I am a homeowner planning to air seal the house. Starting with the basement because it will be easiest.

At the rim joist I am going to use rigid foam because it is cheapest and will be a good starter proejct.

I understand some locales do not require a thermal barrier to cover the foam, but I would like to add one for safety.

Here is a list of thermal barriers: http://www.foam-tech.com/theory/firebarriers.htm

A spray on sounded interesting, but none of those listed appear to be in current use, and they appear to be asbestos based.

So now I am thinking of gypsum board because it is relatively thin.

Would the boards be attached to the rigid foam with caulk, glue, or something else?

I have searched a lot for information on how to apply the thermal barrier and not found answers. Perhaps most locales do not require it, or the spray foam is more popular now? Is a thermal barrier not worth the effort if it is not required by code, i.e. it does not provide noticeable safety improvement?

Thank you.