Firestopping Pex lines? Let's get it right.

Welcome back to the series where we talk about “stuff we see wrong in the field.” This blog is going to discuss a few challenges we have found with PEX lines in wood framed buildings.  If you are working on a concrete project that is using PEX, you should still read this just in case you are making the same mistake.  We hope it is useful.

Here is our field condition:

The plumber drilled a hole through the two by fours that are sitting on the plywood floor to frame the wall that will be built. The hole is less than ½” larger than the pex line they are running. This gives them just enough space for the bracket the plumber is using. In the field, they call them mickey mouse ears. I’m not sure what they call them in your area but here is an example of one.

The firestop installer simply smeared firestop around the pex line and covered the mickey mouse ears. It wasn’t until we did destructive testing that we discovered the problem. So, if you are an inspector on a project that is not going to require special inspection, please walk the site before the firestop is installed to see if they are using these things. If they are, you may want to ask a few questions. If you need some help give us a call.

The problem:

The mickey mouse ears use up all the annular space that you need for the installation of the firestop material. With plastic pipes you typically need to have an intumescent firestop material. This is one that is capable of expanding to fill the void created when the plastic pipe melts away during a fire. The intumescent material can close down the opening and prevent the passage of fire.

Intumescent materials act like most things in nature. That is to say that they move in the area of least resistance. That means if it is sitting on the top of the two by four and adjacent to the pex pipe, when it starts to expand its going to move in the area of least resistance. This will be away from the pipe.

For this reason, the intumescent material needs to be forced into the opening so that the two by four, the concrete or the drywall can contain the sealant as it expands so it is forced into the center of the opening. This enables the material to close down the opening as the plastic pipe softens in a fire and yields to the expanding intumescent sealant.

This is also why, when a plastic pipe touches the side of the opening, its required to have a bead of sealant, which is a build-up of material along the edge of the penetrant and against the rated assembly.

However, when a detail allows for annular space to be 0-1” for example it does not mean that you can have 0 annular space all the way around the opening. If this is allowed the detail should say “continual point contact” and few details do.

The solution:

There are a few ways to handle this. One would be to not use the Mickey Mouse ears. Another would be to install the firestop first and then force the sealant into the opening as you push the bracket into place. Inspection would be difficult and ensuring proper sealant depth during installation would be imperative.

If you run into this issue, let us know how you handle it.

Thanks for taking the time to read this. We hope you found it valuable. If you did, please leave comments and let us know what other topics you would like to see us address in future blogs. Share this with anyone who can benefit and keep learning. Check back for more in this blog series as we discuss other field issues we encounter.