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Area Modification and Fire Barriers

S

ShouldKnowThisBut

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Mar 20, 2020
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I've got an existing building with a proposed addition. We want to build Type VB Sprinklered to save money. Our floor plan exceeds the allowable area factor. So I did the frontage increase, and it helps but we are still short. We don't want to cut sf or change to Type VA if we can help it.

This is what I should know, but don't.

If we divide the building with a fire barrier to meet the allowable area factor...
Does each space need to be under 28,500sf/story individually, giving us a total of 57,000sf allowed on the ground floor?
OR
Do the two divided spaces need to be added together to not exceed 28,500sf/story?

Yeah, basic question I should know. Can any of you help?
 
A fire barrier will not work. Fire barriers only create separate fire areas.

What you are looking for is a fire wall; however, keep in mind that a fire wall requires structural independence.
 
More clues may be helpful. Occupancy classification(s), number of stories, existing area and proposed area and frontage increase taken? Just shooting in the dark, you mention a 28,500 sf area limitation, looking at Table 506.2 it appears your project may be an R2 Occupancy (single story sprinklered VB= 28,000 sf/story, multiple story sprinklered VB=21,000 sf/story). In my experience in an R2 building there is little difference between a VB and VA Construction since all units need a separation. The only BIG difference is a one-hour roof assembly is required in VA. As I said, the more clues the better we can help.
 
With an E Occupancy taking an assumed maximum frontage increase of 75% for a VB sprinklered building, it appears your maximum area per floor is 48,875 sf. If this still exceeds the proposed area of the building a two-hour (Table 706.4, footnote a) Fire Wall thru both stories at the addition may be your solution. See Section 706 for the requirements.
 
So the answer is...
Divide the building with a 2-hr firewall. This, in a sense, makes it 2 buildings. Each of those "buildings" cannot exceed 28,500sf/story individually. Correct?

And yes, it is 28,500sf because it's an E-SM (IBC 2015 Table 506.2). With our frontage calc it bumps to 33,400sf. But if we split up the building that changes the frontage calc, so I am going to split it to meet 28,500sf for each portion for simplicity's sake. It should work out.

Thanks for your help.
 
As quoted


“””keep in mind that a fire wall requires structural independence.””””


Not sure how you will do that? And that is if either side burns
 
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