May 2022 Lessons in Firestop: Goldilocks and the Plumber

Lessons in Firestop by Sharron HalpertDoes the title of this column sound like a love story? If it does, then I apologize to all of you romantics out there. This is more like a tragedy or maybe a horror story.

In our last Lessons in Firestop I told you the Goldilocks story of a plumber who had different-sized hole saws for the same-sized pipe. Some of the holes were too small to allow the required ¾-inch depth of firestop sealant, and some of them were too big.

In this lesson, I want to tell you the horror story I promised you last month.

Imagine you’re bidding your project. Let’s say you called out all of your pipes to be firestopped for, I don’t know (I’m making this up; I have no idea what people bid firestop at) $100 per hole. (It doesn’t matter if you think that’s the right price or if you think it’s crazy high or low. That isn’t the point. I just need a reference point, so I could have said $3 and we all know that’s not right either. Just go with it for now.)

Let me set the groundwork first. When you look at a penetration firestop detail, you will see some common things. They all will list a required sealant depth as well as an annular space. The sealant depth will be critical to the performance of the firestop assembly. If you don’t have enough sealant depth, the installation could allow fire through prematurely. This is of particular concern when running combustible penetrations (plastic pipes or many different types of common insulations).

The annular space is the gap that will be filled with firestop. If there is no gap, it will be impossible to achieve the sealant depth, so these two things—annular space and sealant depth—are very much tied together and both are important to a good installation.

If a firestop system says that the annular space can be zero to ½ inch, that doesn’t mean the annular space can be zero all the way around the pipe because it will also call out a sealant depth that must be achieved. The only exception to this is when a system specifically allows for continual point contact. There are a few such systems, but they are going to be for metal pipes, not for plastic pipes. I will explain why in another lesson, but for now we have to get back to our horror story.

Let’s assume the plumber ran a pipe through a hole that is just big enough for the pipe to pass through—perfectly sized, if you don’t think about the firestop in advance.

If the plumber is running a metal pipe, it’s not as likely to be a big problem. If there isn’t a tested and listed detail that can accommodate continual point contact, which is the case when the pipe is snug in the hole, then the manufacturer might be able to write an engineering judgement that will work.

If you are running a plastic pipe, this is a very different story. Let’s say you are running a 4-inch plastic pipe or maybe a small PEX line or a 6-inch roof drain. These will all be firestopped very differently, but here are some universal elements you can expect:

  • They will all require some annular space around the outside of the opening.
  • They will all require that the annular space be filled with firestop sealant.
  • They will all specify a particular sealant depth depending on the fire-rated assembly it is penetrating.

Now the obvious exception would be a cast-in-place firestop device, but for this discussion let’s assume you are not using one. (I promise to introduce you to a whole cadre of awesome devices in another firestop lesson, but stick with me for a bit.)

On this project, our crews ran PEX pipes and small-diameter PVC pipes that could easily have been firestopped with a prescribed depth of firestop sealant if only they had the annular space that would allow it. They made the openings too small, so the field installation required a collar on the underside of the subfloor as well as the underside of the top plate. The small-diameter PEX lines don’t have a factory-fabricated collar, which means the collars have to be field fabricated. Suddenly the installer has a field application that should have cost—what did we say?—$100 per penetration, but now it will cost $100 for the materials alone and the field team will take three to four times longer to create the collar—and all of that is on top of the labor required to install this little baby collar.

Hopefully, if you are reading this you are the type who wants to build better, and hopefully this will help. If it does, please reach out to me and let me know what you think about this Lessons in Firestop segment and what else you want to learn.

Check back next month when we will do an autopsy of this horror story, and after that I will talk to you about the code changes of which you need to be aware.

See you there!

Connect with Sharron

A former kindergarten teacher turned firestop expert, Sharron is President of Halpert Life Safety Consulting LLC, a leading provider of firestop-related life-safety and passive fire protection solutions.

If you like what you read here and want to know more, email [email protected] or connect with her on LinkedIn or Twitter to tell her what else you want her to cover in this column. You can also follow her on Instagram. If you find this information valuable, please like, share, comment, repost, retweet, and throw it on IG to help people build better.

The opinions expressed in this article are those of the author and not the American Society of Plumbing Engineers.

Want news delivered right to your inbox?

Sign up for our free newsletter, delivered every other Thursday.

Scroll to Top