives design criteria for the entire building.

That's correct, pretty much eliminates being able to use it as an accessory occupancy because it's on level 4. Being on level 4 also prevents me from using the non-separated occupancy. My only hope is separated occupancy, only because it doesn't specifically mention that you cannot do a height increase with sprinklers.

 

[RLGA]

Making the whole 4th floor would increase the occupant load by too much for the existing stairs. Just FYI, the building right now is under construction, but it will be existing by the time we get to permit.

Occupant load is not based on occupancy group...it is based on the use of the space. If a space is used for business, then the occupant load factor will still be 100 sf/occupant. Only the actual assembly use will be based on the assembly occupant load factor.

 

[kilitact]

That's correct, pretty much eliminates being able to use it as an accessory occupancy because it's on level 4. Being on level 4 also prevents me from using the non-separated occupancy. My only hope is separated occupancy, only because it doesn't specifically mention that you cannot do a height increase with sprinklers.

Can't see the trees for the forest sometimes. Have you look at a B occ, training and skill development?

Thanks,

 

[RLGA]

It depends on the building official. I usually take the conservative route and any assembly space over 750 sq. ft. and has an occupant load greater than 49 I will classify as a Group A-3. The only exception to this is Group E. I do a lot of university and college work, and every plans examiner that I have encountered has considered a classroom with more than 49 occupants as a Group A-3, even though it is adult education.

 

[kilitact]

It depends on the building official. I usually take the conservative route and any assembly space over 750 sq. ft. and has an occupant load greater than 49 I will classify as a Group A-3. The only exception to this is Group E. I do a lot of university and college work, and every plans examiner that I have encountered has considered a classroom with more than 49 occupants as a Group A-3, even though it is adult education.

Depends on the use of the space. If its an office space with rooms that are used for skill and training B occ would work. l

 

[cda]

Also they can ask the BO for lower occupant load

 

[JBI]

I'm leaning the same way as Ron on this one. The structure should already have the required one hour rating for construction type to be correct.

Creating a fire barrier does not automatically create a load that would alter the existing load path(s) in the building, so creating separated mixed uses on the 4th floor should not be that difficult. Falling back on 'accessory' provisions is probably not workable because of the 10% area limit on accessory spaces. (or is that a NY thing also?)