# Rigid Form Board and Fire Retardant



## sbkim (Apr 30, 2012)

Hello,

I have an attic area that shares an interior wall. Rather than just putting fiberglass batt, I thought about placing rigid form insulation against the attic facing wall to minimize wind washing? The area is most similar to a knee wall. The question I have is whether I need to place some fire retardant over the rigid foam and if so what do I use other than drywall? I thought I heard FSK 25 paper was fire retardant but I could be wrong.

To complicate the matter, there is direct fireplace vent that runs close to the foam but still 2" away which concerns me.










Thanks!


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## user1007 (Sep 23, 2009)

In most cases, I believe code will require that you drywall it. The paper will unlikely be viewed as a sufficient fire barrier. Why are you opposed to fiberglass batts? If you have ever seen a piece of non fire rated foam ignite and melt you would not want it in your home without a fire block!


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## sbkim (Apr 30, 2012)

Sorry for not making it clear. I am definitely putting fiberglass batt (r 21) I want to add sheathing as well. I thought rigid foam would add more r value but concerned with fire code. So would you recommend drywall on both sides of this common wall?


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## user1007 (Sep 23, 2009)

I am saying that with non fire rated foam I think you will have to drywall both sides. Check with your building department. I could be wrong.


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## sbkim (Apr 30, 2012)

Other than Thermax are there any other fire rated rigid foam or less expensive way to make it such without using drywall?


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