Firestopping Penetrations Through Shafts- Are you getting it right? Part 3

Welcome back everyone. On Monday I left you with a bit of a challenge. I asked you if you could use WL1222 for a firestop application for a metal pipe going through a gypsum shaft wall. Then, I told you that the answer to that first question was NOPE, but I asked you to look closer at the detail to find the reason, and then I LEFT YOU.


The suspense is over, keep reading and you will find not only why you can’t use that detail, but we will share a detail that is applicable and a few cautions about the proper use of this detail.


Were you able to identify WHY you can’t use the WL1222 for a shaft wall application? If not, look at the detail once more, but this time focus on item 1A. Please click on the link above and open the detail so you can look at it.


Did you find the answer this time?


How many shaft wall assemblies have a stud that is 3-1/2” wide?


If you are thinking that the gap doesn’t matter, you need to tune in to a future blog post about T ratings. That discussion will take me into several different directions; so, I will side bar that discussion for a later date, but hopefully some time this year.


For now let’s just say that if your field conditions don’t match your paperwork then you are non-conformant. If you are non-conformant then you are creating a position of liability for your company and whatever company you are working for regardless of whether you are an installer, inspector, GC or owners representative.


For now, let’s get back to identifying the right solution. In this case, our contractor is using STI firestop. We know this because item 3 of WL1222 lists LCI and also because the firestop detail has the STI logo on it. Again, I don’t have a favorite firestop manufacturer. I have favorite sales people and favorite products but not a single favorite manufacturer. My stance is, if they have the tested and listed details to support whatever project I am working on, then they are good for my project! Even if I am stuck with a sales guy I don’t like, I still have resources within the various companies to get what I need.   That said, it has been a while since I have run into a sales person who has not been capable, qualified, professional and helpful. They are out there, but I have been lucky enough to not run into them.


Since our installer is using STI, let’s try to stick with this manufacturer as we look for a detail. In this case when we go to their website, or contact the sale rep, the search for me ended with WL1251. Please click on the link and have a look at this detail. Take a moment to think about the things you want to be sure the installer does right.


Item 1 in this detail allows for C-H or C-T studs that are min 2-1/2” wide and 1-1/2” deep (item 1A). Item 1C offers a caution that the circular cut out cannot be larger than 10”.


Item 2 notes a sleeve. It does not say OPTIONAL so this means the sleeve is a requirement.  If you don’t have one of these fun toys I suggest you get one because it will help you verify that the sheet metal is the proper gauge. This detail says you must have a min 30 gauge galvanized sheet metal sleeve.


Item 3 is the penetration and the annular space. Obviously a larger pipe or different type of pipe than what is listed will not be acceptable for use with this detail.


Item 4 is where you will find the information about how to install the firestop material and what is required



If you have a 6” pipe centered in an opening that is 3” larger than the pipe, you will be okay. However if you have an 8” pipe in the same scenario you would not be able to use this detail because in 1C it says the opening can’t be larger than 10”. This means that despite the fact that the detail allows for a max 2” annular space you cant have more than 1” all the way around if you have an 8” pipe.


  1. The sleeve is a requirement and not optional:
    1. If you don’t use a sleeve then the mineral wool and sealant will not stay in place during installation.
    2. If you tell me that the wall cavity is already filled with mineral wool so you don’t need the sleeve, then you are not thinking about what will happen in a fire scenario after the shaft liner has burned away and the mineral wool falls out along with the burnt gypsum board. The sleeve is a requirement for a reason, don’t let the installer skip this part.
  2. You need to ensure the gauge of the sleeve is accurate.
  3. The overlap on the sleeve needs to be 2” minimum in order for it to:
    1. Comply with the detail
    2. Be expected to maintain its integrity in a fire scenario when we remember the fire side of the wall is going to be gone as the fire rages
  4. The sleeve has to be long enough to be captured both by the shaft liner as well as the outer layers of the shaft wall. If it is too short you may have a problem in an actual fire scenario.


The only caution I have to share with you here is to be sure that the annular space is sufficient to allow for the installation of the mineral wool and the required sealant.



  1. If you are on a stick built project and the roofers are using 2pound density mineral wool on the roof, DO NOT ALLOW THIS TO BE USED FOR FIRESTOP. Installers may tell you, “it’s the same stuff….it’s rotten cotton” What they are missing is that the detail calls for a minimum 4pcf and I have yet to find a firestop detail that allows the use of 2pcf. It is probably fine for roofers, but it is not okay for firestoppers.
  2. If you have the chance to watch the installation, you need to be sure the mineral wool is recessed 1” into the wall so there is enough space to install the 1” of firestop sealant.
  3. If annular space is tight, installing 1” of sealant will be tough, if not impossible


That was with a gypsum wall. Below is a detail for a concrete or block wall. Take a look at the detail.  What are the critical items you will verify if you are doing an inspection?




Is your head spinning yet? I will go easy on you with the next post. I promise! But if you are wondering how to firestop shaft applications, this is valuable information and we have only addressed the 1000 series details. These are the EASIEST details to deal with in our mechanical shaft application.


Thanks for reading this all the way to the end. I know there was a lot here. See you next time for more firestop information.