Hi all. I've searched but cannot find the answer to my specific question. I have a bonus room with 5' knee walls with R-19 insulation and want to increase the R value while air sealing the walls. Some sites say that I need to protect against radiant heat. I have sealed all outlets in the room so I'm ready to air seal the knee wall.
I believe there are 2 good options but I'm not sure which is best. Add 2" rigid foam board (R-10). Or add reflective bubble wrap (fixes radiant heat). The foam board is ~55% more expensive which I don't mind unless I will have the same performance with the cheaper option.
This site talks about using foam board but is geared towards snow bound states: Fine Home Building - Two Ways to Insulate Attic Kneewalls