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Townhome Fire separation wall as sheer wall?

steveray said:
R302.2.6 Ex. 2 allows them to share the shear.....Not sure if that is engineerically possible, but allowed by code....
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I disagree. That refers to the exterior walls, when/where the sheathing bridges the gap between two adjacent units.

When you have two interior, transverse stud walls separated by a nonstructural gypsum shaftwall assembly, there nothing "common" about the wall framing within each unit. Commentary:

Exception 2 allows roof and wall sheathing that
cover the outside of common walls between units to be
continuous. While adding shear strength to the townhouse
by being continuous, each unit can still be structurally
independent if connected to the adjacent unit’s
sheathing.
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steveray said:
....Not sure if that is engineerically possible, but allowed by code....
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It's not possible or allowed by code. I am certain the engineer knows the former.

So much time on this thread discussing something so ridiculous. The OP drew one line, that's all you really needed to see. Maybe the engineer only needs it on one side? Maybe they understand if you can put plywood on one side, you can put it on the other in the same place? I don't know the details, but I do know it's ridiculous to think the engineer doesn't know he can't pass shear through the burn clips.
 
The exterior sheathing is rarely nailed to the common wall framing....

2.Structural roof and wall sheathing from each unit fastened to the common wall framing.
 
steveray said:
The exterior sheathing is rarely nailed to the common wall framing....

2.Structural roof and wall sheathing from each unit fastened to the common wall framing.
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I think the key is "Structural roof and wall sheathing ..."

The interior party walls are not, to my frame of reference, covered with "sheathing." Interior shear (braced) walls can -- and often are -- covered only with gypsum wallboard for the shear resistance. The I-codes regard gypsum wallboard as a finish, not as sheathing. Exception #2 seems to me to pretty clearly refer to a continuous exterior wall that runs the length of a building, spanning and connecting multiple townhouse units. I don't see any other way to read the commentary on Exception #2.

That's my story and I'm sticking to it. :cool:
 
Shams Gannon said:
I’m working on a townhome project in Austin Texas and my engineer is requesting a sheer wall along my UL 336 building separation wall, is this permitted?? His notes call for 1/2” plywood sheathing on the interior side of the wall.

View attachment 14301
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Getting back to the original question, which I take to mean "Is shear panel allowed to be added to a rated fire assembly without compromising the tested fire rating?"

IBC table 721.1(2) contains footnote L which reads:
Wood structural panels shall be permitted to be installed between the fire protection and the wood studs on either the interior or exterior side of the wood frame assemblies in this table, provided that the length of the fasteners used to attach the fire protection is increased by an amount not less than the thickness of the wood structural panel.​

For adding plywood or other wood structural panels to rated UL assemblies, see: https://code-authorities.ul.com/about/blog/plywood-panels-in-ul-fire-resistant-wall-assemblies/

1727195304087.png​
The structural engineering question of whether lateral loads should be allowed to transfer across the gap in the wall assembly is also worthy of discussion, but I just wanted to make sure we were addressing the original fire rating question.
 
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Yankee Chronicler said:
I was referring to the fact that each wood stud wall (call them unit A and unit B) are one-sided shear assemblies, but also that the detail as show only calls for plywood on the wood stud wall of unit A. If unit A requires plywood to achieve satisfactory shear resistance, why doesn't unit B require plywood to achieve satisfactory shear resistance? Those break-away clips and the gypsum shaftwall assembly can't transfer shear from the wall in unit A to the wall in unit B.
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We are assuming that unit type A and type B are identical in plan and thus need identical shear wall placement.
It is possible that unit B is a different floor plan and has its lateral resistance system elsewhere than this party wall.
 
Yankee Chronicler said:
Perhaps the OP could clarify if the question is about using plywood on one side of the assembly or on both sides of the assembly. The detail in the OP shows plywood on one side only.
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The structural engineer supplied this for the shear wall diagram (2nd floor only for example). I've highlighted where I have a building separation, in this case a UL366 assembly. My question was really about whether adding a layer of plywood as the P1 triangle would require, would be in conflict with the UL design.


1727206908560.png
 
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