UL 341 question

[dpohlman]

I am using UL 341 assembly in our project. Normally what I see is that the drywall will be run continuously behind all non-rated wall connections.

I am now working with a new sub contractor who refuses to run the drywall behind the non-rated wall so I told him to do the following detail as provided in the assembly

Can someone tell me what the purpose of the sides of the U-framing are? To me, it looks like you are just providing a fastening location at the end of the gyp so there is no gap for the fire to get into the wall. Also insulating the 3.5" cavity created by the U never gets completed.

Couldn't this be accomplished by running a 2x6 behind the 2x4 (#9) of the non-rated wall so that there is 1" overhang on each side and use that for the drywall and prevent any gaps that fire could enter through, and not installing the sides of the U-framing

Thoughts on this, I know this is a tested assembly but have any other configurations been tested, an L or the solution I am suggesting?

 

[bill1952]

I can't tell you purpose but if it's in the standard, I believe it's been tested and doubt what you are proposing has been tested.

 

[e hilton]

Can you mark up the diagram to show what you are talking about. Where is the u framing?

 

[dpohlman]

Can you mark up the diagram to show what you are talking about. Where is the u framing?

#9 in the diagram, I cannot mark it up I can only paste a link to an image not paste the image itself. You have the Stud of the non-rated partition, and then you have a U of framing in the rated assembly where that connection exists

 

[dpohlman]

I can't tell you purpose but if it's in the standard, I believe it's been tested and doubt what you are proposing has been tested.

The purpose is if we meet the intent of what they are trying to achieve it saves money on lumber. With lumber costs where they are that would be 2 less studs at every connection, so this would be 10-20 studs per unit and 200-400 studs per building and 1000+ studs per project for us, so huge cost savings.

 

[bill1952]

Seems like less cost if your sub would do as proposed and slip gwb behind. (Not to mention better acoustic performance.) You nor I can know how the variation you propose will perform in a fire.

As a 20+ year principal member of the Fire Doors committee, I've seen enough tests to know that minor changes can affect the way an assembly performs in a fire test drastically. What's that 2x6 on the flat going to do after it's all been hit with 1700 degrees in the test oven and then hit with a hose stream at 30 psi?

 

[dpohlman]

Seems like less cost if your sub would do as proposed and slip gwb behind. (Not to mention better acoustic performance.) You nor I can know how the variation you propose will perform in a fire.

As a 20+ year principal member of the Fire Doors committee, I've seen enough tests to know that minor changes can affect the way an assembly performs in a fire test drastically. What's that 2x6 on the flat going to do after it's all been hit with 1700 degrees in the test oven and then hit with a hose stream at 30 psi?

Yeah that is what we are moving towards on our next project. Looks like I will just tell him that he needs to do what is spec'd.

 

[bill1952]

Yeah that is what we are moving towards on our next project. Looks like I will just tell him that he needs to do what is spec'd.

You could get a fire protection engineer to look at it but could cost more than a few studs.