Firestop in Shafts is Often Done Wrong (part 2) 

Okay, so I am hoping that in this last week you have walked around your projects that have plastic pipe and identified the sizes of plastic pipes you have on your jobsites. Remember, firestop in shafts is often done wrong, so be sure to check what type of plastic they are, if they are solid or cellular core, if they are open or vented, and that you have firestop submittals for each and every one of your field applications, whether they are going through a shaft or not. I know our discussion focuses on shafts, but the information I’m sharing applies to more than just shaft wall assemblies.

Now we are going to look at what the firestop detail tells us we need to verify when we do the field inspection.  Here is the link to the detail, so you can follow along with 

The first step of the installation comes with the plastic pipe coming through the shaft liner.  Pay particular attention to this because its going to be tricky.

3B says that the collar needs to be friction fit. This means that if the outside diameter (OD) of the collar is 5” then the hole needs to be 5” and the collar needs to slide into the opening touching the cut edge of the drywall. If the cut isn’t tight or if the drywall saw makes jagged cuts, it won’t conform to this detail.

But wait that is not the only issue here. This detail requires you to secure the collar to the shaft liner with toggle bolts. If that’s the case, those are the only types of anchors you can use. This means that drywall screws are NOT acceptable.  I could sidebar for a while on the reasons, and I’ll cover that another time. For now, just know it needs mechanical fastening, and drywall screws don’t qualify as mechanical fasteners.

Did you notice that there is another requirement?  The anchors need to include a ¾” washer.  Other details may call for 1” or even 1-1/4” washers.  If you don’t use these, the anchors may pull out of the wall as the intumescent material expands. The collar will face significant movement and pressure, so you must secure it firmly to the wall. These are requirements, not suggestions.

Firestop in shafts is often done wrong, and it’s crucial to get these details right

Okay, so back to our firestop detail:

You may have noticed that there is no requirement for sealant on the shaft liner.  That is because the collar is friction fit into the opening and this will limit any air movement that would be stopped by sealant.

The outer layer of drywall will allow for a gap, but how much of a gap?  The detail says that the maximum size of the opening in the outer layers shall be 5”. Fill that annular space with FS One, an intumescent firestop sealant. Next, install the collar on the outer layer of the shaft wall assembly. Use the same anchor tabs, toggle bolts, and washers. We didn’t mention that the collar comes with anchor hooks. For pipes 1-1/2” to 2”, use 2 hooks. For pipes 3” and 4” in diameter, use 3 anchor hooks.

As you can see, there is a LOT to look at!  There are a lot of steps to this as well. Now imagine how to do this same type of installation on a block or concrete wall. Clearly you cant, so how will you address that type of shaft wall assembly?  Check in next week and we will go over this and introduce you to a great problems solving product.  If your contractors forgot to install the collar on the shaft liner side, you may be able to use this solution as long as the hole in the shaft liner is not a mess.

Remember, if you want us to take a look at your project to be sure you are on the right track, we are offering a complimentary review through the month of July. Contact us for more information.