Multi-Family Gypsum Separation wall at exterior wall ..Need Advice Please

[Arcanumarchitect]

typically a Townhouse gypsum separation wall extends to the interior side of the exterior sheathing of the perpendicular exterior wall. Of course the exterior sheathing is fire rated and extends 4' to each side . My questions are...1. can the separation wall terminate into solid blocking within the wood framed exterior wall...solid 2 x 6's..rather than the back of the exterior sheathing. 2. If there is a gap between the separation and the exterior sheathing..1" or so..can that gap be filled with a 2 hour rated foam or firestop material.
With respect to the exterior sheathing projecting to each side of separation wall...is the distance of 4' required at each side of the centerline of the separation wall or 24" from the centerline. I have seen details showing both.

 

[Yankee Chronicler]

Are you asking about a townhouse structure constructed under the IRC (if so, why is the question posted in the Commercial Building Codes discussion area?), or are you asking about something else?

Assuming this is an IRC townhouse building:

My questions are...1. can the separation wall terminate into solid blocking within the wood framed exterior wall...solid 2 x 6's..rather than the back of the exterior sheathing.

See the exception to R302.2.2:

2. If there is a gap between the separation and the exterior sheathing..1" or so..can that gap be filled with a 2 hour rated foam or firestop material.

No.

With respect to the exterior sheathing projecting to each side of separation wall...is the distance of 4' required at each side of the centerline of the separation wall or 24" from the centerline. I have seen details showing both.

What makes you think the front or rear walls of townhouse building need any fire-resistance rating at all? Where did you come up with this 4' number?

 

[steveray]

typically a Townhouse gypsum separation wall extends to the interior side of the exterior sheathing of the perpendicular exterior wall. Of course the exterior sheathing is fire rated and extends 4' to each side . My questions are...1. can the separation wall terminate into solid blocking within the wood framed exterior wall...solid 2 x 6's..rather than the back of the exterior sheathing. 2. If there is a gap between the separation and the exterior sheathing..1" or so..can that gap be filled with a 2 hour rated foam or firestop material.
With respect to the exterior sheathing projecting to each side of separation wall...is the distance of 4' required at each side of the centerline of the separation wall or 24" from the centerline. I have seen details showing both.

OH.....And Welcome to THE Forum!

 

[steveray]

R302.2.2 Common Walls​

Common walls separating townhouse units shall be assigned a fire-resistance rating in accordance with Item 1 or 2 and shall be rated for fire exposure from both sides. Common walls shall extend to and be tight against the exterior sheathing of the exterior walls, or the inside face of exterior walls without stud cavities, and the underside of the roof sheathing

As code allows it to terminate interior at walls without cavioties without cavities, I would allow solid blocking with no prenetrations or properly treated ones...

 

[Firestop Guy]

can that gap be filled with a 2 hour rated foam or firestop material.

Others have addressed termination. My comment is that there is no such thing as a "rated" foam or any other firestop material. None of the expanding PU foams marketed for fireblocking are listed as acceptable in the IRC or IBC. Many AHJs will not approve them in lieu of the other eight categories of acceptable materials listed in R302.11.1 or IBC 718.2.1
Materials that are acceptable for firestopping must be installed in conformance to firestop system. No material carries a fire-resistance rating in and of itself. Only systems carry ratings. See attached for more info.

 

[Yankee Chronicler]

Materials that are acceptable for firestopping must be installed in conformance to firestop system. No material carries a fire-resistance rating in and of itself. Only systems carry ratings. See attached for more info.

Irrespective of what materials may or may not be acceptable as firestopping materials, the code does not allow "firestopping" for this application. The code language is clear. I posted it, and steveray posted it. The fire-resistive rated common wall must either extend to the inside face of the exterior sheathing, or may terminate against the inside of the exterior walls IF the exterior wall at that point is filled with a minimum of two 2-inch nominal thickness wood studs.

There is no mention of firestopping or fire blocking as an alternate for compliance.

 

[Firestop Guy]

Irrespective of what materials may or may not be acceptable as firestopping materials, the code does not allow "firestopping" for this application. The code language is clear. I posted it, and steveray posted it. The fire-resistive rated common wall must either extend to the inside face of the exterior sheathing, or may terminate against the inside of the exterior walls IF the exterior wall at that point is filled with a minimum of two 2-inch nominal thickness wood studs.

There is no mention of firestopping or fire blocking as an alternate for compliance.

Are you thinking I was suggesting otherwise?

 

[Yankee Chronicler]

Are you thinking I was suggesting otherwise?

Yes, it certainly appeared so. Why else mention firestopping materials in response to a question where the code does not contemplate firestopping?

 

[Firestop Guy]

Perhaps I could have been clearer, but that is why I started with "Others have addressed termination". I was trying to correct his comment about "2-hour rated foam or firestop material". I am amazed that the so many in the AEC industry still thinks in terms of "fire-rated" materials instead of "approved... firestop system installed as tested..." I just started inspection of my 360th project and I needed to convey the same message to the architect and GC. All the joint details in the plans referenced "Fire rated caulk. Typical" and when I request system submittals the GC said, "Oh, were using the good Hilti stuff." Also, there are still numerous times people try to solve construction issues with firestopping. Thankfully, more AHJs are saying, "No more convenience EJs. Build it right the first time." I am compelled to try and educate when I see/hear that type of language precisely because it runs wholly counter to the code. Because I deal with this every day and even most AHJs don't, much less AEs and GCs, I try to be careful to break things down from my level of understanding to meet people at their level. I can see here that it would have been better to lead with something along the lines of your "does not contemplate firestopping" to eliminate all possibility of being misconstrued. Thank you for your comment. It helps me be better.