2hr fire rated assembly question

[Nicole Brooks]

This is a project I'm not the architect on, so didn't provide the detail, but I have been asked about it by the contractor (am an in-house architect for the contractor). They had an inspector ask for a rating for the detail below. I told them she asked because they penetrated the 2hr UL U419 assembly by screwing through the two layers of drywall into blocking in the assembly. They responded with "it's no different than hanging cabinets on a fire rated wall and we do that all the time". I always fur out a fire rated wall if I'm mounting anything to it. I haven't seen notes of frt blocking in any of the rated assemblies that I would normally spec for a rated drywall partition. Also because our tenant spaces will get renovated in the future, I don't want to deal with the contractors compromising the rating when they demo the millwork or whatever is mounted to it. What do you guys all usually do as best practice when it comes to mounting millwork and such on rated wall and do you agree with my assessment as to why the inspector asked for the rating in the first place?

 

[walker.t]

They had an inspector ask for a rating for the detail below

Is it common for an inspector to ask for a rated detail? Should that not have been on the drawings that were approved in the plan review process?

What do you guys all usually do as best practice when it comes to mounting millwork and such on rated wall

Sorry, no personal experience with this to be able to share a best practice, but found this old thread which may be of interest to you:

Thread 'UL Fire Resistive Wall Assemblies'

Aug 23, 2011

This may be a dumb question, then again, maybe not. I have a wall which is required to be one-hour rated. We have provided details on the plans for a U465 wall assembly. I have had it engrained in me that you cannot add or subtract to a UL listing as now the assembly is no longer listed,at least not according to the one specified. So my question is can blocking of any kind, regular wood, fire retardant treated or metal, be allowed within the assembly?

• Codegeek
• Replies: 29
• Forum: Commercial Building Codes

I told them she asked because they penetrated the 2hr UL U419 assembly by screwing through the two layers of drywall into blocking in the assembly…do you agree with my assessment as to why the inspector asked for the rating in the first place?

You might want to touch base with the inspector to identify for certain what their concern is so you can respond with information that will address the concern.

 

[Penguin87]

Blocking is typically exempt from fire rating requirements per chapter 6.

See 603.1 - Allowable Materials in the IBC.
Blocking is item #14.

Blocking materials comprise a very small % of the material inside of a wall that it will not meaningfully impact the fire performance of a fire rated wall. Per the IBC's commentary.
Additionally, it is the responsibility of the contractor and building owner to maintain the integrity of any fire rated constructions including during demolition and additional construction work.