Gypsum Board Area Separation walls as fire walls

[steveray]

This one is the gift that keeps on giving.

I spoke with technical resources, they said the same things as already articulated. Not bearing, not shear, no openings, old design for townhomes...
I got a '21 GA-600, and the only thing it says is no openings, I also got The Wood Book, which does show a method for placing an opening into a 3-hr ASW, but not ASW2600, which is different from the assemblies they show in The Wood Book.

The response (again) from the DP is that the wood framing is not part of the assembly, therefore it is an interior wall and allowed to be combustible, and since it is not part of the assembly it can be load-bearing and used for shear. I understand the theory. In the new edition of GA-600 ASW2600 there is new language not shown in my previous editions (not sure when it was added) that says the following:

"Where required for structural support lateral bracing walls constructed with steel or wood studs and 1/2" gypsum panels (shown in detail with dashed lines)." (The illustration clearly shows the 1" gyp and mineral fiber in solid lines and the wood studs and gyp in dashed lines.)

This new language, though it has some curious sentence structure, seems to support that theory. Since it was not in previous versions of GA-600 I surmise it was added because someone else asked these questions.

So if we accept the interior wall/combustible issue as OK, and we accept the lateral bracing walls as not part of the rated assembly so they can be bearing and shear walls as OK, we are now down to 'are openings permitted?'.

GA-600 very clearly says no:
"Openings and through-penetrations, including protected openings and penetrations, are not permitted in the area separation fire walls contained in this manual".
However, The Wood Book clearly illustrates how to install an opening in a 3-hr ASW basd on a UL454. So I am skeptical of the statement, though I don't think I have a choice but to accept it. I would note that the opening shown in the W454 assembly makes sense, but it is different than ASW2600 and doesn't work as drawn.

ASW2600 is based on a 1982 fire test, WHI-495-0393. I can't find any information about that test, which may explain why the GA rep snickered a little when I brought it up.

If I am reading this situation wrong please chime in.

Tell them to use ASW with no openings (per GA) or U347 (which does allow metal studs BTW) with openings but the studs are part of the rating/ assembly?.... Can't have it both ways....

 

[Sifu]

The Wood Book does show how to construct openings for some of these types of assemblies, but not for any specific ASW, rather they appear to all be based on the fire test used by the ASW's. I can't find any that would work for ASW2600 not for the fire test used for it. Interestingly, though GA-600 clearly does not permit openings in any of the ASW walls in the manual, their Wood Book contains the following key feature:
"New area separation wall details including egress door installations"....sooooo allowed or not?

These 3-hr fire walls are also a horizontal exit with double egress cross corridor doors. I think this DP (out of state) has been using this for "thirty years" and never been challenged on it. Maybe they have never used it under these conditions. Or maybe they have and it is fine, but I'm too dense to get it.

 

[classicT]

The root of the issue is in 706.2. ASW being light weight framing (shaftliner and H-studs w/ aluminum clips), they are not self supporting. Hence, the very specific prohibition on openings or penetrations through ASW.

706.2 says nothing about self supporting, just allowing collapse on either side....

Agreed, but that wasn't my point exactly.

A masonry wall can be self-supporting. Building on either side (or both sides) of said masonry fire wall can collapse and the wall could remain. These walls can even be strong enough that piping or other penetrations would not exert enough pull during a collapse to overturn the walls.

With ASW, that is simply not the case. They require a structure on one side of the ASW to provide support for the wall. Hence, they are not structurally independent. Even electrical cable, plastic piping, etc. can exert enough pull during a collapse to compromise the fire resistance capability of these light-frame assemblies.

 

[Sifu]

GA-600, ASW2600, now contains the language I mentioned: "where required for structural support lateral bracing walls constructed with steel or wood studs and 1/2" gypsum panels". Seems like the structure that supports the clips is only needed on the side that does not collapse under the fire conditions. The core of the wall is not self-supporting, but needs only one side to support it.

 

[classicT]

GA-600, ASW2600, now contains the language I mentioned: "where required for structural support lateral bracing walls constructed with steel or wood studs and 1/2" gypsum panels". Seems like the structure that supports the clips is only needed on the side that does not collapse under the fire conditions. The core of the wall is not self-supporting, but needs only one side to support it.

Framing on one side only works if it is an exterior wall.

If it is a fire wall, clips are required on both sides. Otherwise, the exposure rating is only from a single side. i.e. - If the fire is on the side with the clips, the clips melt away during the fire and the wall fails before the 2-hr mark.

 

[Sifu]

Framing on one side only works if it is an exterior wall.

If it is a fire wall, clips are required on both sides. Otherwise, the exposure rating is only from a single side. i.e. - If the fire is on the side with the clips, the clips melt away during the fire and the wall fails before the 2-hr mark.

Yes, clips are on both sides.

 

[classicT]

Yes, clips are on both sides.

Perfect.

You threw me off there for a moment.

Seems like the structure that supports the clips is only needed on the side that does not collapse under the fire conditions.

but needs only one side to support it.