# California 2-hour party wall question



## Derrick Carter (May 2, 2020)

Hi all,
We are doing a project that contains town homes with two hour separation walls between each unit. A year ago we did a similar project, and we ended up the a 4" gap (3.5" min req'd) between walls as part of a 2-hour assembly.
My client is stating that another architect whom she trusts told her the gap required between the two walls is 8.5" per "the earthquake code".

"Earthquake Code"

I have been unable to locate this requirements anywhere. If anything, it looks as though the 2019 CBC is less restrictive at party walls (CBC 706.1.1).

Am I missing something? Can I assume that if I build the units with a 4" gap as part of my 2-hour assembly, that I will be code compliant?


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## cda (May 2, 2020)

Derrick Carter said:


> Hi all,
> We are doing a project that contains town homes with two hour separation walls between each unit. A year ago we did a similar project, and we ended up the a 4" gap (3.5" min req'd) between walls as part of a 2-hour assembly.
> My client is stating that another architect whom she trusts told her the gap required between the two walls is 8.5" per "the earthquake code".
> 
> ...




Not into earthquakes moved 40 years ago to tornadoes

What gap does the listing show? 

And in case of an earthquake  I don’t think four inches will matter in a townhome


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## Derrick Carter (May 2, 2020)

cda said:


> Not into earthquakes moved 40 years ago to tornadoes
> 
> What gap does the listing show?
> 
> And in case of an earthquake  I don’t think four inches will matter in a townhome


lol.
If by listing you mean the assembly. The one I prefer is a 2-hour shaft liner with 3/4" gap on each side then the studwalls on each side.


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## e hilton (May 2, 2020)

This might be a little harsh ... tell your client you are the AoR for the project and you will design it to meet all codes.  If she wants to get another architect involved ... bring out the check book and pay you off, its time to move on.


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## cda (May 2, 2020)

LA code



Where a fire sprinkler system in accordance with Section _R313_ is not provided, the common wall shallbe not less than a 2-hour fire-resistance-rated wall assembly tested in accordance with ASTM E119 or UL 263.


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## cda (May 2, 2020)

Let the Calif people answer it next week


Or ask her to get a code reference for you

My client is stating that another architect whom she trusts told her the gap required between the two walls is 8.5" per "the earthquake code".

From The Guy


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## Derrick Carter (May 2, 2020)

e hilton said:


> This might be a little harsh ... tell your client you are the AoR for the project and you will design it to meet all codes.  If she wants to get another architect involved ... bring out the check book and pay you off, its time to move on.


Indeed!


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## Derrick Carter (May 2, 2020)

cda said:


> Let the Calif people answer it next week
> 
> 
> Or ask her to get a code reference for you
> ...


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## Derrick Carter (May 2, 2020)

I have requested she get some sort of code reference to hang our hats on. I have also informed her of the expense and additional work involved of doing such a large gap between units.
Part of me wants to just design it with huge gaps and let it work itself out as we reach condocs and everybody on the team starts asking... protesting. But, I know the code, and I know the correct answer.  "Earthquake Code"???  At the end of the day, my name will be on it. I have prepared a little package with code references, 2-hour assembly details, and structural details from a project I have under construction currently with similar situation permitted under 2016 CBC.


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## mark handler (May 3, 2020)

There is no earthquake code that requires a 4 inch gap.


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## Derrick Carter (May 4, 2020)

mark handler said:


> There is no earthquake code that requires a 4 inch gap.



"Earthquake Code" is the funny part of that statement. There are seismic requirements that have no bearing on the situation at hand.
There is a 2-hour rating requirement between units and the code states “Fire walls shall be designed and constructed to allow collapse of the structure on either side without collapse of the wall under fire conditions.” 

So you end up needing a gap in order to accomplish these two requirements. I have found no code reference requiring 8.5". And it would seem that none of you folks have either.


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## cda (May 4, 2020)

Derrick Carter said:


> "Earthquake Code" is the funny part of that statement. There are seismic requirements that have no bearing on the situation at hand.
> There is a 2-hour rating requirement between units and the code states “Fire walls shall be designed and constructed to allow collapse of the structure on either side without collapse of the wall under fire conditions.”
> 
> So you end up needing a gap in order to accomplish these two requirements. I have found no code reference requiring 8.5". And it would seem that none of you folks have either.




For townhouses?????


“Fire walls shall be designed and constructed to allow collapse of the structure on either side without collapse of the wall under fire conditions.”

California thing???

Plus not sure how you design for that??   Are you talking using like Densglass two hour wall??


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## mark handler (May 4, 2020)

cda said:


> For townhouses?????
> “Fire walls shall be designed and constructed to allow collapse of the structure on either side without collapse of the wall under fire conditions.”
> California thing???


CRC R302.2.6 Structural independence
Each individual townhouse shall be structurally independent.


But it is NOT a CA thing look in your IRC, it should be there.


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## Derrick Carter (May 4, 2020)

cda said:


> For townhouses?????
> 
> 
> “Fire walls shall be designed and constructed to allow collapse of the structure on either side without collapse of the wall under fire conditions.”
> ...



California = no
Densglass = Yes a shaftliner assembly will work.


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## cda (May 4, 2020)

mark handler said:


> CRC R302.2.6 Structural independence
> Each individual townhouse shall be structurally independent.
> 
> 
> But it is NOT a CA thing look in your IRC, it should be there.




Is this the CRC wording:::

With exception:::::::::



*R302.2.6 Structural independence*

Each individual townhouse shall be structurally independent.

*Exceptions:*

Foundations supporting exterior walls or common walls.
Structural roof and wall sheathing from each unit fastened to the common wall framing.
Nonstructural wall and roof coverings.
Flashing at termination of roof covering over common wall.
*Townhouses separated by a common wall as provided in Section R302.2.2, Item 1 or 2.*


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## cda (May 4, 2020)

Derrick Carter said:


> California = no
> Densglass = Yes a shaftliner assembly will work.




Not sure how a Densglass wall meets it, 

When the two sheets are held together by a "H" channel?


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## mark handler (May 4, 2020)

mark handler said:


> CRC R302.2.6 Structural independence
> Each individual townhouse shall be structurally independent.
> 
> 
> But it is NOT a CA thing look in your IRC, it should be there.


It's even in the Texas R code


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## Derrick Carter (May 4, 2020)

Derrick Carter said:


> California = no
> Densglass = Yes a shaftliner assembly will work.





cda said:


> Not sure how a Densglass wall meets it,
> 
> When the two sheets are held together by a "H" channel?


I have used the National Gypsum 2 hour assembly that uses channel s well. Worked great.


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## Derrick Carter (May 4, 2020)

cda said:


> Is this the CRC wording:::
> 
> With exception:::::::::
> 
> ...


Exception 5, item 2 is interesting.


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## cda (May 4, 2020)

mark handler said:


> It's even in the Texas R code




Along with exception

Plus our ahj sprinkles them


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## cda (May 4, 2020)

Derrick Carter said:


> Exception 5, item 2 is interesting.




So with H Channel 

How does one side fall down and on stay up??


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## TheCommish (May 4, 2020)

by using a approved rated 2 hour wall design and  assembly, with structural l independence for each side.

google 2 hour rated gypsum wall


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## cda (May 4, 2020)

TheCommish said:


> by using a approved rated 2 hour wall design and  assembly, with structural l independence for each side.
> 
> google 2 hour rated gypsum wall




Agree

Sorry was talking about densglass type shaft liner 


“””I have used the National Gypsum 2 hour assembly that uses channel s well. Worked great.””


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## Paul Sweet (May 4, 2020)

"So with H Channel
How does one side fall down and on stay up??"

The assemblies designed as firewalls have aluminum clips on both sides to connect the gypsum board to the structure.  If one side catches the aluminum clips on that side melt so the framing can fall away without pulling the gypsum board down with it.


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## cda (May 4, 2020)

Paul Sweet said:


> "So with H Channel
> How does one side fall down and on stay up??"
> 
> The assemblies designed as firewalls have aluminum clips on both sides to connect the gypsum board to the structure.  If one side catches the aluminum clips on that side melt so the framing can fall away without pulling the gypsum board down with it.



https://www.clarkdietrich.com/products/specialty-clips-connectors/aluminum-burn-clip-ab

Well isn't that interesting, learn something everyday, And I have been looking at Densglass two hour walls/ not my responsibility, for awhile and I was told the clips were there for another reason. 

Thanks!!!


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## e hilton (May 4, 2020)

Or you could build separate masonry walls (or other load bearing walls) for each unit with a 1/4” gap.   Several ways to skin this cat without the clients friend calling the inaccurate shots.


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