Question on Closed-Cell Foam

I know this is DIY, but I'm having trouble finding an answer to my question.

I want to spray closed-cell polyurethane foam on the rim joists all the way around my house. Currently, it just has some type of brownish, fiberglass looking insulation that the builders just stuffed in the rim joists.

The problem that I am running into, is that with the Froth-Pak 650 solution I want to use, the recommendations are to not spray over 2" thick without an additional fire barrier. This recommendation would only amount to an R-value of around 12. I would like to go at least 3" thick, what is the "additional fire barrier" that is recommended?

submitted by /u/Hairbear2176
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