Membrane Penetration Firestop Part One

Firestop applications that only breach one side of a rated assembly are called membrane penetrations. They are often poorly reviewed. This is true of wall penetrations but even more true of floor penetrations.   If you have been following this blog for a while, you know we are big on offering information in multi-part series and this topic will be NO DIFFERENT. We will start with two different documents one from UL and the other from the IFC and we will build on those documents in hopes of helping you see what to look for on job sites. This doesn’t matter if you are an AHJ part of a QA/QC team or a special inspector. You need to know the information in this series to help increase the level of life safety and reduce liability. So please read and challenge yourself to apply this information on your projects.

We will start you on this UL document.

Here are a few key takeaways-

Plastic Electrical outlets-

  • Look for the UL logo
    • be sure it is listed for use in a rated floor/wall/ceiling that it is installed in
    • if you don’t find it, the box is not tested to be used in a fire rated assembly. You can’t just throw a putty pad on the non-rated boxes to fix the problem. It’s not that simple.
  • Check the size of the boxes, because even if it is UL listed it can only be up to a certain size before it requires a putty pad, regardless of its proximity to any other boxes. Metal boxes cant exceed 16 sq in, plastic boxes may vary by manufacturer depending on what was tested (and what passes) so look at the paperwork
  • When you are reading the firestop detail (because that’s everyones favorite thing to do RIGHT?!) pay attention to whether or not the application requires
    • a metal cover plate
    • a ball of putty  inside the box (I have never seen anyone do this unless they get called out- and I rarely see people called out even when it is a requirement)

Metal Outlet Boxes-

  • don’t assume that you can throw a putty pad on any sized box. Refer to the CLIV (the tested detail) for the limitations
  • depth of box is a big deal. We will get into this in a future discussion, but if you recall our conversation about shaft wall assemblies it is related too that. If you didn’t see that you can review here. 
  • Again if you install a box in a wall/floor/ceiling you have to be sure it is rated for that use. If it is rated for use in a wall, it can automatically be used in a ceiling or floor.

I know the firestop details for putty pads are cumbersome and painfully boring so if you have any questions, ask your electrician or your firestop installer for the CLIV document, email it to me and then let’s have a chat. I can help get you on the right track to ensure these are done right.