When to SM (with height increase) or SM (without area increase) in table 506.2?

[ElArch]

I have A-3 occupancy (more than 10% of the first floor area) in the first floor of a 4 story residential building with NPSF 13 sprinklers. The building is type VA. The building height is less than 50'. When I calculate the allowable area for A-3. Should I use SM (without height increase) or SM (with height increase) in table 506.2?
I had a similar project, the plan check comment said that I have to use SM(with area increase). I don't understand why I have to use this.
In table 504.3, allowable height for A is 50(NS), 70(S without area increase) and 50 (S with area increase). My building height is lower than 50'.

 

[Yankee Chronicler]

I'm not certain I understand the question. It is a multi-story building, so you would look at the SM column. If your building is small enough to fit under the allowable height and area without increase, IMHO there's no need or reason to look at height or area increases, whether by sprinklers or by excess frontage.

 

[ElArch]

It is a 4 story building. Each story is 20,000sf. The 2nd to 4th floor is R-2(apartment). The first floor A-3 (2,500sf), B (2,500sf), R-2 (15,000sf). Should I use SM (without height increase) or SM (with height increase) in table 506.2?

The plan checker said SM (with height increase) in one of similar building I did before. I checked another building done by former coworker and they also use SM (with height increase). I don’t understand.

 

[ElArch]

This is CBC 2022. In CBC there is SM (without height increase) and SM (with height increase). The allowable area in SM (without height increase) is 34,500sf, in SM (with height increase) is 11,500sf. It is huge different.

 

[Yankee Chronicler]

I'm from the opposite corner of the country and I gave up my California architect's license many years ago, so I'm not at all up to speed on the CA codes. I should stay out of the discussion.

 

[ElArch]

Here is the plan check comments:
The sprinkler increase provisions must be viewed for the entire building. Since this Type VA building is four stories in height, the sprinkler system shall be used to increase the allowable height and number of stories. The allowance to use the sprinkler system for the area increase in addition to the height and story increase is limited to an individual Group R-2 occupancy and cannot be used for the allowable area increase for any other occupancies in this building, even if an occupancy is only a single story. At Group A-2/A-3 occupancy, please revise the tabular allowable area to be 11,500 square feet. Sheet A0.50. CBC Table 506.2 footnote k.

 

[Joe.B]

Here is the plan check comments:
The sprinkler increase provisions must be viewed for the entire building. Since this Type VA building is four stories in height, the sprinkler system shall be used to increase the allowable height and number of stories. The allowance to use the sprinkler system for the area increase in addition to the height and story increase is limited to an individual Group R-2 occupancy and cannot be used for the allowable area increase for any other occupancies in this building, even if an occupancy is only a single story. At Group A-2/A-3 occupancy, please revise the tabular allowable area to be 11,500 square feet. Sheet A0.50. CBC Table 506.2 footnote k.

That seems to make sense to me, and they were kind enough to tell you how to comply, I'm not going to go through all the work to verify this though. Does this cause a problem for the project?

 

[ElArch]

That seems to make sense to me, and they were kind enough to tell you how to comply, I'm not going to go through all the work to verify this though. Does this cause a problem for the project?

I don't understand the comment. Does the comment mean that since R-2 already used the area increase and height increase, any other occupancy can't use area or height increasement? Therefore, the A-3 has to use area under NS? I also had S-2, B and M occupancy in the first floor. The plan check comment says that I should use area under SM for these occupancies. Why not area under NS for these occupancies?
Since the A-3 height under NS is 50'. My building is under 50'. Why can't I use area under SM without height increase which is 34,500sf. If I use area under NS or SM (with height increase) the area is 11,500sf. This number does not work for my current project.

 

[RLGA]

I assume you are referring to the CBC.

You also have to consider the allowable height in terms of the number of stories per Table 504.4. Group A-3 is limited to 3 stories without an area increase and 2 stories with an area increase. Thus, you cannot use the nonseparated occupancies method to determine your allowable area. However, Group R-2 occupancies can be four stories with or without an area increase since your building is under 60 feet in height.

Thus, you will need to separate the Group A-3 occupancy on the first story from the second story with a 1-hour horizontal assembly as an occupancy separation per Table 508.4 (which you have to do anyway for dwelling unit separation per Section 420). Since the Group A-3 occupancy does not exceed the allowable height in stories, you can use the "without height increase" allowable areas in Table 506.2, but now you have to determine your allowable area based on separated occupancies per Section 508.4.

 

[ElArch]

I assume you are referring to the CBC.

You also have to consider the allowable height in terms of the number of stories per Table 504.4. Group A-3 is limited to 3 stories without an area increase and 2 stories with an area increase. Thus, you cannot use the nonseparated occupancies method to determine your allowable area. However, Group R-2 occupancies can be four stories with or without an area increase since your building is under 60 feet in height.

Thus, you will need to separate the Group A-3 occupancy on the first story from the second story with a 1-hour horizontal assembly as an occupancy separation per Table 508.4 (which you have to do anyway for dwelling unit separation per Section 420). Since the Group A-3 occupancy does not exceed the allowable height in stories, you can use the "without height increase" allowable areas in Table 506.2, but now you have to determine your allowable area based on separated occupancies per Section 508.4.

I used separated method. I used without height increase area but the plan checker said that I should use area 11500. I don't know if he is using 'NS' or 'SM with area increase'. I don't understand his comment. I also have other occupancy in the first floor. He said to use SM in other occupancies. Below is his whole comment. the building is 4 story. A-3 only allow 2 or 3 story. Does "without height increase" include story increase? A-3 is only in the first floor.
"The sprinkler increase provisions must be viewed for the entire building. Since this Type VA
building is four stories in height, the sprinkler system shall be used to increase the
allowable height and number of stories. The allowance to use the sprinkler system for the
area increase in addition to the height and story increase is limited to an individual Group
R-2 occupancy and cannot be used for the allowable area increase for any other
occupancies in this building, even if an occupancy is only a single story. At Group A-2/A-3
occupancy, please revise the tabular allowable area to be 11,500 square feet. Sheet A0.50.
CBC Table 506.2 footnote k
2
nd Review Comment: This issue has been addressed. However, it is unclear from review
of the newly revised allowable area calculation how Groups S-2 and M occupancies have
been accounted in the area ratio calculations and why the Group S-2 parking garage has
been reclassified as a nonseparated Group B occupancy. Furthermore, since the building is
four stories in height, the allowable area ratio calculation for Groups S-2, M and B
Occupancies shall be based on the SM (not S1) tabular values. Sheets A0.50, A0.61,
A0.71. CBC Sections 506.2.3, 506.2.4 "

 

[Joe.B]

I don't understand the comment. Does the comment mean that since R-2 already used the area increase and height increase, any other occupancy can't use area or height increasement? Therefore, the A-3 has to use area under NS? I also had S-2, B and M occupancy in the first floor. The plan check comment says that I should use area under SM for these occupancies. Why not area under NS for these occupancies?
Since the A-3 height under NS is 50'. My building is under 50'. Why can't I use area under SM without height increase which is 34,500sf. If I use area under NS or SM (with height increase) the area is 11,500sf. This number does not work for my current project.

I don't think I can explain it on a forum. If we we're sitting at a table with the code books and the plans, I think we could get to an understanding. I've been in a similar place as you and was fortunate to have a mentor break it all down for me, and I have had situations come up on specific projects that take some deep dives. Is the plan reviewer willing to do that with you?

If the numbers don't work, could you turn the first floor into a podium and treat it as a separate building? That might be your solution.

 

[ElArch]

I don't think I can explain it on a forum. If we we're sitting at a table with the code books and the plans, I think we could get to an understanding. I've been in a similar place as you and was fortunate to have a mentor break it all down for me, and I have had situations come up on specific projects that take some deep dives. Is the plan reviewer willing to do that with you?

If the numbers don't work, could you turn the first floor into a podium and treat it as a separate building? That might be your solution.

Do you mean I have to use 11500? If I use 34500 in SM without height increase it works. I don't want to change construction type or add Podium. It will cost too much.

 

[ElArch]

Do you mean I have to use 11500? If I use 34500 in SM without height increase it works. I don't want to change construction type or add Podium. It will cost too much.

Do you mean I have to use 11500? If I use 34500 in SM without height increase it works. I don't want to change construction type or add Podium. It will cost too much.

I am not bad in code analysis. Can you just explain why I have to use 11500? Thanks!

 

[ElArch]

I am not bad in code analysis. Can you just explain why I have to use 11500? Thanks!

I already used up all other methods: separating the building to two buildings, frontage increase. If only that number can be changed I am good.

 

[Joe.B]

If I end up with some free time, I may try to do an analysis because it's great practice, but I won't make any promises.

 

[Joe.B]

I assume you are referring to the CBC.

You also have to consider the allowable height in terms of the number of stories per Table 504.4. Group A-3 is limited to 3 stories without an area increase and 2 stories with an area increase. Thus, you cannot use the nonseparated occupancies method to determine your allowable area. However, Group R-2 occupancies can be four stories with or without an area increase since your building is under 60 feet in height.

Thus, you will need to separate the Group A-3 occupancy on the first story from the second story with a 1-hour horizontal assembly as an occupancy separation per Table 508.4 (which you have to do anyway for dwelling unit separation per Section 420). Since the Group A-3 occupancy does not exceed the allowable height in stories, you can use the "without height increase" allowable areas in Table 506.2, but now you have to determine your allowable area based on separated occupancies per Section 508.4.

And there's this. Even if I spent the time, I doubt I could give you a better explanation than this.

 

[ElArch]

I got the answer. It is because the building is 4 story. The R-2 used the height increase, then A-3 is not allowed to use without height increase area.