Rim joist thermal barrier
The rim joist in my unfinished basement is insulated with 3 inches of rigid polyiso along with one part spray foam to air seal around the edges. My understanding is that building code exempts up to 3 1/4 inches of spray foam in this area from the thermal barrier requirement, but that this exclusion does not apply to rigid foam boards. I have seen some postings on this site (http://www.qa-greenbuildingadvisor.com/community/forum/building-code-questions/36030/spray-foam-ignition-barrier) which suggest that installing R15 mineral wool over the rigid foam would meet the thermal barrier requirement, but I have not been able to find much in the way of actual documentation to support this assertion. Will the mineral wool actually meet code? What would be a code compliant way of installing 1/2″ gypsum over the rigid foam? The one part spray foam applied around the edges of the rigid foam has not created a ‘flat’ surface amenable to gluing the gypsum directly to the foam. Can I glue the gypsum to some sort of 1/4″ to 1/2″ spacer material (maybe more gypsum) and then glue the spacer to the central area of the rigid foam, thus avoiding the unevenly foamed edges?