DIY Home Improvement Forum banner

does putting fire breaks in XPS foam ruin vapor/moisture barrier?

802 Views 1 Reply 1 Participant Last post by  MLMIB
I live in Maryland (4a-marine) so I'm required to have a vapor/moisture barrier. For my basement I plan on putting 2 inches of EPS foam (R-8) on the wall which is against ground but to meet the strict reading of code I wouldn't need to cut in a 1/2" piece of drywall or 2" piece of wood to count as a fire break every 10 ft. If I do this, and still tape over the seam/fire break does the foam still count as a vapor/moisture barrier? the EPS has integrated studs so the drywall will be just up against the EPS.

On the opposite wall I have a walk out basement wall (so it's just a CMU wall with no dirt on the other side) that I plan on putting 2" XPS (R-10) against in a similar fashion, so again I will require a 1/2" piece of drywall every 10 ft or run a stud all the way to the CMU (have a 2x6 rather than a 2x4 every 7 studs) so I'm curious. On this one I am studding with 2x4's so I would tape most seems but the seems with fire breaks I'd spray a ~ 1" layer of spray foam on to try and get a better seal.

thoughts? I'm hoping the foam counts as my moisture and vapor barrier, so that all I have to do is put drywall up after that with no paper faced insulation. on the studded wall I may put roxul comfort batts (rock wool) in to get some more insulation.

just want to make sure I meet fire code but also don't screw up my moisture and vapor barrier I was hoping to get with the foam.

Thanks for the help!
1 - 2 of 2 Posts
New idea, can I just use greatstuff fireblock every 10 feet floor to ceiling to qualify as the fireblock? if so, I don't see a required thickness so I'm guessing an inch or so would be plenty? The fireblock greatstuff has a lower R value, R-2, would this compromise the vapor/moisture barrier?
1 - 2 of 2 Posts
This is an older thread, you may not receive a response, and could be reviving an old thread. Please consider creating a new thread.