I'm sealing up some holes and gaps in my attic and dutifully using fire block caulk where some electric cables are coming through the studs and gaps. In other locations, I'm using Great Stuff like spray foam for simple air gaps. However, a couple of hard to reach places make spraying the foam difficult. It would make the job easier if I'm allowed to foam over the fire blocking caulked holes and gaps where the electric cables are coming through.


The entire point of the fire blocking foam is prevent/slow fire from spreading from one area to another; it has less to do with the electrical/plumbing between two areas than the hole that was created to allow them through. As long as you have fire grade blocking to the prescribed thickness, there is no issue with other foam on top of it.

  • The only concern is that if the "regular" foam hides the "fire block" foam, you may not pass an inspection since it would appear that "regular" foam was used and the only way to tell would be to cut away the "regular" to see the "fire block". (From what I know, they look different when expanded/hardened, but I'm not 100% on that.)
    – FreeMan
    Apr 27 '20 at 15:42

Easy enough (if a tad more expensive per can) to grab a can or two of the fire block foam to use in the area where it would be over the fire block caulking.

fireblock great stuff foam - image from zoro, not a customer and no endorsement implied.

Your Answer

By clicking “Post Your Answer”, you agree to our terms of service, privacy policy and cookie policy

Not the answer you're looking for? Browse other questions tagged or ask your own question.