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Mixed use Multi story building and Non-separated Occupancies

S

SteveZ

Registered User
Joined
Aug 13, 2019
Messages
14
Location
Montana
First post, thank you for your input.

I am having a difficult time reconciling the provisions between IBC 2018 508.3 Non-separated Occupancies and 506.2.4, Mixed Occupancy, multi-story buildings.

Most of what I am seeing is that if the Non-separated provisions are to be used, the most restrictive aspects will apply to the entire building with respect to building area and height/stories. As an example, for a building of type VA construction with an A-3 and B spaces within, it would seem that the building would be limited to 3 stories due to the A-3 occupancy if we were to employ the non-separated provisions. Assume accessory occupancies is not an option.

However, section 506.2.4 states that "Each story of a mixed occupancy building with more than one story above grade plane shall individually comply with the applicable requirements of 508.1" Does this mean the building could be 4 stories and employ 508.3 as long as the A-3 space was not located above the 3rd floor?

Thank you!
 
SteveZ said:
Does this mean the building could be 4 stories and employ 508.3 as long as the A-3 space was not located above the 3rd floor?
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Yes
This permits 4 stories in a VA sprinklered type "B" occupancy
503.1 General.
Unless otherwise specifically modified in Chapter 4 and this chapter, building height, number of stories and building area shall not exceed the limits specified in Sections 504 and 506 based on the type of construction as determined by Section 602 and the occupancies as determined by Section 302 except as modified hereafter. Building height, number of stories and building area provisions shall be applied independently. For the purposes of determining area limitations, height limitations and type of construction, each portion of a building separated by one or more fire walls complying with Section 706 shall be considered to be a separate building.

This clarifies the "A-3" occupancy can be on the 3rd floor.
504.2 Mixed occupancy.
In a building containing mixed occupancies in accordance with Section 508, no individual occupancy shall exceed the height and number of story limits specified in this section for the applicable occupancies.
 
Thank you both for your input, this website and its users are an invaluable resource. Your reply makes sense based on real world buildings, was just having trouble understanding how this issue relates to the code, much appreciated!
 
Thank you. I'm an architect in Montana and have been using the site whenever a code question comes up; seems there is usually always someone who has had a similar question in the past and I appreciate user's thought out responses and useful discussions.
 
SteveZ said:
First post, thank you for your input.

I am having a difficult time reconciling the provisions between IBC 2018 508.3 Non-separated Occupancies and 506.2.4, Mixed Occupancy, multi-story buildings.

Most of what I am seeing is that if the Non-separated provisions are to be used, the most restrictive aspects will apply to the entire building with respect to building area and height/stories. As an example, for a building of type VA construction with an A-3 and B spaces within, it would seem that the building would be limited to 3 stories due to the A-3 occupancy if we were to employ the non-separated provisions. Assume accessory occupancies is not an option.

However, section 506.2.4 states that "Each story of a mixed occupancy building with more than one story above grade plane shall individually comply with the applicable requirements of 508.1" Does this mean the building could be 4 stories and employ 508.3 as long as the A-3 space was not located above the 3rd floor?

Thank you!
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If using Section 508.3 for nonseparated occupancies, then the Group A-3 occupancy would be the most restrictive for height and area for the entire building or the portion that is considered nonseparated.

If applying Section 508.3 for the entire building, then in a sprinklered Type VA building, the height of the building would be limited to 3 stories...period. A fourth story could not be added even if the Group A-3 occupancy was limited to no higher than the third story.

Now, you could consider stories 1 through 3 as nonseparated and separate the fourth story from the stories below per Table 508.4. Thus, the Group A-3 portion of the building is no higher than three stories and the fourth story can be a Group B occupancy since it is permitted in a 4-story sprinklered Type VA building. The complication here is that the horizontal assembly separating the fourth story from the third story is required to be supported by construction having an equal or higher rating. Since a 1-hour occupancy separation is all that is required per Table 508.4, then the Type VA construction, which is required to have 1-hour construction, would not be an issue. However, if the construction type was IIB, then all of the supporting construction for the fourth-story floor would need to be rated; thus, making it more logical to go to Type IIA construction. If constructed as Type IIA construction, now the Group A-3 is permitted 4 stories and you can consider the entire building nonseparated.

Isn't the building code just fun!
 
I am having a hard time understanding your point about separating the 4th from the 3rd floors and how this relates to building height / area and multi-story mixed- occupancy buildings.

You said: "you could consider stories 1 through 3 as nonseparated and separate the fourth story from the stories below per Table 508.4. Thus, the Group A-3 portion of the building is no higher than three stories and the fourth story can be a Group B occupancy since it is permitted in a 4-story sprinklered Type VA building".

Why would the 4th and 3rd floors need to be separated in this case as it seems there is no limitation for the B occupancy as located on the 4th floor? The 4th floor would appear to comply with 508.3 non-separated for heights/areas, same as 3rd. Each story would seem to be individually complying with 508.1 and the provisions of 506.2.4 as dictated and no separation would be required between 3rd and fourth floors. What is triggering the separation requirement between 3rd and 4th floors?
 
SteveZ said:
I am having a hard time understanding your point about separating the 4th from the 3rd floors and how this relates to building height / area and multi-story mixed- occupancy buildings.

You said: "you could consider stories 1 through 3 as nonseparated and separate the fourth story from the stories below per Table 508.4. Thus, the Group A-3 portion of the building is no higher than three stories and the fourth story can be a Group B occupancy since it is permitted in a 4-story sprinklered Type VA building".

Why would the 4th and 3rd floors need to be separated in this case as it seems there is no limitation for the B occupancy as located on the 4th floor? The 4th floor would appear to comply with 508.3 non-separated for heights/areas, same as 3rd. Each story would seem to be individually complying with 508.1 and the provisions of 506.2.4 as dictated and no separation would be required between 3rd and fourth floors. What is triggering the separation requirement between 3rd and 4th floors?
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If the 4th story is not separated from the 3rd story, then, in essence per the requirements of nonseparated occupancies, the 4th story is a part of the Group A-3, even though the actual Group A-3 occupancy is not located on the 4th story.

The same thing applies to building area. Let us assume a large Group B single-story building includes several Group A-3 occupancies that could not be considered accessory occupancies. If the Group A-3 was not separated from the Group B, then the entire building area is considered Group A-3, which would limit the building area, even though each occupancy group does not exceed the allowable per the table in Chapter 5.

Going back to your example, without that separation, the entire building (all four stories) is considered a Group A-3 building. If the construction type, limits Group A-3 buildings to 3 stories, then you would be exceeding the allowable height requirements. Thus, the need to separate the Group A-3 portion from the 4th story (i.e., limit the Group A-3 portion to a maximum of three stories, which is permitted).
 
RLGA said:
If the 4th story is not separated from the 3rd story, then, in essence per the requirements of nonseparated occupancies, the 4th story is a part of the Group A-3, even though the actual Group A-3 occupancy is not located on the 4th story.

The same thing applies to building area. Let us assume a large Group B single-story building includes several Group A-3 occupancies that could not be considered accessory occupancies. If the Group A-3 was not separated from the Group B, then the entire building area is considered Group A-3, which would limit the building area, even though each occupancy group does not exceed the allowable per the table in Chapter 5.

Going back to your example, without that separation, the entire building (all four stories) is considered a Group A-3 building. If the construction type, limits Group A-3 buildings to 3 stories, then you would be exceeding the allowable height requirements. Thus, the need to separate the Group A-3 portion from the 4th story (i.e., limit the Group A-3 portion to a maximum of three stories, which is permitted).
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I bet you hear this all the time, but you should write a book on this stuff.
 
Thank you Ron for the thoughts. Taking this discussion a little further and sticking with the same example, does having an assembly occupancy above level of exit discharge always necessitate an NFPA 13 sprinkler system for the story containing the assembly occupancy as well as the stories below, regardless of separation strategy used? What if the assembly occupancy could be qualified as accessory?
 
For Groups A-1 through A-4, if the occupancy is located on a floor other than the level of exit discharge, a sprinkler system must be installed on the floor with the Group A occupancy and all floors below down to and including the level of exit discharge, regardless of occupancy separation requirements.

If the occupancy is an accessory occupancy per Section 508.2 (2018 IBC), it still must be sprinklered, because an accessory occupancy is still individually classified per Chapter 3.
 
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