# Rated wall assemblies



## rktect 1 (Dec 5, 2019)

So, I have a townhouse in review at the moment.  They want to use U373 for the rated wall.  It is a 2 hr rated wall assembly for load bearing.  They want to use configuration B which is shown in section as:

1/2" drywall 
2x4 studs at 24" o.c.
3/4" air space
(2) 1" drywall liners using friction fitted H shaped studs
3/4" air space
2x4 studs at 24" o.c.
1/2" drywall

Now, to me, this is one common 2 hour rated wall assembly where no plumbing or mechanical duct or equipment can be installed in either inside cavity.

Thoughts?​
link to UL website  for configuration A and B
https://iq.ulprospector.com/en/profile?e=14938

link to Georgia Pacific for only Configuration B
https://www.buildgp.com/assembly/area-separation-wall-2/

Configuration A shown as:

1/2" drywall 
2x4 studs at 24" o.c.
3/4" air space
(2) 1" drywall liners using friction fitted H shaped studs​


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## rktect 1 (Dec 5, 2019)

Also, we are looking at this from 2006 IRC, not 2009 or later where if there is a fire sprinkler they can drop down to a common 1 hour rated wall assembly.


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## classicT (Dec 5, 2019)

Hmm... interesting to ponder.

My thought is that because 1/2-in GWB is used on the exterior, it is the (2) 1-in shaftliner panels that produce the 2-hr separation. A fire will burn through the 1/2-in GWB and stud on one side, but the (2) panels and studs on opposing face would get you to the 2-hrs. If it were documented as such, I would see no issue in membrane penetrations of the 1/2-GWB.

This is supported by the U373 Configuration A design, which omits the doubled wall (stud and 1/2-in GWB). In practice, this indicates that the framing unique to Configuration B is similar to a furred wall, and is not integral to the fire separation except when facing exposure from both faces.

My opinion is that it would be permissible to have membrane penetrations of the 1/2-in GWB and framing given that the 2-hr separation is maintained (per Configuration A).

(NOTE - H clips will need to attach to both framed walls per Configuration B for this to work)


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## cda (Dec 5, 2019)

I thought irc allowed plumbing in the rated wall


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## classicT (Dec 5, 2019)

cda said:


> I thought irc allowed plumbing in the rated wall


*R302.2 Townhouses*
Common walls separating _townhouses _shall be assigned a fire-resistance rating in accordance with Section R302.2, Item 1 or 2. The common wall shared by two _townhouses_ shall be constructed without plumbing or mechanical equipment, ducts or vents in the cavity of the common wall. The wall shall be rated for fire exposure from both sides and shall extend to and be tight against exterior walls and the underside of the roof sheathing. Electrical installations shall be in accordance with Chapters 34 through 43. Penetrations of the membrane of common walls for electrical outlet boxes shall be in accordance with Section R302.4.

Where a fire sprinkler system in accordance with Section P2904 is provided, the common wall shall be not less than a 1-hour fire-resistance-rated wall assembly tested in accordance with ASTM E 119 or UL 263.
Where a fire sprinkler system in accordance with Section P2904 is not provided, the common wall shall be not less than a 2-hour fire-resistance-rated wall assembly tested in accordance with ASTM E 119 or UL 263.


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## TheCommish (Dec 5, 2019)

is the core providing the rating or is the membrane?


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## TheCommish (Dec 5, 2019)

Link  DCA3: Fire-Resistance and Sound Ratings for Wood-Frame Assemblies AM (BCD500) 

link Shaft wall solutions


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## rktect 1 (Dec 5, 2019)

Yea, but configuration A is only rated from one side, the wall side.  If it was a shaft wall that had the 2 hour rating, it shouldn't matter if there was the wall framing on one side.  It should still be rated from both side.  Instead, configuration B is rated on both sides.


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## rktect 1 (Dec 5, 2019)

I do have Georgia Pacific manual open which shows configuration B UL U373 and WHI GP/WA 120-04.  2 hour rated area separation wall.  Below that is WHI 495-0743 which is only two 1" layers of shaftliner inserted into the H studs at 24" o.c. but then covers the metal H studs with 6" wide 1/2" DensArmor Plus FireguardC interior panels.  no wall framing on either side.  Which I think is what is shown in the attic area for separation.


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## classicT (Dec 5, 2019)

The shaftliner panels need wall framing to be structural stable. The panels are in-themselves non-structural and require a supporting wall. 

So, if a fire burns through one face, the 2-hr Configuration A system remains. The doubled wall framing serves to provide the support given exposure from either direction.


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## cda (Dec 5, 2019)

Ty J. said:


> The shaftliner panels need wall framing to be structural stable. The panels are in-themselves non-structural and require a supporting wall.
> 
> So, if a fire burns through one face, the 2-hr Configuration A system remains. The doubled wall framing serves to provide the support given exposure from either direction.




Thanks, not sure why I thought that. 

They build the wall out from the rated wall, to put the pipes and stuff in.


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## khsmith55 (Dec 5, 2019)

This is the assembly I always use. The 2-1" shaft liners provide the required 2-Hour wall and the 2x4 walls are basically "furring" out side of the 2-Hour wall so anything can happen in the 2x4 walls. Idiot proof assembly.

Ken


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## TheCommish (Dec 5, 2019)

The shaft liner assembly probably has aluminum clips attached to the wood framing on both sides,  on the fire side the aluminum clips melt so the shaft wall stays in place and the destroyed unit can collapse.


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## cda (Dec 5, 2019)

Correct me again, if I am wrong.

A townhouse does not have to have """*structural stability*"""


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## classicT (Dec 6, 2019)

cda said:


> Correct me again, if I am wrong.
> 
> A townhouse does not have to have """*structural stability*"""


No, but the rated wall assembly has to withstand 2-hrs of exposure without collapse.

If only framed on one side, and that side is exposed to fire, the framing burns out and the shaftliner panels fall. No 2-hr rating.


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## rktect 1 (Dec 6, 2019)

I wish they would explain this in the reports.


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## cda (Dec 6, 2019)

Ty J. said:


> No, but the rated wall assembly has to withstand 2-hrs of exposure without collapse.
> 
> If only framed on one side, and that side is exposed to fire, the framing burns out and the shaftliner panels fall. No 2-hr rating.




Would that be part of how it is supposed to be installed??


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## classicT (Dec 6, 2019)

cda said:


> Would that be part of how it is supposed to be installed??


It is a part of the listing.

Configuration A (one side framed) is for area separation only and provides fire protection in only one direction (think of an exterior wall).


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## cda (Dec 6, 2019)

Ty J. said:


> It is a part of the listing.
> 
> Configuration A (one side framed) is for area separation only and provides fire protection in only one direction (think of an exterior wall).



Wrong thread


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## classicT (Dec 6, 2019)

cda said:


> Wrong thread


Wrong thread... Me or you?


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