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Achieving 2-hour horizontal separation

C

Code Neophyte

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Joined
Oct 17, 2009
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271
Location
Central Missouri
Here comes another one of my famously-dumb questions! (If this generates any interest, I'll try to provide some pictures)

The situation is an existing A-3 (theater) beneath a 'B' use on the second floor (two-story building). This is a c.1920 building (Type III), full dimension 2X14 joists with 3/4 T&G flooring, overlayed with 1/2 ULF. Non-sprinklered building.

The scope of the project is a change of use and complete renovation of the main floor A-3 to an A-2 (Restaurant / Bar). Designer has used the performance approach. There is a required 2-hour separation between occupancies, but there is no work being done on the second floor. Is there a way to create a 2-hour separation when the floor surface of the second floor (top side of the horizontal assembly) is not being addressed? The area in question has a number of existing plumbing penetrations (drains from 2nd floor restrooms) which would be "challenging" - to say the least - to deal with at this point.

Is it possible to build a structural ceiling beneath the existing floor/ceiling assembly (anchored to the existing 2-hour exterior walls) which would have the required 2-hour membrane?
 
The 2 hour separation appears to be if you utilize the separated approach for mixed occupancies. Is the building small enough that you can use the non separated approach? The building might also classify as Type IV, which allows more area. In general, you can create a 2 hour membrane, but how would you support the membrane? The support of the membrane would also need to be two hour.
 
I hadn't thought about non-separated...good point! Although I think the performance-based approach of the designer depends on the 2-hour separation to "pass".

As to your second question (support of the 2-hour membrane): If you can visualize the typical old 'downtown building' - 20+ feet wide, exterior walls 3-4 wythes of brick thick - if the anchorage of a ledger into those existing walls could be engineered, then joists hangered from the ledgers to span the 20+ feet, with the required gypsum membrane to achieve the 2-hour rating (from the bottom side only)?

Would that work?
 
Yes there are UL listed suspended steel ceiling grids made just for this application. Shouldn't be too hard to find...
 
US Gypsum has a few assemblies we use. One required a layer of 5/8 type x drywall, then install a 1 hour drop ceiling assembly.

Easy as pie.
 
Mac said:
Yes there are UL listed suspended steel ceiling grids made just for this application. Shouldn't be too hard to find...
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I did a (admittedly brief) search for this, and wasn't able to find a two-hour tested assembly with a wood-framed floor - everything seemed to be steel joists with concrete deck above. Any ideas where such a creature could be found?
 
cda said:
So are you getting sprinklers due to change of occupancy??????
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They presented a compliance report from Section 3410 (2006 IBC) which achieved passing scores in each of the three criteria - fire safety, means of egress safety, and general safety - and consequently "passed" without sprinklers.
 
 
I don't know that I'd necessarily say it's a more hazardous occupancy than existed before, so I'd look at whatever existing building code is in place before I'd start designing a fix (where one might not be required). Since fewer places allow smoking (I remember when theaters had smoking and non-smoking sections), I'm not convinced that a bar/restaurant is more dangerous per se.. (particularly with 2x14 joists).
 
They'd be better off to sprinkle and get it over with. Make sure they evaluate the sprinkle option once they find an assembly for the 2 hour. They might be surprised.
 
Again, Yankee, I don't know that it's necessarily more dangerous than what was there (existing, approved).. I don't know that they will really find a 2 hour assembly to cover all "what ifs" ... I'd use the existing building code, if that's an available option in your jurisdiction. Sprinkling isn't always the answer.
 
peach said:
Again, Yankee, I don't know that it's necessarily more dangerous than what was there (existing, approved).. I don't know that they will really find a 2 hour assembly to cover all "what ifs" ... I'd use the existing building code, if that's an available option in your jurisdiction. Sprinkling isn't always the answer.
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I don't know that it is either. Do we know it is existing/approved? Or just existing?
 
The building has been in service, so we need to assume (I guess) that it's been both approved and existing.
 
In answer to the "existing" question: This one's really interesting. It was built in the '20s as a 4-story theater. Then a tornado took off the top two stories in the 40's. The second story was never used again. The main level was used as a theater until the mid-90's.

I agree that from almost a non-code perspective, the improvements create a much safer situation - especially in light of the 'smoking ban' that has been enacted state-wide.

It's just that the designer's Chapter 34 evaluation included a two-hour horizontal separation. I'm not sure that it would have 'passed' without the compartmentalization.
 
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