In my cold space (back of my attic knee wall) I have 2X8 (71/4")floor joists. I am going to seal up behind the knee wall as I am finishing the attic space so it is air tight (except for the air channels that I have installed that carry into the cold space). Since I am having a hard time finding R25 in my area, I was planning to use R-13 faced on the bottom layer (Vapor facing down to my 1st floor) then adding another layer of R-13 unfaced on top of that within each bay then replacing the flooring. Or would it be better to use R-30 faced in each bay and don't put the flooring back so not to squeeze the insulation. I have seen the knee wall diagram on one of the websites, now just trying to figure out what size insulation I should use.
more insulation is better if not squished as you noted. But R26 is okay in some areas and not in others. All depends on where you are at. The floor boards add some structure stability so they are to be considered in all of this.