Replies

1. 
   Patrick_OSullivan | Feb 16, 2025 09:14pm | #1

   I've not seen any intumescent paint that's tested for use on rigid foam, but the manufacturers will know best. I would suggest contacting a manufacturer like No-Burn (https://noburn.com).

   Failing that, you need to meet the provision of R316.4: "Unless otherwise allowed in Section R316.5, foam plastic shall be separated from the interior of a building by an approved thermal barrier of not less than 1/2-inch (12.7 mm) gypsum wallboard, 23/32-inch (18.2 mm) wood structural panel or a material that is tested in accordance with and meets the acceptance criteria of both the Temperature Transmission Fire Test and the Integrity Fire Test of NFPA 275."

   A final option would be something like Dow Thermax, which is rigid foam tested and rated to be used without a thermal barrier. It's more expensive and trickier to procure. I have it in my own basement, but I actually ended up covering it with 1/2" drywall because I wanted better protection against damage. Note: you mention framing a wall, etc., but you can glue drywall directly to rigid foam without building a stud wall.

1. 
   chrislene | Feb 17, 2025 10:54am | #2

   Thermax is expensive. I read a Dupont white paper that claims its XPS boards can be left exposed too but I cannot find an XPS board with documentation that supports this claim.
   https://www.dupont.com/content/dam/dupont/amer/us/en/performance-building-solutions/public/documents/en/meeting-the-fire-code-with-continuous-foam-plastic-insulation-43-D100637-enUS.pdf

   Im wondering if that bubble wrap used on ductwork would qualify as a thermal barrier.

   I will call Noburn about their paint. There should be an inexpensive option.

   Thanks

   
2. Expert Member
   BILL WICHERS | Feb 17, 2025 03:39pm | #3

   I doubt the foil-like bubble wrap would qualify as any kind of fire/ignition barrier here. That stuff is basically metallized plastic film -- it's not a fire-rated material. There is a provision in the code that allows a metal sheet as an ignition barrier, but there is a minimum thickness specified (which I don't remember exactly off hand), and it's thick enough to require an actual piece of sheet metal, NOT a fraction of a mil worth of metallization on something like Reflectix.

   Bill

3. Expert Member
   Akos | Feb 17, 2025 04:03pm | #4

   I'm curious as well as to what you find, would make life easier. Post back here if you hear from the manufacturer.

4. 
   Deleted | Feb 17, 2025 09:46pm | #5

   Deleted