• Welcome to the new and improved Building Code Forum. We appreciate you being here and hope that you are getting the information that you need concerning all codes of the building trades. This is a free forum to the public due to the generosity of the Sawhorses, Corporate Supporters and Supporters who have upgraded their accounts. If you would like to have improved access to the forum please upgrade to Sawhorse by first logging in then clicking here: Upgrades

Mixed Use Occupancy

E

E87

Member
Joined
Feb 23, 2011
Messages
8
Location
Pennsylvania
Hello everyone, I have another question I was hoping to get some discussion about. Here's my situation:

I have a mixed use occupancy consisting of 7500 SF of F-1, and 4100 SF of S-1. Construction type is 5B. So when looking at the allowable areas for each occupancy, F-1 is allowed 8500 SF, and the S-1 is allowed 9000 SF. So each occupancy, when looking at separately, are under their allowable square footages. And after looking at Table 508.4 (Fire separations required between occupancies), I found that there is no separation requirement between S and F occupancies.

So my question is wether or not I am correct in saying that I do not need to have a fire wall separation between the two occupancies. Maybe I am just confusing myself but when you look at the building as a whole, the total SF of the building is 11,600 SF, which is over the allowable area of the two occupancies.

I understand that when you are over your allowable fire areas in a single use facility, you can divide the facility into several "separate buildings" by using fire walls to get each piece under the allowable SF. I am getting confused with this mixed occupancy facility.

Any thoughts, suggestions are much apprecitated!
 
You will need to look at 508.1

506.5 Mixed occupancy area determination.

The total allowable building area for buildings containing mixed occupancies shall be determined in accordance with the applicable provisions of this section. A single basement need not be included in the total allowable building area , provided such basement does not exceed the area permitted for a building with no more than one story above grade plane .

506.5.1 No more than one story above grade plane.

For buildings with no more than one story above grade plane and containing mixed occupancies, the total building area shall be determined in accordance with the applicable provisions of Section 508.1.

506.5.2 More than one story above grade plane.

For buildings with more than one story above grade plane and containing mixed occupancies, each story shall individually comply with the applicable requirements of Section 508.1. For buildings with more than three stories above grade plane , the total building area shall be such that the aggregate sum of the ratios of the actual area of each story divided by the allowable area of such stories based on the applicable provisions of Section 508.1 shall not exceed 3.
 
Come walk with me down the path...

508.4 Separated occupancies. Buildings or portions of buildings that comply with the provisions of this section shall be considered as separated occupancies.

508.4.1 Occupancy classification. Separated occupancies shall be individually classified in accordance with :Next('./icod_ibc_2009_3_sec002.htm')'>Section 302.1. Each separated space shall comply with this code based on the occupancy classification of that portion of the building.

508.4.2 Allowable building area. In each story, the building area shall be such that the sum of the ratios of the actual building area of each separated occupancy divided by the allowable buildingarea of each separated occupancy shall not exceed 1.

508.4.3 Allowable height. Each separated occupancy shall comply with the building height limitations based on the type of construction of the building in accordance with :Next('./icod_ibc_2009_5_sec003_par001.htm')'>Section 503.1.

508.4.4 Separation. Individual occupancies shall be separated from adjacent occupancies in accordance with Table 508.4.

When you get to table 508.4 you find no separation is required between the F & the S.

Go back to 508.4.2, the 'sum of the ratios' allows you to consider the proportion of allowable area each occupancy is using unto itself as if there was a physical separation.

As long as the sum of the ratios is equal to or less than 1 it complies.

Where it gets tricky is applying things like sprinkler requirements... for that you are looking at the entire fire area and applying the most restrictive requirement (whichever occupancy has the lower threshold for sprinklers will dictate).

If they do hit the threshold but want to not install sprinklers, then the rated separation (fire wall or fire barrier) would create the separate fire areas to obviate the sprinkler requirement. That's when you go to...

707.3.9 Fire areas. The fire barriers or horizontal assemblies, or both, separating a single occupancy into different fire areas shall have a fire-resistance rating of not less than that indicated in Table 707.3.9. The fire barriers or horizontal assemblies, or both, separating fire areas of mixed occupancies shall have a fire-resistance rating of not less than the highest value indicated in Table 707.3.9 for the occupancies under consideration.

TABLE 707.3.9 FIRE-RESISTANCE RATING REQUIREMENTS FOR FIRE BARRIER ASSEMBLIES OR HORIZONTAL ASSEMBLIES BETWEEN FIRE AREAS

And if I could post the actual table, you'd see the F-1 to S-1 rating requirement is 3 hours.
 
Last edited by a moderator:
Thank you so much for the responses. I really appreciate it. I did some calculations and after doing the math, I found that the sum of the ratios indeed add up to more than 1 (1.33 to be exact). So I will have to place a fire separation afterall, although not really for the reasons I first suspected! But that is why I love this forum so much. Thanks again guys!
 
E87, does your building not have yards or public ways to allow area increases?
 
E87: To add to texasbo's post, is the building sprinklered throughout?

If you can't get a sprinkler or frontage increase, then the separation will have be in accordance with the requirements for a fire wall as you originally stated.
 
Thanks for the ideas guys, but I already tried that route. There is some frontage in the front and very little on the 3 other sides (not more than 20'), so my area increase was minimal.

And no the building is not sprinklered unfortunately.

So I am now looking into a 3 hour fire separation as per table 707.3.9

Nothing is ever easy!
 
Not Section 707.3.9...that is only for fire barriers required between fire areas. You need a fire wall per Section 706, but it still needs to be 3 hours. It's just that the requirements for a fire wall is much different than those for a fire barrier.
 
I'd like some clarification on this. When I read 508.4 I see nothing that says uses can be unseparated.

508.4.2 Allowable building area. In each story, the building area shall be such that the sum of the ratios of the actual building area of each separated occupancy divided by the allowable buildingarea of each separated occupancy shall not exceed 1.

When I read this I see it saying that separated uses must be within this 1. It doesn't say that if it's below one you don't have to separate.

I might be missing something, please clarify.

JBI said:
Come walk with me down the path...508.4 Separated occupancies. Buildings or portions of buildings that comply with the provisions of this section shall be considered as separated occupancies.

508.4.1 Occupancy classification. Separated occupancies shall be individually classified in accordance with :Next('./icod_ibc_2009_3_sec002.htm')'>Section 302.1. Each separated space shall comply with this code based on the occupancy classification of that portion of the building.

508.4.2 Allowable building area. In each story, the building area shall be such that the sum of the ratios of the actual building area of each separated occupancy divided by the allowable buildingarea of each separated occupancy shall not exceed 1.

508.4.3 Allowable height. Each separated occupancy shall comply with the building height limitations based on the type of construction of the building in accordance with :Next('./icod_ibc_2009_5_sec003_par001.htm')'>Section 503.1.

508.4.4 Separation. Individual occupancies shall be separated from adjacent occupancies in accordance with Table 508.4.

When you get to table 508.4 you find no separation is required between the F & the S.

Go back to 508.4.2, the 'sum of the ratios' allows you to consider the proportion of allowable area each occupancy is using unto itself as if there was a physical separation.

As long as the sum of the ratios is equal to or less than 1 it complies.

Where it gets tricky is applying things like sprinkler requirements... for that you are looking at the entire fire area and applying the most restrictive requirement (whichever occupancy has the lower threshold for sprinklers will dictate).

If they do hit the threshold but want to not install sprinklers, then the rated separation (fire wall or fire barrier) would create the separate fire areas to obviate the sprinkler requirement. That's when you go to...

707.3.9 Fire areas. The fire barriers or horizontal assemblies, or both, separating a single occupancy into different fire areas shall have a fire-resistance rating of not less than that indicated in Table 707.3.9. The fire barriers or horizontal assemblies, or both, separating fire areas of mixed occupancies shall have a fire-resistance rating of not less than the highest value indicated in Table 707.3.9 for the occupancies under consideration.

TABLE 707.3.9 FIRE-RESISTANCE RATING REQUIREMENTS FOR FIRE BARRIER ASSEMBLIES OR HORIZONTAL ASSEMBLIES BETWEEN FIRE AREAS

And if I could post the actual table, you'd see the F-1 to S-1 rating requirement is 3 hours.
Click to expand...
 
I think I answered my own question. I see that JBI was referring to the table which shows it doesn't need a separation, so you treat it as though there was a physical separation. Hasty reading = misunderstanding
 
Last edited by a moderator:
Actually, Rooster, look at Sec. 508.3.2, and especially 508.3.2.2. Even if Table 508.3.3 required separation, if both occupancies were within the allowable area and height for the most restrictive, the separation could be eliminated.
 
Examiner:

Yes there is an existing building in which owner wants to put an addition onto. But the problem is there is no certificate of occupancy which makes the existing building uncertified. Therefore, I am looking at the entire building (addition included) as a new structure.
 
You must log in or register to reply here.
Top