# Corridors in Allowable Area Calculation?



## Markmax33 (Apr 22, 2013)

I have a building that will be separated with A-3 and B occupancies throughout.  I am trying to do the allowable area calculation but I can't decide where to count the corridors should be included in the floor area for the B or A-3.  This is a 2 story building so unlimited area provisions will not work.  Do you just pick what occupancy is near the corridor or is there some prescribed method?  Thanks!


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## brudgers (Apr 22, 2013)

If the building is separated occupancies then the corridors are counted in the fire area in which they are located. If the occupancies are unseparated,  they count against the most restrictive allowable area. Just like the other occupancy.


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## cda (Apr 22, 2013)

What are you calling the major occupancy of the building??

Is it more assembly with offices to support

Or is it a business office with meeting and training rooms?


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## Markmax33 (Apr 22, 2013)

It's about 60% (B)  business - 40% assembly (A-3).  It's a military facility with an auditorium and some workout/drill rooms and a bunch of office space.  It would be similar to a middle school.


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## Markmax33 (Apr 22, 2013)

I guess the real question is:  If the auditorium and gym areas have fire separations around them (2-hr) and the rest of the building is Business, does the corridor outside of the separated A-3 area count as B or A-3?


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## cda (Apr 22, 2013)

Both occupancies probably use the corridor???


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## Builder Bob (Apr 23, 2013)

Building area is building area.......The separated use would dictate where the area would be separated - along a rated wall. If  non-separated use, then you would use the entire building area and figure the allowable area based on the most restrictive use...

If the fire barriers are true fire barriers and have a rating of two hours - are these considered hortizontal exits in the IBC and would place the corridors in the B Occupancy?


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## RLM-Architect (Apr 25, 2013)

Try this:

Calculate the assembly spaces based on their NET square footage (per code)

If conference type spaces with tables and chairs, 15 sf per occupant

If moveable furniture, 7 sf per occupant

If fixed seating, count the seats.

Then take the balance of the building square footage (including the corridors) and use 100 sf per occupant.

Based on available information, the Occupancy classification of the building would be Group B.

Sounds like you have a National Guard Armory or something similar.

GO NAVY!


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## mtlogcabin (Apr 25, 2013)

I agree with brudgers. If the A-3 area needs the corridors to provide exiting then they should be include in the overall A-3 use to calculate allowable area since it is the most restrictive.


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## north star (Apr 25, 2013)

*: = :*

I agree with **RLM-Architect**,  *...GO NAVY !*   :mrgreen:

*: = :*


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## brudgers (Apr 25, 2013)

mtlogcabin said:
			
		

> I agree with brudgers. If the A-3 area needs the corridors to provide exiting then they should be include in the overall A-3 use to calculate allowable area since it is the most restrictive.


  If the corridors are in a separate fire area from the A-3, then they are part of that fire area. Once the people in the A3 fire area are on the other side of the fire barrier, they are considered to have reached safety.


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## mtlogcabin (Apr 25, 2013)

I am not following you with regards to the "Fire Area" comment

2009 IBC

506.5 is for mixed occupancy area determination. 506.5.1 and 506.5.2 both send you to 508.1

508.1 references 508.4 for seperated occupancies and Table 508.4 would only require a 1 hour seperation between a A and a B occupancy. A fire area requires a minimum 2 hour fire barrier.

I can't find where the code uses "fire areas" to increase the allowable area of a building


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## mtlogcabin (Apr 25, 2013)

Correction to the above post

One hour in a sprinklered building, two hours in a non-sprinklered building


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## RLM-Architect (Apr 26, 2013)

Regarding the building, my guess, without seeing the plan, and Markmax33, correct me if I am wrong, are in a Guard Armory or something similar.

The primary occupancy is Group B and the corridors probably serve the Assembly and Business use areas.  The corridors are not counted in the Assembly use because they are not simultaneously occupied by the assembly occupants.  Meaning, the folks in the assembly areas are not ALSO in the corridor.

By allowing the total occupant load of the assembly areas to be added to the load of the balance of the building, corridor width will be addressed properly.

Calculation of assembly is based on the NET square footage of the assembly use space which increases the load to be served by the corridor.

MM33 did not indicate any intent nor would it be required, to separate the two occupancy uses.  If he uses the "non-separated" permissions of IBC 508.3 and protects the building according to the most restrictive applicable provisions of sections 403 and Chapter 9, then all is well on the home front.

Note that Section 508.3.3 states "No separation is required between non separated occupancies".

I rest on my case! (or something like that)

(being a damage controlman helps you understand how to fix stuff)


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## mtlogcabin (Apr 26, 2013)

RLM

I agree with your assesment on calculating occupant load but I believe the OP is asking about calculating the building area for mixed occupancies

The OP stated he is using separated occupancies so 508.4.2 is applicable and it does not matter where the corridors are the area is calculated on where the fire separation walls are located. If the corridors, broom closet and mechanical rooms are located on the "A" side of the fire separation wall then that floor area is include in the "A" use building area calculations.

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 building area of each separated occupancy shall not exceed 1.


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## Markmax33 (Apr 26, 2013)

All,

   Thanks for the input.  This is similar to a Reserve Center.  The ironic and complicating factor about the Navy is that we follow the Life Safety Code for egress, so I am only worried about calculating the allowabe area correctly.  Don't even ask me why the Navy why we use 1/2 IBC and 1/2 LSC.  I found this article that seems give some insight on the issue as well.  I like the fire area approach.  If they put rated walls around the rooms then the corridors aren't in the same fire areas and we can maximize the building space.

http://www.specsandcodes.com/Articles/The%20Code%20Corner%20No.%2027%20-%20Fire%20Areas.pdf

PS.  Sorry I've been at NAS Lemoore for 2 days doing a BOQ final inspection and didn't get to check the thread!


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## RLM-Architect (Apr 26, 2013)

If I had know this was Navy, I would have answered even sooner!

Why half LSC and half IBC? Because sometimes half is all you get.  LSC is easier to comprehend.

I have been taking a poll in all of my seminars.

I ask for a show of hands of everyone that really believes the IBC is so well arranged that you can find anything you are looking for real easily.

No hands raised in 7 years.

Was in San Diego for boot camp YEARS AGO! Back when sailors started folding their clothes instead of rolling them.

If you gotta be on a ship, I highly recommend a supply ship (lobster and steak almost every night)


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## mtlogcabin (Apr 26, 2013)

> I ask for a show of hands of everyone that really believes the IBC is so well arranged that you can find anything you are looking for real easily.No hands raised in 7 years.


That would depend on your audience. I haven't used a LSC since 1996 when I left Fl


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## RLM-Architect (Apr 27, 2013)

Agree that if you don't use it you lose it.

If LSC included all the same stuff as IBC, it would not be an easy read either.

Been using the LSC though for 20 years now since I was with the SFM in Louisiana.

Now in FL, better sun here.


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## north star (Apr 29, 2013)

*: - :*

RLM-Architect,

If you don't mind saying, ...what year did you Boot at San Diego?

I Booted in Orlando in `76, and yes, we ...we folded instead of

rolled !  

*: - :*


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## cda (Apr 29, 2013)

RLM-Architect said:
			
		

> If I had know this was Navy, I would have answered even sooner!Why half LSC and half IBC? Because sometimes half is all you get.  LSC is easier to comprehend.
> 
> I have been taking a poll in all of my seminars.
> 
> ...


well if you were based at 32nd street between 72-76 I may have fed you!!!!!!

last ship my dad was on was the Kitty Hawk, you could fly a plane on that one!!!!!!!


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## RLM-Architect (May 2, 2013)

As I recall, 'twas circa 1967

Does the Navy even do boot in Diego any more?


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