# Vertical Step in 3 hour Horizontal Assembly 510.2 vs. 706



## swalton315 (Nov 24, 2015)

I'm working on a building under the 2013 California Building Code based on the 2012 IBC. The building is fully sprinklered.

Because of the sloping site we are saving money by trying to have the type I-A construction and podium step down at one point. The plan was to have a 3 hour fire wall continue the "horizontal" building separation. Above the building separation or podium the plan is to have a 2hr fire barrier which is much easier and cheaper to construct. We are under our area, story and height allowance without needing to split the building into two but if we lower the 3hr horizontal separation to the lower slab we would need to change to type III construction and add cost. If we were to continue the 3hr slab on the right over to the left it would add extra cost. The plan checker suggests continue the 3 hour wall per section 706. It is only 2 extra floors of fire wall but will add cost. I have heard of some cities allowing alternate means and methods to allow the jog we are looking for. Does anyone have and ideas or precedents. 510.2 doesn't prohibit vertical jogs but the plan checker says the words "horizontal building separation" by definition need to stay horizontal.

thanks


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## swalton315 (Nov 24, 2015)

http://s7.postimg.org/dra5t5rwr/3hr_podium.jpg' alt='3hr_podium.jpg'> photoupload[/img]


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## cda (Nov 24, 2015)

Welcome!!

Can you send some sourdough bread this way??


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## cda (Nov 24, 2015)

You want to mix construction types,,, if the ahj allows your separation??


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## swalton315 (Nov 24, 2015)

Mixed construction type



			
				cda said:
			
		

> You want to mix construction types,,, if the ahj allows your separation??


The only mix would be type V-A above type I-A whether or not they allow the separation to change from 3hr fire wall to 2hr fire barrier


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## cda (Dec 3, 2015)

No one answered your question???


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## swalton315 (Dec 4, 2015)

cda said:
			
		

> No one answered your question???


No not yet. The plan checker said we could do an alternate means and methods and do a 4 hour wall at the jog. But I think we will just run the 3 hour wall all the way up since we don't want to wait for the AMMR to be processed.

I'll put some sourdough in the mail if you can come up with another solution


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## steveray (Dec 4, 2015)

I didn't believe that that was prohibited....but I don't have a code section right now...


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## Yikes (Dec 4, 2015)

for sake of discussion, let's say your red line represents a 3-hour concrete construction, approx 1' thick.  The red horizontal line on the south/left I will call "A"; the vertical red is "B", and is about 9' tall; and the horizontal line on the north/right I will call "C".  The yellow area of wall above I will call "D".

Your plan checker is stuck on the wording, and is not seeing the intent behind it.  Clearly, because heat and flame like to rise, if a fire can be successfully blocked for 3 hours by a horizontal separation in A and C, it can be blocked in a vertical configuration by "B".

If the checker is stuck on thinking of B as a vertical wall, then have him think of it as a 9' thick x 1' wide horizontal slab.

Or have him look up the definition of "horizontal assembly" in CBC 202, which simply says "a fire resistance rated floor or roof assembly of materials designed to restrict the  spread of fire in which continuity is maintained".  Think about it: roofs slope all the time, and so do floors (as ramps).  The key issue is, does it contain the fire?

Here's another way to look at it:  CBC 510.2.4 allows shafts, stair enclosures, etc to be 2-hour fire resistance rated.  What if you could think of B and D as being equivalent to 2-hour shaft wall?


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## steveray (Dec 4, 2015)

510.2 Horizontal building separation allowance.

 A building shall be considered as separate and distinct buildings for the purpose of determining area limitations, continuity of fire walls, limitation of number of stories and type of construction where all of the following conditions are met:

If the horizontal separation can be used for termination of firewalls, I do not see where the above concept doesn't work....The whole concept is basically a horizontal firewall IMHO


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## VermontDrafter (Jan 25, 2016)

I am dealing with a very similar issue currently and I wonder where you have ended up in your thinking about this? It seems that it is not a trivial question as to whether the podium exception can include vertical jogs. Our conversations with IBC seemed to indicate a reluctance on their part to accept that argument. Did your AHJ accept the vertical portion as part of the horizontal assembly?

Another question I would have involves the grade plane. You seem to indicate two separate grade planes for the North and South buildings, but I'm not sure if that is a valid interpretation unless you continue the fire wall all the wall through the garage to create two separate "buildings". How do you justify those separate grade planes? Because if there is only one grade plane, then it seems your South building would have two stories above grade plane in violation of the conditions of 510.2?


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## ADAguy (Jan 25, 2016)

The yellow "vertical" separation wall you show should extend all the way above the highest floor roof to be viewed as a separation wall, No?

You keep stressing cost, how wide would the yellow wall be?

I don't see where you have indicated use of the building?


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## georgia plans exam (Jan 27, 2016)

We have accepted the vertical jog in a podium separation in our jurisdiction. Alternate method, no problem. No need for the vertical portion to continue above.

GPE.


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