UL vs GA

[Sifu]

I have a proposed gypsum association file for a rated assembly, WP 5105. It requires a minimum 1" gap between the two rows of studs. The fire test for the assembly is U420. U420 shows the gap in the drawing but does not list a minimum. The contractor and DP are claiming the UL design has no minimum therefore they don't need it. I have reached out to GA, UL and a few other personal contacts for opinions, but this site offers access to so many smart people with one shot I thought I would ask here. FWIW the USG assembly also requires the minimum 1" gap.

 

[cda]

Is the GA detail, the one submitted for review and construction ?

 

[RLGA]

In the UL assembly, the bracing (item #2) is indicated to be 4-1/4 inches long. With the studs at 1-5/8 inches, that is a total of 3-1/4 inches, and since the bracing is required to be 4-1/4 inches, that means the gap must be no less than 1 inch. The GA assembly does not match exactly with the UL assembly, but they are close and the GA assembly does not provide all of the alternates that the UL assembly provides.

That's why I tell my clients and students to look at GA to find the assembly you like, whether it's proprietary or not, then see if it has a UL equivalent. If it does, I suggest they use the UL assembly in lieu of the GA unless there is something unique about the GA assembly that benefits the design then go with the GA assembly (provided the GA assembly is a generic assembly).

 

[Mark K]

Look to the code. If the code requires qualification in accordance with a standard such as the UL standard and you have test results in accordance with that standard then the building must be consistent with the testing.

What does the code say about which standard should be used.

 

[RLGA]

Look to the code. If the code requires qualification in accordance with a standard such as the UL standard and you have test results in accordance with that standard then the building must be consistent with the testing.

What does the code say about which standard should be used.

The IBC does not stipulate which fire-resistance directory must be used--all it states is that fire-resistance-rated assemblies must be tested in accordance with either ASTM E119 or UL 263 per Section 703.3, or as provided in Section 703.3.

Section 703.3 allows any method listed (designs in approved sources, prescriptive assemblies per Section 721, calculated methods per Section 722, engineering analysis based on ASTM E119/UL 263 tested assemblies, an alternate method per Section 104.11, or assemblies certified by an approved agency) as long as it is based on ASTM E119 or UL 263.

 

[Sifu]

To answer CDA, the GA assembly is the submitted design. However, since they have failed to provide the 1" gap, they are now asking to use the UL design, which is a little different. So now I need to review it as a revised design.

To Ron, I totally understand your logic, and if it were that easy I would be a happy man. BUT, a general explanatory note to the GA design allows larger studs, which they have used. In some cases a double 3 5/8", in others a 6" and a 3 5/8". So the bracing could work with the walls closer together. UL also permits larger studs. So the drawing of U420 shows a gap but I can't find a minimum gap size, whereas the GA, USG and at least one other drawing of U420 show a minimum of 1". What's a girl to do? Maybe UL will get back to me...............if not, in the absence of a minimum I don't think I have a basis to not approve it.

If the minimum gap is to limit temperature transfer from the back of the gypsum panels to each other I think they have improved the condition because their distance is greater than the minimum. If it is to limit transfer across the studs from one wall to the other I think they have made it worse. AND, I don't even know if that is the reason for the gaps in the first place. This is where I have to rely on the published assemblies, they just don't quite match up and since I have one document that is more restrictive, and the other document somewhat ambiguous, I am leaning on the more restrictive. However, since the GA is based on U420 I am right back befuddled.

 

[RLGA]

Since they submitted the GA assembly, then that is what they should provide--with the minimum 1-inch gap as stated. Although GA allows larger studs, the gap is not permitted by the GA assembly to be reduced. If they had submitted the UL assembly, then I could see your confusion, because UL also allows larger studs and there is no specific stipulation for the gap depth.

 

[Paul Sweet]

WP5105 is a chase wall assembly with a fairly high sound rating. A chase less than 1" deep isn't very useful. The 1" separation is probably more for acoustic isolation than fire rating.

 

[Sifu]

Yes, the sound is a huge concern, so much so they were going to try to eliminate the bracing because they are worried about it creating a vibrational bridge. I think if they had installed the bracing they wouldn't be in this mess to begin with, an observation I made when I was brought in to this. I have inquiries out to GA and UL, GA wasn't any help. Still have a few others I am waiting to hear from.

 

[Sifu]

Update: After speaking to several learned and respected experts in code and UL assemblies, who acknowledge the apparent inconsistency, they and I came to the conclusion that the minimum gap being reduced was not a concern in regards to the fire resistance of the assembly (sound, as Paul said) and that they could resubmit the U420 assembly since it had no minimum gap. It quickly became a moot point when, after all the work and favors I called in to arrive at that conclusion, they decided they didn't want the cross bracing (again, for sound). So they came up with another assembly, that didn't have the minimum gap or the bracing. HOWEVER, that assembly requires screws or welds to the top track, unfortunately this is a dynamic joint and we are back to square one. As of today, no new assembly has been proposed. I think they are headed for an EJ.